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U. S. National Museem

j Division of Fishes,
DEPARTMENT OF COMMERCE

BULLETIN

OF THE

UNITED STATES
BUREAU OF FISHERIES

VOL. XXXVII
1919-1920

HUGH M. SMITH
COMMISSIONER

2561S,
F .)
ationg\ Mvs®

WASHINGTON
GOVERNMENT PRINTING OFFICE
1922

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CONTENTS.

&
Page.

EARLY HISTORY AND SEAWARD MIGRATION OF CHINOOK SALMON IN THE COLUMBIA AND SAC-

RAMENTO RIVERS. By Willis H. Rich. (Document 887, issued July 26, 1920)......... I-74
NATURAL HISTORY AND PROPAGATION OF FRESH-WATER MUSSELS. By R. E. Coker, A. F.

Shira, H. W. Clark, and A. D. Howard. (Document 893, issued May 2, r921)........... 75-182
PERITONEAL MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOID FISHES AND THEIR SIGNIFI-

CANCE IN FISH-CULTURAL PRACTICES. By William Converse Kendall. (Document gor,

ASSHECeMALCH2 8. BLO 2) Leet ate tee tate coc met \evelenci< clients Pladtensisiiae cies sine oder ee LO3=208,
FURTHER LIMNOLOGICAL OBSERVATIONS ON THE FINGER LAKES OF NEw York. By Edward

A. Birge and Chancey Juday. (Document 905, issued October 8, r921)................. 209-252
DISTRIBUTION AND FOOD OF THE FISHES OF GREEN LAKE, WIS., IN SUMMER. By A. S.

Pearse: (Document goo, 1sstied | October 75 ;1927)\e.cc.2 ejatare «a ciciarei ois atscicieio.c 2 deine viele nie 253-272
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EARLY HISTORY AND SEAWARD MIGRATION OF CHINOOK
SALMON IN THE COLUMBIA AND SACRAMENTO RIVERS
Pod
By Willis H. Rich

Field Assistant, U. S. Bureau of Fisheries

CONTENTS.
&

Page.
DG iCh covs hte (0) sete OR ete an Geen Ata SoS eaten ac SM eOE nt Sortaciaoroncin nos case cers ad evens 3
History (of theinivestipationys sale stave esc) nie Sin oon ore aie. Siete so eisai ro tena oee ate ak [eae 3
Statement of the problems........ Bee erate nee ate tear crams At ad oo Go da tciacitst 5
Methods:)...8.;.SAah. Haka 4-2 PPE REESE. Soe A ee de Skee hk Hodes a dee eee «ee cee 6
Presentation of data ge oe te i. cray cre: apes <p easy sep eins Ee haees+ Peete = ae te ae eee 7
Fish trom the Cotumbigo Rivers .s ms... son Oe 5 ee) ee ee ee 7
Fish fromthe ‘SacramentouRivetir io. cece se ee eat aa ee eee te ere Cease eee cee ee 32
Miscellaneous: collections3 -.\AcdeocnsF ces als ORD Satis eee eee ECR eee 42
Conclusions 6 oj fae) Sei ie sm pardister-ia 3 sani ghe abc eee ae CIR Ete eA eS ee oles tale 45
RAte OF SPO Wthy. pis. Fos 0's Beh ye lca eee ie eee cle pace esate aye 4 Pe ogee nie 45
Development iofiscales’ $5: (1. zhu 0.) cose paiel acl Sees tea: ge cee eee 5r
Migrations ,.,cccmec cise eee = Sidickale bis iota etter b ny ME eh Sth ene oe Oe 62
Watiations: due toisex: 55-6. 25.284 shack Saeco cers oeiee Sole Ain Se RE ee cee eee 65
Sexiproportions.. eevee. ase Sa Ree ee oe octtan Yoo ou Saat 65
Relative sizes ofimalesiand: females. h.23. 25. <sse0 ue eect etecii ieee & ene eee 66
Precociously: mature males). 520 Wicics antes te ae eee tec s eee Ree ne Ue ee he eee 67
PFacticalistteeestionis si jor rerace.sruisres<rdes joes ohinct dou ovens wpepenens eee cca SO aA A tetera Oe EE 68
SSE AL Yio 22 eicpw ayers PE apa aaeobets Opec ate a a aeas aise omeNe ely Slee ieaie Reatnte tans 2 SOT ee eR 69
Bibliography: -acae..2,552'-.< Yate eaacrciee es SR simsag cis Uma ake Sree ie ELIE IE oe ee eT ao Cees qr
Explanation of plates i). cce coe opote eso ota ate lakers See ee Ae Sere eee eee 72

2

EARLY HISTORY AND SEAWARD MIGRATION OF CHINOOK
SALMON IN THE COLUMBIA AND SACRAMENTO RIVERS.

&

By WILLIS H. RICH,
Field Assistant, U. S. Bureau of Fisheries.

&
INTRODUCTION.
HISTORY OF THE INVESTIGATION.

The present study of the chinook salmon (Oncorhynchus tschawyischa), of which this
paper forms the first contribution, was started in the summer of 1914 at the instance of
the U. S. Bureau of Fisheries. The importance and necessity of such a study had been
made apparent, especially by the work of Gilbert on the sockeye salmon, and it seemed
advisable to extend in detail the outline of the life history of the chinook as given
by Gilbert (1913). The method employed—that of analysis on the basis of scale
studies—is now too well known and too widely used to need description. The paper
just cited and subsequent studies of the sockeye by the same author contain a complete
description of the methods employed and form admirable examples of studies prosecuted

on this basis.
Our knowledge of the life histories of all the Pacific coast Salmonide was dis-

tinctly unsatisfactory previous to the discovery of the value of scale studies. The
descriptions given by Jordan and Evermann (1896-1900), Jordan (1905), Rutter
(1903), Scofield (1898), and Chamberlain (1907), contain the most accurate informa-
tion regarding the chinook which was available prior to Gilbert’s first study. The
general features of the early life in fresh water and of the seaward migration were well
known, and Chamberlain had shown quite conclusively that the sockeye and chinook
salmon mature commonly at about the fourth year, although this is subject to variation.
The work of MceMurrich (1912) on the chinook salmon, based on the scales, has been
shown by Gilbert (1913) to be unreliable because of the small number of specimens
examined and an incorrect interpretation of the central (nuclear) area of the scales.

It remained, therefore, for Gilbert (1913) to give us the first accurate description
of the general features of the life history of the chinook salmon in his paper, ‘“The Age
at Maturity of the Pacific Coast Salmon of the genus Oncorhynchus.” In this he shows,
among other things, that: (a) The chinook, or king, salmon spawn normally either in
the fourth, fifth, sixth, or seventh year, the females more frequently in the fourth year;
(6) the “‘grilse” are exclusively males and are of two sizes, representing two and three
year fish; (c) the young may migrate as fry soon after hatching, or may remain in the
stream until their second spring, migrating as yearlings; and (d) among the fish of any
given age, the larger specimens will be those which migrated seaward as fry, although
these do not attain the average stature of those fish, one year older, which migrated
as yearlings.

3

4 BULLETIN OF THE BUREAU OF FISHERIES.

In a recent paper Fraser (1917) has verified some of Gilbert’s findings and has
extended the study to the spring salmon found in the Straits of Georgia. He has
worked out quite conclusively the rate of growth during the life in the sea and also the
time of formation of the winter check.

The present study is a continuation of that begun by Gilbert, and the results thus
far have been in perfect agreement with his, although the material has been much more
abundant and diverse. The outline of the life history of the chinook as given by him
may be almost indefinitely extended, but it seems most unlikely that results may be
obtained which are not in agreement with his original conclusions.

At the beginning of this investigation it was supposed that an examination of the
adult scales would give the data necessary for an understanding of the life history.
Most of the summer and autumn of 1914 was, therefore, spent on the Columbia River col-
lecting scales and data from adult fish. Small series of young, seaward migrants, were
also taken at Astoria and Ilwaco, at the lower end of the Columbia estuary. Several
collections of adult scales taken at spawning stations on various tributaries of the
Columbia and Sacramento Rivers and collections of yearling chinooks made at Baird,
Calif., were available for study through the courtesy of Dr. C. H. Gilbert. Access
was also had to a collection of young migrants from the Sacramento River through the
kindness of N. B. Scofield, of the California Fish and Game Commission. These various
collections were studied during the winter and spring of 1914-15. It was possible to
verify the main conclusions reached by Gilbert (1913), as follows: (1) The scales present
two types of nuclear growth—one, the stream type, indicating that the fish migrated
to the ocean after spending one year in fresh water, and the other, the sea type, indi-
cating that the fish migrated as a fry; (2) the chinodk may reach maturity at any time
between the second and the seventh year. Those maturing in the second or third year
are exclusively males.* The prevailing ages at which maturity is reached by the chi-
nooks of the Columbia River are 4 and 5 years, although fish in their sixth year are fairly
common. Specimens maturing in their seventh year are very rare.

Although it was possible to distinguish typical specimens of the two types of nuclear
growth, it was found that there were many modifications of both types which were
often confusing, although at the same time they were very significant. In the case
of the young migrants taken in the Columbia estuary, the scales showed a well-defined
area of narrower rings succeeded by a marginal band of wider rings. (See Pl. II, fig. 5.)
At first it seemed that these fish must be in their second year; but this conclusion was not
considered tenable, since, if this were true, the amount of growth which had taken
place during the second year would be surprisingly small compared with that taking
place in other cases where there was no doubt as to the proper interpretation of the
scales. It seemed much more likely that the wide marginal rings represented a period
of vigorous growth initiated by the young migrants on reaching the brackish water of
the estuary. The problems presented were so complex that it was considered impera-
tive that a careful study be made of the young migrants before proceeding further with
the study of the mature fish.

To this end the writer undertook in the spring of 1915 the collection of the neces-
sary data. Asa result of unavoidable delay in getting a suitable net for this purpose,

@ More recently females have been seen maturing in their third year, but in every case the scales indicated unmistakably
that the fish had migrated asa fry. This is an important point for future consideration.

SEAWARD MIGRATION OF CHINOOK SALMON. 5

effective collecting was not begun until October. Collections were made chiefly on the
lower Columbia between the mouth of the Willamette River and the ocean during Octo-
ber, November, and December, 1915. Owing to the unusually severe winter of 1915-16
the river contained so much ice that further collecting had to be deferred until March,
1916. From March until September frequent samples were taken at various points.
These collections made in the Columbia River in 1914, 1915, and 1916, the collections
from the Sacramento River mentioned above, and certain collections from the smaller
coastal streams in California and Oregon contained in the Stanford University collec-
tion constitute the material on which this paper is based.

Thanks are due especially to Dr. C. H. Gilbert for assistance and advice given freely
throughout the course of this investigation. The author is indebted also to Henry
O'Malley, in charge of operations on the Pacific coast, and to Supts. Dennis Winn and
Hugh C. Mitchell, of the U. S. Bureau of Fisheries, for advice and assistance in the collec-
tion of material. The friendly cooperation of the Oregon Fish and Game Commission,
through Supt. R. E. Clanton, has also been of great assistance. John Larson, of the
Oregon Fish and Game Commission, accompanied the writer on many of the collecting
trips during 1916 and proved an invaluable assistant. To N. B. Scofield, of the Cali-
fornia Fish and Game Commission, acknowledgment is due for permission to examine
young salmon collected by him from the Sacramento River. Mrs. W. H. Rich aided
in the preparation of scales for study and in the correction of manuscript.

STATEMENT OF THE PROBLEMS.

On beginning this work in June, 1914, the following tentative list of the more im-
portant problems relating especially to the Columbia River fisheries was made as a
guide for determining the character of the future work:

1. What is the value of the hatchery work done on the river? Do the chinook fry
planted from the hatcheries return as mature fish; and if so, when, and in what
proportions ?

2. At what ages do the young migrate to the ocean? What proportions migrate
at the different ages, and what are the sizes of these migrants?

3. What age groups are represented in the different runs of the various species
(chinook especially), and what are their average sizes and weights? Do these sizes and
weights vary during the season?

4. What are the proportions in which these age groups are represented, and do the
proportions vary during the season?

5. What are the relative sizes and proportions of males and females?

6. What results are being obtained from the marking experiments started in 1911
on the Sacramento River?

In addition to the above problems it was very soon found that one of the most im-
portant practical problems on the Columbia River has to do with the difference between
the spring and the fall runs of chinook salmon. ‘This has been kept in mind, therefore,
throughout the work. The spring fish are much more valuable than the fall fish, being
richer in oil and of better color, and the great desire of the commercial fisheries is to
increase the spring run. It is obvious that the only opportunity to influence the history
of the salmon is during the early life in fresh water before the young have migrated to
the ocean. To do this intelligently, an exact knowledge of the early history, prévious

6 BULLETIN OF THE BUREAU OF FISHERIES.

to migration, is necessary. The author has attempted, therefore, to give in this report
as complete an account as possible of the early history of the chinook salmon. Im-
portant as these observations are, they are merely preliminary to the still more im-
portant study of the adult fish. Abundant material is at hand for this purpose, and
the author hopes to present in the near future a report covering those problems which
relate to the adult fish.

METHODS.

The methods usually employed at the present time in studies of the life histories
of fish by means of scale analysis have been followed.

The length of the fish was determined by laying the specimen flat on a rule and
measuring from the tip of the snout to the end of the middle rays of the caudal fin.
These measurements were made in millimeters. ,

In counting the number of rings (circuli) on the scales the count has always been
made in the anterior quadrant of the scale, since the number of rings has been found
to be less variable there than in the lateral quadrants. The different areas of growth,
such as the summer and winter bands (annuli), are also more sharply differentiated in
the anterior quadrant.

Any measurements of scales and portions of scales which are given, were
made by means of a camera lucida. The apparent image of the scale projected to the
level of the base of the microscope was measured by a millimeter rule. ‘There is ob-
viously no significance to the actual size of this apparent image, since this would vary
with the degree of magnification employed. The only value such measurements have
is for comparative purposes. Therefore, the units of measurement have been considered
as purely arbitrary, and no actual value is assigned. It seems hardly necessary to state
that the same magnification has been used throughout this study. The actual mag-
nification of the image was approximately X 120. This: would give an actual value
of 0.00834 mm. for each unit of measurement. The measurements as given in the
tables were made from the center of the innermost ring along the anterior radius of the
scale.

One method of study used has not, to the author’s knowledge, been previously
described. This is the employment of large series of photographs for the purpose of
deciding doubtful points. It not infrequently happens that the scales from different
lots of fish will vary consistently in one or more minor characters which are very difficult
to determine by the successive examination of scales from individual fish. The memory
seems incapable of carrying all the necessary details in such form that a logical con-
clusion could be reached. When, however, fairly large series of photographs, say 50
of each category, can be spread out side by side, the comparison may be made very
readily, and often important conclusions may be drawn.

After some experimenting, in order to reduce the expense of plates, printing, etc.,
the scheme finally adopted for this purpose was to photograph directly on paper. Bro-
mide paper was tried at first, but it did not prove satisfactory. Either Azo, F, hard X,
or contrast Cyco was finally found to give the best results. Since the light values have
no particular significance in scale photographs, where the main requirement is to show
the lines well, these paper negatives are as favorable for study as prints taken from plates
would be. In case duplicates are wanted; these negatives may be used in the same

SEAWARD MIGRATION OF CHINOOK SALMON. 7

way as ordinary films and positive prints produced. The prints included with this
report were made in this manner. A Leitz photomicrographic apparatus fitted with
a 24-mm. mikro-summar was used and a small Bausch & Lomb arc lamp with condens-
ing lens as a source of light. For the magnification used, 35 diameters, Azo, F, hard
X requires an exposure of about 90 seconds and contrast Cyco about 15 seconds. The
paper is placed in the regular plate holder behind a piece of clear glass. Another piece
of glass or of stiff cardboard is placed behind the paper in order to hold it flat. The
best focus is one which makes each line of the scale appear on the ground glass as a
bright line having a narrow black line in the center. Considerable experience is nec-
essary before one can obtain this focus properly. The size of the arc light will deter-
mine the amount of time required for a proper exposure, and the same size of are should
be used, therefore, for all photographs in a series. The printing requires an exposure
to bright daylight (not sunlight) of about five seconds.

PRESENTATION OF DATA.
FISH FROM THE COLUMBIA RIVER.

The earliest collections made during any year were taken in the latter part of
March and early in April, 1916. At this time a trip was made by launch from Portland
to Astoria. Frequent hauls were made at different points, but many were unsuccessful
because of the flood stage of the river. Also poor acquaintance with the river made it
impossible to select the most favorable spots for seining. A seine 100 feet in length
was used. This had half-inch mesh in the wings and one-fourth inch mesh in the bag
The smallest salmon fry could be collected with this gear, as is proved by the fact that
fry which had not completely absorbed the yolk sac were frequently captured. The
later trips were more successful than the earlier ones, since the favorable places for
seining had been learned and attention confined to these.

Collections were made March 31, 1916, at Mayger, Oreg., and at Grims Island, near
Clatskanie, Oreg. On April 1 and 2 several collections were made at different points in
the lower part of the Columbia estuary. The best collections were obtained on Sand
Island and near Point Ellice, Wash. One hundred and forty-nine specimens in all were
taken. Forty-seven of these were yearlings and 102 were fry. The study of the
yearlings will have greater significance if delayed until after the development of the
fry during the first year shall have been followed. The collections of fry made on this
trip have all been studied separately, but no significant variations appeared, and the
data are therefore presented in a single table (1).

Less than one-half of the fry had developed sufficiently to form even the central
nuclear plates of the scales. Gilbert (1913@) describes a similar condition in the case
of the migrating fry of the sockeye. Twenty-three individuals show the central plate-
lets only and 19 have scales well enough developed for rings to be present. The aver-
age length® is 38.7 mm., with the mode at 38 mm. The average number of rings on the
scales of the 19 specimens possessing scales sufficiently developed to show rings is 1.7.
The average length of the anterior radius of the scales is 6.3 on the arbitrary scale. (See
p. 6.) The following table (1) gives all the data regarding these collections.

@ The averages employed in this paper are invariably the weighted mean,

8 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 1.—FRy FroM LOWER COLUMBIA RIVER, MAR. 31 TO APR. 2, 1916.

Number of speci-

periittee Scale record. 4
Length. Number. nee Scales Average frenbets in
5 with number of .
lets only. eines rings. 5 anterior
eS. ‘ radius. €
46 to somm ° 2 3-0 20-5
41 to 45 mm 4 6 2-0 8.5
36 to 40 mm 17 9 1-3 5-5
31to35 mm 2 2 1-5 4-2
PROC Saree feta leratetg stoksgete a el cial tele ptale ade cial etolas clots esta stamens le ielalmietelerate ateiaie site 23 | Bees egaqe ad bAmeaoecccar.
Aya Sey TIARTR are ate le aenaleisiet= che wi cteisir erie ala lia tinietels Inisteteicl te mitaters erdbeam ora aletaiais Lia cetera aietaiete aioe Spray I-7 6.3

@ For units of measurement used in the scale records in this and all succeeding tables see explanation on p. 6.
> Estimated from those specimens only which have scales with rings.
¢ Estimated from all specimens with either scales or platelets.

It is apparent from this table that the scales are usually formed by the time the
fish reach a length of 4o mm. It is not surprising that this condition is subject to a
considerable amount of variation, especially when so few individuals are involved.
The increase in the number of rings and in the size of the scales parallels the increase
in total length of the fish.

Owing to the difficulty in sexing these small fry, no information is available regarding
either sex proportions or variations due to sex.

A collection of 62 fry from the Clackamas hatchery, maintained near Oregon City,
Oreg., by the U. S. Bureau of Fisheries, was made April 11, 1916. (See Table 2.) It
will be interesting to compare this with the wild fish taken in the Columbia River.
These hatchery fish average considerably larger than the wild individuals. This is
presumably due, at least in part,.to the warmer water in which they were hatched and
reared. At the time this collection was made the water supply at the hatchery came
from a spring, and the temperature was uniformly 50° F. throughout the year. None
of the specimens are less than 40 mm. in length. The average is 46.5 mm., with the
mode at 43 mm.

TABLE 2.—DATA FOR 62 FRY FROM CLACKAMAS HaTCHERY, APR. 11, 1916.

Scale record.
Length. Number. x Average
Average Jength of
number of teri

rings anterior

. tadius.
61 to 65 mm.... I 8.0 28.0
56 to 60 mm... 4 7-5 25-5
51to55mm. 9 7-5 25-8
46 to somm... Ae eee 4. moe 17 5:5 20.3
Pay C7 Ob 0 CBO gO ETRE HES EE Cer P Inc SOAGORAn BoD bae Ser cor tieciom Gate: teres Sareoeasrinac ( 24 4:7 17-2
BGO AG ITI, ona :aieiaininpninienialavelainie Palais ara/ainys nial slab in sleipte bina aclabtinafe naeicar teinarciieeen tabiceetuiaer s 7 3-2 13-7
Be aie tetas TO AED CRAB eT AS AOE AR HERTS! a SoM Oh ORE iRoom Secon pinbe Sansa A eee Bee a | 5-4 18-8

The obvious skewing of the curve of length toward the smaller sizes is probably due
to constant additions to the smaller fish as a result of the hatching of the eggs spawned
later in the season. The data at hand are not sufficient to prove this, however. Almost
all the collections of small fry show such skewing which is apparently due to some such
fundamental cause as the one suggested. The scales show a progressive increase in

SEAWARD MIGRATION OF CHINOOK SALMON. 9

the number of rings and in the length of the anterior radius as the size of the fish increases.
In comparison with the fry taken in March and April on the lower Columbia River, one
is impressed by the fact that all of these hatchery fish, even the smallest, are provided
with scales having well-developed rings. The smallest number of rings found on the
scales of any specimen was three. A considerable proportion of the wild fish less than
45 mm. and more than 40 mm. in length have no scales, or at most only platelets. It
seems likely that something in the conditions of life at the hatchery is responsible, but
no direct evidence proved that this is available. The scales of the larger specimens
have already acquired some of the characteristics of the scales of typical hatchery fish.
Compared with the scales of wild fish, those from hatchery specimens show an irregular
growth. There are frequent minor checks, indicated by narrower rings; but, as a rule,
the true winter check is less well marked. The rings themselves are frequently slender
and more or less broken. Plate I, figure 9, and Plate IV, figure 3, illustrate scales from
hatchery fish. It is possible that a careful study of these characteristics might give a
means of identifying adult fish which had been reared for the first few months under
hatchery conditions.

In a collection of 26 fry from Cottonwood and Deer Islands, lower Columbia River,
on April 13, 1916, the average length of the specimens is 43.2 mm., with the mode at
38 mm. (See Table 3.) The skewing of the curve toward the smaller sizes is even
more marked in this collection than in the first one. The average length has increased
4.5 mm., but this seems largely due to the capture of several individuals which were
considerably larger than any contained in the first collection, the one made on the lower
river March 31 to April 2. The mode of the curve of length has remained the same.
No important changes appear in the scale record, although, as would be expected from
the larger average size of the fish, a slightly greater proportion has formed scales, and
the average number of rings is greater.

Eighteen specimens were sexed. Males and females are in equal numbers, nine each.
The average length of the males is 42.3 mm. and of the females 44.1 mm.

TABLE 3.—F RY FROM COTTONWOOD AND DEER ISLANDS, LOWER COLUMBIA RIVER, APR. 13, 1916.

Number of speci- |

reristwathiee Scale record.
Length. Number. ;

Plate. | Seales | Average | (Qveaes

lets with number of tes ji 2

: rings. rings. en

radius,

GA Gaerne Gu Re condoe so b SEBUSbEUCCHOE Aone sec Se neOeo: OGoaEoetE cose I ° I 6.0 23-0
I ° I 8.0 23-0
I ° I 5-0 18.0
2 ° 2 4:0 25-5
° ° DD Jac c nie cedic nce) tla wiedeia ale cele
7 ° 6 2-3 13-8
13 I I 2-0 10.5
PSMA SS PMLENTR rere icin lcheteiet acts ie eis. eielainisleaie cies oe gio Pisiave\s sisien wieinioinimeiseiviewierte I ° Oia nisin ele veis io) MaRte ae SORE
pL cater ee erect ete a sicko crelote SE ace cae deol tous Ne OM iste cw: olole ei otbnarssohe Stauston’ 26 I HW) | saSarat ae cag ee tone Sagano
BPA ew Arg wea SURITN ed ata ters ee AL Tier Cotchaim ciclo aie Letehefeteis cin ke che Volete: wisi feist cians ae l aslomialsaveteied k sicte asks aul taciecaraas 3-3 17-1

A small series of 19 specimens was preserved at the Clackamas hatchery May 2,
1916. (See Table 4.) The average length is 46.7 mm., with the mode at 48 mm. All
of the specimens have well-developed scales, none with less than four rings.

10 BULLETIN OF THE BUREAU OF FISHERIES.

Ten of the specimens are males and have an average length of 46.5mm. ‘The nine
females average 46.9 mm.

TABLE 4.—DATA FOR 19 FRY FROM CLACKAMAS HATCHERY, May 2, 1916.

Scale record.

Length. Number.

Several good collections were made May 10 and 11, 1916. ‘These have been divided
into two lots. The first was collected on Puget Island and at Crandall’s seining ground
on Grims Island. (See Table 5.) ‘These points are located about 30 miles above
Astoria. The second lot comprises collections made at several points on the lower
part of the estuary, the best series coming from Sand Island and Point Ellice. (See
Table 6.)

Two hundred and eighteen fry were taken at Crandall’s seining ground and on
Puget Island. Thirty-nine yearlings were taken at the same time. The length of the
fry ranges from 33 to98mm. ‘The average length is 52.5 mm., with the mode at 43 mm.
The sex proportion in this collection is 54.1 per cent males to 45.9 per cent females. The
average length of the males is 52.3 mm. and of the females 52.8 mm. The following
table (5) contains the data for this collection:

TABLE 5.—FRY FROM CRANDALL’S SEINING GROUND AND PuGET ISLAND, LOWER COLUMBIA RIVER,
May to, 1916.

Number of speci-
ane ie Scale record.
Length. Number.

Plate. | Scales | Average ea?

1 with number of thiol

ets. rings rings anterior

: 3 radius,

e
96 to 100 mm ° I 12.0 63.0
91 too5 mm ° 3 10.6 48.0
86 to 90 mm ° 2 10.0 48.0
81 to 85 mm ° 7 10.0 46. 5
76 to 80 mm ° 7 9-3 41-0
71 to 75 mm ° 7 8.1 41.0
66 to 70 mm ° Ir 8.1 37-0
61 to 65 mm ° 14 6.4 31-0
56 to 60 mm... ° 22 6.2 28.2
5rtoss5mm... ° 2 5-2 26.5
46 to somm... ° 30 4.6 22.6
41 to 45mm I 38 2.9 16.5
36 to 40 mm 6 ar 1.3 12-0
31 to35mm ° ty SSeoecdcaser GeduosoccAci-
i i

otal .p. cedics soanaae Sap ataiees sa See eaale care st ABs eerie tape re eBeidleeaweioe 7 XQi lots tela ro cas RG TE Ss
AS aise TREN fs aiptslaiaisfaicisiorelesatoVo lie’ s oiaiere we miain si etele etetois alataiars etl stalstereietencia elebtal eicieiieialaae lalealeamcaiee Lamiate ere 49 22.4

The collections made May 11 in the lower part of the estuary include 103 fry and 10
yearlings. There are 52 males among the fry averaging 46.7 mm. in length. The
51 females average 48.8 mm. ‘The following table (6) gives the data regarding the fry:

SEAWARD MIGRATION OF CHINOOK SALMON. II

TABLE 6.—FRy FROM LOWER Part oF COLUMBIA EstTuARY, May 11, 1916.

Number of speci-

ae eS Scale record.

Length. Number. ante, pees Average

Plate- e 8 length of

lets. with | number of | “anterior

Tut ee pelt radius,

I ° I 9-0 43-0
° ° © fo cnnncvenncsfeccvcccecens
° ° © [onsen cecccrcfeececceccccs
° ° © Joc ncceeccccfecvecesscces
2 ° 2 6.5 33-90
13 ° 13 6.2 29-90
14 ° 14 5-4 24-9
23 ° 23 4-0 21-2
25 ° 25 302) 17-3
22 3 Ir 1-6 10.5
3 ° hiboooodaacondl bocupdiisedas
103 3 oe i ctncta Suction ponaeocmnechis
sae bdooond Nermecodned Bntosicksn 4-2 20-6

In comparing these collections with the ones made the day before, the average
smaller size of the fish is the only conspicuous point of difference. This is obviously
due to a scarcity of fish of the larger sizes, since the modes of the two curves are the
same, 43 mm. ‘The water in the lower part of the estuary is quite brackish owing to
the considerable admixture of salt water, while that in the part of the river where the
collections of May 10 were made is perfectly fresh. Therefore it would seem probable
that on reaching the brackish water the larger fish tended to continue their migration
on into the ocean, while the smaller ones remained behind.

The next collection to be considered was made in the Columbia River near the mouth
of the Little White Salmon River, about 50 miles above the point where the Willamette
River joins the Columbia. This collection was made May 25, 1916, at which time 24 fry
and 1 yearling were captured. The fry average 44.6 mm. in length and range from
37 to 61 mm. ‘The mode is at 49 mm. Six specimens“have no scales, 7 have only
platelets, and 11 have scales with rings. Males and females are present in this col-
lection in equal numbers and are also of equal size, both sexes averaging 44.6 mm. in
length. The following table (7) contains the data:

TABLE 7.—FRY FROM COLUMBIA RIVER NEAR MoutH oF LittLE WHITE SALMON RIVER, May 25, 1916.

Number of speci-
A Scale record,
mens with— |
Length. Number.

| Average

Plate- sa Ayersee f length of

Jet pete numer Of | anterior

| rings. rings. iiss

61 to 65 mm... I ° I 7-0 28.9
4 ° 4 6.7 28.0
I ° I 6.0 23-0
2 ° 2 4-0 20-5
4 2 rT I-0 8.0
2 5 2 I-5 8.0
4-7 21-3

12 BULLETIN OF THE BUREAU OF FISHERIES.

The smaller size of these fish as compared with those from below the mouth of the
Willamette River is distinctly shown and is in accord with our explanation of the
excessive proportion of small fish in the collections from the lower river; that is, that
smaller fish are constantly being added to those in the estuary as a result of migration
from above.

Eight specimens were preserved at the Clackamash atchery, May 27, 1916. These
average 56 mm. in length. All have well developed scales. The average number of
rings on the scales is 7.5, and the average length of the anterior radius of the scales is
28.5. There are four males averaging 53 mm. in length and four females averaging
59 mm.

A good collection of fry was made near Astoria, in the lower part of the estuary
June 12 and 13, 1916. (See Tables 8 and 9.) In all, 132 specimens were taken, and it
is worthy of note that none were yearlings. Yearlings do not appear in any subsequent
collection from the lower part of the river, and it may be concluded from this that the
yearling migrants quit the river for salt water about the first of June, if not earlier.
This point is given more detailed consideration later.

Thirty-six of these fry were taken just within the mouth of a small creek near Point
Ellice. They differ so distinctly from the remainder of the collection that they are
considered separately. (See Table 8.) The average length is but 47.7 mm., with the
mode at 38 mm. All of the individuals have formed scales, and in all but one, rings
are present on the scales. The average number of rings is 4.1, and the average length
of the anterior radius is 20.5. Nineteen of these specimens are males averaging 47.5
mm. in length. Seventeen females average 48 mm.

TABLE 8.—FRY FROM WITHIN MOUTH OF SMALL CREEK NEAR Point ELLicE, COLUMBIA RIVER, JUNE 13,

1916.
Number of speci-
biens with | Scale record.
Length. ed Number.
Plate- | Scal Average rata
lets. with | number of =
: is rings. anterior
radius.
ae ae x o} I 8-0 33-0
Jtwuasee 2 ° 2 7-o 23.0
4 ° 4 7-0 29-2
7 o!} 7) 5-3 25-0
6 ° 6 43 20-5
Sceecoe 5 ° s| 3-4 18.0
Ir I 10 I-s 13-0
af = Ree ea ee 36 | I 35 SPE TT ee th
RR aR a Re PAB eR SPE SOC coe ey ee Se ke 4-1 20 5

The remaining 96 specimens collected in the estuary at this time are distinctly
larger, averaging 76.5 mm. in length. In these specimens it is found for the first time
that the scales of some of the fish have developed the wider marginal rings which have
been designated “‘intermediate rings.’”’ This marginal band of wider rings is usually
sharply differentiated from the central part of the scale and begins abruptly—not by a
gradual increase in the space between rings. It may even be preceded by a slight
narrowing, especially in the older fish. Gilbert (1913) has found similar intermediate

SEAWARD MIGRATION OF CHINOOK SALMON. 13

growth in sockeye and silver salmon which migrated as yearlings. These intermediate
rings represent a period of growth more rapid than the normal growth in fresh water
and yet not so vigorous as the true ocean growth (PI. II, figs. 3, 4, 5, and 6). Inter-
mediate rings are not present on the scales of every specimen, but among the larger fry
and yearlings taken in the estuary after the first of June some are always found which
show this type of growth at the margins of the scales. For the purpose of ready com-
parison those fish whose scales show the band of intermediate rings are given separate
consideration.

The fry contained in the collection of June 13 which do not show this intermediate
growth (80 in number) average 75.2 mm. in length. The length ranges from 53 to 105
mm., with the mode at 73 mm. ‘The average number of rings is 9.6, and the average
length of the anterior radius is 38.1. The males number 35 (44 per cent) and average
78.3mm. The 45 females average 72.8 mm. in length.

Sixteen specimens have scales which show the intermediate growth. These average
83.1 mm.inlength. Seven males average 80.3 mm.; and 9 females, 85.3 mm. The follow-
ing table (9) presents the data for this collection:

TABLE 9.—FRY FROM COLUMBIA ESTUARY, JUNE 12 AND 13, 1916.

EIGHTY SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.
-
Length. Number. Averase eta
number of rerioed
rings. Get?
jus.
PRE SRUR AMOS Cb SERIM Eo tert nteteray seta eetatst ntatelatetas ciel alars\alevelalereieleisiiin .s/eisia,aidaia hatwieraia/s staidiala’ sieteih) a; <)aicla eisistateta viele te I IIo 48.0
COREL aoe paar er
11-2 43-6
10-5 41-9
10.5 38.0
9-2 36.7
9-0 35-0
7-6 30-8
7-0 28.8
4-0
9-6

SIXTEEN SPECIMENS WITH INTERMEDIATE GROWTH.

Scale record.

Average
estimated
Length of anterior | length of

~ radius— fish at
beginning
of inter-

Number of rings—

Length. Number.

mediate
Total. | growth. 4

To inter- | In inter-
mediate | mediate Total.
growth. growth.

3 12-3 4-6 16.9 51-3 63-0
3 13-0 6.0 19-0 46.3 49-6
5 10.6 4-6 14-6 42-0 52-0
2 10-0 4-0 14-0 38-0 53-0
a 8.5 4-0 12-5 33-0 50-5
I 9-0 4-0 13-0 33-0 48-5
Daim vislsieie w euiewee an a]asin ccm ce. 11-6 4-6 16.2 42-4 53-3

9 For explanation of estimated length of fish in this and succeeding tables see p. 14.
75412°—22. 2

14 BULLETIN OF THE BUREAU OF FISHERIES.

The smaller size of the fish taken within the mouth of the creek near Point Ellice
is of interest and may be accounted for by one of two hypotheses: (1) These may be
fry which are just migrating from the stream into the Columbia estuary. It is not known
definitely whether chinook salmon spawn in this stream, but it is rather unlikely. Two
attempts were made to determine this, but only silver salmon were obtained. The
stream is quite small and is not a typical chinook stream, being for the most part shallow
and with sandy bottom. Furthermore, since the stream is so near the ocean, it should
be expected, owing to the warmer and more equable climate, that development would
be more rapid than in the higher tributaries. If this were the case, it would be expected,
unless growth were modified by some other factor, such as racial difference, that the
fish coming from this stream would average larger than those from the higher tributaries.
(2) The more probable hypothesis is that the smaller individuals among the migrating
fry have run up into the mouth of the stream. This might be for the sake of the probable

‘greater safety in such a location or because of the reduced salinity of the water. It
has been shown by Rutter (1903) that the larger fry are more resistant to the effects
of salt water, and also that alternations in the salinity of the water are a distinct aid
in accustoming the young fish to sea water. The second hypothesis, therefore, seems a
reasonable explanation for the presence of the smaller fish in the mouth of this stream.
It is quite probable that if these fish remain for any length of time in the fresh water of
such a stream it will have a tendency to slow up the growth rate and result finally in
developing irregularities of scale growth.

Among those fish taken in the Columbia estuary proper it has been shown that those
specimens whose scales show a band of intermediate rings average larger than those
whose scales do not show this band. Since the wider rings indicate a more vigorous
growth this result was quite to be expected and hardly calls for special comment. It is
worthy of note, however, that the estimated length of the fish at the time of beginning
this intermediate growth is distinctly less than the length of those fish which have not
begun this intermediate growth. This estimated length was found by the method in-
vented by Dahl and since used to advantage by Gilbert, and also by Fraser. This method
involves the following proportion:

Total length of scale : total length of fish : : the length of the scale at some particular point : the
length of the fish at the time this point was at the periphery of the scale.

By applying this proportion to each individual it is found that in the 16 individ-
uals which have formed an intermediate band the average length at the time this inter-
mediate growth was begun was 53.3 mm. The average length of those fish present in
the estuary at this time, but which have not begun the intermediate growth, is 75.1 mm.
This shows that the fish whose scales do not have an intermediate band have arrived
in the estuary more recently than those whose scales do show this band of wider rings.
The greater length of the fish which have been longer in the estuary is the result of the
more rapid rate of growth maintained in the estuary as compared with the slower growth
in fresh water upstream. The cause of the accelerated growth in salt water is at present
unknown but is probably due to the increase in the food supply. One other possibility
suggests itself in explanation of the fact that some individuals do not show the more
rapid intermediate growth, namely, some individuals may not respond as readily (or
perhaps not at all) to the stimuli encountered in the estuary which, in other individuals,
initiate the accelerated growth.

SEAWARD MIGRATION OF CHINOOK SALMON. 15

One hundred and sixty-six specimens of migrating fry were captured at Point
Ellice, July 19, 1916. (See Table 10.) The average length is 92.1 mm., ranging from
60 to 128 mm., with the mode at 93 mm. It will be noted that here and in the subsequent
tables there is very little skewing of the curve of length toward the lower end. This
indicates, undoubtedly, that no more of the smallest fry are being added from the upper
waters. This is proved by the fact that no fry less than 60 mm. in length were taken.
Such fry as are entering the estuary from above must be more nearly the same size as
the fish already in the estuary.

The scales of these fish show an average of 12.9 rings. One hundred and sixteen
have started a more rapid intermediate growth, which is indicated on the scales by a
marginal band of wider rings. There is an average of 7.6 rings within the intermediate
band, the band itself comprising 5.3 rings. Seventy-six of the specimens are males,
averaging 90.1 mm. in length. Ninety females average 93.6 mm.

TABLE 10.—FRY FROM Pornt ELLice, CoLumBIA ESTUARY, JULY 19, 1916.
e
FIFTY SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.
|
Length, Number. Average
| Average length of
number of >
rings. anterior
radius.
irr to 115 mm.. 3 14-3 66.3
106 to 110 mm... I II-o 48.0
ror to 105 mm 4 15-0 56-7
96 to roo mm... 8 13-2 52-8
otto 95mm.. Io 12-6 48.0
86to 90mm 5 10.6 43-0
8r1to 85mm.... TO 10.5 40-5
76to 80mm 5 II-4 40.0
-71to 75mm I 10.0 33-0
66to 7omm I 10-0 33-0°
6rto 65mm.... I 9-0 33-0
56to 60mm I 9-0 28.0
NRPS A LILL sey sacalale ds ele see eta ala rae iss clases a ej afeh slaty nha cve a alasv 0!sTal ave Yates Chaye binve nl gia ote eee Sore elsiall oraieta ata wvelels II-9 46-4
ONE HUNDRED AND SIXTEEN SPECIMENS WITH INTERMEDIATE GROWTH.
Scale record.
Average
; estimated
Number of rings— Length anterior | length of
Length. Number. Tadius— fish at
(oe beginning
of inter-
To inter- | In inter- To inter- mediate
mediate | mediate | Total. mediate | Total. growth.
growth. growth. growth.
126 to 1330 mm 7-0 13-0 20.0 28.0 78.0 43-0
avi Uae an titer Pateehn en aia ieimniccicee ee aee Mae Ol cura acterepteliene stale arcienite llaieiaters eiche ciara cturatatche cies elle lwstaroteisnrcbcn oetnmtcurs
116 to 120 mm 9-6 7.1 16.7 37-0 63-0 76.5
rrr to 115 mm 9.2 7-3 16.5 30-5 60.8 60. 5
106 to 110 mm.... 77 7-0 14-7 30-8 57-0 54:5
ror to 105 mm.. 8-4 6.9 15-3 31-3 56-5 58-0
96 to roo mm... 8-0 5-4 13-4 30-2 5I-0 60. 5
orto 95mm 7-2 5-6 12-8 28-5 48-3 54-5
86 to. 90mm 7-3 4:9 12.2 27-1 44-9 55-5
81to 85mm 9-2 4-2 II-4 27-2 41-3 52-6
76to 80mm 6.9 4-7 11-6 24-4 39-5 47-3
71to 75mm 6.2 4-0 II-2 21-0 36-4 43-0
66to 7omm 5-0 5-0 10.0 13-0 28.0 38.0
6rto 65mm 6.5 5:0 Im.5 23-0 B55 50.5
Avy. 93.1 mm 7-6 55 13-1 28.3 49-8 23

16 BULLETIN OF THE BUREAU OF FISHERIES.

With few minor exceptions, the results obtained from the study of this collection
are similar in all respects to those obtained from a study of the June collections. The
difference in length between the fish which have begun the rapid intermediate growth and
those which have not is less but is plainly indicated, the fish having the intermediate
band being larger. The average estimated length at the time of beginning the inter-
mediate growth is approximately the same, 55.3 mm.

A collection containing 51 specimens was made at Point Ellice, August 12, 1916.
Another series of 13 specimens was collected from the same place August 26, 1916.
Since no particular difference in these two collections has appeared as a result of their
study, they will be considered together. (See Table 11.) The average length is 93.9 mm.,
ranging from 49 to122mm. The modeisat 93mm. It will be noticed that the average
length of this collection is approximately the same as that of the July collection. It
might be concluded from this that an average length of 92 or 93 mmis the maximum
attained in the estuary, but this conclusion is not borne out by subsequent collections.
Forty of these specimens are males, averaging 92 mm. in length. Twenty-four females
average 97.2 mm.

The scales do not differ greatly from those of the July collection. The number of
rings has increased slightly, although the size of the scale, as indicated by the length of
the anterior radius, remains practically the same. The estimated length at the time of
beginning the intermediate growth is nearly the same as in June and July. Six of the
specimens collected August 26 begin to show at the periphery of the scales narrow
rings, indicating the slower winter growth.

TABLE 11.—FRY FROM Point ELLice, WASH., AUG. 12 AND 26, 1916.

TWENTY-SEVEN SPECIMENS WITHOUT INTERMEDIATE GROWTH.

| Scale record.
Length. Number. Average
Average length of
number of ei
rings. anterior
| radius.
106 to 110 mm 18.0 55°5
ror to 105 mm 14-0 48-0
96 to 100 mm A 16.0 54-2
orto 95mm 53 14-4 47-0
86to 90mm as 13-7 45-7
8rto 85mm Di 14-0 43-0
76to 80mm Balle 2) | MGA lerateRe sloteielninle| tafaleln lata ttetetete
7ito 75mm ae 10-0 43-0
66to 7omm.. fe 10.0 38.0
6rto65mm... 4a 9-0 33-0
s6to 60mm.. bd ee 8 eset) tasantmaguccd Hconpbe sacs”
SECO GS MAM oe ce coe sss cule ctarscserscscasvceseveliscenteerteeeiiescaneesiercinadicesncccseli _ | Ollelwsepinnsnsins| cieicinaiale enviar
46to somm 4:0 18.0

i SEAWARD MIGRATION OF CHINOOK SALMON. 17

TABLE 11.—FRy FROM Point ELLICE, WASH., AUG. 12 AND 26, 1916—Contd.

THIRTY-SEVEN SPECIMENS WITH INTERMEDIATE GROWTH.

-

Scale record.

= Average

EyaE estimated

Number of rings— Length ob anterior fae oe

Length. ber. mee

gth. Num beginning

of inter-

To inter- | In inter- To inter- mediate

mediate | mediate Total. mediate Total. growth.

growth. growth. growth.

iar to 125mm... I 13-0 720 20.0 38-0 63-0 73-0
116 to 120mm... 2 13-5 8.0 21-5 45-5 68.0 80. 5
tir to 115mm... 2 13-0 5 20-5 38.0 55-5 73-0
106 to 110mm... 3 9-0 9-0 18.0 29:6 58-0 65-5
ror to 105 mm 8 9-1 7°3 16.4 29-6 54-2 58.0
96to 100 mm... 4 9-2 8.2 17-4 30.5 56.7 54-2
orto 95mm... 9 6.2 9:3 15-5 22.3 51.3 44-1
86to 90mm... 4 5 8.0 15-5 24-4 43-0 51-5
81to 85mm... 3 6.0 5-8 11-8 23-0 38-0 51-3
76to 8omm I 6.0 6.0 12.0 23-0 43-0 48-0
g AV. 98-5 MM... 2... eee eee eee ee eee ne eee eee eleee eee ees 8.5 7-9 16.1 | 28.2 52-3 54:8

Three specimens of young chinook salmon were caught August 23, 1916, by hook
and line from the wharf of P. J. McGowan & Sons at Ilwaco, Wash. These young
fish were under the cannery and were feeding voraciously on the offal resulting from
the cleaning of the adult salmon. ‘Their stomachs were quite filled with eggs and
small pieces of kidney, flesh, etc. There was very little evidence that they had been
feeding on insects or crustaceans. Several other collections were made under this can-
nery and one other in Astoria, and in every case the young fish were found to have
eaten heavily of the offal. These three specimens are all females averaging 118 mm.
in length. The scales of one specimen show a distinct intermediate band of eight rings.
The average number of rings on the scales is 21.3. The length of the anterior radius
averages 61.3.

Ten specimens of young chinooks were collected in the Clackamas River, August
go and 31, 1916. (See Table 12.) The collection was made by hook and line near the
Clackamas hatchery, about 2 miles above where the Clackamas River flows into the
Willamette. Five of these are males averaging 113.8 mm. in length. The five females
average 112 mm. Four of the males were approaching maturity, as was indicated by
the enlarged and white testes. The average length of these four is 118.2 mm. The
scales of these precocious males are in every respect similar to the scales of the other
individuals. Such precociously matured males have been previously described by
Rutter (1903). The scales of these fish indicate unmistakably that they were fry, less
than 1 year old. The scales of 8 out of the 10 individuals show a distinct narrowing
of the marginal rings corresponding to the slower growth of the fall and winter. Since
the number of specimens is so small, no attempt is made to segregate the specimens
showing different types of scale growth.

18 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 12.—YOUNG CHINOOKS FROM CLACKAMAS RIVER, AUG. 30 AND 31, 1916.

j
Number— Scale record,

Average
| Soaperme ty

| ength of

I xy - | Average length of
Average length. ae Number of rings arterial ae
V

Total. check. formations

heck.

Tocheck.} Total. |Tocheck.| Total. cher’
0X29 MM. 2. ive ec ce certs eeewsccsccesescunsd Io Ci 6-7 20.7 17-3 58-2 43-4

The check found on these scales, while in some respects similar, can not be con-
sidered as identical with the check preceding the intermediate rings, which is a feature
of the scale growth of the fish taken on the lower river. The central part of the scales,
within the check, is composed of a fewer number of rings, is smaller in size, and the
rings succeeding the check are not so wide. (See Pl. I, figs. 7 and 8.) While it seems
probable that the fundamental causes underlying the formation of these checks are
similar (probably a change in the food supply or other environmental conditions), the
change in the case of the fish entering the brackish water of the estuary is more pro-
found. In order to distinguish these two types of checks in the discussions, the term
“primary check” will be used for that formed in the upper parts of the stream and
“migratory check”’ for that formed on entering the estuary. The next collection to be
mentioned will throw further light on this question.

In April and May, 1915, the Oregon Fish and Game Commission planted, from the
hatchery at Bonneville, several carloads of chinook fry in a small artificial lake near
Seufert, Oreg. The fish were fed daily with offal from Seufert Bros. cannery, which is
located at this point. At the time the plant was made the writer measured a small
series of the fish. The average length was 44.6 mm. September 2, 1915, a collection
of 55 specimens was made by hook and line from this lake and the outlet which con-
nected the lake with the Columbia River. (See Table 13.) The average length was
80.9 mm. ‘Twenty-seven were males averaging 81.5 mm. in length and 28 were females
averaging 80.3 mm. ‘There were three mature males in the lot, and these averaged 94
mm. in length. The most interesting point which appeared in the study of this collec-
tion has to do with the formation of the primary check mentioned above. Such a check
was apparent on the scales of 84 per cent of the specimens, and an average of 6.7 rings
was included within this check. The general appearance of the scales is similar to
that of fish reared under typical hatchery conditions; that is, the rings are more or
less irregularly spaced and may be broken. (See Pl. I, fig. 6.) The central portion
was missing from many of the scales examined, so that it was frequently necessary to
examine several scales from the same fish before a perfect one was found. Not infre-
quently a similar central portion would be dislocated in reference to the scale as a whole,
as though it had been loosened and turned within the delicate pocket of the skin in
which the scale is formed. This appearance has also been described by Gilbert (1914, p.
62), who has found it on the scales of the sockeye salmon. These blank and dislocated
centers correspond in size to the area within the check on the perfect scales, and there
could be no doubt that the same cause was responsible for all three of these abnor-
malities in the scale growth. Nineteen specimens (35 per cent) had begun the slower

SEAWARD MIGRATION OF CHINOOK SALMON. 19

winter growth, as is indicated by the narrower marginal rings. The following table (13)
gives the data regarding this collection. No attempt is made to segregate the few
specimens whose scales do not possess this primary check.

TABLE 13.—YOUNG CHINOOKS FROM LAKE AT SEUFERT, OREG., SEPT. 2, IQI5.

Number— Scale record.

Average

estimated

: length of

Length. | Number of rings— renee ee anterie fish at

otal. | With sees

. check, |————_—_—— | A pena

heck.

Tocheck.| Total. | Tocheck.| Total. eiGiea
CUE CEL OTE Nera sails bolts sie/elsisieiete(nivialetelejeleiatalsie/=la 2 2 8.5 14-0 25-5 45-5 63-0
arias Se Se oe ocgdpdnecacocnos oonoonanenoaDdo 2 2 9-5 17-0 33-9 55°5 63-0
DY AES enc cGoS DD Do LOSNRBEOADOOCeM CONE OSOON ° CY ocoponocod Wponeanciaces DEDadUnAoT poooodesese bogsooponus
91 to95 mm.. 3 3 5-6 13-6 21-3 41-3 49-5
86 to 90 mm, 7 7 8.3 14-6 28.8 44-4 54:5
81 to 85mm I2 Ir 6.7 12-9 22-5 39-2 46-0
Wat ONT a5 pp didupido Jee 2oo0nace boda dan soe II 8 6.1 12-3 21-1 37-5 45-0
pe Oyy G ATIIEE pte arte niet=isin\e'slalolals/siefsls)cl=]a\ele\efslslaisiaie 12 7 5-6 II-4 17-3 32-5 41-0
Or eT Be bar boets ae O Soon oor GpOBOeEnOBESpor 5 5 6-4 II-2 18.0 31-0 39-0
PEAT ONO rede ait Wiape ie Talo\s hes talp\ ciel iatniaietelatot dia\eisieretcraisie/sjata\a\e I I 4.0 II-o 13-0 28.0 33-0
pasiobeal Greet teratercrateth cetera iste oscieiets Vetsisictal=.cia.armcieis niclejsio = 55 715M | PROBEHERCaA MSS aeBeeee Ho eReH esa SCUGGDOSSEN Haceaaeaue
Jy ae NES sp atacoroo sara: Sosnosaroncen sal poccentinne|Souscecnnd 6.7 12-7 22-2 37-9 47-9

The almost exact correspondence between the estimated length at the time of the
formation of the primary check and the actual observed length at the time of planting
proves conclusively that in this particular instance the altered rate of growth following
the formation of the check was in response to the changed environmental conditions
resulting from the removal of the fish from the hatchery at Bonneville to the lake at

Seufert.
Sixty-nine specimens were collected September 15, 1916, at Crandall’s seining ground

on Grims Island. In several respects this is an unusual collection. The average length
is but 74.4 mm., the smallest recorded since June. The proportion of specimens whose
scales show the intermediate growth is also very small, only three in the entire collection.
None of the other collections made at this point are remarkable for the small size of the
fish as compared with other collections made at the same time of year in other localities,
so that it is unlikely that selection has taken place here as was evidently the case with the
collection made within the mouth of the small stream near Point Ellice. A possible
explanation may be that we are dealing here with a series composed largely, if not
wholly, of fish migrating seaward from some particular tributary or region of the Co-
lumbia River watershed, in which the fry do not attain, before migration, as large a
size as is common for other parts of the watershed. Gilbert (1912@) has described such
differences among the young migrating sockeyes in different tributaries of the Fraser
River system. This explanation seems, therefore, plausible in the case of these young
chinooks, although admittedly unproved.

The three specimens which show a band of intermediate rings are among the largest
taken and average 89.3 mm. in length. The average number of rings preceding the
intermediate growth is 7. The number of intermediate rings averages 9, and the
average total number of rings is, therefore, 16. The average length of the anterior
radius of the scale is 21.3 to the beginning of the intermediate growth and 47.3 to the

20 BULLETIN OF THE BUREAU OF FISHERIES.

periphery of the scales. The average estimated length at the time of beginning the
rapid growth is 39.3 mm. ‘The whole collection contains 36 males and 33 females. The
males have an average length of 74.2 mm. and the females 74.8 mm. In the following
table (14) are presented the data relative to those specimens whose scales do not show a
band of intermediate rings:

TABLE 14.—DATA FOR 66 YOUNG CHINOOKS FROM CRANDALL’S SEINING GROUND, SEPT. 15, 1916.

SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.

Length. Number.
sumer | Lenthf
of rings. radius.

4 15-5 54-0

6 14-9 45-1

20 13-4 42-0

14 12-9 41-0

14 II-9 36.5

Cr TOIT Hae R doc as Gost DESHOE GMS UDEanos 2onAd AgEnd Ie CoDRE Hares eeor cl Is eaaopnensostigne 7 11-9 33-5
ROUGH Se SSeS ques Taba tbdoe BoE none e M68 ISHS Bote iodasonbecok dats cia acoaseotosccdags r 13-0 33-0
TAG Ete BASSO e fC ARSE SEDs SOSN ATA AR SERN Rae ae Hae ee Sa ae 8 ee Bon Pree eric 13-1 40-1

Thirty-five young chinooks were taken by hook and line September 17, 1914, from
beneath the McGowan cannery at Ilwaco, Wash. ‘The scales of 28 (80 per cent) of these
show a marginal band of intermediate rings. As a rule these intermediate rings are
distinctly heavier and wider than is the case with the average fish collected elsewhere
in the estuary. It is also found that the rings immediately preceding the intermediate
band are sometimes distinctly narrower than the more central rings. (See Pl. II,
figs. 5 and 7.) This same appearance characterizes the scales of a few specimens from
Crandall’s seining ground, just mentioned, and, to anticipate, is found in varying
proportions in all later collections from the estuary. There are not, however, two
distinct categories of scales, one exhibiting a distinct narrowing preceding the inter-
mediate growth and the other without such narrowing. All stages in the development
of this band of narrow rings may be observed from examples where the intermediate
band begins merely as a sudden widening (PI. II, fig. 6) to those where the intermediate
band is preceded by a very clear and well-marked band of narrow rings (PI. II, fig. 5).
Plate II, figure 7, represents an intermediate condition. Among the seven fish whose
scales do not show intermediate growth are five whose scales terminate in narrow rings
of the winter type. These are somewhat smaller than the specimens whose scales do
show the intermediate band, and there can be little doubt that they are the more recent
arrivals from upstream which had not yet begun the intermediate growth.

The scales of some of the specimens contained in this collection have also a more
or less well-developed primary check in addition to the migratory check which imme-
diately precedes the intermediate growth. This also is found in varying proportions
in the subsequent collections and will be considered more in detail later. Eighteen
males average 121.3 mm. in length and 17 females average 124.7 mm. ‘The following
table (15) contains the data for this collection:

SEAWARD MIGRATION OF CHINOOK SALMON. 21

TABLE 15.—YOUNG CHINOOKS FROM UNDER THE CANNERY, ILwaco, WASH., SEPT. 17, 1914.

SEVEN SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.

Average length.

Length of
Number :
rae anterior
of rings radius.
120.2 TMT oe ee ete eee eee eee tree ee eee teense teen eerste eee ee se neee | 20.2 59-4
|
TWENTY-EIGHT SPECIMENS WITH INTERMEDIATE GROWTH.
Scale record.
Average
F estimated
Number of rings— Length of anterior | length of
Length Naanee radius— fish at
. beginning
of inter-
| To inter- To inter- mediate
mediate | ‘Total. mediate | Total. growth.
| growth. growth.
1st to rss mm I 17-0 28.0 53-0 88.0 98-0
146 to 1530 mm (OE fRUaerad- eects ratend Gye rape ale ahede lerutd ova’ (Sve ereral chute Sarovovater ameter unadd oti aierate oreleiere
141 tor45mm.. 2 17-0 24-5 55-0 75-0 I05-0
136 to 140 mm... I 25-0 30-0 53-0 78.0 98-0
131 to135mm.. I 20-0 23-0 53-0 58-0 118-0
126 tor30 mm.. 6 I7-0 20-7 48-0 61-0 100-0
121 to1z25mm.. 5 18.6 21-4 50-0 60.0 105-0
116 torz2omm.... 6 16.6 20-3 47-0 59-0 95-0
111 to1r5 mm 4 16.2 19.6 45-0 55-0 89.0
106 to r1o mm 2 se baee cdr Ga desc hdd! Soooeke seed Beaoeogosatl hens odoa she
ror to 105 mm 2 13-0 19-5 40-0 60.0 70-0
J SGOD Gio ae ORS SAU ODES Heme b eet Tent eeoete> SoU BEL He ape pace 17-2 21-4 48.1 62-0 96-8

Seven specimens were collected from the Clackamas River near the hatchery on
October 13, 1915. These were obtained by hook and line fishing, and the collection is
too small and too variable to deserve detailed attention. The average length is 118 mm.,
and the average total number of rings on the scales, 21. Several show the primary
check, and one at least had apparently started a new period of vigorous growth. ‘This
is indicated on the scales by a marginal band of five slightly wider rings. The scales of
all of the other specimens terminate in rings of the winter type.

October 16, 1915, a collection consisting of 119 young chinooks was made at Point
Ellice, Wash. The total average length is 112.7 mm. Sixty-one males average 112.2
mm. and 58 females 113.3 mm. ‘Twenty-nine specimens (24 per cent) have a distinct
intermediate band at the margins of the scales. The scales of the remaining 90 speci-
mens terminate uniformly in narrow winter rings. The scales of a considerable pro-
portion show the primary check about 9 or 10 rings from the center. The following
table (16) presents the data.

22 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 16.—Younc CuINooxs FRom Point Etiick, WaSH., Oct. 16, 1915.

SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Number— Scale record.
| Average
aner
set Length of anterior length ol
Length. With Number of rings Sanaa aatiae
otal: P\| primary) |stes see Sues eh) ee EE ear iation’
: check, of check.

Tocheck.| Total. | Tocheck.| Total.

146 to 50 mm
141 to 145 mm
136 to 140 mm
131 to 135 mm
126 to 130 mm
121 to 125 mm
116 to 120 mm
tir to 15 mm
106 to rr1o mm
ror to 105 mm ot
QO FEO AMET ain ceccp see ehate eiuois ala alainislaatnlaletnlotelntelale

SPECIMENS WITH INTERMEDIATE GROWTH.

Number— Scale record. Average estimated
length of fish at
time of forma-

Ss Number of rings— Length of anterior radius— tion of—
Length: With
Total. ees To To inter- To To inter-

primary | mediate | Total. | primary | mediate | Total.
check, | growth. . check. | growth.

131 to135mm......... 2 I 9.0 22.0 25.5 28.0 58.0 68.0
126to130mm......... I CJ AS4boee Sar 23-0 ECS geons dc * 53-0 63-0
rarto1z25mm......... I Ons seeeeat 19.0 24H eh aces 48.0 63.0
116tOrz20mm......... 5 5 9-8 22.8 25.6 26.0 55-0 65.0
rirto1m5mm......... 5 5 10. 6 21.8 25.2 29:0 50-0 60. 0
ro6 to1romm......... 9 5 7-0 19. 4 22-3 24.0 49-6 58.5
rortO1o5mm......... 4 I Ilo 18.2 21.7 33-0 46. 7 56.7
96to1oomm.......... 2 GN Ponanne os 17-0 TQ Bellet es cisintotd 48.0 55:5
A iis: Cee a pee 29 |e Al BOSD RST] DGOn ER SGECe Dee asc eee [atece ce) nee one coel HeeAs coeeelbArteen. ea
PW keep tye See oe Pema neatac! Seo oc eae a 9. 25 20.3 23-4 26.8 50.7 60. 6

In connection with the series just considered another collection made the following
day, October 17, 1915, is of considerable interest. This second collection was made by
hook and line under one of the canneries located at Astoria, Oreg., the Union Fisher-
men’s Cooperative Cannery. As has been already mentioned, fish taken under these
conditions are always found to be feeding heavily on the offal from the cannery. ‘This
collection consists of 61 specimens, of which 43 (70 per cent) have scales which show
the intermediate growth. The average length of this collection is considerably greater
than for the Point Ellice collection, 127.5 mm. ‘The specimens which had begun the
rapid intermediate growth average 130.5 mm., and those which had not done so average
but 120.2 mm. All of the specimens whose scales do not show intermediate rings have
the narrow winter rings at the scale margins. Thirty-three males average 127.9 mm.
in length and 28 females 127.0 mm. The following table (17) gives the data for this
collection:

SEAWARD MIGRATION OF CHINOOK SALMON. 23

TABLE 17.—YOUNG CHINOOKS FROM UNDER CANNERY, ASTORIA, OREG., OCT. 17, 1915.

SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Number— Scale record.
EV ETASS,
. estimat
Number of rings— em ante an length of
Length. fish =
With time o!
Total. check. To To cee
: : heck.
primary Total. primary Total. ae
check. check
1sr to 155 mm 7
146 to 150 mm °
141 to 145mm... °
136 to 140 mm °
131 to 135 mm. °
126 to 130 mm 2
121 to 125 mm... 6
116 to 120 mm... 3
111 to 115 mm... 3
106 to 11o mm 3
PLOTS crac t Re etee Oe tA IS OG as wiaie s'o\siaioereaplelete Se 18
JaNins SUG Sas soe ease dist Anos sodad 6 eee Gaede Sol oases anee

SPECIMENS WITH INTERMEDIATE GROWTH.

Number— Scale record. x
Average estimated
— - length of fish at

s . time of forma-
aeage Average number of rings— Average a eae anILeTOr tion of—
eth.
Total. With -
check. I
To nter- To TInter- Inter-
check, | Mediate | Total. check, | Mediate | Total. Check. | mediate
* | growth. * | growth. growth.
176 to 180mm......... I °
171to175mm......... ° o |.
166tor7omm......... ° o}.
161to165mm......... ° °
156to160mm......... I x | 23-0 28.0 28.0 58.0 73.0 63.0 123.0
rsrto1ssmm......... 2 2! 24.0 28. 5 30. 5 65. 5 88. 0 53-0 115-5
146to 150mm. . 3 3 24-3 29.3 33-6 66. 3 83.0 58.0 118.0
141 to 145 mm 3 2 24.0 29.0 35-5 64.6 81.3 63.0 109. 6
136 to 140 mm 3 2 22.3 26.9 28.0 58.0 79-6 50. 5 106. 3
131 to135 mm. . 8 6 22-9 27-0 23-0 58.0 73-0 43-0 106. 1
126to 130mm. . . 5 4 21.6 26.0 30-5 59-0 73-0 53-0 106. 0
a21to1z5mm......... 9 6 20.4 23.8 26.5 56. 3 69. 2 45-8 103.0
116to 120mmM......... 3 3 20. 4 23-0 31-3 51-3 59-6 63.0 104.6
rirto 115 mm......... 2 2 20.0 24.0 23-0 50. 5 60. 5 45-5 90. 5
106 to 110 mm......... rr I 19-9 24-9 28.0 43-0 63.0 48.0 78.0
tor to 105 mm......... I I 22.0 24-0 33-0 53-0 58-0 63-0 93-0
96 to roo mm.......... I ° 14-0 Teed ac. cere eins 48.0 EH | est were 93-9
Lota yo wcceisesctene 43 Se egos eee Joctseesece[ereeeesezefameceeeees
J Quiescent SSB Read Pespeee BOR ooae se: ooe 9-3 21.8 26.0 28.2

Four young chinooks were collected October 22, 1915, from the Little White Salmon
River, Wash. ‘These were taken near the hatchery maintained by the Bureau of Fish-
eries, which is about a half mile above the point where the Little White Salmon enters
the Columbia River. These four fish are all females and average 92.5 mm. in length.
The average number of rings on the scales js 15.8, and the average length of the ante-
rior radius of the scales, 52.5. There is no indication of wider marginal rings on the
scales of these fish.

24 ; BULLETIN OF THE BUREAU OF FISHERIES.

A collection consisting of 100 specimens was made October 24 to 27, 1914, from
under the cannery at Ilwaco, Wash. Ninety-four of these show the marginal band of
wider rings. In all cases where the scales do not show intermediate rings the scale
growth terminates in winter rings. The average size is greater than that of any other
collection studied, 146.7 mm. Most of these fish were measured, a few scales were
removed, and the fish were then returned to the river. The fish which were preserved
were selected for unusual size. On this account data regarding the number and relative
lengths of males and females are not available. The scales of these fish present no
unusual features. The following table (18) contains the data:

TABLE 18.—YouNG CHINOOKS FROM ILWaco, WASH., UNDER THE CANNERY, OCT. 24, IQr4.

SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Number— Scale record.
Average
no
length
Average number Average length of
Average length. y of rings— anterior radius— fish at
With time of
Total. eck formation
ol #
Tocheck.| Total. | Tocheck.| Total.
Vey ease bs Seng eign obondise Con OLS pAS ESS SS Ssbee 6 3 7-6 21-5 24-3 61-3 49-7
!
SPECIMENS WITH INTERMEDIATE GROWTE.
Number— Scale record. :
4 Average estimated
j | ieneee ve fish at
; y - | time of formation
Average number of rings— BvEXaEe a ee Ua of—
Length. Ta
Total. ae | |
; Interme- Interme- Interme-
Tocheck.| diate Total. |Tocheck.| diate Total. Check. diate
growth. growth. growth.
| |
| = }
zor to 205mm......... a | I 10.0 21-0 34-9 65-5 TIO. 5 48.0 123-0
196 to 200 mm......... o} CU) bana esd Panera Beg ares CSGonepeste) bEoreracod pecteoc dod ceagesgodh eA scons
191 to195mm......... 2 OH ees sdoss 18.0 31-5 58-0 BOSS) fare vie sania IIo. 5
186to 190mm......... I Ones ea sine 18.0 | 31-0 68.0 RIGO). secon 113-0
181 to 185 mm......... ° Col Pacer aad Mecgagns sa aone 6-0 A GESERose AGA Sdin6 78 Ancsnaceve ngrtoweelsatasse wae
176to 180 mm......... 2 2 8.5 19-0 3I-0 60. 5 93-0 53-0 TI5-5
171to175mm......... 3 I 10-0 20-0 30-3 53-0 88.0 48-0 106.3
166to 170 mm......... 10 3 6.3 19-1 30-0 56.5 90-3 38.0 103-5
161to 165 mm......... 3 2) lamrpScn a 20-3 27-6 58.0 8629 | Secs eee 108.0
156to 160 mm......... 6 I 12-0 18.3 26.9 48.0 57-1 87-% 88.0 103-0
is1toissmm......... 7 2 8.0 19-7 27-0 23-0 53-7 78.7 48-0 109-4
146to r50mm......... 10 6 10-0 19-4 26.4 29-6 54-0 72-0 58-2 108.0
141to 145 mm......... 12 6 9-0 20-5 26.2 24-6 53-8 69.6 52-2 TIO. 5
136to1g40mm......... 12 5 7-2 20-9 27-0 24-0 53-0 72-5 46-0 101-3
131to135mm......... 9 3 10-0 18.9 24-2 26. 7 55-0 69.1 55-5 104-1
126to r30mm......... 5 2 10.0 18.8 23-2 25-7 54-6 65-0 53-0 102-0
r21to125mm......... 8 4 7-7 19-5 24-7 24-2 47-3 63-0 48.0 94-8
m16torzomm......... I ° i) re) re) +o a
rrrto1msmm......... ° °
106 torr1omm..,....... 1] °
Totals oe se sees o4 36
Average, 148.3 mm..|.......... Ses

Fifty-two specimens were taken in the McKenzie River near Leaburg, Oreg., No-
vember 2 and 3, 1915. (See Table 19.) The Oregon Fish and Game Commission maintains
a hatchery here, and the fish were collected just below the point where the hatchery is

SEAWARD MIGRATION OF CHINOOK SALMON. i 25

located. The average length is 106.4 mm. The males, 24 in number, average 107.1
mm. in length; the 28 females, 106 mm.

A particularly interesting feature of this collection is the fact that a considerable
~ proportion of the specimens have scales which show a distinct widening of the marginal
rings. Fourteen (27 per cent) of the specimens have scales of this character. The
other specimens all have scales whose marginal rings are of the narrow, winter type.
The series of collections from the upper regions of the Columbia River basin is not
complete enough to allow conclusions to be drawn regarding the character of this widen-
ing of the marginal rings, but it can be shown on material from the Sacramento River
that the new growth of the second year usually begins during the fall. Previous to
beginning this “new growth” there has been formed a more or less distinct band of
narrower rings, the winter band. This is unquestionably the same phenomenon which
is evident in the present case, namely, the beginning of the vigorous new growth which
will continue during the growing season of the following year.

This question naturally presents itself: If this widening of the marginal rings in the
case of the fish from the upper parts of the stream is to be interpreted as the new growth
belonging to the second year, is it certain that the similar widening which has been found
on the scales of the young fish in the estuary is not, in reality, the same thing which has
merely been hastened by the migration to the brackish water in the estuary? In other
words, why give different interpretations to the two phenomena?

Similar physiological causes are, in all probablity, behind the accelerated growth in
each instance. The intermediate growth, however, is directly the result of changes
brought about by the migration into brackish water, while the ‘“‘new growth” is a
response to environmental changes which are independent of any special activity on
the part of the fish. The changes resulting in new growth are seasonal and affect all
of the fish in any particular locality at nearly the same time of the year. The stimulus
is probably not a simple one but is a complex of several factors, such as temperature, food
supply, degree of maturity, etc. Racial differences in different localities may also enter
as modifying factors.

The change brought about by migration is the more profound as is indicated by
the fact that the rings of the intermediate growth are usually heavier and more widely
spaced than those composing the new growth accomplished before migration. The
difference between the two types of rapid growth is not, however, diagnostic, and
it is usually impossible to distinguish in individual cases between intermediate bands
and bands of new growth. Many of the fish taken in the upper part of the stream and
which have begun the new growth could not be distinguished by the scales from fish
taken in the estuary whose scales show the intermediate growth. From October on,
therefore (and probably for some weeks previous to this time), one is likely to encounter
fish in the estuary whose scales would be practically identical—having a marginal band
of wider rings—but some of which will have formed the marginal band as a result of
migration into brackish water, while others will have formed the marginal band in the
upper parts of the stream previous to migration. Undoubtedly as the season advances
the percentage of fish which have formed this band in response to the migration will
decrease, while the percentage of fish which have started the new growth of the second

26 : BULLETIN OF THE BUREAU OF FISHERIES.

year will increase. Since there is no method of distinguishing with certainty between
the two types, the marginal band of wider rings found on the scales of the fish taken in
the estuary will be referred to as the ‘‘intermediate band.” In the case of fish from the
upper waters, however, where the interpretation is unquestioned, we shall designate
the marginal widening as “‘new growth.”

Such a marginal band of wider rings is not always formed on the scales of fish found
in the estuary. It is not apparent on the scales of the smaller migrants owing to the
fact that the first few rings formed on the scales are almost always wider than those
normally succeeding. They are not, however, wider than the intermediate rings but
are of approximately the same width, so that no break appears at the point where the
intermediate growth actually begins. The absence of the intermediate band on the
scales of some of the larger migrants is probably due to the fact that those fish have not
been in the brackish water long enough for the wider rings to have developed. When
the intermediate growth is not found on the scales of the adult fish, which show a
nuclear area of true stream growth, it probably indicates that during the seaward
migration the individual did not remain long in the brackish water but continued the
migration so rapidly that typical ocean rings were formed immediately succeeding

typical stream rings.
The following table (19) gives the data relative to the McKenzie River collection:

TABLE 19.—YOUNG CHINOOKS FROM MCKENZIE RIVER, NOV. 2 AND 3, 1915.

SPECIMENS WITHOUT NEW GROWTH.

|
| Scale record.
Average
Number— | | oe
Averagenumber | Average length of Be:
Length. | of rings— | anterior radius— Smear
| ; ane
} tion o!
With | To | |) "To
Total. maneeee | Gree | Total. cheske Total. | check.
ae |_ |
tart to 125 mm... I I | 8.0 22.0 28.0 58.0 58.0
116 to 120 mm I I 7-0 19.0 28.0 58.0 63-0
Tir to 115 mm. 9 4 7-7 19-4 23-0 55-2 49-2
106 to 110 mm... Ir 8 7 18. 7 25-5 53-0 53-5
tor to 105 mm Vi 2] 8.5 18.3 23-0 52-3 48.0
96 to roo mm. . 6 2 8.5 17-0 23-0 48.8 45-5
gt togs mm... I I 10-0 15-0 33-0 48.0 63-0
86 to90 mm... I I 9-0 16.0 28.0 43-0 58.0
81 to 85 mm... I (orl eebacabore 5 roe Mlosiaouortade igScon Pace eeeeee
ADOCEL atest. PRE RR ae, eth a Mh eee 38 Pi BBR Saal BASS BAB aa| Manette 4| Aer Be Serr | paeepecc sce
USSR cr eR OE CREME SOBPB n PE oneane| lbcatnbodar) boaaueGoee 8.0 18.5 25-2 52-2 5397
SPECIMENS WITH NEW GROWTH.
Scale record. .
acre ee
Number— length o h at
ae Average length of anterior time of formation
Average length. Average number of rings adtiee of—
With To In first To In first New
Total check, | check year. Total. | check. year. Total. |. Check. | cowth:
108.0 MM............ 14 5 6.6 | 15-7 19-8 19-0 43-4 555 40-0 85-1
|

SEAWARD MIGRATION OF CHINOOK SALMON. 27)

Six young chinooks were taken at Astoria, Oreg., November 7, 1914. These were
captured by hook and line from under the Union Fishermens’ Cooperative Cannery.
Nothing of particular interest appeared in the study of this small collection, and the table
(20) is therefore presented without comment.

TABLE 20.—YOUNG CHINOOKS FROM AsTORIA, OREG., Noy. 7, 1914.

Scale record. :
Average estimated
Ne jeneth “ fish at
time of formation
Average number of rings— | Average set ie anterior of—
Average length. | radius
|
|
* To inter- | To inter- Inter-
Total. Migs pee mediate | Total. | bast mediate | ‘Total. Check. | mediate
5 * | growth. growth, growth.
SRO SUUETAS lela fotoreiate’ ajalai 6 | 5 9:0 21.0 25-0 27-0 66.6 78.0 48.8 | 111.6
|

November 19, 1915, seven small chinooks were collected by means of a seine on a
small sand bar near Warrendale, Oreg. (See Table 21.) This is on the Columbia River
about 40 miles above the point where the Willamette River joins the Columbia. These
fish average only 93 mm. in length, and it is worthy of note that the scales show no
indication of the beginning of a period of rapid growth. The scales of one specimen
show a primary check four rings from the center of the scales. Four specimens show the
narrow, winter rings at the margins of the scales. The other three specimens have scales
whose marginal rings are still of the summer type, no narrowing being apparent.

TABLE 21.—YOUNG CHINOOKS FROM WARRENDALE, OREG., Nov. 19, 1915.

Scale record.

Average length. Number. Average
number of | lenath of
cd anterior
g radius,
EMBLEM: (2 Wedu tan ole ot cls) Ste wth al ake) ibn! vince defnieta gies ime) sinipinia Wis wiayaln (abel v fie tls =) <)uieh~ iguana) «is (e1<\~ sinning fatal « 15 nine | 7 Is 45

Scales were taken December 4, 1914, from 52 specimens of young chinooks which had
been reared at the hatchery of the U. S. Bureau of Fisheries at Clackamas, Oreg. These
fish were measured but not sexed. The scales of these are no exception to the rule that
the scales of hatchery fish exhibit uneven and abnormal growth and are seldom of much
value in scale study. Since these are fish of known age, having been reared from eggs
which were spawned in the fall of 1913, it will, however, be interesting to make a com-
parison between them and wild fish of the same approximate age. These hatchery fish
are quite irregular in their growth, so much so, in fact, as to indicate a bimodal curve.
The average length is, however, about the same as the average of other collections made
at the same time of year, being less than some and greater than others. The scale growth
is also, in spite of its irregularities, quite comparable with that observed in the wild fish
in the number and the general arrangement of the rings. The data regarding these fish
are collected in the following table (22).

28 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 22.—YOUNG CHINOOKS FROM CLACKAMAS HATCHERY, OREG., DEC. 4, 1914.

Seale record.

= ion Average estimated
Number Se ee Ae BS a ee ee Coe tO ol mshiatyeenn
yerieeinaber otcnps BIS a ical anterior of formation of—
Length.
With To— of—
Total. os To To Tonew New.
check, check... | check. growth. Total. Check. growth.

|

151 to 1s5 mm
146 to r50 mm
141 to145mm,..
136 to 140 mm.
131 to 135 Nm.
126 to 130 mm.
121 to 125 Imm.
116 to 120mm.
j1rtorr5 mm...
106 to 110 mm
ror to 105 MmM.........
96to1oomm..........
QE LO OsuMI Saintes ast

2m

°

4 4

HORWNR OWOANKONHH
4

OWN OKO AN

3 The fact that this is less than the length to the beginning of the new growth is due to the fact that the specimen not having
the new growth had unusually large scales.

All but nine of the specimens have winter rings at the margins of the scales. Of
these, four have a marginal band of wider rings, indicating that a period of more rapid
growth has begun. This is probably the new growth of the second year. The remain-
ing five specimens still show at the margins of the scales the wide rings of the first sum-
mer’s growth. ;

December 3 to 8, 1915, several collections were made at different points on the
Columbia River between the mouth of the Willamette River and Astoria. Collecting
was rather difficult on account of inclement weather and unusually high water for this
time of year. Collections were made in the following places: Upper Willow Bar, Lower
Willow Bar, Deer Island, Mayger, Oreg., Wallace Island, and Seal Island. Unsuccessful
attempts to collect were also made at several other places. The collections are all quite
small, and the total number of fish taken was but 38. This represents the results of over
30 hauls with the roo-foot seine. One of the specimens collected is a small fry only
35 mm.inlength. This is obviously a fish of the year, and therefore one year younger
than the other individuals. No scales have been developed. ‘This specimen is not in-
cluded with the older fish in the following table. Fourteen of the older specimens are
males averaging 95.5 mm. in length. Twenty-four females average 93.4 mm. ‘The av-
erage length of all specimens is 94 mm. No significant differences have been observed
in the several collections, and they are therefore cast together in the following table (23) :

TABLE 23.—YOUNG CHINOOKS FROM LOWER CoLuMBIA RIVER, DEC. 3 To 8, 1915.
SEVENTEEN SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.
Average length. Average Average
number | length of
of anterior
rings. radius.

6S TUERD 070; 0jejoisiniaye(o.binnjelafufu(e\eraiuja)u/a(n’acn) elalniave/afelevavalatula a)atainia\siaiais ac a’ale Wate eisdara’atnle wiete Sek raiaia a kiniciesafaltie tele ial ejeteckT ER 16. 5 49-5

SEAWARD MIGRATION OF CHINOOK SALMON. 29

TABLE 23.—Younc CuHINooKS From LOWER COLUMBIA RIVER, DEc. 3 To 8, 1915—Continued.

TWENTY-ONE SPECIMENS WITH INTERMEDIATE GROWTH.

— =
Scale record.
Average
| estimated
Average number of Average sents of eee of
tings— anterior radius— sh at
Length. Number. beginning
of inter-
To inter- To inter- mediate
mediate Total. mediate Total, growth.
growth. growth.
|
126 to 130 mm,. I
121 to125mm °
116 to 120 mm °
111 to115 mm I
106 to 1190 mm 3 18. 7 43-0
tor to 105 mm I 14-0 18.0 43-0
MEG TOOSSUENED pie ata niniatotet ver s)s a0 «ipicfe\ctehe aie! =\</afalthaiee'e|«| niin =icfela 4 14-5 18. 5 36. 7
SiO att. Gaberteud ocbaGed JOSCCSAenOCD Lo RAAOeoCoe, I 18.0 22.0 33-0 73-0
BOLO MILT eerie eerie aietererpeincieie niciaieielsicis sisters ee bie eleteteleteietaicte 4 14-2 18.2 36. 7 68.0
fei PASTE Regs Gao osoosodonOs MOrpoceornoonooonaanoscdc en 5 13-5 17-5 39-0 63.0
FOG TEEEL bee nein SC ODO DCIOU OSDOUCCOUCIAQOM ier Ja OC b pote I 13-0 14.0 33-0 68.0
LW C HOTT 8295 Gon cao DAC Ad OS Ubsoe SONG DOSE. soe ahistel (Saogh aneicsp 14-7 18. 7 38.6 50.4 72-8

Owing to the unusual severity of the winter of 1915-16, no more collections were
made after the one just considered until the following March and April. The fry taken
during the spring and early summer have already been considered, and it remains now
to discuss the yearlings which were taken during the second year after hatching.

During the course of the seining on the lower river in March and the early part of
April, 1916, a total of 47 yearlings were captured. (See p. 7.) Although these were
obtained from several different localities, separate tabulation shows no special difference
in the fish from different places, and the entire collection is here tabulated together.
There are 26 males in the collection averaging 97.6 mm. in length and 21 females
averaging 93.2 mm. ‘The average length of the entire collection is 95.6 mm. Thirteen
of the specimens do not show the wider rings at the margins of the scales, but narrow,
typically winter rings. The remaining 34 specimens have the wider marginal rings
which are characteristic of the young migrating fish. It has been previously indicated
that the marginal band of wider rings in these yearlings which were captured in the
spring are probably in large measure indicative of the new growth of the second year.
The term ‘‘intermediate growth” is retained, however, for the reasons given on page 25.
The following table (24) presents the data for this collection:

TABLE 24.—CHINOOK YEARLINGS FROM LOWER COLUMBIA RIVER, Mar. 31 TO APR. 2, 1916.

SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Number— Scale record. Average
estimated
A ber of h of a es
verage number o Average length o! ish at
Average length. With rings— anterior radius— time of
iCotaltes|ppuimaary.|\t 2. 2 eet Th pee hae A et bye ¢4-'| formation,
check, of primary
Tocheck.| Total. | Tocheck.} Total. check.
MPS a APRAUEAR effete iahen cinta os6, bipinjaleislalarsiuty(uiviarera:a €'eintele[alxistats 13 3 7-6 18. 7 16.0 35-7 | 43-0

30 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 24.—CHINOOK YEARLINGS FROM LOWER COLUMBIA RIVER, Mar. 31 TO APR. 2, 1916—Contd.

SPECIMENS WITH INTERMEDIATE GROWTH.

Scale record. E
Average estimated
Number— length a eS at
4 time of forma-
Average number of rings— Average dength of anterior tion of—
Length.
ar i To be- & To be-
it a) ginning to) ginning . Inter-
Total. | primary| primary | ofinter- | Total. | primary | ofinter-| Total. Pom mediate
check. check. | mediate check, | mediate eneck- | growth.
growth. growth.
zirto 115 mm......... 2
106 to 110 mm. °
Tor to 105 mm 6
96 to roo mm 9
91 to 95 mm. Ir
86 to 90 mm. 6
‘Use, onrganbsanass 34
PA590-4 PAMNER swore cles | iain sinie'a vere

- April 13, 1916, collections which contained specimens of yearlings were made on
Deer Island and on Cottonwood Island. The total number of yearlings in these two
collections is but 22. Of these, 10 are males and 12 females. The two sexes have
the same average length, 107 mm. Five specimens have scales which terminate the
growth in winter rings. The scales of the remaining 17 individuals show a distinct
intermediate band. The following table (25) gives the data for these collections:

TABLE 25.—CHINOOK YEARLINGS FROM DEER AND CoTronwoop ISLANDS, APR. 13, 1916.

FIVE SPECIMENS WITHOUT INTERMEDIATE GROWTH.

Scale record.
Average length. Average Fabia
number o! Fi
. anterior
Eh radius.
WTO NI os cies clocks Sicinis ewe cmce ce nle rn aWainte aaleeie Cetalete by deica nila d stately e slele elvis |wiale/clelelaininya ale\e\e/N a mfes [aimba! sje foie a/eib hed 19-6 42-0
SEVENTEEN SPECIMENS WITH INTERMEDIATE GROWTH.
Scale record.
Average
estimated
Average number of Average dength of ne of
rings— anterior radius— ish at
Average length. beginning
of inter-
To inter- To inter- mediate
mediate | Total. | mediate | Total. | growth.
growth. growth.
|
LOS. 7 WAM. « o.sleieig das ap vic wiviaele bielv'n a \e nlnle alvidie ww mlewisidie'sp\eleiv ia ee.svinojs's baie’ n\n\s 15-0 17-8 34-9 41-0 87-2

SEAWARD MIGRATION OF CHINOOK SALMON. 31

A somewhat larger collection of yearlings was made May 10, 1916, at Crandall’s
seining ground on Grims Island. Thirty-nine specimens were taken here—16 males and
23 females. The males average 106 mm. in length, and the females 1o1.1 mm. All of
these fish have the characteristic marginal band of wider rings on the scales. The table
(26) follows:

TABLE 26.—DATA FOR 39 CHINOOK YEARLINGS FROM CRANDALL’S SEINING GROUND, ON GRIMS ISLAND,
May to, 1916.

Scale record.

Average

estimated

Average number of | Average length of | length of

rings— anterior radius— fish at

Length, Number. Giak tax beginning

en of inter-

To inter- To inter- mediate

mediate | Total. | mediate | ‘Total. | growth.

growth. growth.

za1to125mm.,. 2 16.0 20.5 53-0 65-5 10085
116 to 120 mm 3 16.6 21-9 46-3 68.0 746
1mr to 115 mm 6 16.0 21-3 48.0 67-0 81.1
106 to 110 mm 6 14-1 19.2 42-0 57-0 76.1
ror to 105 mm... 7 16.3 20-7 42-5 59-5 73-0
SOE CHL OCHIEETIE ete tet ele beatnfe ster cleis\eisjalnisuiawiaiaisialnistaiaye 4 15-2 19.9 41-7 55-5 75:5
CR OOS OD Ss oGedogciugadodoge des cudnbomsdsoodae 3 15-3 18.9 43-0 54-5 71-3
SG LOlGo ITH ere stalaahe viele televieleleieieleteieiaivisieteicle eeretakereis\ As 7 12-9 17-6 33-0 49-5 62-3
Sew OS BEET ras coigtascue sh oooe Dons UA DOUDULOUCCEOD GaSe I 12-0 20.0 33-0 53-0 53-0
PELs ILITIR Sala laieleleteloleinfaleiststelete'misialainie’s'atuteiefelela’stsie siaialsisic)=\six'ec< wiereicis’s/e\s 15-0 19-9 41-7 58-5 74-0

Eight specimens of yearlings were taken May 11, 1916, at Point Ellice and two at
Tenasillihee Island. (See Table 27.) These are quite similar to the fish contained in
the collection from Crandall’s seining ground, although they average somewhat larger
in size.

TABLE 27.—CHINOOK YEARLINGS FROM POINT ELLICE AND TENASILLIHEE ISLAND, May 11, 1916.

|
Scale record. 3
Average estimated
Number— [Hh Dis Jt plane DO, aoe un Heals of fish A at
éj ime of formation
Average number of rings— Average deniech of ESSE aT of—
Average length. xa
With To pri- | To inter- To pri- | To inter- Inter-
Total. check mary mediate | Total. mary mediate | Total. Check. | mediate
r check. growth. check. growth. Zrowth.
HCGH RED oar oosdecae Io 3 8-0 17.2 23-4 39-6 45°7 67-0 46.3 73-7

One yearling chinook was captured in the Columbia River just above the mouth
of the Little White Salmon River on May 25, 1916. This specimen is a female, 98 mm.
long. The scales show three rings of the new growth of the second year. The first
year’s growth comprises 15 rings. The anterior radius measures 45 mm. to the beginning
of the new growth, and the total length is 59 mm. ‘The estimated length at the time of
beginning the new growth is 75 mm.

32 BULLETIN OF THE BUREAU OF FISHERIES.

Fourteen yearlings were taken in the Clackamas River June 8, 1916, after which
date no more yearlings were taken in any of the collections. Nine of these are males
averaging 112 mm. in length. The 5 females average 112.6 mm. The scales of all
these specimens show the wider rings of the new growth at the margins. The following
table (28) gives the data for this collection:

TABLE 28.—CHINOOK YEARLINGS FROM CLACKAMAS RIVER, JUNE 8, Ig16.

Ninnber— | Scale record. Average estimated
length of fish at
ae of formation
of—

Average length of anterior

| Average number of rings— a

Average length.

Total.

To inter- To inter- Inter-
To check.) mediate | ‘Total. /To check.| mediate | Total. Check, | mediate
growth. growth. growth,
EIAs ATTN oo, )0 15,0 o)ehsinss oye 14 2 | I2-5 15-5 21-6 40-0 49-1 72-6 63-0 78-3
|

FISH FROM THE SACRAMENTO RIVER.

The young Sacramento River chinooks available for study may be divided into two
distinct groups. ‘The first consists of young migrants which were collected by N. B.
Scofield, of the California Fish and Game Commission, in the spring of 1911. This was
done during the progress of an investigation into the loss of fish resulting from the
overflow of the Sacramento during the spring floods. The second group consists of
collections made from the McCloud River near the hatchery of the U. S. Bureau of
Fisheries at Baird, Calif. These collections were made at the request of Dr. Gilbert
during 1911 and 1912. The writer is indebted to both Dr. Gilbert and Mr. Scofield for
the privilege of studying these collections.

The collections of young migrants from the lower part of the Sacramento were
made under quite variable conditions and in several localities. Some were made from
the river proper and others from the ponds formed by the overflow of the Sacramento
during the spring floods. For the most part the collections were small and in several
instances were so poorly preserved that many of the specimens had lost all of the scales.
Very few of the collections were well enough preserved so that the individuals could
be sexed.

Most of these collections comprise so few individuals that a detailed consideration
of each collection would be useless. No unusual results were obtained from a separate
study of these smaller collections, and therefore the totals and averages for each have
been collected in the following table (29). There are included also, for the purpose
of comparison, three collections of young fry from the State hatcheries at Sisson and
Brookdale. ‘The few collections which are large enough to deserve more detailed study
will be considered later.

@ This poor preservation was in nowise the fault of the collector. The collections had been set askie as valueless several years
before the writer found use for them and had received no care during the interval.

SEAWARD MIGRATION OF CHINOOK SALMON. 33

TABLE 29.—CHINOOK FRY FROM THE SACRAMENTO RIVER.

Scale record.
Dat Localit: Numb a en A
ate. ocality. umber.} len, verage
(mm.). averies, length of
of rings anterior
= radius,
1910
Maran ss| eexookdale hatchery. delsoayeivs tu 0 Has SseaseccisiorebeaSsccneassacescesteee 26 36-3 (2) (2)
IQII
Mar 9s) Sissonthatcheny s.r es. cave ccissa ce taecee eee ee ae eee eae aE 13 38-7 (b) (>)
Nei NEP | eb od (1 i eemc- RCH HOSOGE DS URD AOR BONCOR tno SBA EReBannCOMOOREOREB CURE Or mernetrs 12 41-2 (¢)2.0 (¢)17
Apr. 13 | Sacramento River, 30 miles above Sacramento...... 2.22... .2. 20.00.00 c00ee 9 57-5 4-4 23-6
PA yea x9) WCACHE GIGI GH re aloes ee cicte cic eratclsteinea a sears elcioleinia ciecouiemerele intel tinalatre ee 2 67 6.0 28.2
Poza GMM OSDECE SIG C erin cer tisterstis si<isfotn sis stators leisin cis larciolniaisinie misters eens eicie vials ier imnvel orate 4 69 7-5 27-6
Mavyaigi Pond rear Butte Slotightsmsccce: sosceeessnie cece crosses seca ceccsGacswecwiecs 13 81.5 9-2 37°5
MaRS IRA SLOT Tice etuyescieie tesa ermsststo store in (cusses oloastote lor sToteiaisiaic lw lerovare ofetots coe iers)aravelatateheratclore 15 17 9-9 34:5
LUD DR |S oh eee ceenet Sepp saisepraseuecre peas Cana Goo maatEe Sear Ena oeesmerne 4 75-2 9-5 32-2
May 27 | Sausilito, Calif. . ne 8 81 10.9 37-5
May 28 | Prospect Slough. . 16 68 75 28.3
June 8 | Pond near Butte 17 95-6 13-3 48-9
June 30] Ponds near Knights Land: 18 107-0 16.4 51-4
SPA vamOUI EE ON Ctl ear Es 11L Cel SLO oid ae ctcin sicicla cele elarcierto iors in overainitictolovovaioiele ecistalafaletorertreloiureretars a 5 92-2 14.8 47-9
1913
Spang tookdale hatchery) ic. ca-.<:.)¢.jeisceenscis (Hues ee snlneiaenieig clalsincih wa elele eter 55 os5.7 17-5 38-9
|

@ No scales formed.

> Only a few platelets present on the largest specimens.

¢ Average of six of the largest.

@ 5 specimens without new growth. Four specimens with new growth show: Average number of rings to new growth, 16. a
of new growth, 3. 7; average length of anterior radius to new growth, 37.4; total length of anterior radius, 44.9; and average esti-
mated length at time of beginning new growth, 92.9.

The following tables (30, 31, and 32) contain the data for those collections of wild
fish which are large enough for separation into the various size groups to be of value:
It was not considered necessary to present in detail the data for the collections from the
Brookdale hatchery, although these are as large as many of the collections of wild
fish so considered. ‘The fry preserved March 5, 1910, have no scales and present only
a slight variation in length. The series of yearlings, preserved January 4, 1913, are
so variable and the scale growth is so irregular that they can not be compared in detail

with the wild fish.

TABLE 30.—DATA FOR 19 FRY FROM WALNUT GROVE, CALIF., APR. 9, IgII.

Scale record.
Length. Number. verave Average
length of
number of teri
rintes! anterior
radius.
71to75 mm 8 32-2
66 to 70 mm 7-3 26.5
61 to 65mm Apoodadone cdl ac congonsec
56 to 60 mm 4:5 23-6
sr1tossmm 3-5 23-6
46tos5omm..... 3-0 14.9
41to45mm... 1.0 14-9
36 to 40mm...

31to35 mm

34 BULLETIN OF THE BUREAU OF FISHERIES.

‘TABLE 31.—DATA FOR 22 Fry FROM ButTrEe SLOUGH, MAy 8 AND 9, Igr1.4

Length. Number.
qr to 75mm 4
66 to 7o mm 7
61 to 65 mm 5
56 to 60 mm. 3
sttossmm.. 2
46tos5omm.... t
IASG-5(6 3c SERIMM So cic a) chs stnldhojosx sista opel asus ovehsiotainrayainn aleieieja stalatnte ain) ajetecarelataisvalaly inital ats avesavafelatsisial=tetericas¢siaia/cte biota wia(aayatel a e?a etait otetel eters aatetet
a The specimens in this collection had all lost the scales as a result of poor preservation.
TABLE 32.—DATA FOR 20 FRY FROM POND NEAR ELKHORN, CALIF., JUNE 3, IgII.
Scale record.
Length. Number. Average Fiebitae
number of 7
rings! anterior
radius.
81 to 85 mm 10.2 35-4
76 to 80 mm 10.0 35-3
71 to 75mm 9.0 34-8
66 to 70 mm 8.5 27-6
Av. 7.0mm 97 34:4

This collection contained 11 males averaging 77.1 mm. in length and 9 females
averaging 76.9 mm. in length.

The largest collection from the lower Sacramento River was made at Woods Break,
June 5 and 6, 1911. (See Table 33.) There is a total of 147 specimens. One hundred
and fifteen of these were taken in a trap located at the point where the water was flowing
through the break from the main river, and 32 were seined from an overflow pond near
the break. The separate study of these two collections shows no essential difference,
and the data are, therefore, placed together in the following table (33). This collection,
undoubtedly, is a fair sample of the migrating fry in the Sacramento at this time of year.
The average length is 71.7 mm. The average number of rings on the scales is 8.2, and
the average length of the anterior radius is 30.5 on the arbitrary scale adopted. There
are 77 males in the collection averaging 72.2 mm. in length. The 70 females average
71.0 mm.

TABLE 33.-—DaTA FOR 147 Fry From Woops BREAK, JUNE 5 AND 6, IogIt.

Scale record.
Length. Number.| 4 Vora, re Average
length of
number of teri

rings. anterior

radius.
SE L095 PUNT, oie ie les oigc own cpa diaclsisinre vee necav scence soisivisie ela enveisie.cisieie civic wise sisisleleemsjnivic avis sini I 32:0 48.3
ogomm.... It. 43-0
81to85mm.... 10.1 37-2
76to 80 mm.... 9.0 334
7rto 75 mm.... 8.5 314
66 to 70 mmm. 7-6 27-9
61 to 65 mm. 6.8 as-8
56to 60mm. 5-6 23-0
sttoss5 mm. 4.0 20.7
46to 50mm. 4.0 20.7
Ay. 71.7 11m 8.2 305

SEAWARD MIGRATION OF CHINOOK SALMON. 35

A collection of 44 specimens was made at Tisdale Wier, June 24 to 26, 1911. (See
Table 34.) The average length is 78.8 mm. The average number of rings on the scales
is 10.3, and the length of the anterior radius is 33.1. “Twenty-one males average 78 mm.
and 23 females 79.6 mm. in length.

TABLE 34.—DatTA FOR 44 FRy FROM TISDALE WIER, JUNE 24 TO 26, IgII.

Scale record.
Length. Number. Ane Average
number of | length of
TO! teri

rings. anterior

radius,
ror to 105 mm I 13-0 33-0
96 to 100 mm 2 Il-5 35°5
or togsmm... 3 12-6 34-6
86to90mm.., 8 10-9 29:9
81 to85 mm... 6 II.0 31s
76 to 80mm... 5 10.2 29-0
OS ee 7 10.1 27-3
0 7OINmM... 7 9-0 25-9
61 to65 mm... 4 8.5 23-0
56to6omm,..... I 8.0 23-0
INS UME Or ig Joonccbe DOG Ic SRO UNET Ob TEE COTE 90 DOB DEOe DIE OC HC Iota Ceoasaqat ded tap fe) Srkidieeoor 10.3 33-1

This completes the description of the young fry taken in the lower Sacramento
River. The skewing of the curve of length toward the smaller sizes, which was noted
in the collections from the Columbia River, is not apparent in this material. It is only
slightly noticeable in Tables 30 and 33. This is, at least in part, due to the fact that
there are few collections of any size which contain specimens of the smallest fish. The
fact that these specimens from the Sacramento were not collected in the estuary, as
were most of the Columbia River fry, would doubtless also have some such effect. In the
estuary the fish hesitate for a time in the brackish water before completing the migration
to the ocean. This gives an opportunity for the smaller fish from above to come in and
form an abnormally large proportion of the collection.

The collections from the McCloud River include two made in July and September,
1909, and a series made during the fall and winter of 1911-12. A constant feature of
the collections made from July to December is the presence of precociously matured
males. ‘These also have been noted among the fish from the Columbia River basin
(p. 18). Such precociously mature males will not be included in the tables with the
immature fish. None of these specimens show a well-defined primary check, as was
met with in the Columbia River collections.

Thirty-eight specimens were taken July 24 and 25, 1909. Nine of these are
mature males and average 124 mm. in length. The scales of the mature fish have an
average of 18.5 rings, and the average length of the anterior radius is 63.9. Fourteen
of the immature specimens are males averaging 85.5 mm. in length and fifteen are
females averaging 91.5 mm. ‘The data for the immature specimens, 29 in number, are
given in the following table (35).

36 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 35.—DATA FOR 29 YOUNG CHINOOKS FROM McCLoup RIVER, BarrD, CALIF., JULY 24 AND 25, 1909.

Scale record.
Length Number. venice Arcus
number of aaterice
Soy tadius.

PRO CS Ty aan pAnnanbasaus a oup ob odobn nO oDrd acoso ow sSoeoobedocnoansabecboodueseocosanaots I5-0 49-0
ROA rE OTE RE AR Ogee Hb SOSA CINE IROOOO AC OAR GUS ScoHCoOn ena pae sonics kbemacodasngcesaceaas se 14-0 55-0
FOX CO TOS MM... 2.0 eccececccecncccss ares scecscscenseseaccsarncesccsscessasesesssssassscccee 14-0 55-0
96 to 1comm.. cele 13-3 SIE
91 too5mm. 12-0 46.6
86 to 90 mm. II-3 43-7
81 to 85 mm. 10-4 36.0
76to 80mm... 9-3 36.0
PNG a PASH OSGOOD DER SN OnOne Gunciodaed sooner csabandconGendse sodbaspeeubuotosadnocaccs 9-5 36.2
Av. 88.5 mm II-5 43-5

A collection consisting of 82 specimens was made September 24, 1909. Seven of
these are precociously mature males, averaging 109.5 mm. in length. The scales of
one has a band of two wider rings at the margins. This undoubtedly represents the
beginning of the new growth of the second year, since, as is presently shown, over one-
half of the immature fish taken at this time have the new growth well developed. The
average number of rings included within the first year’s growth (extending to the periph-
ery of the scales of all but the one specimen which shows new growth) is 15.3. The
average length of the anterior radius is 43.

Seventy-five of the specimens included in this collection are immature fish, aver-
aging 96.9 mm. in length. Forty individuals have definitely begun the new growth of
the second year, as is indicated by a marginal band of wider rings. The scales of the
remaining 35 individuals have marginal bands of the narrow, winter type. Thirty-two
specimens are males averaging 97.9 mm. in length. Forty-three females average
96.3 mm. The data are presented in the following table (36):

TABLE 36.—YOUNG CHINOOKS FROM McCLoup RIVER, Barrp, CALIF., SEPT. 24, 1909.

THIRTY-FIVE SPECIMENS WITHOUT NEW GROWTH.

Scale record.

Length. Number. Average Average

number of
rings.

radius.

rar to 125 mm
116to120mm....
111 to115 mm.
106 to 110 mm.
ror to ro5 mm.
96to1comm.....
grttoosmm...
86 to 90mm...
81 to 85mm...

SEAWARD MIGRATION OF CHINOOK SALMON. 37

TABLE 36.—YouNG CHINOOKS FROM McCLoup River, Barb, Cauir., SEPT. 24, 190g—Continued.

FORTY SPECIMENS WITH NEW GROWTH.

Scale record.

Average

estimated

Average number of | Average length of | length of

Length. Number. rings— anterior radius— fish at

beginning

of new

Tonew Of new To new Total growth.

growth. | growth. | growth. g

116to120mm,... I5-0 4.0 49-5 61.0 93-0
amrto1ismm.,... 13-0 4-0 43-0 55-0 83-0
106 tor1omm.... 13-2 Bur 43-7 56.0 86.0
tor to ros mm.... 13-4 3-2 43-7 52-3 86.0
g96tor1oomm..... 12-9 3°3 49.3 50.2 78-0
ortogsmm...... 12-4 2.8 35-7 43°7 75.0
GEO GO SITS ia ccc cies ainnn oe wins wleivinin a cin bein 0is.0.0 00 ole sels nieivie.ciacie 11.8 2-4 36.8 44-9 73-0
Av. 99.5 mm 12.9 3.1 39-3 50-5 80.9

It is interesting to note that the scale records to the beginning of the new growth
are approximately the same as the scale records of the fish which are equal in size to
the estimated length at the time of beginning the new growth (80.9 mm.). Table 36
shows that the scales of fish 81 to 85 mm. in length have an average of 13.5 rings and
an average length of 42.2. In the collection of specimens with new growth the average
number of rings preceding the new growth is 12.9, and the average length of the
anterior radius is 39.3.

September 18, 1911, 104 specimens were collected. Of these, 9 are mature males
averaging 99.6 mm. in length. The scales of these males have an average of 14.2 rings,
and the length of the anterior radius averages 50.7. None of the 95 immature fish had
begun the new growth, the scales of all terminating in winter rings. This is in striking
contrast to the condition found in 1909 when 53 per cent had started the new growth
by September 24. Evidently the conditions in the same locality may vary from year
to year in such a way as to materially alter the time for beginning the period of active
growth. The possible results of such annual fluctuation may be of considerable import-
ance in its effect on the future history of the fish. There are two possibilities: (1) The
fish may tend to migrate earlier in those years when the new growth is started earlier;
and (2) they may reach a greater size before migrating, but migrate at the same time
of year. A detailed study of the fish in some one tributary extending over a series of
years would be necessary to a solution to this problem. Careful attention should be
paid to fluctuations in climatic conditions. Fifty-one of the immature specimens in
this collection are males; 44, females. The males average 94.5 mm. in length; the
females, 91.8 mm. ‘The following table (37) presents the data regarding the immature
specimens.

38 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 37.—DATA FOR 95 YOUNG CHINOOKS FROM McCLoup River, Barrp, Caur., SEPT. 18," ro9rr.

Scale record.
Length. Number. a erire nee
number of teri
pings | Maen
radius,
TOG EMR IE SS oo ogee cela bid aehgag SEB Gain cP ace ose ee ance ee anebane oheetan seer I "37.0 61.0
rortorosmm....... vale : a 15-2 51-7
96tor1oomm........... 14-0 49-5
grtoo5smm............ 13-6 45-4
86to9omm............ 12.9 42.6
LC OPS Hh bsgec ooce mci MOae he nas Sea abein acne Saris onood eID aap pnp cssatecoessretsenctssssor 11.8 36.8
Cea auitap rte Beas Sears ob Ostimudc codn. Jdescotis spec corns isc II.0 38.0
Av. 93-2Mmm.......... 13-6 46.6

The next collection was made October 18, 1911. One hundred and forty-six
specimens were taken. Two of these are mature males 97 and 106 mm. in length.
Their scales have an average of 15 rings, and the average length of the anterior radius
is 53.2. One of the immature fish had started the new growth, as is indicated by two
wider marginal rings. This specimen is 110 mm. long, and the scales have 15 rings
belonging to the first year’s growth. The length of the anterior radius is 36 to the end
of the first year’s growth and 45 to the periphery of the scales. Sixty-two males aver-
age 99.8 mm. and 81 females 98.9 mm. in length. The data for the immature fish
which had not begun the new growth are given in the following table (38):

TABLE 38.—DATA FOR 143 YOUNG CHINOOKS FROM McCLOup RIvER, Barrp, CALiF., Oct. 18, ror.

SPECIMENS WITHOUT NEW GROWTH.

Scale record.

Length. Number. aeeree prenes
number of | ‘anterior
° FINES: radius.

ph pth ee a SARS OAL Costes en 58.0
106 to 110 mm... ale aie iGphatelniaisiniecn siaas mi nine 50-5
ROK LES LOG RULED ph, Sip Peete e cieta) ete enlist tata atatalm 49-3
96 to 1comm.,.. : 46.2
QUILO SS MEME Soars cls cfolers! Fa 2 alten eae te taiete ele 44.6
BG CO OOMMM sacs ae nielecialsteneleiaieleieieis itlocinls 40.2

TSE RR Rec born oootcn anreaee.s Sere 47-1

One hundred and thirty-six specimens were collected November 18, 1911. Six of
these are mature males which average 110.5 mm. in length and whose scales have
an average of 15.2 rings. The average length of the anterior radius of the scales is
53-2. Thirty-six of the remaining 130 specimens had begun the new growth of the
second year. ‘The scales of the other 94 individuals show marginal rings of the winter
type. The collection contains 53 males and 77 females. The average lengths of the
two sexes are the same, 101.2 mm. ‘The table (39) follows:

SEAWARD MIGRATION OF CHINOOK SALMON. 39

TABLE 39.—YOUNG CHINOOKS FROM McCLoupD RIVER, Bair, Cauir., Nov. 18, rorr.
NINETY-FOUR SPECIMENS WITHOUT NEW GROWTH.

Scale record.
Length. Number. Avenee Average
number of | Men As of
Tings es
tadius.
RANTLE CEA EMENTAE peter actete eyes ctele ite syepsie die clare cuslelsiw stoke) Cais mis fais a 'c\e\a\aisie,esklais)teenals siaye/slarevepoteis,<seleictecela siete 2 17-5 59-8
116 to 120 mm. I 17-0 55-0
rrrtorrsmm. 2 15.5 55-2
106 to rromm. 15 15-3 SIE
ror to 105 mm, 27 15-3 48.9
96to roomm,.............. 35 15.0 47-1
COUR OD FETE 6 oo: indetgoebocceesu 59 cis Geno BUOSO GUS UU SORES OU LES DORSROE SNE Sore sarabrsbeclobc 12 14-3 46.0
Jy ECGS TO). ato: a dadecemati God cObTISES DG GCOS CH GER C ODE OCUSE EE UEgGEE pe ceenisE Sec bem eel Geramcas ire 15.2 48-7
THIRTY-SIX SPECIMENS WITH NEW GROWTH.
Scale record.
Average
estimated
Average number of | Average length of Hate
Length. Number. rings— anterior radius— Fi
time of
beginning
new
To new Ofnew | Tonew Total growth.
growth. growth. growth.
rrr to 115mm Is-0 40 49.0 59-0 88.0
106 to 119 mm 14.6 1.8 50.0 58.0 92.5
rorto1o5mm... 13-4 m8 45-4 51.2 90. ft
96 to 100 mm 13-4 1.8 41-4 51.4 83.0
grttog5mm..... 13.0 2.0 35-7 43-7 80.0
86tooomm..... 12.0 2-0 32-2 43-0 73-0
Av. 100.5 mm 13-7 | lg 43-1 51-8 85.9

A collection made December 18, 1916, contains 92 specimens. Only one is a
mature male, 108 mm. long. The scales of this individual show 16 rings, and the length
of the anterior radius is 59.8. Fifty-one (56 per cent) of the 91 immature specimens had
begun the rapid growth of the new year. The average length is 101.2 mm. Forty-five
males average 101.9 mm. and 46 females 100.6 mm. ‘The table (40) follows:

TABLE 40.—YOUNG CHINOOKS FROM McCLoupD RIVER, Barrp, Cauir., DEc. 18, rrr.
: FORTY SPECIMENS WITHOUT NEW GROWTH.

Scale record.

Length. Average

Average | jength of

number of TETInG

aUtes tadius.

116 to 120mm.,,.. 18.0 55.0
trrtor1rs mm, 17-0 49-0
106 to 110mm. 16.5 53-4
tor to 105 mm. . 50.0

40 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 40.—YouNG CHINOOKS FROM McCLoup River, Bairp, CauiF., DEC. 18, 1911—Continued.

FIFTY-ONE SPECIMENS WITH NEW GROWTH.

Scale record.
Average
estimated

Average number of | Average length of length of

Length. Number. rings— anterior radius— cate
beginning
Tonew | Ofnew | Tonew is
+ trowth.
growth. | growth. | growth. Total. gro

SANA CCP HUT SOU ARS ARCO Ucn oCocdo sano Caricactaacacgacha: 13.0 3:0 38-0 49-0 98.0
rrrto1msmm....... “4 ate 13-6 3-0 47-1 52.0 96. 3
106 to 110 mm... 14-4 1.8 43-7 50. 6 91-0
ror to 1o5 mm. 13-6 2.0 42.0 48.3 88. 5
96tor1comm,., 13-3 2.1 40.6 47-4 81.2
grtogsmm..... - 12.4 2.0 36.8 44-8 79.0

Avy. Ior.7 mm 13-4 2.1 40-3 48-5 86.0

January 22, 1912, 75 specimens were collected. There were no mature males
among them. One of the males, however, was of unusual size, 142 mm., and the testes
of this specimen were found, upon dissection, to be slightly enlarged. It is shown later
(p. 68) that precociously matured males may recover from the effects of ripening the sex
products, and there is no doubt that this has occurred in the individual in question. No
new growth is recorded on the scales, the terminal rings being of the winter type. The
large size, enlarged testes, and delayed new growth all point to the interpretation given.
The scales indicate clearly that the fish was a yearling, the same age as the other speci-
mens. They show 20 rings, and the anterior radius measures 75 on the arbitrary scale.
This specimen is not included in the tables. Forty-three (58 per cent) of the other
specimens had begun the new growth. ‘Thirty-one males average 104.1 mm. in length
and 43 females 102.3 mm. ‘The table (41) follows:

TABLE 41.—YOUNG CHINOOKS FROM McCLoupD RIVER, Barrp, CALIF., JAN. 22, 1912.

THIRTY-ONE SPECIMENS WITHOUT NEW GROWTH.

Scale record.
Length. Number. Agence Average
length of
number of ter

rings. ane

radius.
Re PALS ee RSE Se AORN SOOCUOS Oda n Soon teOUACOCUUD angUdoocioocdconcceonsoancoosbsacesaccon 5 16.6 55-1
106 to 110 mm.,,,.... 2 16.5 49-5
tor to 105 mm.,...... Ir 15-7 51.0
96to Icomm........ 7 14-7 48-5
g1togsmm......... 5 14-6 46.0
CUS Seer Sob 8 Issn One doosedeoucigso Oo nod der depcapacnaddde v boo SoeSS os SaUate I 14.0 38.0
LEAVE ON S17 MERMEN oy. 5 0: oveiuiv obete (ale ofetasareea eobuisioiapaie wal seeteloieverelateceal ostetaicisiaastaretetete staieis stots sic eter ciatate state abies] etter ener ees 15-5 49-9

SEAWARD MIGRATION OF CHINOOK SALMON. 4I

TABLE 41.—YouNG CuHINooKs From McCLoup River, Barrp, Cair., JAN. 22, 1912—Continued.

FORTY-THREE SPECIMENS WITH NEW GROWTH.

Scale record.
Average

estimated
Average number of | Average length of eaatl of
Length, Number. rings— anterior radius— tien er
| of
- | ; beginning
| new
To new Of new To new th.
growth. | growth. | growth. Total. Lhe
|
111 to 115 mm 6 13-7 3:5 44-3 55-2 90.5
106 to r11o mm Ir 13-3 2.7 44-9 55-8 90.0
tor to 105 mm - 13 13-2 2.6 40. 2 49-5 85.5
QBS CO KOON oon ec te tec anne neerscencccas ‘ 12 12.9 2-7 39-7 49-5 81.5
Er UNGA AUN, 5 oencagaccanednasonus Topo OOnaDnoeusIasesecny I II-o 3-90 32-0 43-0 73-0
AS TEATS Goo mos AaB doO so OAD ODN IE SODO DOS Hes SObigm easel lagees Sbooe 13-2 2.8 41-5 51-7 86.0
- February 27, 1912, 26 specimens were taken. One is a mature male, 127 mm.

long. The scales of this individual show 18 rings in the first year’s growth and 1 in
the second year’s growth. The length of the anterior radius is 51 to the beginning of
the new growth and 57 to the periphery of the scale. The estimated length at the
time of beginning the new growth is 114 mm. Twelve of the immature specimens
show the new growth at the margins of the scales. The other 13 specimens terminate
the scale growth in winter rings. The average length of the entire collection is 111.6 mm.
Twelve males average 110.9 mm. in length; 13 females, 112.2 mm. ‘The table (42)
follows:

TABLE 42.—YOUNG CHINOOKS FROM McCLoup River, Barrp, Cauir., FEB. 27, 1912.

THIRTEEN SPECIMENS WITHOUT NEW GROWTH.

Seale record.

Average length. Ising “eae
number anterior
of rings. radius,

Were ES Ogos SEAS So Sas Sad Soe 5 - SAS Re 4d Bano 85 SSP ogp se Se Sores pa Sore a ose eee Eanes: | 16.9 52-2
TWELVE SPECIMENS WITH NEW GROWTH.
Scale record.

Average
estimated

Average number Average length of peer je

Average length, of rings— anterior radius— GHISGE
beginning

new

Tonew | Of new To new (Sheree owth,

growth. | growth. | growth. CEST SS ea ;
114.2t1m....... : oie a/statermisbatsiatature(da]sratssetire\sterersintalatetsih pte 15-6 2-4 48.0 56.5 95-9

42 BULLETIN OF THE BUREAU OF FISHERIES.

The last collection from Baird was made March 2, 1912. This contains 31 speci-
mens averaging 109.6 mm. in length. There are no mature fish. Twelve males
average 110.5 mm. and 19 females 109 mm. in length. Twenty-two (71 per cent) had
begun the new growth. The table (43) follows:

TABLE 43.—YoOuUNG CHINOOKS FROM McCLoup RIVER, Barrp, CAir., MAR. 2, 1912.

NINE SPECIMENS WITHOUT NEW GROWTH.

Scale record.

Average length, Average
Average length of
auaber anterior
ES: radius.
KOS AMIEL Gs a ato ole niols|ofeialeluiclalaials/ere\inioi-inip eicial cla) s elels/=lelete| siete) rial nletr/qtotinte aiuie (s/s lalal sTeinis)s)alsivie)a/ei@lninlolnie ish eisieiei=iet= (nis is iy 16.4 50-7
TWENTY-TWO SPECIMENS WITH NEW GROWTH.
Scale record.
Average
estimated
Average number Average length of ago
Length. Number- of rings— anterior radius— tiarieiak
beginning
Ti Of ne To new Eats
‘onew new ‘on 0 ;
growth. growth. growth. Total. ze
epee COS Tes a caep or Aogaanrecedc obdcorincaadasorciacues £ - 2 16.0 3-0 49-5 61.0 98.0
NLC ae AETANE ate cata otek ov etoba mals ofat detapeeiainistaintstsyajsials) atelata lattes totais I 17-0 2.0 49-9 55-0 103-0
EL NMC YE Se AELIED ate te et erercheyciplotersicieletelciaiepaisleteiotetstereiselsletsinterateteraieiets 9 15-9 2:3 47-5 55°38 97-0
TOG CO TIO MMM, cece cee ewer ennnscandasesssceeserers 7 I5-I 2.1 48.5 57-0 93-5
Gye 2s Bao pans donosomcndmes ooo: ssoqoA gees oone sone: 3 13-7 2.3 41-4 53-3 84.5
PA Were CN Z EEIEN eo cic e ccc niet ce cites ble mnlelile srerisitmestatoe aieietee| ciate rcere 15-4 2.5 47-3 56.2 94-8

MISCELLANEOUS COLLECTIONS.

With but two exceptions the miscellaneous collections were made by Prof. J. O.
Snyder, of Stanford University, during the progress of biological investigations of the
coastal streams of California and Oregon carried on during the summers of 1897 and
1899. One of the exceptions referred to is a collection, consisting of but three specimens,
which was made by the writer in 1915 at Hope Island, Puget Sound, Wash. The other
exception is one specimen which was collected in the ocean at Half Moon Bay, Calif.,
some 20 miles south of the mouth of the Sacramento River.

The collections from the coastal streams are for the most part small, and a detailed
consideration of each collection will be unnecessary. Measurements of the scales were
not made. ‘The data are presented in the following table (44):

SEAWARD MIGRATION OF CHINOOK SALMON.

43

TABLE 44.—MISCELLANEOUS COLLECTIONS OF YOUNG CHINOOKS FROM COASTAL STREAMS OF CALIFOR-
NIA AND OREGON.

Date.

Scale record.

Number.
Number of rings—
A Length
Locality. Gann)!
With With To _ To
Total. | primary |migratory] primary |migratory| Total,
check. check, check. check.
Bear River, Calif., not far 76 to 80 4 ° 14-5
from the mouth. 71 to 75 Ir ° 12-9
66 to 70 8 ° IIe5
61 to 65 3 ° 12-0
56 to 60 3 ° 12.3
SOR On nnn ggg nn nth cn nnnnnnn! Cnt nnn nnn nnn 29 ° PRD | EAR eh oae snk Ce eosc] bopoooRten
z ST
PP Sater cetae vce tcehdadeannes Gos Moss cece Pome tse eatue see bead eee ae 12.6
Little River, Calif., from 81 to 85 2 ° 14-5
mouth up about soo yards. 76 to 80 3 ° 12.6
71 to 75 9 ° 11.9
66 to 70 9 ° II-9
61 to 65 I ° II.0
Dimin ce /datnioletals(nqs(nialejn ia mibih i> .a\elecela wim] asinine pie «area avaln 24 ° 2 bie to teictale fa aiding daly tpl ans clea asic
Peccisiak inlet hea amici ecteee ts Creed | Won Cepe ob [Re Rae ae) PECReL 5 36h lhe se § ke 12.2
Deer Creek, Oreg., 40 miles 2 68.0 7 GARE eee eclh Ll FiGa Salk cotta es 211.0
from the mouth.
Shasta River, Calif., triou- a 75.8 b6 Mec earelt A uGign Bul memset ee @ 13.5
tary to the Klamath River.
Flores Creek, Oreg., near 76 to 80 I ° 14-0
tidewater. 71 to 75 6 ° 13-8
66 to 70 12 ° 13-3
61 to 65 8 ° 13-1
56 to 60 3 ° II-o
Slevelatalstataal olata thi meai aelteloocle Tote atade eel ereisTe veins ie tala acne 30 ° POR ae eee teres |picisiate/atose ois | Siete otaiaye
Dinistntaletaieiclatelopatalefaleletates/eiateTaterttal-(t CV ACH RBEGbe Soccer PORDOACORE Mash ScOnne HSeeneecce 13-2
Elk Creek, Curry County, gt to 95 2 Ole” Meetlities prciges 17-5
Oreg., near tidewater. 86 to 90 3 ° 18.0
81 to 85 4 ° 14-5
5 76 to 80 12 ° 12 14-2
71 to 75 4 ° 13-7
66 to 70 2 ° 13-0
9.45 Joes Sande FeO SOOO Lo arene Boma ae es 27 ° CVA he Ot eet il beara aoee aac one
B SAciosinaane a stodepbandeaderc see OAS | okie nto be [lee eee ce cle ea tomaad sone ee stele 14.8
Sixes River, Oreg., near tide- 277.6 6 ONTO G Vara RE gos oe 215.0
water.
Siletz River, Oreg., about 20 @ 93.2 4 Oo) Malham aon saws 217.5
miles above mouth, |
Nestucca River, Oreg., 10 @115.5 4 3 4 23.6 215.0 @ 21.2
miles above mouth,
Trask River, Oreg., just ors 13 ° 7 15.2 218.5
above tidewater.
Nehalem River, Oreg., just @ 104-0 19 ° TOL ach ote 215.8 4 20.5
ahead of incoming tide.

a Average.

>’ Two mature males.

The fish contained in these collections are obviously all fry, hatched from eggs

laid down during the fall previous to the date of capture.

No striking variation in size

is noticeable, other than that which is apparently dependent on greater age, those

fish collected later in the year averaging somewhat larger.

The same uniformity is

44 BULLETIN OF THE BUREAU OF FISHERIES.

characteristic of the scale growth. A more detailed study of much larger collections
might, however, discover special characteristics of growth or of scale record in the
different streams. The primary check appears in only one of the collections which
were made close to tidewater, the one from the Nestucca River. The check observed on
the scales of the specimens from Shasta River and Deer Creek (collected toward the
headwaters of these streams) is undoubtedly the same as the primary check noted in
upstream fish from the Columbia River basin. (See p. 18.) A band of intermediate
rings is characteristic of varying proportions of the fish contained in all of the collections
made near tidewater and is in every respect similar to the intermediate growth of the
Columbia River migrants. Although the available data are meager, it seems safe to
state that the history of the fish in these smaller streams is, in its general aspects, similar
to the history of young fish collected in the Columbia River at the same time of year.

‘The three specimens taken near Hope Island, Puget Sound, were the only chinooks
among some 70 specimens captured by hook and line in one of the fish traps located at
this point. The remaining specimens were yearling silver salmon averaging about
100 mm. in length. There is no means of knowing whether this is the normal propor-
tion existing between young silvers and young chinooks in this part of the sound at
this time of year. It may be that the young chinooks do not lead into the traps as
readily as the silvers; or they may be less willing to take the hook. These three chi-
nooks were, respectively, 130, 97,and 94 mm.inlength. Allwere males. On examining
the scales it was surprising to find that, in spite of the negligible difference in size between
the two smaller fish, the smallest individual was a fry and the two larger ones both
yearlings. The record on the scales is perfectly clear, leaving no doubt as to the proper
interpretation. The scales of the two smaller individuals, differing but 3 mm. in length,
are reproduced in Plate IV, figures 6 and 7. The scales of the smallest individual show
no indication of stream growth, and there is no doubt that this fish migrated as a young
fry and that the scales represent a purely ocean type of nucleus in the process of forma-
tion. ‘The scales of the fry show 13 rings, and the length of the anterior radius is 50.
The scales of the smaller yearling have 13 rings to the end of the first year’s growth
and 5 in the intermediate growth. Those of the larger yearling have 1g rings to the
end of the first year and 8 in the intermediate band. The scale measurements are as
follows: 130mm. specimen, 55 to beginning of the intermediate growth, total, 92; 97 mm.
specimen, 28 to intermediate growth, total, 47.

The young chinook from Half Moon Bay, Calif., is of particular interest, since it is,
so far as the author knows, the smallest individual which has been captured in the open
ocean at any distance from the mouth of the parent stream. Unfortunately, there are
no data as to the date of capture, except that it was previous to 1913. ‘The specimen
presumably came from the Sacramento River, since at the time this was captured no
chinooks were known to spawn in the streams south of San Francisco.¢ ‘This fish was
approximately 100 mm. long. The scales (Pl. IV, fig. 8) indicate clearly a period of
life spent in the stream followed by a sharply demarked area representing ocean growth.
That part of the scale indicative of stream growth is precisely similar to the scales of
young migrating fish taken in the spring and summer on the lower Sacramento River
(Pl. III, fig. 6).

2 Within the past six or seven years a run of chinook salmon has been established in the San Lorenzo River, Santa Cruz
Co., Calif., by the late Supt. F. A. Shebley, of the California Fish and Game Commission.

SEAWARD MIGRATION OF CHINOOK SALMON. 45

CONCLUSIONS.
RATE OF GROWTH.

An analysis of the data from the Columbia River shows that all of the collections
are not strictly comparable, since the rate of growth is markedly variable in different
parts of the river. The environmental conditions in different regions of the watershed
are so variable that this is not surprising. Therefore the collections have been separated
into four groups, each group having been taken under approximately similar conditions.
These four groups are as follows: (1) From the main river above the estuary (the estuary
is considered as that part of the river below Tenasillihee Island, about 18 miles above
Astoria); (2) from the estuary exclusive of the collections made under the canneries;
(3) from under canneries in the estuary; (4) from Clackamas hatchery and the Clacka-
mas River near the hatchery. In addition, there are the collections from the Little
White Salmon River, from the McKenzie River, and from the lake at Seufert, Oreg.;
but these are not included in this grouping.

In the following table (45) the data which have been previously presented in sep-
arate tables are recombined, so as to show the average lengths, during each month of
the year, of the fish captured in each of the four divisions of the river and in the Little
White Salmon and McKenzie Rivers. These same data, with the addition of those
for the collection from the lake at Seufert, Oreg., are presented in graph 1. In the
graph, however, the collections from the mouth of the small creek near Point Ellice
and from the Columbia River near the mouth of Little White Salmon River have
been kept separate.

TABLE 45.—AVERAGE LENGTH OF SPECIMENS FROM THE COLUMBIA RIVER FOR EacH MONTH.

Group 1. Group 2. Group 3. Group 4.
Month. ]
Locality. Length. Locality. Length. Locality. Length. Locality. Length,
...| Grims Island.....
.| Cottonwood and
Deer Islands.
Crandall’s_ sein-
ing ground.
Near mouth of
Little White
Salmon River .
June... elect cece eee eal ieee ees Siac rasa estes [he errr lee See at sanamndd Hadedood s-Seaesoaccaonoocd Bkaaasad
Point Ellice. |
: CO EO ET Npirelbo o ose seersadconse| 2c 7e20 4 speadc capcoue laced hacoeed °
estuary.
AOE Sane ee OR Co encbae rae Be rod faae sack Point Ellice...... Gat aig sre siarkaeepncaiecven geil Ccbrmanel watew wimiclduis cites octal Ceeeets Sats
TOUS Hs Sosenbatel seonsoseodendcricced| Hioooodod |aoacs el tomeodesdan 94-0 | Ilwaco, Wash. 118-0] Clackamas 112-9
7 River.
September....... Crandall’s sein- (7 -ot | RRA Cee Amand peneee [tone dose sees MADCON] Ses cisacherechineweice [specs eee
ing ground. 4
October cn nee seositen cocetee es oe|eerieiee Point Ellice,..... 112-7 | Astoria, Oreg....| 127-5 | C Ke ckamas 118.0
ver.
Ilwaco, Wash..} 146-7 | [Little White 92-5]
Salmon River.
November........ Warrendale, Oreg|| 99350) | 5.0. sees cece ence ces |ecwececs Astoria, Oreg....| 135-0 |[McKenzie River.] 105.8]
December........ Several points on Gebt) ih soar ccoeddeaoosere eoecoscel hacnsacumt acledocc| yocegnae Clackamas 121-1
the lower river. hatchery.
YEARLINGS
March sree cet cody ces dowe etc. Cech hal sneedsnoecacscee| Aerce sso] t(ebacssscapteneboe| tc doen 4 Gaccpooncdodaddoad bc SopAcs
Aprilir ys 2 (Graal Ga Sere Ry | Ren oapcbbeciser baorcsod bheégecoostonocidoe-| RoI8G004 Apooddo sp usesooosd Pecennos
Deer Islands.
Mayet eset. (GCrandallsisem-= x03: a! |(Pomt ellice anid) 5208.71 |B eos ae aed acice + «-|tioew oncic| ties ootececlees pietv<[oictewetene
ing ground. Tenasillihee Is-
land.
[ECE Se ciodinaaaisg SSP chee hoses Rose oeee) SB ec ase Beas Sdoe soa Basroess ie Seeccerpeeredsoed bocceced Clackamas 112-2
ver,

75412°—22—_4

46 BULLETIN OF THE BUREAU OF FISHERIES.

One of the most striking features of the growth as shown by this tabulation is the
constant difference in average size maintained in different parts of the stream.

The smallest fish taken are those comprising group 1, from the main river above
the estuary. The rate of increase in the size of these fish is quite regular, although
there is a period from November until March when the growth is practically negligible.
In April and May a second period of rapid growth is apparently started, although more
data collected during subsequent months would be necessary to prove this. Since no
yearlings are found in the river after June, it is impossible to get this information.

a

140

Mch. Apr. May dune duly Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mch. Apr. May June
Yeartings.

Grapu 1.—Rate of growth of young chinook salmon from different regions of the Columbia
River Basin. Figures at left of graph indicate length of fishin mm.; solid line, group 1; broken
line, group 2; dots and dashes, group 3; dotted line, group 4; a, Columbia River near mouth
of Little White Salmon River; b, small creek near Point Ellice; c, lake at Seufert, Oreg.;
d, Little White Salmon River; and e, McKenzie River.

Until after May there is no particular difference in the size of the fry from different
portions of the stream. However, in later collections it is seen that those composing
group I are smallest, followed, in the order of increasing size, by those of group 2 (from
the estuary), group 4 (from the Clackamas River), and group 3 (from under the can-
neries at Ilwaco and Astoria).

The greater size of the fish of group 2 as compared with those of group 1 is un-
doubtedly due to the more rapid rate of growth maintained in theestuary. In the same
manner the greater size of the fish taken from under the canneries is due to the more
rapid rate of growth of those fish which acquire the habit of feeding on the abundant
offal. The fact that fish taken under canneries are so uniformly different from those
taken but a short distance away indicates that the young salmon congregate at these

SEAWARD MIGRATION OF CHINOOK SALMON. 47

points and that individuals may remain here for some time feeding heavily on the offal
and as a consequence growing with unusual rapidity. The greater size of the fish from
the Clackamas River, as compared with those of groups 1 and 2, may be due to a racial
difference characteristic of the fish in this tributary or to the fact that many of these
fish have, in all probability, been reared for a part or all of their lives in the hatchery.

The rate of growth in the estuary, and especially under the canneries at Ilwaco
and Astoria, is distinctly more rapid than in the higher waters. ‘The increase in length
is especially rapid during June, July, and August, by which time the fry in the estuary
have far outstripped those in the upper part of the stream—in fact, have reached a
greater size than will be attained during the remainder of the year by those individuals
that do not migrate early. The growth in the estuary during September and October
is positive, but much slower than that which took place during the three months just
preceding. After the month of October the data pertaining to fish from the estuary is
very scanty, but apparently a period during which little or no growth takes place follows,
this coinciding with a similar condition in the regions upstream.

It will be noted on the graph that the final tendency of each of the curves is down-
ward. ‘This seems conclusive evidence that the larger individuals migrate earlier.
Gilbert (1915) has found this to be true of young, seaward migrants of the sockeye
salmon. The present author’s conclusion that the young fish in the tributary streams
tend to migrate shortly after beginning the new growth, if not before, also indicates that
the larger specimens migrate earlier, since it has also been shown that the specimens
which have begun the new growth invariably average larger than those which have not
done so.

The single collections from Seufert, Little White Salmon River, and the McKenzie
River do not offer any basis for estimation of the actual rate of growth during successive
months, but it will be seen that they agree in general with the growth of fish in the main
river, averaging somewhat more than the fish in group 1, but less than those of group 2.

In the case of fish taken from the Columbia River proper it may not be strictly
correct to speak of the increasing size as growth. In all probability fish that have
once entered the main river continue, more or less steadily, their migration to the ocean.
We would thus be dealing, in successive months, with entirely different lots of fish. In
a general way, however, our figures should show the main features of the growth.

At the time the fry become free swimming they are between 35 and 40 mm. in
length. During March, April, and May the average length does not exceed 50 mm.
Above the estuary the growth is quite regular from the time the fry first appear until
October or November, by which time an average length of between 90 and 100 mm. has
been attained. For the next several months no particular growth is recorded. The
collections of yearlings made in April and May from the Clackamas River indicate that
a new period of growth has been initiated, but because of the fact that about this time
the last of the fish leave the tributary on their downward migration no further data are
available. The rate of growth as indicated by these data has undoubtedly been modi-
fied by the migration of part of the fish. As has been shown, the larger fish tend to
migrate earlier than the smaller ones. This would tend to slow up the growth curve
and to obscure the sharp rise during the early summer so conspicuous for the curves
for the other groups.

48 BULLETIN OF THE BUREAU OF FISHERIES.

It has been shown that new growth is recorded on the scales of fish in tributary
streams as early as October or November (p. 25). Since there is no conspicuous increase
in the amount of new growth between this time and the following May or June, and
since, also, it has been shown that the fish entering the estuary during the late fall or
winter may show a marginal band identical with the ‘new growth” observed in the
tributaries, it seems safe to conclude that the young fish start the downward migration
soon after beginning the new growth, if not before. This matter is given further con-
sideration in the sections dealing with scale development and with migration.

The estimated size at the time of beginning the new, or the intermediate, growth
is given in the following table (46) and in graph 2. (Consideration of the collection
made at Seufert, which has already been discussed, and of the one made at the Clacka-
mas hatchery in December, 1914, is omitted here.)

TABLE 46.—AVERAGE EstiMaATED LENGTH AT TIME OF BEGINNING NEW GrowTH (GROUP 4) OR INTER-
MEDIATE GROWTH (GROUPS 1, 2, AND 3).

Group 1. Group 2. Group 3. Group 4.
Month.
Locality. Length. Locality. Length. Locality. Length. Locality. Length.
FRY
Mm Mm, Mm Mm
Tol igor cond] bendeeeccodHopaaananriq Pocerctn Estuary, except EHOW oa Bbc 20 dd0a00Io0c Paceieged fisriio Saoocbr crenadl faEc G00
from small creek
near Point Ellice.
UR ers sie teeta Point Ellice........ SOAs) sheeabocessadene | sSegdege BasncBhtasesacecod badgers
August....... ee Men once (: (o ane pee omogocaic 54-5 | Ilwaco.......... BL Ol |S meqete ostn sterelnin abe eet
September xa Fae vcrotars ete cleversiaie oie, otcee | atu ete tata era |i latapasa ana a nvose otal tata inl'n)ai| =e] n/atejete\ | azeiaial CG rragmnansnd BYP eesoneeonnncanobod og occdoc
October...... Point Ellice........ 94-7 | Ilwaco and As- | ror.9 | Clackamas River. 99+3
toria.
IN fev carlal aatind Plggasddaseetanhieaan trees 144 ietvosdoaceoasocoan son sccroeor Astoria.......... 111-6 |[McKenzie River.| 85.1]
December....| Several points on PIB AA leis atrestertie ts -<tctats\ape aiatera| otelaterojetn'o olviatajalevele|elelefeisfmve)ainrel|\e(eietaie /<faial| olsiavnlelalele/eis win {elelntelats| afuls loin wrele
lower Columbia.
YEARLINGS.
MACON cise cers retin COs ress nice VEC dood bobedoaccaecascee| paccsber| Gsepondnsadscceaed bene cee bocccddocieoads sone bosouaso
Aprils. io. .2.7 Cottonwood and ETP bmocbeesemoneassod0cc bdOsepod Wocer coda 7JoDStuC a Mocmaged pauccencapcescdeos Poacdsoa0
Deer Islands.
May.......... Graridallts ye 3.ceeer 74-0 | Point Ellice and PE BO APC ROO RO FOCCIOEE, ho mdotice Moreno nondp xonsca 539 a05
Tenasillihee Is-
land. }
AOS SBSF cep od eseascas ccdennosescac| badbontc jasddenboronctacteSdad boo sec baddadspectcetabod Haakeeic Clackamas River 78-3
4

There is a distinct grouping of the estimated lengths at the time of beginning the
intermediate growth about three modes, as follows: During June, July, and August the
mode is approximately 55 mm.; during September, October, and November, approxi-
mately 100 mm.; and during the remainder of the time in which the young are taken
in the river, approximately 80mm. ‘This may be an accidental result due to insufficient
data; but it is believed that there is something fundamental concerned. The mode at
55 mm. agrees fairly well with the length of the young chinooks planted in the pond at
Seufert. (See p. 18.) Itseems probable, therefore, that the check from which this
estimate was made represents some incident in the early history of the fry com-
parable with the transfer from hatchery to more natural conditions. Therefore, this
estimated length may represent either the size at the time of planting from the hatcheries,
the size at the time the fish left the smaller streams on their downward migration, or the
size at the time of entering the brackish water of the estuary. The mode at 80 mm.
represents the size attained at the time of beginning the new growth of the second year.

SEAWARD MIGRATION OF CHINOOK SALMON. 49

This is shown by the close correspondence in estimated size of the yearlings at the time
of beginning the more rapid growth of the second year. This correspondence also
indicates that the yearlings migrating in the spring are a homogeneous lot and that the
check preceding the intermediate growth (in Groups 1 and 2) is the same as that pre-
ceding the new growth (in Group 4) ; that is, that this check in both instances is in reality
the winter band. (See discussion on p. 57.) The mode at 100 mm. undoubtedly repre-
sents, in the fall migrants, the size at the time of entering the estuary. It is possible
that these differences in the estimated size at which the intermediate growth begins may
be of value in determining, from the adult scales, the time at which migration took place.

130

2.2 Cute e ene

June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. St Apr. May June
Ery.. 2arte
Graru 2.—Estimated length at time of beginning intermediate growth (groups 1, 2, and
3) and new growth (group 4). Figures at left of graph indicate length of fish in mm.; a,
group 1; 6, group 2; c, group 3; d, group 4; e, creek at Seufert, Oreg.; f, McKenzie River;
and solid line, growth curve for group x (from fig. r).

The rate of growth of the migrating fry in the Sacramento River is given in Table 47
and is shown in graph 3.

TABLE 47.—MIGRATING FRY FROM SACRAMENTO RIVER.

Date. Locality. Length. Date. Locality. Length.
. Mm.

3 SER EAU atic nsonoodnenoenoone 17-0

<7 Hass!Sloigh). cadens = esies me 75-2

-2 Sarisalitonen: ese itunttkarere(on is 81.0

2 8.1 Prospect Slough............. ae 68.0

Sacramento River 30 miles above 57-5 Pe lichiortien, saciee attests oa 76.8

Sacramento. d Woods 3 Break. . 71-0

Cache Slough. . . 67-0 Pond near Butt 95-6

..| Prospect Slough 69-0 ne PIS Re wien ners setters 78.8

..| Butte Slough... 64-1 ..| Ponds near Knights Lan 107-0

.| Pond near Butt 81.5 .| Pond near Butte Slough, . 92-2

50 BULLETIN OF THE BUREAU OF FISHERIES.

The average length of the fry at the time of hatching is the same as for the Columbia
River fish, 35 to 40 mm. The data here presented give only the earlier part of the
growth. The rapid rise of the curve during April, May, and June is conspicuous. In
comparison with the rate of growth in the Columbia River it is seen that, while the rate
itself is approximately the same, the time at which the most rapid growth takes place
is fully a month earlier. This is, in all probability, due to the fact that, as a whole, the
water in the Sacramento Basin is warmer than that in the Columbia River Basin. Asa
consequence, the eggs hatch sooner and the growth is somewhat more rapid.

ee Aen

Baa

fa
coy
a
he

Rel
She

0
Mch. Apy. May June July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mch.
Fry. Yearlings.

Grapu 3.—Rate of growth of young chinook salmon in the Sacramento River Basin. Figures at
left of graph indicate length of fish in mm.; dotted line represents probable growth of McCloud River
fish, May to July; 1, lower part of river; 2; McCloud River.

The rate of growth in the McCloud River is shown in the following statement and in
graph 3.

Growra oF Younec Cutnooxs 1n McCLoup RIvER at Barrp. Length,
m.

tly aey he lo: aan Sitloe OD adnoe spp aaac pasos snoc 200 panip DaBode Bap oan Ooo Or 88. 5
September 24, 1909... 0... 62. e ese ce ee nee ene nee cence sree teen eme gece ace . 96.9
September 28, 192T. ccc ce eee cee vee ee ee etree ce tener tet e reeset tense ras ences se 93-2
Metober- 18; LOLs ce AH BING tae s here ee eRe ote Mite ievede sl nyeler etek e7eheh Par eue te tee . 99-2
November 18 roxt. diester. to see ica rae opp miei tee eispel ogee ie let essere erase IO. 3
DD yao sri oper@ad: hie) U ieR ETS SSSR ONE Pierre cA OON OM ch dribOOUROGADN SO abocr Homo CIM Ie “el: IOI. 2
artery: 22) ) QT aH soiee. teeta ett ay -sereedn ete vetsts)n alts tale -L\tese Pl c)p fale teaie (to alan eee 103.0
February 273 Love blades 4. elk vxfelebietete ike ; II rn es 111.6

4
°

2
QO

March 2 'noraies sce tiger: raiadttels igticat arate acne hele susan

SEAWARD MIGRATION OF CHINOOK SALMON. 51

There is here merely the upper end of a curve of growth which began in the early
months of the year, when the fry were 35 to 40 mm. in length. The earlier part of the
curve is undoubtedly represented quite accurately by the data obtained from the col-
lections from the lower part of the river.

In graph 3 the lines give a generalized curve combining the data from the two
regions of the Sacramento. The dotted line represents the probable growth of McCloud
River fish during May, June, and July. This curve represents approximately the normal
_ rate of growth in the Sacramento Basin. It is interesting to note that the indications
are quite clear that the growth of the migrating fish does not slow up during June and
July, as is the case with the fish from the McCloud River. It is more than likely that the
yearlings in the McCloud River would begin to show the slower growth in May if data
were available.

The single collections from the coastal streams offer no basis for the analysis of
growth. The collections from the Siletz, Trask, Nehalem, and Nestucca Rivers average
about the same as those taken at the same time of year from the Sacramento and Colum-
bia Rivers. The rate of growth in these streams is, therefore, probably about the same
as in the larger rivers. ‘The collections from the Bear, Little, Shasta, and Sixes Rivers
and from Deer, Flores, and Elk Creeks average smaller in size than the collections from
the Sacramento and Columbia Rivers. It may be concluded that the rate of growth
in these streams is slower than in the others studied. Any conclusions, however, based
on such scanty material must necessarily be merely tentative.

It may be stated in a general way that the growth of young chinook salmon in
fresh water is most rapid during the first three or four months after the appearance of
the fry. The time of year during which this rapid growth takes place varies in different
streams, according to the time at which the fry make their appearance. ‘The prevailing
temperature of the water is also an important factor. After this first period of rapid
growth the rate rapidly decreases during another period of about three months, until
finally growth practically ceases for the year. A new period of rapid growth is appar-
ently begun during the early months of the second year in case the fish remain in fresh
water.

At the time the yolk sac is absorbed and the fry become free-swimming the average
length is between 35 and 4omm. By the end of the first period of most active growth a
length of 80 or 90 mm. has been attained. The average length attained during the entire
first year is approximately 100 mm.

The effect of migration into the brackish water of the estuary is to decidedly
stimulate the growth.

DEVELOPMENT OF SCALES,

This section, dealing with the development of the scales, is, in certain respects, the
most important part of this study. The work on the young fish was undertaken pri-
marily, as has been previously mentioned, in order to supply an established basis for
the interpretation of the nuclear portion of the adult scales. The especial need was data
sufficient to permit a reasonably accurate determination, from the adult scales, of the
time of migration. To this end are recorded here in detail the data bearing both on
ring counts and the length of the anterior radii. The data for the Columbia River fish
are given in Table 48 and in graphs 4 to 7.

52 BULLETIN OF THE BUREAU OF FISHERIES.
TABLE 48.—FISH FROM THE COLUMBIA RIVER: AVERAGE LENGTH AND SCALE DEVELOPMENT FOR EACH
MonrH. ;
GROUP r. ;
Specimens. Scale record.
Number of rings— Length ph ontenios
Month. Locality. With | With
scales | BeWOr
Teneth. | with | mediate | Tobe To be-
rings. ginning ginning
growth. ofirapid Total. ofrapid Total.
| growth. growth
1
— SS SS SS SS
FRY.
Mm. | Per cent. | Per cent.
March........ Grams Tslanid eiieaias iaellaen ise ieee esl is = 40-0 38-0 0.0 1-4 70
Bore sy-pees Cottonwood and Deer aplasia 43-2 96.0 +O}.. 3-3 17-5
Mayan cnt aacs Crandall’s seining ground............. 52.5 88.0 +O 4:9 22-4
Near the mouth of Little White
Salmon River............. ostosedcct 44-6 78.0 so pe ie <i ll Paseo Seg a 16.5
September ...| Crandall’s........ See ee Rte sense 74-5 100.0 5:0 (2) IZeKd| Nanas teres 40-5
b7.0 16.0 21-3 47-3
November....| Warrendale. ............:-+e,eeeeeeees 93-0 100-0 fey eReAeA a Cee TS Oil eieninneece 45-0
December. ...} Several points on the lower river. ..... 93-9 100.0 55-0 (2) Oe | Sararsce c 49-5
014.7 18.7 38-6 50-4
YEARLINGS
March........ Several points on the lower river...... 95-9 100-0 72-0 (¢) 18.7 35-7
415.8 20-0 39-8
Aprile occ Cottonwood and Deer Islands......... 107-0 100-0 77-0 (¢) 19-6 42:0
415.0 17-8 41-0
May acckicceccs Search al se ererate ersteteloterelaterastere riot etalstetet 103-0 100.0 100-0 15-0 19-9 41-7 58-5
GROUP 2.
FRY.
April isaac ores points in estuary.............. 38-0 13-0 Chot| feceteerac . 6.3
SG Wamp adadae| loedtceleh ms aasisdsnomote pemseenoon 47°3 86.0 Do) Bre stir - 20.6
Jiities een os Small creek near Point Ellice. . 47-7 97-0 AGH ie saangoa4 - 20.5
Other points in estuary............... 77-0 100-0 17-0 (c) : 38.1
r 411.6 b 42-4
TEL eS ececcod Pomt Hllice. 2. so seen eect aes 92-2 100-0 70.0 (¢) é 46-4
d7.6 3 49-8
PCIQUISES «oc noe] aan ate [: (eee ae ee opetisabade cneecce 93-9 100-0 58-0 (¢) : 45-7
48.5 5 52-3
Wctoberccrei-a| sna ¢: See AB APC UEEpaoode dobosensacne pe 112-7 100-0 24-0 (¢) Cre alls amanearns 59-8
d 20.3 23-4 50-7 60.6
YEARLINGS.
My Sericctemene Point Ellice and Tenasillihee Island. . 108.7 100-0 100-0 17-2 23-4 45-7 67-0
GROUP 3.
118.0 100.0 61-3
123-0 100-0 59-4
62.0
127-5 100.0 64-5
73-0
146.7 100-0 . 61-3
} d 77-1
135-0 100-0 5 73-0
22-6 65-4 78.0

@ Without new growth.
> With new growth.

© Without intermediate growth.
@ With intermediate growth.

SEAWARD MIGRATION OF CHINOOK SALMON. 53

TABLE 48.—FISH FROM THE COLUMBIA RIVER: AVERAGE LENGTH AND SCALE DEVELOPMENT FOR EACH

Montu—Continued.
GROUP 4.
=
Specimens. Scale record.
Number of rings— Length of anterior
3 tadius—
Month. Locality. With With
Length. scales ae teen
i mediate To be- To be-
Tings. ginning ginning
growth. of rapid Total. iptixaritcl Total.
growth. growth.
FRY.
Mm. Per cent.
46-5 100.0 18.8
49-5 100.0 29-1
112-9 100-0 58.2
118.0 100-0 64-6
77-O
Little White Salmon River¢.......... 92-5 100-0 52-5
November....| McKenzie Riverc..................... 106.4 100-0 52-2
55-5
December... .} Clackamas hatchery................... 121-1 100-0 56.0
73-0
YEARLINGS:

Jue s: Sosecs Clackamas River...........2.2000-e00- 112-2 100.0 100.0 15-5 21-6 49-1 72-6

swale
¢ These collections are given with the Clackamas series for the purpose of comparison.

The chief generalizations derived from the data recorded here are:

1. The increase in the number of rings on the scales and the increase in the length
of the anterior radii are proportionate to the increase in length of the fish.

2. Hatchery-reared fish develop scales with rings earlier than do wild fish.

3. The length of those fish whose scales show a marginal band of wider rings (inter-
mediate or new growth) is usually greater than that of fish taken at the same time and
place, but whose scales do not present such a marginal band. As a corollary to this,
the length of the scales and the total number of rings are greater in those fish which
have started a period of active growth than in those, taken at the same time, which
have not done so.

4. The number of rings in the intermediate band (or the band of new growth in
Group 4) and the width of this band are somewhat greater in the spring yearling migrants
than in the fall fry migrants.

5. This increase in the size of the intermediate (or new) band is not due to an in-
crease in the size of the fish, which is not apparent, but to the fact that the part of the
scales central to the beginning of the intermediate band is smaller in the spring than in
the fall fish. This indicates that the fall migrants are larger before beginning the inter-
mediate growth than are the spring migrants and is indicative of the earlier migration
of the larger fish noted elsewhere.

6. In collections which contain both specimens whose scales show the intermediate
growth and those which do not, the number of rings and the length of the anterior radius
are less to the beginning of the intermediate growth than to the periphery of the scales
on which such growth is not present. Since the fish which have not begun the inter-
mediate growth have, in all probability, entered the estuary more recently than those

54 BULLETIN OF THE BUREAU OF FISHERIES.

which have begun such growth, this would seem to indicate that the later migrants
reach actually a greater size before migrating than do the earlier migrants. It is possi-
ble, however, that the scales are larger proportionately in the later migrants, the fish
themselves being the same size, or even smaller. In such a large river as the Columbia,
where the young migrants are coming from numerous tributaries, such generalizations
require careful confirmation.

The author has been unable to see any systematic arrangement in the occurrence
of the primary check. The cause of the formation of such a check has been traced in
the collection from Seufert; but it is not to be inferred that the change from the hatchery
environment to one approximating normal, wild conditions is the only cause behind the
formation of such a check. Other somewhat similar environmental changes early in
the life of the fish would undoubtedly result in a similar check.

In Table 49 are presented in percentages the data regarding the type of marginal
rings found on the scales during successive months on the Columbia River. During the
early months the marginal rings of the fry are always of the summer type [type (1) in
the table]; that is, are not conspicuously narrowed. In August is encountered the first
development of narrow, winter rings [type (2)], and from this time on until April vary-
ing proportions of the specimens have marginal rings of this type. After the time when
the marginal winter rings begin to be a feature of the scale growth it may be expected
that the intermediate band, when formed, will be preceded, in some instances, at least,
by a distinct band of narrower rings. After the winter bands begin to appear there is
a constantly decreasing percentage of specimens whose scales show marginal rings be-
longing to the growth of the first summer in fresh water.

TABLE 49.—PERCENTAGE OF FisH WHOSE ScaLES SHOw MarGINAL RINGS OF (1) SUMMER TYPE NOT
ASSOCIATED WITH INTERMEDIATE OR NEw GrowtH, (2) WINTER TYPE, (3) SUMMER RINGS oF NEW
OR INTERMEDIATE GROWTH.

Group r. Group 2. Group 3. Group 4.

Month.

(x) @) | G) (x) (2) (3) (x) (2) (3) (x) (2) (3)

October ica eases tar bt00 ° ° ° 76 24

aSeufert. — ” ¢ Warrendale. e Clackamas hatchery.
b Little White Salmon River. d McKenzie River.

With the exception of the collection from Clackamas hatchery none of the fish taken
after November shows marginal rings belonging to the first summer’s growth. Such
changes as these, combined with the development of an intermediate band, will result

SEAWARD MIGRATION OF CHINOOK SALMON.

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Frees css eile lu ae bel cc 2

ieiret tig ela ea TL

Mch. Apr. May dune July Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mch. Apr. May June
Y
Fry Yearlinga.

Grapu 4.—Columbia River (group 1): Rate of growth, increase in number of rings, and increase
in length of anterior radii of scales. Figures at left of graph indicate ordinate values for the
three types of curves, as follows: (1) For curve of length, centimeters; (2) for number of rings,
ordinary numerical values; (3) for length of anterior radii, arbitrary units (actual value, 0. 00834.mm.).
Solid line indicates length of—1, specimens without intermediate growth; and 2, specimens
with intermediate growth. Broken line indicates number of rings on the scales—x, to inter-
mediate growth; 2, total for specimens without intermediate growth; and 3, total for specimens
with intermediate growth. Dotted line indicates length of anterior radii—r, to intermediate
growth; 2, total for specimens without intermediate growth: and 3, total for specimens with
intermediate growth. a indicates collection from Coliumbia River near mouth of Little White
Salmon River.

55

56

BULLETIN OF THE BUREAU OF FISHERIES.

( a
= 3.
1
/
/
i]

Ll

ee eee eee
/

Pehl ih ae Eta
ip —
Ee are elas eeted

Pak Ua NUNES Te
AER See

EN EA a a cd ele

EMG AS aa
Fig
Bl
ral

Apr. May June duly Aug.Sept Oct. Nov. Dec. Jan. Feb. Mch Apr. May

GrapH s5.—Columbia River (group 2)! Rate of growth, increase in number of rings, and increase
in length of anterior radii of scales. Significance of curves is same as in graph 4, with the fol-
lowing exception: a indicates collection from mouth of small creek near Point Ellice.

SEAWARD MIGRATION OF CHINOOK SALMON.

57

in a constantly increasing percentage of fish whose scales show an intermediate band pre-

ceded by a band of distinctly narrowed rings.

The fry migrating in August and Septem-

ber will contain a relatively small percentage of specimens whose scales are of this type.
As the season advances this percentage gradually increases, as the percentage of fish
entering the estuary from above and having begun the slower winter growth,

increases. When fish which have not begun the slower growth
enter the estuary, the vigorous intermediate growth may begin
immediately, so that no distinctly narrow rings will intervene
between the growth of the first summer and the intermediate
growth. All possible gradations between these two types of scales
may be seen among the fall migrants. The migrating yearlings
taken in the spring all have the band of narrow winter rings pre-
ceding the intermediate growth.

The question arises: Is there any criterion whereby fry migrat-
ing seaward in the fall and yearlings migrating seaward in the
spring can be distinguished? It has been shown that there is an
average difference in the following respects: (1) Spring yearling
migrants show a larger average amount of intermediate growth,
both on the basis of ring counts and scale measurements; and (2)
the intermediate band in the case of fall migrants is less frequently
preceded by a band of narrower rings. Although these average
differences in the scale growth of the fall fry and the spring year-
ling migrants are well enough established they are not diagnostic,
and it would be impossible in many cases to determine from the
scales the time at which migration took place.

Owing to the practical importance of determining, if possible,
any discernible difference between the scales of fish migrating at
such widely separated times, a series of each group was photo-
graphed in order to see whether some criterion, independent of the
data presented in the tables, might be established by means of
which the fish could be identified. The necessity for such series
of photographs was discussed on page 6. For this purpose there
were selected, at random, 50 specimens collected at Point Ellice,
October 16, 1915, as representative of the fall migrants, and 50
specimens of the spring, yearling migrants collected on the lower
Columbia River during March and April, 1916. A careful study
of these series of photographs has disclosed no such criterion as
was sought, and the conclusion is forced that, so far as the nuclear
growth alone is concerned, it can not be hoped to distinguish in
all cases adult fish which have migrated as fry in the fall from

<i
ia

N
[a
Lal

iI SILy

ESS cise |
Bee IIS ea
SSECE ON aca
ENE Ce Sane

A)

Aug.
Fry
Grapu 6.—Columbia River
(group 3): Rate of growth,
increase in number of rings,
and increase in length of an-
terior radii of scales. Signifi-
cance of curves is same as in
graph 4.

cpt Oct. Dow Deo

those which have migrated as yearlings in the spring. Plate II, figures 1 to 4, and
Plate III, figures x to 4, were selected from these photographs as examples of the scales

of the fall and spring migrants.

The available data regarding the scale growth of the Sacramento River fish do not
indicate that there is as much variation as has been shown to exist in the case of the

58 BULLETIN OF THE BUREAU OF FISHERIES.

Columbia River fry and yearlings. With the exception of the three earliest collections,

made at hatcheries, all of the fish possess scales with rings. Very few of the wild fish

taken on the lower river show the marginal band of wider rings, the intermediate band,

which is so characteristic of the young migrants on the Columbia River. This may be
22

- oer
b.3. Ta SS
x
b.2 ‘\
ie baa :
XN

Apr. May dune duly Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mch. Apr. May dune.
Fry. Yearlings.

Grapu 7.—Columbia River (group 4): Rate of growth, increase in number of rings, and increase
in length of anterior radii of scales. Significance of curves is same as in graph 4, with the follow-
ing exceptions: a indicates collection from Little White Salmon River; 6, collection from
McKenzie River; and ‘“‘new growth”’ takes the place of “intermediate growth.”

accounted for by the fact that none of these collections from the Sacramento was made
in San Francisco Bay, which corresponds to the estuary of the Columbia, where inter-
mediate growth was found most commonly. The collections of yearlings made at
Brookdale and the majority of the collections made in the McCloud River contain

SEAWARD MIGRATION OF CHINOOK SALMON. 59

specimens whose scales show the marginal band of wider rings indicative of the new
growth of the second year.

The “primary check’? which has been noted on the scales of the Columbia River
fish does not appear conspicuously in the Sacramento series. In the case of the fish
from the lower part of the river this is not surprising, since such a primary check has not
been found on the scales of specimens from the lower part of the Columbia until autumn,
considerably later in the year than the last collection from the lower Sacramento. ‘The
absence of the primary check in the collections from the McCloud may well be a racial
characteristic, just as the presence of such a check is a racial characteristic of the young
fish in the McKenzie River. (Compare PI. I, fig. 8, a scale from one of the McKenzie
River fish, with Pl. III, fig. 9, a scale from one of the McCloud River specimens.)

. Table 50 gives the data, averaged for each month, for the collections from the lower
part of the river. Table 51 gives the data for the collections from the McCloud River.
Graph 8 gives the data regarding scale growth based on all the available data from the
Sacramento River system. In this graph the line representing the growth of the fish
is the same as the generalized curve developed in graph 3.

TABLE 50.—RATE OF GROWTH AND SCALE DEVELOPMENT IN LOWER SACRAMENTO RIVER.

Average
Average
Month. Length, | number of Jenett of
rings. ns
radii,
at Mm

RNAS COM ae tsa eek shes ENS ct AEF acaba oe aac wise cele ge: cunza Sin ote bu aN wa mah ovasayes vet SRS ie opneveisin yl yanc mi BP rz esta teroremraieta lacie met cres ni
1NGTe ea cas SER OC EA BATE SEBESEE HASBRO Ye GNPReL treiete ae cae eI 50.8 4:5 22.3
LIES Pagoasbco ma sa Stine SEE SE epee cor MS Leta Crater aces 2-7 9-1 33-7
Ao t chaz qos mebntinon us aanecine condone se asad daGebOBepanGoose 17-3 9-6 34-1
pT des oO OHOrSn nb or GBeneoe AE Reon cts 2.2 14-8 47-9

TABLE 51.—McCioup RIvER: AVERAGE LENGTH AND SCALE DEVELOPMENT FOR Eacu Monvu.

Specimens. Scale record.
B . Length of anterior
Number of rings— adie
Month, ee
With new
Length. | growth. | To begin- To begin-
aumteo Total ning of | ‘Total.

@ Without new growth. > With new growth.

60 BULLETIN OF THE BUREAU OF FISHERIES.

Tables 50 and 51 and graph 8 show that, as in the case of the rate of growth,
the general features of scale development are not conspicuously different in the Sacra-
mento River from those found in the Columbia River. As a result of the earlier
beginning of the growth (noted on p. 50) the scale development also starts earlier.

So far as can be judged by the available data, none of the fry migrating in the
spring will show a distinct narrowing preceding the intermediate growth. Inasmuch as
the water of the Sacramento River becomes so warm during the summer that young
salmon can not survive in it, it seems probable that the collections studied represent
quite completely the migrating fry, and therefore it may be concluded that few, if any,
of these will show a band of narrow rings preceding the intermediate band. ‘There is
very little evidence to show when the yearlings migrate, if at all, or whether there is
any migration of fry during the late fall or winter. It would be logical to expect to find
that fish older than the fry migrating in their first spring do migrate, and it seems prob-
able that many, if not all, of such older migrants would show a band of narrower winter
rings preceding the intermediate band. ‘The evidence for this is given in Table 52, in
which it is seen that none of the fish taken later than August has scales whose marginal
rings belong to the first summer’s growth. None of the fry collected in the lower part
of the Sacramento shows scales whose marginal rings are of the winter type. There have
been entered, therefore, in the following table (52) only the data on the collections from
the McCloud River:

TABLE 52.—PERCENTAGE OF FIsH FROM McCLOUD RIVER WHOSE SCALES SHOW MARGINAL RINGS OF
(1) SumMER TyPE BELONGING TO THE First SUMMER’s GROWTH, (2) WINTER Type, (3) SUMMER
Rincs oF NEW OR INTERMEDIATE GROWTH, ASSOCIATED WITH THE SECOND PERIOD OF RapIp
GROWTH.

Month. (x) (2) (3)

45-0 55-0 2.0

+o 47-0 53-0

° 100. 0 +o

° 99.3 7

° 72.0 28.0

° 44-0 56.0

° 42.0 58.0

° 52-0 48.0

° 29.0 7I-0

If the author’s supposition is correct that there is a migration of older fish sharply
separated from the spring migration of fry, it would be expected that there would be
two distinct types of nuclei found on the scales of the adults—one characteristic of
fish which had migrated as fry in the spring and which shows no particular narrowing
preceding the intermediate or ocean growth, and the other type showing a narrowing
preceding the intermediate or ocean growth representative of fish which had migrated
either in the fall as fry or as yearlings in the spring. A more detailed study of the
young migrants in the Sacramento, involving collections made throughout the year,
would be necessary to firmly establish this hypothesis. The spring and fall runs of
adult fish in the Sacramento River are sharply separated, and a study of the scales of
adults belonging to these two runs would seem to offer interesting possibilities.

SEAWARD MIGRATION OF CHINOOK SALMON.

19
| a ce Clda
Pali lici va pen
pee je |
Beal 2=5
15 U
ba ole
/
14 Zi
fai
13
; 3
; el
Eeerilod
10
: ar
shel 3

my OF
()

PMs Se
par) ses

Mch. Apr. May June duty Aug. Sept. Oct. Nov. Dec. Jan. Feb. Mch.

GrapH 8.—Sacramento River; Rate of growth, increase in number of rings on scales, and
increase in length of anterior radii of scales. Significance of curves is same as in graph 4, with
the following exceptions; Solid line indicates the generalized curve of length developed on
graph 3. Broken line indicates number of rings on scales—x, to beginning of new growth; 2,
total for specimens not showing new growth; and 3, total for specimens showing new growth.
Dotted line indicates length of anterior radii—z, to beginning of new growth; 2, total for speci-
mens not showing new growth; and 3, total for specimens showing new growth. A indicates
collections from lower part of river; B, McCloud River, 1909; and C, McCloud River, ror1-12.

75412°—22 2)

Ss

So

61

62 BULLETIN OF THE BUREAU OF FISHERIES.

The scale growth of the fish from the coastal streams presents nothing unusual or
of particular value because of the scarcity of data. Certain racial characters are sug-
gested by the data from one or two of the streams, but the evidence does not warrant
drawing even tentative conclusions.

MIGRATION.

In the preceding sections the matter of migration has been dealt with in only a gen-
eral way, and an attempt will now be made to summarize the available facts.

In the Columbia River migration takes place throughout the year. The fry hatched
during the fall and winter may migrate immediately after the yolk sac is absorbed or
even before this process is entirely completed, since occasionally specimens which still
retained part of the yolk have been found in the estuary. The earliest hatched fry
may migrate as early as December, and by March the migration is well under way.
The data regarding the time at which the greater proportion migrate are not especially
satisfactory, as the accurate determination of this would involve collecting either with
some form of stationary gear or by frequent and uniform hauls with a seine at some one
point. Such collecting would need to be continued during each month of the year.
The nearest approach that can be made with the present data to a determination of the
time of most frequent migration is by finding the average number of fish contained in
each collection made in the lower part of the main river (exclusive of the collections
made under canneries). This method is subject to considerable error, especially owing
to the fact that at the times when the young fish were relatively scarce the collecting
was more persistent and more seine hauls were made, on the average, at each point
where collections were made, in order to get as large a representation of the migrants
as possible. Obviously, such a source of error will tend to broaden the mean time of
migration over more time than is actually the case. The data are presented in Table
53- The process of “smoothing,” by which the figures in the fifth column were ob-
tained, is the one commonly used. The smoothed figure for each month is obtained
by taking the average of the actual figures for the month in question, plus those for
both the preceding and succeeding months. Graph 9 gives the smoothed curve.

TABLE 53.—COLUMBIA RIVER: AVERAGE NUMBER OF FIsH IN EacH COLLECTION.

|

gulpesscer
ber of | Precedin,
Number of | Number of | 2U™™ g
Month. : specimens. | collections, | SP¢Cu2&NS column
to each smoothed.
collection
FRY.
MER OCHS 5a el gm hake ein aid eloines Cato wie eshie Se Ceo POURS TORT en eeee Somer Ree zon 4 25-2 19.1
April... 26 2 13-0 39-4
May.... 321 4 80. 2 37-8
June... 80 3 20.2 89.0
July... 166 I 166.0 72-6
August...... 64 a 32.0 8.0
September 69 I 69.0 73-3
October 119 I II9.0 65.0
November 7 I 7-0 46.6
December 38 3 12.6 10.6
1 Te Bigg SOO DE OO OCIS COO SOUONSr DAC OU UME aSODGE Ube ancesns sabe occas asonnad Ade 47 4 12.0 11.9
OTA ES se Ny icles wre, sloke pret Melejarais breton tinlee chatre acaetnd a mintetecoslelsta cleotciten a oaione temic 22 2 Ir.0 12.3
BS REIRSON 5Oe ANCE DO QOD A oclOP oe aCe rs Canon none em Be obo acc DAC MObuaEencoee 57 4 14-0 12.2

SEAWARD MIGRATION OF CHINOOK SALMON. 63

As stated above, migration in the Columbia River takes place throughout the
year, but the data here presented indicate clearly that the chief period of migration
for the fry is during the months from June to October, inclusive. On account of the
source of error mentioned above it seems probable that the main period of migration
is actually somewhat shorter than is here indicated. The mode of the curve, showing
the height of the migration, would not necessarily be affected by error of this sort.
The migration-of yearlings is completed by June. This wide range in the time of migra-
tion is not surprising in such a large river system as that of the Columbia, where
a great diversity of climatic conditions obtains in different regions. There are two
possible explanations for the wide extension of the migration period: (1) Fish from
each tributary may migrate gradually, a few at a time, through the year; (2) fish from
each tributary may all migrate at about the same time, but migration from different
tributaries takes place at different times of the year.

No.
100

Mch. Apr. May dune July Aug. Sept. Oct. Nov. Dec. dan. Feb. Mch. Apr. Moy
. Yearlings.

°
Graru 9.—“‘Smoothed”’ curve showing average number of specimens taken in each collection
in the main Columbia River and the estuary for each month.

ig

There is some evidence to show that the young fish from particular tributaries
tend to migrate at the same time and, moreover, that they tend to school together
during the seaward migration. The collection made at Crandall’s seining ground,
September 15, 1916, especially suggests this interpretation, as the fish are noticeably
smaller and the character of the scale growth different from other collections made
during the same time of year under approximately similar conditions. (See p. 19.)

The time at which the fry leave the tributary streams for the main river and the
rate of downward migration have not been determined. Undoubtedly, the time of
leaving the tributary streams is subject to great variation. On purely a priori grounds
it seems certain that the earliest fry to migrate—such, for example, as those taken in
March and April—must have come from the lower tributaries. The spawning season
in the different tributaries does not differ more than a few weeks over the entire Columbia
system, but the much colder water of the higher streams delays development so markedly

64 BULLETIN OF THE BUREAU OF FISHERIES.

that there may be a difference of several months in the time at which the yolk sac will
be fully absorbed and the fish begin an active existence. It can not well be doubted,
then, that the earliest fry to migrate have been hatched in the lower tributaries, and
it seems reasonable to assume that, in a general way, at least, the successively later
migrants have come from successively higher tributaries.

The abnormally large proportion of smaller fish found in the lower part of the river
during the spring and early summer, which causes the ‘“‘skewing” of the frequency
curve of length noted on page 8, may also indicate that the height of the migration
has not been passed and that the smaller fish entering from above are doing so in
constantly increasing numbers. After the height of the migration the skewing effect
of the constantly decreasing numbers of smaller fish would not be noticeable. This
skewing of the curves of length is not found to any noticeable degree after the early
part of the summer, a fact which seems to give additional evidence that the height of
migration comes, in the lower part of the Columbia River, during the latter half of the
summer or early in autumn.

The migration of fry in the Sacramento River has been given in detail by Rutter
(1903). He found that fry were migrating in the lower part of the river during the
months from January to May, inclusive, and that they started the migration from
the streams in which they were hatched as soon as the yolk sac was absorbed, as early
as October. This migration is much earlier than that observed by the author in the
Columbia River, a fact associated with the earlier hatching of the eggs and the more
rapid development of the fry in the warmer water of the southern stream. The data
presented in this study add nothing to Rutter’s conclusions on this point. No migrating
yearlings were taken by Rutter (1903) nor by Scofield (1898) in their work on the lower
river, but, as no collections were made during the fall and early winter, it is quite
possible that there is a migration of the older fish at this time of the year. It is
possible that yearlings migrating in the spring are so scarce that none were captured.
It has been shown (p. 36) that the new growth of the second year may begin in the
case of the young chinooks in the McCloud River as early as September, varying, how-
ever, in different years. It has also been shown (p. 48) that in some cases, at least,
there is a tendency for the older fry or yearlings to migrate soon after beginning the
new growth of the second year. Consideration of these two facts lends considerable
probability to the theory that there is a fall migration of older fry in the Sacramento
River. An investigation of this matter would be pertinent, since a distinct difference
in the scale growth between fry migrating in the spring and those migrating in the fall
would be expected. The relation between the young migrating at these two periods
(granting that such a later migration takes place) and the adults comprising the sharply
separated spring and fall runs of spawning fish might well prove to be of considerable
practical importance.

SEAWARD MIGRATION OF CHINOOK SALMON. 65

VARIATIONS DUE TO SEX.
SEX PROPORTIONS.

The proportions of males and females in the collections from the Columbia River,
while subject to considerable variation in different collections, are on the whole remark-
ably even. The data for each collection are presented in Table 54. There seems to be
no regularity to the variations noted, and the conclusion that males and females
migrate seaward in equal numbers throughout the year seems justified.

TABLE 54.—COLUMBIA RIVER: PROPORTION OF MALES AND FEMALES, AVERAGE LENGTH OF MALES
AND FEMALES, AND LENGTH OF FEMALES AS PERCENTAGE OF THE WOneee oF MALES.

Males. | Females.
Length—
Date. Locality.
Length
Receene: | in snl lial) ACen As per-
ee. meters. ge. | In milli- |centage of
meters, | the male
length.
a \
Cottonwood and Deer Islands: ...............-5+ 50 42-3 50 44-1 104
Clackamas poses, He Se atlesisisisisivia vin’ are 53 46-5 47 46-9 | 101
| Lower Golrirtisia erin cite ierctect ie oHC 54 52-3 46 52-8 IOI
| sac 50 46.7 5° 48.8 105
| - 5° 44.6 5° 44-6 100
| Clackamas hatchery............0...0-+ aa 50 53-0 5° 59-0 I1r
| Small creek near Po : 53 47-5 47 48-0 Ior
| Estuary......-..... : 44|* 78-5 56 74-9 | 95
| Point -tillice BASS Boe 46 90-1 54 93-6 104
ata ats Gl Osta rere tc ete ate cttcretaielslatabsln/ sl ais nte(nielsisls iin 62 2.0 38 97-2 106
interns PRA Veneer oiete cterotefetcipiens tetera rreyonters(raide 50 113-8 50 112-0 99
Sertfer tet a: ctercrta tae oe eayeivtebsyane wialstlalot olnie/ahessistele 48 81.5 52 80.3 99
(Ogeet bie AG LS. 8 CaP nGE = BUnbace a ABOLEBEEOOGUrO 52 74-2 48 74-8 ror
|
MEW ACO eraetseicisteteeicicte <telelctelmesters ofelel oicieleie urufe victe’s.aive 5r 121-3 49 124-7 | 102
|
PPR GIING FOLGE seer acenteisicreterieivisicveieteineve elaictsinieiovets sien SI 112-2 49 113-3 Ior
Octsa7; wacaake san AStorial. sane. dese 50 54 127-9 46 127-0 99+
Nov. 2 and 3......... McKenzie River.... 46 107-1 54 106.0 99
DEC sitOiSiss vis ces Lower Columbia 37 95-5 63 93-4 | 98
|
YEARLINGS.
1916:
Mar. 31 to Apr 2....! Lower Columbia............ 55 97-6 4S 93-2 | 96
. Cottonwood and Deer Island 45 107-0 55 107-0 100
‘ Crandall’s 41 106.0 59 IOI-0 95
. Clackamas River. 64 112-0 36 112-6 100+
|

The only collections from the lower Sacramento River which were large enough to
give significant data and in which the specimens were sexed are those from Woods
Break, June 5 and 6, 1911, and from Tisdale wier, June 24-26, 1911. The sexes
were quite evenly balanced in both of these collections, 52 per cent males in the first
and 48 per cent males in the second.

The situation in the McCloud River is somewhat complicated by the presence of
precociously matured males. Table 55 gives the percentages of males, both mature
and immature, and of females for each collection made in the McCloud River. The
sexes are present in approximately equal numbers, although there is a slight pre-
ponderance of females. Five and eight-tenths per cent of the total number of speci-
mens are mature males. ‘This signifies that between 10 and 12 per cent of the males
which do not migrate during their first spring mature precociously during the following
summer and fall.

66 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 55.—PERCENTAGES OF MALES AND FEMALES IN McCLoup RIVER COLLECTIONS.

Males.
Date. Females.
Imma.
Total ice Mature.
1909: FRY.
nf). ARREARS IRC ee re right fee Qe are AAU AGO OC OBeoh aoMoticn saloon cereus: ted 39 61 37 24
September me eiciiececiseticteeeh ok nietgays nies mc Hie nee a ictele eelate crate aneiniararotelnierefaveiatere . 53 47 39 8
191
42 58 49 9
56 44 43 I
SaaS SegcNG 57 43 39 4
December’, hk os iss cece 50 50 49 I
I9I2:
January. . 57 43 42 I
5° 5° 46 4
6x 39 39 °

RELATIVE SIZES OF MALES AND FEMALES.

Table 54 gives, for each Columbia River collection in which the specimens were
sexed and which was large enough so that conclusions seem warranted, the average
length of the females as a percentage of the average length of the males. Dividing this
series roughly into quartiles, it is found that the average for the first six collections is
103.6; for the next five, 101; for the next five, 100.4; and for the last six, 98. The
cumulative evidence seems conclusive that among the younger fish the females average
slightly larger. In the case of the fish taken during and subsequent to September,
however, this condition is reversed, and the males are slightly larger than the females.
No explanation for this is offered, but the facts seem undoubted and worthy of record.

The males and females from the two collections from the lower Sacramento are
approximately the same size. ‘The length of the females in the collection from Woods
Break averages 98.3 per cent of that of the males. In the collection from Tisdale
wier the percentage is 102.4.

Table 56 gives for each collection made on the McCloud River the length of the
females and of the mature males as percentages of the length of the immature males.

TABLE 56.—McCLoup River: LENGTH OF FEMALES AND OF MATURE MALES AS PERCENTAGES OF THE
LENGTH OF IMMATURE MALES.

Males.
Date. Females,
Imma-
Cire Mature.
1909: FRY.
Mayes ceicinse aiarct cas cro uncdiers Oa iaih artaVerw port orale © b erevaleloraferene avs geval ls ete eis a1s ee etsae fe cTalatatasle aie Mine teieretclepeaioe 100 145 107
September: 2 22 Dek atts «eeepc Sibi nierla ate ce cutee « ane se ere places state siaiaiat afo s{atsys) a ateleteen eletetent (aera 100 112 98.3
IQII:
Sep terri ben siateratsietaeciciriate teveiajertiioiore b etuinisteiatniniele erare ntelata pevelsiatarsietscleters nies ntain mretaiee eters siarestetsieiaiete sheet 100 I05 97-5
O@to bens eee ela ae ctcderstel tae ateeberolas ele cig ha eteteh is nhal intel = ateneretelelaiers labels alelaln/s/ol sia eine (elec atarsetsieleiecaie 100 10I- 5 98.9
TIVO VCR CL eo etat eater are ota fefoha felts atereiniaretele Cheseaste cl aia attra te ele ete) ef eleetetetateleietaia] et cotratsy ate oiatetatetnteds telco ete 100 109 100
DeEcemibers Sos oS VPs weridas ceyceiacidate ih nice MeN ee aioe cle tle ae eet iierddots aeteisieains ietviete catetate 100 106 99-7
1912 YEARLINGS
CP RELAY oo acc vile ninsatetaloiatsloce Silete ale] sieteTe AaToTe cikote ahaa Mists ncoenee eel faasta Uistoin)<faie ata ale Velatater ela baleti ataian r00 136 98.2
TERTIARY nis sie croe cease ele nhalele sisiohate viaiateiere ate biaiarorermtal stawtctelniaie metarn ein te eacieracte te intate a oiniein eae tatet rateranet 100 IIs 101.2
1 Cgc | RISB SoS RNCISD GMEDAe OAL ORCC ES OnE oua retor: Garin ea Sescrns SaTOsbOte pocatontem aes tin TOGd een 98.6

SEAWARD MIGRATION OF CHINOOK SALMON. 67

There is apparently no significant difference in the length of immature males and
females, but the mature males are distinctly larger than the immature specimens.
This indicates either that they are slightly older or that they have, for some unknown
reason, grown more rapidly than the other individuals of the same brood.

PRECOCIOUSLY MATURE MALES.

The precocious maturing of young chinooks has been noted by Rutter and is a
phenomenon well known to many hatchery men. Most of these precocious males are,
without question, the same age as the immature fish taken at the same time, but, as we
have just shown, average distinctly larger (about 16 per cent). The time for maturing
corresponds with the normal spawning time for the adult fish, late summer and autumn,
although, as shall presently be shown, they may be found during the winter and spring,
long after the normal spawning season is past. In addition to the precocious males
from the McCloud River they have been also found in various collections from the
Columbia River system, as follows:

1. Clackamas River, August 30 and 31, 1916: Four out of 10 specimens. Length of the mature
males is ro5 per cent that of the immature specimens.

2. Seufert, Oreg., September 2, 1915: Three out of 52 specimens. Length of mature males is 116
per cent that of immature specimens.

3. McKenzie River, September, 1916: Eight out of 11 specimens. Length of mature males is 122
per cent that of immature specimens. (These were collected from a pond used for holding spawning
fish and have not previously been considered because of the small size of the collection and the great
irregularities in size and scale growth.)

4. Hatchery ponds at Bonneville, Oreg.: Specimens of mature males were not infrequently found
here during the spring of 1915, while the author was engaged in marking a series of yearling fish.

It will be noticed that the mature males are only recorded in collections from
tributaries fairly well upstream.

In appearance these precocious fish are, when fully mature, strikingly different
from the immature specimens. In addition to the greater size, the head is relatively
larger, the body is deeper and thicker, the skin covering the entire body and fins is
thickened so that the scales appear smaller, and the coloration is distinctly modified.
The general color is a dark yellowish brown, becoming distinctly yellow ventrally. The
color of the spots is deepened so that they are conspicuous even against the darkened
background. ‘There is also a tendency toward the development of bright yellow or
rose-colored borders to the fins. - The testes are large and white, in every respect resem-
bling the testes of normal, mature, sea-run males. The scales are normal and show no
absorption along the edges, as is so characteristic of the scales of spawning sea-run adults.

The habits of these fish do not apparently differ greatly from the habits of the
immature fish with which they areassociated. They feed regularly and are, to allappear-
ances, fully as well conditioned as the others. This probably accounts for the fact that
the scales are not absorbed at the margins. Rutter (1903) reports that they do not seem to
beattracted by the females as are the sea-run adult males. Our observations are, however,
to the contrary. The fish contained in the collection from the McKenzie River, made in
September, 1916, were taken from a pond used for empounding spawning fish and the
percentage of mature males is much higher than in any of the other collections. Rutter
reports that the milt from such males will fertilize eggs normally.

68 BULLETIN OF THE BUREAU OF FISHERIES.

The fate of these precociously matured males has been a matter of some specula-
tion. It has been both claimed and denied that these died as do the sea-run adults
after the spawning season. The writer had an opportunity in the spring of 1915 of
testing this. He was at this time marking series of young blueback (sockeye) and
chinook yearlings at the Bonneville (Oreg.) hatchery. Mature male chinooks, with
fluid milt which could be expressed, were frequently encountered. A number of these
were marked and held in a tank at the hatchery until July. Some had died in the
meanwhile, but in some of those which remained the testes had practically recovered
the normal immature appearance, and the characteristic coloration above described
was much less conspicuous than it had been at the time the fish were marked and placed
in the tank. The fish were apparently in perfect condition, and the scales show that
they were growing actively at the time they were preserved. It is not known whether
young males which have thus recovered from the effects of ripening the sex products
will migrate to the sea.

PRACTICAL SUGGESTIONS.

Although information of still greater practical value may be expected to come
from the study of the adult fish, some of the conclusions reached in this study appear
to offer important suggestions, which may be applied in practical fish culture, as to the
proper time for planting fry from the hatcheries.

In the early days of the artificial propagation of salmon it was an almost universal
practice to ‘‘plant’’ the fry as soon as they were hatched. The mortality among the
helpless alevins, encumbered by the heavy yolk sac, must have been enormous, and the
hatcheries probably inflicted as much, or more, damage to the salmon runs as they did
service of value. More recently the tendency among the more intelligent and scientific
hatchery men has been to abandon the practice of planting alevins and to hold the fry
at least until the yolk sac is absorbed. The system of holding and feeding fry after the
yolk is absorbed has followed and with this, a not unnatural idea, that the longer the
fish are held and fed the greater the chance of their surviving. The validity of this
assumption is, however, dependent upon several factors which have not been suffi-
ciently considered. The following more important ones may be mentioned here:
(1) The possibility of an increasing percentage of loss among fish so held which would
ultimately seriously reduce the number of fish planted; and (2) the effect of holding
fish beyond the normal time of migration on (a) their chances for survival and return
as adults, (b) the time of return as adults and whether they will return as spring or as
fall fish, and (c) the development of the normal feeding and protective reactions
(instincts) which are essential to their survival after planting.

It is a well-known fact among hatchery men that salmon fry held and fed in hatchery
ponds will, after a time, “go bad.” At such times the fish usually refuse to eat well
and show a distinct tendency to collect toward the lower end of the trough, tank, or
pond in which they are held. If persistently held the loss rapidly increases but finally
lessens as the critical period is passed, after which there is usually no more serious diffi-
culty experienced in holding the fish. This critical period usually comes after the fish
have been held and fed from 6 to 12 weeks—on the Columbia River in May or June

@ The greater value of fish composing the spring run has been noted above (p. 5).

SEAWARD MIGRATION OF CHINOOK SALMON. 69

and on the Sacramento River a month or two earlier, the exact time varying at different
hatcheries and even in different ponds and tanks at the same hatchery. It has been
shown above that the most normal time for migration on the Sacramento River is
during the latter part of the spring, and on the Columbia River during the latter part
of the summer. Therefore, it seems quite probable that these critical periods occur at
times when the fry would normally quit the stream in which they were hatched and begin
the seaward migration. There may or may not be a causal connection between these
two phenomena, but even though the fry were allowed to leave the streams at these
times—as the majority will, if permitted to do so—their time of migration would coin-
cide well with the normal time observed, and the certain loss resulting from holding them
over this critical period would be prevented. ‘There is, of course, the possibility that
this loss will occur under any circumstances, but such a conclusion is unwarranted from
any data at present available.

Suggestions, then, as to the care of fry are as follows:

1. The practice of planting alevins before the complete absorption of the yolk can
not be too strongly condemned. No hatchery should be allowed to take a larger number
of eggs than can be hatched and reared until the fry are at least ready to feed. Rather
than plant the alevins before the yolk has been absorbed it would be infinitely better
to allow the eggs which can not be properly accommodated in hatcheries to be deposited
normally by the parent fish, and to thus rely upon natural propagation for the outcome.

2. The liberation of chinook fry at such a time as will enable them to migrate sea-
ward at the normal migrating season for the stream in question is advised. This, on
the Columbia and Sacramento Rivers, will ordinarily come within about three months
after the fry have absorbed the yolk sac and begun feeding. Within this limit it would
seem that the longer the fish are held and continue to feed well and grow normally
(a point which should be carefully watched) the greater would be their chance for sur-
vival. If after several weeks’ feeding the symptoms indicative of the approach of the
critical period mentioned above appear, it would seem advisable to allow the fish to
migrate. Where practicable the fry should not be liberated all at once, but should be
allowed to begin the migration gradually and naturally, each fish leaving the parent
tributary as the “‘instinct’”’ to migrate develops. These conditions will be fulfilled if,
at the proper time, the screens be removed from the retaining tanks or ponds so as to
leave the way clear for the fry to enter the open stream.

These suggestions are of a general nature only. It is possible that in particular
tributaries or in particular regions of a large watershed the conditions and habits of the
fish are so different that these suggestions will not apply. In the absence, however, of
definite information on these points the practical application of the above suggestions
will, as a rule, be found advantageous.

SUMMARY.

1. Chinook fry first appear in the Columbia River as early as December of the
same year in which the eggs are deposited. By March and April they are fairly numerous
in the lower part of the river. Fry appear about two months earlier in the Sacramento
River.

70 BULLETIN OF THE BUREAU OF FISHERIES.

2. The average length of the youngest fry is between 35 and 40 mm. The rate
of growth is especially rapid during the first five or six months, by which time the
average stature for the first year has been attained. The average length of yearlings
is approximately 100 mm. (4 inches), both in the Columbia and Sacramento Rivers.

3. The length of the scales and also the number of rings formed on the scales par-
allel quite closely the increasing length of the fish. Many of the youngest and smallest
fry have not developed scales before migrating seaward.

4. Migration into the brackish water of the estuary is usually accompanied by an
increase in the rate of growth, which is recorded on the scales as a marginal band of
wide rings—the intermediate band. No intermediate band has been demonstrated on
the migrating fry of the Sacramento River, but this is undoubtedly due to the lack of
material collected at the right time and place.

5. The scales of fry remaining in fresh water develop a marginal band of narrow,
winter rings during the latter part of the summer. The new growth of the second
year begins soon thereafter.

6. The normal time for seaward migration among Columbia River chinooks is
during the summer next succeeding the fall in which the eggs are laid. Seaward mi-
grating chinook fry are, however, found throughout the year in the Columbia River,
and the collections taken in March, April, and May include also migrating yearlings.
There is, therefore, for each brood of fish, a period extending over about 18 months,
during which the young may migrate seaward.

7. In the Sacramento River there is a distinct migration of fry lasting from
January to June, inclusive. Although definite proof is lacking, it is probable that
there is another period of seaward migration during the late autumn.

8. In the younger migrants of the Columbia, including practically all the fish
migrating previous to June, the intermediate band is not to be distinguished from the
preceding scale growth, due to the fact that the first few rings formed on the scales
are always somewhat wider than the latter ones. After the first of June the intermediate
band may be (but not always) distinguished as a marginal band of distinctly wider
rings. Beginning in August or September this intermediate band may be preceded
by a more or less distinct band of narrow rings that correspond to the winter band
forming on the scales of upstream fish. The percentage of fish, whose scales show such
a narrowing preceding the intermediate band, increases through the autumn and winter,
so that by the following spring this narrowing becomes characteristic of the scales of all
the yearling migrants. Although there is this average difference in the scales of fish
migrating as fry during the fall and those migrating as yearlings in the spring, it is
impossible, with our present knowledge, to distinguish in many individual cases between
fish migrating at these two periods.

g. A sudden change in environmental conditions, such as removal from hatchery
to wild conditions, may result in modified growth, recorded on the scales as a distinct
break or check in the scale growth. This we have designated as the ‘“‘primary check.”
Characteristically this appears as a more or less distinct narrowing of the rings succeeded
by a series of wider rings.

10. There is apparently a distinct tendency for the larger specimens among the
fish of any particular tributary to migrate earlier than the smaller specimens. It is

SEAWARD MIGRATION OF CHINOOK SALMON. 71

also apparent that the fish from the lower tributaries of a river system will, in a general
way at least, migrate earlier than those from the higher tributaries.

11. Among the male fry which remain in fresh water over their first summer, about
ro per cent will mature precociously during the fall, the normal spawning period for
adult sea-run chinooks. The proportion of male fry thus maturing presumably differs
in different streams. These precociously mature males may recover from the effects
of ripening the sex products, in this respect differing markedly from the known habits
of the sea-run fish.

12. The suggestion is made that chinook fry be liberated from the hatcheries at
such a time as will enable them to migrate at the normal period for seaward migration
for the stream in question.

BIBLIOGRAPHY.
CaLpERWooD, W. L,.
1908. ‘The life of the salmon, with reference more especially to the fish in Scotland. London.
CHAMBERLAIN, F. M.
1907. Some observations on salmon and trout in Alaska. U.S. Bureau of Fisheries Document
No. 627. Washington.
CunNINGHAM, J. T.
1904. Zones of growth in the skeletal structures of Gadide and Pleuronectide. V.—Part III,
Twenty-third Annual Report of the Fishery Board for Scotland, for 1904. Glasgow.
Dau, Knut.
(z911). The age and growth of salmon and trout in Norway, as shown by their scales. (Translated
from the Norwegian by Ian Baillee.) The Salmon and Trout Association. London.
Fraser, C. McLean.
1917. Onthescales of the spring salmon. Contributions to Canadian Biology. Supplement to the
Sixth Annual Report of the Department of Naval Service, Fisheries Branch. Ottawa.
Gr.Bert, C. H.
1912. The salmon of Swiftsure Bank. Appendix, Report of the Commissioner of Fisheries,
Province of British Columbia, for 1912. Victoria.
tgi2a. ‘The Fraser River sockeye run of 1912. Idem.
1913. Age at maturity of the Pacific coast salmon of the genus Oncorhynchus. Bulletin, U. S.
Bureau of Fisheries, Vol. XXXII, for 1912. Washington.
t913a. Contributions to the life history of the sockeye salmon. (No. 1.) Appendix, Report of
the Commissioner of Fisheries, Province of British Columbia, for 1913.
1914. Contributions to the life history of the sockeye salmon. (No. 2.) Idem, for 1914.
1915. Contributions to the life history of the sockeye salmon. (No. 3.) Idem, for rors.
HorFFBAvEr. C.
1904. Zur Alters und Wachstums Zerkennung der Fische nach der Schuppe. Allgemeine
Fischerei-Zeitung. Miinchen.
Hutton, J. ARTHUR. :
1g09. Salmon scales as indicative of the life history of the fish. London.
1g1z. Wye salmon—results of scale readings during 1908-1911. London.
1913. Wye salmon—results of scale readings during 1908-1912. The Salmon and Trout Magazine,

No. 5. London.
1914. Wye salmon—results of scale readings during 1909-1913. The Salmon and Trout Magazine,
No. 7. London.

1916. Wye salmon—results of scale readings during 1908-1915. London.
Jounston, H. W.
1904. ‘The scales of Tay salmon as indicative of age, growth, and spawning habit. Appendix II,
Part II, Twenty-third Annual Report of the Fishery Board for Scotland, for 1904.
Glasgow.
1906. ‘The scales of salmon. Part II, Twenty-fifth Annual Report of the Fishery Board for
Scotland, for 1906. Glasgow.

72 BULLETIN OF THE BUREAU OF FISHERIES.

JORDAN, DAviD STARR.
1905. <A guide to the study of fishes. New York.
Jorpan, D. S., and Evermann, B. W.
1896-1900. ‘The fishes of North and Middle America. Parts I-IV. Bulletin, U. S. National
Museum, No. 47. Washington.
Maier, H. N.
1906. Beitrage zur Altersbestimmung der Fische. I. Allgemeines. Die Altersbestimmung
nach den Otolithen bei Scholle und Kabeljau. Wissenschaftliche Meeresuntersuchungen-
VIII Band. Abteilung Helgoland. Oldenburg.
McMourricuH, J. PLAYFArR.
1912. ‘The life cycles of the Pacific coast salmon belonging to the genus Oncorhynchus as revealed
by their otolith and scale markings. Transactions, Royal Society of Canada, Vol. VI.
Ottawa.
RuTTER, CLOUDSLEY.
1903. Natural history of the quinnat salmon. Bulletin, U. S. Fish Commission, Vol. XXII, for
1902. Washington.
ScoFIELD, N. B.
1gco. A report on the planting of quinnat salmon fry in the short coastal streams of Marin County,
Calif. Appendix, Fifteenth Biennial Report, California State Board of Fish Commis-
sioners, 1897-1898. Sacramento.
1gooa. Notes on an investigation of the movement and rate of growth of the quinnat salmon fry
in the Sacramento River. Idem.

EXPLANATION OF PLATES.

[The magnification of all photographs is the same, X 35. Abbreviations: 1 indicates lateral line; c, primary check; g, point distal
to which is intermediate growth; x, check indicative of time of planting; rst yr., first year of growth; and 2d yr., second year

of growth.]}
PLATE I.

Fic. 1.—Fry from Deer Island, Columbia River. April 13, 1916. Female, 51 mm. Part of skin
from near center of body, showing scales with from one to five rings.

Fic. 2.—Isolated scale from the same specimen from which the skin shown in figure 1 was taken.

Fic. 3.—Fry from Point Ellice, Columbia River. June 12, 1916. Male, 68 mm.

Fic. 4.—Fry from Point Ellice, Columbia River. August 12, 1916. Female, 113 mm. Showing
a weakly differentiated intermediate band not preceded by a band of narrow rings.

Fic. 5.—Fry from Crandall’s seining ground, Grims Island, Columbia River. September 15, ro16.
Male, 76 mm. Showing winter rings at the margin of the scale.

Fic. 6.—Fry from lake at Seufert, Oreg. September 2, 1915. Male, 83 mm. Showing check at
x indicative of the time of planting.

Fic. 7.—Fry from Clackamas River. August 30, 1915. Female, 114 mm. Showing primary
check and marginal winter rings.

Fic. 8.—Fry from McKenzie River. November 3, 1915. Male, 107 mm. Showing primary check
and well-developed winter band at the margin.

Fic. 9.—Fry reared at Clackamas hatchery, Oreg. December 15, t911. Male, 125 mm. A scale
with but slight differentiation, characteristic of hatchery fish.

PLATE II.

Fic. 1.—Fry from Point Ellice, Columbia River. October 16, ror5. Female, 116mm. Typical
fall migrant, showing marginal winter band. No primary check.
Fic. 2.—Fry from same collection as figure 1. Male, 117 mm. ° Showing primary check and mar-

ginal winter band.
Fic. 3.—Fry from same collection as figure 1. Female, 110 mm. The intermediate band is pre-

ceded by a distinct band of narrow rings. No primary check.
Fic. 4.—Fry from same collection as figure 1. Female, 118 mm. Similar to figure 3, except that

the primary check is present.

es

SEAWARD MIGRATION OF CHINOOK SALMON. 73

Fic. 5.—Fry from under cannery at Ilwaco, Wash. October 26, 1914. Sex not determined. 141
mm. The intermediate band is composed of unusually wide rings, characteristic of fish found under
the canneries. The band of narrow rings preceding the intermediate band is conspicuous.

Fic. 6.—Fry from same collection as figure 5. Sex not determined. 166 mm. Similar to figure
5, except that the intermediate band is not preceded by a distinct band of narrow rings.

Fic. 7.—Fry from same collection as figure 5. Female, 143mm. The check preceding the inter-
mediate band (which is not strongly differentiated) is intermediate between the conditions illustrated
in figures 5 and 6.

Priate III.

Fic. 1.—Yearling from Deer Island, Columbia River. April 13,1916. Female, 103mm. Showing
marginal winter band and no primary check.

Fic. 2.—Yearling from Crandall’s seining ground, Grims Island, Columbia River. March 31,
1916. Male, 92 mm. Similar to figure 1, except for the primary check.

Fic. 3.—Yearling from same collection as figure 1. Female,99mm. A typical scale characteris-
tic of the spring yearling migrants, showing an intermediate band preceded by a distinct winter band

of narrow rings. No primary check present.
Fic. 4.—Yearling from same collection as figure 1. Male, 113 mm. Showing intermediate band

and also primary check.

Fic. 5.—Yearling from Clackamas River. June 3, 1916. Male, 105mm. Showing weil developed
new growth of the second year.

Fic. 6.—Sacramento River fry from Walnut Grove, Calif. April 9, 1911. Male, 75 mm.

Fic. 7.—Sacramento River fry from Butte Slough. June 8, 1911. Male, 97 mm.

Fic. 8.—Sacramento River fry from near Butte Slough. May 9, 1911. Male, 103 mm. Showing
intermediate growth.

Fic. 9.—Fry from McCloud River. July 24, 1909. Mature male, 128 mm. Showing marginal
winter rings.

PiaTE IV.

Fic. 1.—Yearling from McCloud River. January 22, 1912. Male, 142 mm. Showing marginal
winter band.

Fic. 2.—Yearling from same collection as figure 1. Male, 110 mm. Showing two wide marginal
rings of the new growth of the second year.

Fic. 3.—Yearling from Brookdale hatchery, Calif. January 4, 1913. Female, 127 mm. Showing
irregularities of growth characteristic of the scales of hatchery fish.

Fic. 4.—Yearling from Bonneville hatchery, Oreg. March 2, 1915. Male, 162 mm. ‘The winter
band is not strongly defined, but the new growth is well started.

Fic. 5.—Yearling from Bonneville hatchery, Oreg. July 7, 1916. Male, 150mm. This fish was
one of the mature males marked in March or April and held until July. The new growth of the second
year has begun, but is somewhat irregular.

Fic. 6.—Fry from Hope Island, Puget Sound. May 28, rors. Male, 94 mm.

Fic. 7.—Yearling from same collection as figure 6. Male, 97 mm.

Fic. 8.—Young chinook taken in Half Moon Bay, Calif.

1 Os sega

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Bui. U.S. B. F., 1919-20. PLATE I.

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PLATE II.

Buu. U.S. B. F., 1919-20.

Buu. U.S. B. F., 1919-20. PLATE ITT.

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Butt. U. S. B. F., 1919-20. PLATE IV.

NATURAL HISTORY AND PROPAGATION OF FRESH-WATER
MUSSELS

Po
By

as

R. E. Coker, Assistant in Charge Scientific Inquiry

A. F. Shira, Lately Director Fisheries Biological Station, Fairport, Iowa
H. W. Clark, Scientific Assistant, and

A. D. Howard, Scientific Assistant

wn

75

CONTENTS.

Prod

Page
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Part 1. Natural IStomyAOl Resi yea LET MILISSEIS ya prays) cleleyays.cindiey/ar Usve¥s nieuennxayctacstetcvetele «hamieitiortehetels ciate 81
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PE ECO Gl pert e pyre a etary Pa er PoP Te ts Meet eh olla es et ldo avert Sea one oV NER eNO i akS Sie 85
Winteria riser rat cnenrdPeysasrieecttarcmtars cosver aerial svar aera rch wlsyclax ice iciis tAd SRSEME Pct ncteaate keane as 85
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Tinea WPrAERC A Sc aan op cee Ope On ee Seer Poe OOO E Date OE On H pce nen ne Rene ntn otis oo. mica 87
Sip titiCAanleeronpen eq propo lettre ctal ayayalatsye) inept ofetastetel = efetseey sheer hotel «rst =1s) f ROTA, se eel te 87
Observations of Franz Schrader on food of mussels. ...............0 00sec eeteeeneeeeees 88
Species studied ann aer-rielsattig eet a Pe eS oe SI Dee cloyinsenarebtinica, seer sim vicina, REM eS hog 88
Hoodicontention Waterss. sya atelier cet Sarena teaiwe es 5 oiaie wicaen nin oa eee SES 88
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Gemeraliopservations sess sescpa ey ateletatet a shoves ete sey crerel olatel oPekelevstotsiecatel + olid Reesctakt ke Mate Reet ede: 90
Observations of H. Walton Clark on food of mussels. ...............000 0. cece cece eens gt
Observations of A. F. Shira on food of juvenile mussels. ..........-..........0 eee eee eee 93
JS Voy Re oa Sabie utes pet oa mere eee SAE NOe OeIE Cae M EEe Reich Aut Abr Reema reshe ES ener) Crain ee cg ai 04
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1D Yeyoieel ol lens Baocic nwo dee eOIeh 6 ecules Gillon eee SDC in Epa ena Ocen GO miatO npectimeeses on 107
RUG A ELL rpen sree seaports tcact es eave) spt Sree ct varolancin eracstskers wate’ ay etesere! ster sietcre a, aensamin/e divi ike are ie IIo
(CURGRST ES 3 a ceta Be tat a onind tates 0 pn roa cat RAE SPI Oc IA ESTO rar ASS be Se ata Ilr
IW LE Ti COMECTI Cette sem cehtare os Net rat Rare Colet es ae feretar ey -heeT caval cLetmien Srooe ictarels tiareiavarena ticle woe cle si 113
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(CHTGHA CMS SVEN GAD Sarees: Gh as bau cduomoct acece ses SOND aD bub ConeCO AD OOH BEneCeae 123
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SBME CATCET Data Te Rent tence ayers Ves torte rarer vache avers euwtedevereiascarexeerererecmese/eie sleereeia-e,¢ eves 132
Abnormaliticsiniprowelvor shelley ic. . eae scle cite cece: pavodobaucosnumgedosuese 133

75412°—22——6 77

78 CONTENTS.
Page.
Part 2. Life history and propagation of fresh-water mussels. ........- 2... 00-200 -eeeeeee eee eee 135
Borer tilyn (oy renee ATaE AAGOD OpAsrT8s MOAB OSP ESC ON ane sosmepovndsonoedsobooDco conasoc 135
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Ovulation and fertilization. oct Sages cen VA a ety eta YORE AER R ove Nore Mr eto Tey ya NACH 138
Brood pouches!of: marsipia s a..<51 [sg deve eseschciere oe clone mw Re UN Neh Rem AICTe Foose le RCT ots ANU REVO 138
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Stage of parasitism............. Fee RT nO acs aN is OS Shc oN 148
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jcftertotarsjrelervals kebsebteietst (epee Reem ano Muah od edadt AdonenA os sc Go oce poser se thio. boi hoot 155
Metamorphosis without parasitisen: ©<:2s.5j.cn se: -icicieislereseseies se ore eieiclereeeYe 2ietcle aE ee 156
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WiL-OW Sheen ean soRaa eR oe aD Sone ARO MOP AR SRARA OH Spas oe odes oN Ub ose deossononaous 163
Parte) Structure of fresh-water mtissels: sj... setae to skelce: tetera elster= er neha tat Rae tee emma EET fel ony 167
aR s(a cos klein (0) Eee ee ee er ERE OOP ere eer SERB aac SoU eG ho Sebo. vcotar =e tO7
Fe SHELL 75, ysfasaveinvsyer ty stag vn cape ci optarey crs Po eye OTR, He Ee Ee ET EEL ORIEN 3 ols oye 168
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Horm and functions ofthe mantles. ya c.2)-ss5ictosie rete fo oretenct rie detslokdoloet orotate ere eee 171
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Qraqilcariesyewits bath (quroncyoyi ndarally Guoggaadsn nor ann aban jb An cost ues Ons codassaooN 174
Babli prepay: cee <:ctiact ates cravayslesedoteserouclsray chorofor}oterei aie o\ainte CRMEIeINCIS a tees eel ere NIN (ated ga tete afc e eYet ete fatetn/ al 177

NATURAL HISTORY AND PROPAGATION OF FRESH-WATER
MUSSELS.

a
By

R. E. COKER, Assistant in Charge Scientific Inquiry,

A. F. SHIRA, Lately Director Fisheries Biological Station, Fairport, Iowa,
H. WALTON CLARK, Scientific Assistant, and

A. D. HOWARD, Scientific Assistant.

ae
INTRODUCTION.

Adult fresh-water mussels are free-living but sedentary in habit. Though attached
to nothing they remain for indefinite periods nearly as still as if their position were irre-
vocably fixed. They have powers of locomotion but only occasionally use them. A
snail is expected to be in travel, however slow, in the search for food; but when a mussel
is found in motion the observer is inclined to look for a special cause of this behavior.

If a living animal remains generally in one place without going after its food, it
must have some effective mechanism for bringing food to itself, and it must also depend
in part upon outside agencies to convey its food within reach. In the fresh-water mus-
sel, the mechanism employed for food gathering consists of hundreds of thousands of
active microscopic paddles covering the flaps that hang from the side of its body. These
paddles are exceedingly minute and all within the shell; each is weak and ineffective
alone, but the effect of their concurrent action is to keep a strong current of water passing
into the mussel and out again. The water is filtered in passing, and the food, of course,
consists of the fine materials suspended and perhaps in part dissolved in the water.
The food in the water that lies within the influence of its currents is thus available to
the mussels; the natural circulation of the outside water must do the rest.

A single animal that finds food brought within its reach might live the full period
of its life in one spot, but all animals of a species can not live in the same spot. It is
inevitable, therefore, that at some stage in the life history of such an animal as the
fresh-water mussel, there must be a period of movement or of distribution by outside
agencies. Through one of nature’s nice adaptations, such a period of migration or dis-
tribution occurs in the life history of the mussel at the stage of infancy. Even then the
mussel shifts the burden of its distribution upon fish, as will be more fully told in the
section on life history. As inactive in youth as in old age, the fresh-water mussel, hav-
ing taken passage upon a fish, may then travel extensively to find a new home far removed
from the scene of its birth. Its living conveyance dispensed with, the mussel settles
down to a relatively immobile existence.

Peculiarly victims of circumstance at all stages of existence, the fresh-water mus-
sels under natural conditions yet throve abundantly and broadly in streams and lakes

79

80 BULLETIN OF THE BUREAU OF FISHERIES.

of this country and in those of other countries, but more especially in the Mississippi and
Great Lakes drainages. For them, however, times changed with the discovery that their
shells formed a good material for the manufacture of a universal necessity—buttons.
Equal as they were to the vicissitudes of natural conditions, they were unable to with-
stand the unchecked ravages of commercial fishery. Thus there has arisen the necessity
for measures of conservation—propagation and protection.

It is the purpose of the present report to present such an account of the structure
and habits and relations of fresh-water mussels as will serve to diffuse knowledge of
fresh-water mussels and interest in them, as may promote intelligent measures for their
conservation and efficiency in propagation and as may stimulate investigation of the many
problems presented by the behavior, distribution, and propagationof mussels. Directed as
itis both to the layman and to the scientist, the report must labor under the disadvantage
of embodying matter that may seem trite to the scientist and much that may seem
overtechnical to the layman. As far as possible, however, the more technical data are
omitted or embodied in tables which can be passed over by those who are not interested
in the details.

The first part, on the natural history of mussels or the relation to their environments,
embodies data from many sources, but more especially from the general experience of
the several authors. In the second part is comprised perhaps the greatest measure of
original data gained from experiments and investigations conducted at the U. S. Fish-
eries Biological Station, Fairport, Iowa, though there are incorporated also results of
the published investigations of Lefevre and Curtis and of others. The third part, pre-
senting a summarized account of the structure, does not pretend to offer new data, but
rather to afford a background of knowledge of the mussel as a complex living animal
with many functions and needs. It might have been placed first but that it seemed best
to begin with the subjects which constitute the essential purpose of the paper.

BULL Ws. bake Tong—20: PLATE V.

Fic. 1.—Rear view of yellow sand-shell in natural position Fic. 2—Rear view of Anodonta corpulenta showing
in bottom under water, showing the two siphonal open- siphonal openings. Note the very smooth margins of
ings, the gaping shell, and the apposed margins of the the upper exhalent opening and the fimbriae or ‘‘feel-
mantle ers’’ protecting the lower or inhalent opening.

Fic. 3.—Tracks of young mussels in crate. Change in the conditions of the water had caused them to wander more than
normally.

PART 1. NATURAL HISTORY OF FRESH-WATER MUSSELS.
HABITS. ;

CONDITIONS OF EXISTENCE.

A mussel, in natural position in a stream, is partly or almost entirely embedded
in the sand, mud, or gravel of the bottom (Pl. V, fig. 1). Almost invariably it will be
found to have an oblique position, the front end of the body being directed down into
the bottom and in a direction with the flow of the current, while the hinder end of the
shell is exposed and is directed upward and against the flow of the stream. Unless the
mussel has been disturbed, the shell will be slightly gaping, with the edges of the mantle
protruding through the opening and closing it everywhere except at the rear (upper)
end where it is so arranged as to form two neat funnel-like openings. The upper open-
ing is usually the smaller, and the edges of the mantle about it are smooth or crinkled.
The lower opening is generally much longer, and the border of the mantle here is com-
monly adorned with a number of delicate feelers, or water testers as these may be called
(Pl. V, figs. 1 and 2). The significance of the two openings can be easily ascertained
if a small amount of some colored liquid, such as finely powdered carmine in water, is
placed near to the openings in a mussel which has been allowed to remain undisturbed
in a small aquarium or dish of water. The carmine may be seen to be expelled forcibly
from the upper smaller opening, while, if placed near the lower opening, it will be drawn
in. It becomes apparent that the water is continually drawn in through the lower
(inhalent) opening and passed out through the upper (exhalent). In view of the func-
tions of the gills and the mantle, described on page 174, it may be understood that this
stream of water not only serves the purpose of respiration but also that, as it is strained
through the minute pores in the surfaces of the gills, it must yield up the microscopic
materials that serve as food for the mussel. The position of the mussel, directed against
the flow of the river, not only insures a more effective resistance should the current of
the river be excessively strong, but it perhaps gives the mussel greater advantage in
collecting the food floating with the current. In lakes where no regular current pre-
vails mussels may lie with their axes in any direction, but the oblique position in the
bottom is virtually constant for those that are not in movement.

The advantages of rivers over lakes for the growth of mussels may readily be in-
ferred. The mussel can draw in and strain only the water that is close about it, and in
the quiet water of a lake or pond new supplies of food are brought to its vicinity only
by the comparatively slow forces that cause the intermingling of the waters of the lake.
In the steady current of a river, on the other hand, the same water is never strained
twice by the same mussel and, besides, the action of the current tends to stir up the
small organisms and nutritive sediment which abound in the surface scum of the bottom.
Observations by Clark indicate that mussels in lakes feed more largely upon plankton
than those in rivers, the latter of which contain in their stomachs chiefly detritus or

8r

82 BULLETIN OF THE BUREAU OF FISHERIES.

finely divided nonliving organic materials. The rate of growth of mussels generally is
much higher and the size attained is greater in rivers than in lakes. Other factors
than currents, of course, enter into consideration, and these will be discussed in the
appropriate places.

A chief condition of rich growth of mussels is a plentiful food supply, and not all
rivers are alike in this regard. There are relatively fertile and relatively sterile rivers
and lakes, and the fertility of streams is likely to correspond in a rather general way
with the fertility of the lands from which the drainage is derived. Whatever materials
suitable for the construction of plant tissues are brought into the waters are likely ulti-
mately to be converted in great part into plant or animal life, and no little part of the
plant life that is formed is likely to be converted ultimately into animal life.

A primary condition for the formation of thick shells of good quality is the presence
in the water of suitable minerals, principally calcium, and all of the important mussel-
bearing streams are those whose tributaries flow from regions of limestone or other cal-
careous deposits. Consequently it is the Mississippi Basin which largely supports the
pearl-button industry, though shells of commercial value are also found in the Great
Lakes and Gulf of Mexico drainages, and some in the Red River of the North. The
streams of the Atlantic and Pacific slopes are almost or entirely barren of valuable
shells.

Many factors, indeed, enter into the suitability of waters for mussels, and of the
various species of mussels—more than 500 in the United States—each has its special
requirements; some will thrive where others will not. Much remains to be learned
concerning the relation of mussels to their environment, and the subject is particularly
complex because of the great number of species involved; but it will be attempted to
place the several phases of that subject in general review in a later section on habitat
(p. 94). Itis the purpose of this section to give such a general account of the habit of life
and the conditions of existence as is necessary to establish the peculiar dependence of
fresh-water mussels upon the immediate environment.

LOCOMOTION.

As regards their place of abode, fresh-water mussels are very largely creatures of
circumstances. Since they are not frequently seen in motion it is probable that most
of them spend their lives after the period of infancy very near to the place where they
first settle down. Nevertheless they can and do move, and certain species, principally
the more elongate forms, manifest a condition of restlessness at times.

All mussels are sensitive to some stimuli; a splash of the water near them, a touch
on the edges of the mantle especially at the siphons, or the passing of a shadow over
them, will cause the siphons to be withdrawn and the shell to be tightly closed. There
are evidences to indicate that when the disturbance is severe, as when the mussel is
taken entirely out of the water, or is exposed to the sun by an unusually low stage of
water, or is affected by extreme cold, the withdrawal of the mantle is so extreme as to
break the living connection with the edge of the shell, and thus to cause, when growth
is resumed, an interruption line or plane in the shell which is present ever afterwards.
(See p. 132.)

The reaction to evident stimuli consists merely in closing up; there are times,
however, when a mussel is impelled to change its position. The movement may then be

FRESH-WATER MUSSELS. 83

in a vertical direction, the mussel going down deeper into the bottom; rarely does it go
completely beneath the surface of the bottom; more frequently the mussel moves
horizontally, leaving a distinct path behind it, which reveals the direction and dis-
tance of travel. Locomotion is accomplished by thrusting the muscular foot forward
into the bottom, expanding the outer end, and then contracting special muscles so as
to draw the shell and body nearer to the end of the’ foot. Mussels that are most likely
to travel in this way are the yellow sand-shell, black sand-shell, and slough sand-shell,
species that are relatively long and narrow. Rotund forms, like most of the species of
Quadrula, are less likely to migrate, but, of the Quadrulas, perhaps the most vagrant
form is the very elongate rabbit’s-foot, Quadrula cylindrica.t The pocketbook, Lamp-
silis ventricosa, and the pink heel-splitter, Lampsilis alata, are also fairly active. Juvenile
mussels are more active than adults. (Pl. V, fig. 3.)

The causes of movements from one location to another are not known and the
subject offers an interesting field of study. Change of pressure (depth), temperature,
or more probably light may be the governing factor. Yellow sand-shells move up on
the shoals or toward shallow water in times of flood, and return toward deeper water as
the stage of water recedes. It is a matter of common report that after high-flood stages
these mussels are sometimes found stranded in the swamps at some distance from the
ordinary channel of a river, but the authenticity of such reports is not established.
Headlee and Simonton (1904, p. 175) observed that fat muckets moved away from shore
during periods of high-wave action.

Isley (1914) tagged and planted large numbers of mussels in comparatively shallow
natural waters and after several months recovered a considerable percentage of them,
finding very little evidence of migration. The Quadrulas placed in water over 3 feet
deep remained approximately where planted; those placed in water as shallow as 1 foot
moved to deeper water, which was easily reached. The species of Lampsilis used in
the experiments showed more activity, but none were discovered which had moved more
than a few yards. He concluded from his experiments and field observations that
mussels, especially the Quadrulas (heavy-shelled mussels) and related species, were
unable to help themselves if conditions became unfavorable, but that, on the other hand,
their power to endure unfavorable conditions was remarkable.

From observations in Lake Maxinkuckee, Ind., Evermann and Clark (1918, p. 256)
say:

The mussels in shallow waters near the shore move into greater depths at the approach of cold
weather in late autumn or early winter and bury themselves more deeply inthe sand. This movement
is rather irregular and was not observed every year. It was strikingly manifest in the late autumn of
1913, when at one of the piers off Long Point a large number of furrows was observed heading straight
into deep water, with a mussel at the outer end of each. The return of the mussels to shore during
spring and summer was not observed. [These were mostly Lampsilis luteola, the fat mucket.]

It is evident from the available data that the locomotion of fresh-water mussels
can play little part in their distribution. Distribution is, in fact, effected principally
during the period of parasitism on fish, when it is governed by the migrations of the
hosts. When dropping from the fish, the little mussels are naturally subject to the
force of the current, and some that fall in unfavorable environments may be carried to
a more suitable place, while others falling upon good ground may drift into a less favor-

@ Wilson and Clark (1914, pp. 35 and 59) have noted a particularly vagrant habit for Quadrula cylindrica.

84 BULLETIN OF THE BUREAU OF FISHERIES.

able situation. Distribution by currents presumably has little practical effect, except,
perhaps, in the case of such a thin-shelled species as Anodonia imbecillis.

DENSITY OF POPULATION.

Strange stories are heard of the density of mussels in beds. It has been said that
_the living mussels in certain beds were in a layer 2 feet deep. Such stories, persistent
among clammers, are, of course, based upon faulty reasoning. A bed is gone over
repeatedly with crowfoot bars, and with continuing success, but the fact is overlooked
that the appliance takes mussels only at random. A layer of mussels is not moved at
each drag. A particular bed in the Mississippi River, more than a quarter of a mile
long and 100 yards wide, was insistently described as being uniformly 2 feet deep in
mussels. Further inquiry elicited the information that the bed was virtually cleaned
up in a season and that about a half dozen carloads of shells were obtained. A simple
calculation showed that, had the bed been as described, at least 30 trains of 100 cars
each would have been required to move the shells obtained. Other stories relate to
such observations as the taking of mussels by suction dredges after excavating deep
holes in the bottom, no consideration being given to the possibility of a mussel falling
in with the caving sand from above.

In planting operations and in experiments involving the retention of mussels for
considerable periods, if normal health and growth are desired it is important to know
how closely mussels may be crowded. ‘The following observations are therefore offered.

The place of densest mussel growth observed by the senior author in the Grand
River, Mich., in 1909, yielded 52 living mussels of 6 species from a space 6 feet long by
3 feet wide, giving a density of about 3 mussels per square foot. Clark and Wilson
(1912, p. 20) found a most favorable place for observations of density in the Feeder
Canal, near Fort Wayne, Ind., which had been recently drained. The bottom of the
canal had been abundantly populated with mussels and from 1 square meter they took
81 mussels of 8 species, or about 734 per square foot. At the place of greatest observed
density in the Clinch River, Tenn., J. F. Boepple took 66 mussels of 10 species from an
area which he estimated to be 4 square feet; if his estimate was correct, the density
was 16/4 per square foot.

At all of these places mentioned, mussels occurred in such striking and unusual
abundance as to suggest to experienced observers the desirability of making actual
counts. It is fair to assume, then, that the natural occurrence of more than three or
four mussels per square foot over any considerable area is unusual and that plantings
of large mussels in greater density are warranted only where the conditions are shown
to be particularly favorable.

Very small juveniles may safely be planted more closely. Howard reared for a
season 217 juveniles in a floating crate 18 by 24 inches, but the rate of growth among
them was very variable. (PI.V, fig. 3.) In other rearing experiments at Fairport (con-
ducted by F. H. Reuling) 2,006 juvenile sand-shells were obtained from a trough 14
feet long and 1 foot wide, a density of 143.3 per square foot. In another trough of the
same size, 3,016 juvenile Lake Pepin muckets were reared, a density of 215.4 per square
foot. It is not to be assumed, however, that the young mussels would have lived long
and grown normally while crowded so closely as were these.

FRESH-WATER MUSSELS. 85
BREEDING.

The internal phenomena connected with reproduction are presented in connection
with the discussion of life history (Part 2, p.138ff). _Wehave to do here only with the very
few external manifestations which have been observed as related to the breeding
activities.

The eggs are fertilized by sperm emitted into the water by males and taken in
with the inhalent current of the female. Ina few species the females, when about to
spawn, are marked by a striking development of lurid colors and elongate flaps on the
margin of the mantle about the inhalent orifice. In addition to the bright colors there
are peculiar spasmodic movements of this part of the mantle. This peculiarity has been
observed in a good many pocketbooks, Lampsilis ventricosa, in a few fat muckets,
Lampsilis luteola, in some L. radiata, L. orbiculata, L. higginsii, and L. ovata (grandma),
and in nearly all of the L. multiradiaia which have come under observation. (See Clark
and Wilson, 1912, p. 54; Wilson and Clark, 1912, pp. 13, 14; and Evermann and
Clark, 1918, p. 284.) Ortmann (1911, p. 319) has described such flaps in Lampsilis
ventricosa and L. multiradiata. He observes that when the gravid females are undis-
turbed the marsupia are pushed outward, so that they project out through the inhalent
opening and even a little beyond the shell, as previously figured by Lea. The waving
flaps lie alongside the marsupia, and he attributes to them a function in promoting a
current of water over the marsupia. It seems more probable that these conspicuous
flaps, which sometimes suggest the appearance of smail fish, may serve as a lure to fish,
bringing them into desirable proximity to spawners when the glochidia are ready for
extrusion, thus rendering the fish liable to infection and so increasing the chance of
survival of the glochidia. The following is quoted from Wilson and Clark (1912, pp.
leew. |) ep

The mussels were thickly scattered everywhere, with especially dense beds along the shore. The
small fish were again noticed playing about in the immediate vicinity of the spawning mussels.

L. ventricosus has a habit of moving its bright-yellow siphon fringes, which are much enlarged during
spawning, back and forth in the water. This undulatory motion seems to attract the small darters
and minnows, particularly Notropis blennius, which could be seen darting in toward the fringes
repeatedly. It also probably assists in furnishing fresh water for the respiration of the young mussels.

At intervals during the undulations small numbers of glochidia are discharged from the brood
chambers of the mussel and carried out of the excurrent aperture. These glochidia are of the hookless
type, and must be taken into the mouth of the fish that is to carry them during their parasitic period.

We can thus understand the advantage of attracting these fish and keeping them in the immediate
vicinity during the discharge of the glochidia.

WINTER HABITS.

Very little is known of the habits of fresh-water mussels in winter. Observations
of rate of growth indicate that growth practically ceases during the very cold months.
(See Isely, 1914; and also p. 132.) Microscopic studies of sections of shell indicate that
there are numerous slight interruptions and resumptions of growth, corresponding to
each period of winter, and these are no doubt related to the fluctuations of temperature
in fall and spring.

According to clammers, mussels cease to ‘‘bite’’ with the approach of cold weather.
The observations of Evermann and Clark on the movement of certain mussels from the
very shallow waters near the shore of Lake Maxinkuckee in late fall have been previously

86 BULLETIN OF THE BUREAU OF FISHERIES.

quoted (p. 83). They do not generally migrate or bury themselves, however, but
simply become benumbed so that they respond very slowly if at all to such stimuli as
the touch of the clammer’s hook. Evermann and Clark (1918, p. 256) also observed that
mussels are not altogether inactive in midwinter:

Occasional mussels were observed moving about in midwinter, even in rather deep waters. During
the winter of r900-1901, an example of Lampsilis luteola, in rather deep water in the vicinity of Winfield’s,
was observed to have moved about 18 inches in a few days. Its track could distinctly be seen through

the clear ice.
FEEDING HABITS.

It has been previously noted that a mussel in normal condition on the bottom
keeps a stream of water continually passing in through one of two siphonal openings
and out through the other. The food is derived from this current as it passes through
the gills. The manner in which the food is collected and taken to the mouth has been
well described by Allen (1914, p. 128 ff) from studies conducted at the Indiana University
Biological Station, Winona Lake, Ind.

The filaments of the gills are covered with cilia which intercept the particles contained in the water
and prevent their passing through the gills with the water. They become entangled in mucus, and
through the action of these cilia such particles are wafted toward the mouth in streams. If they are of
a harmless nature or of food value, they are permitted to enter the alimentary tract. During the incuba-
tion of the glochidia, the female gives up a greater or less part of one or both of the gills for marsupial
purposes. At this period these parts are of little use for respiration or for the collection of food.

Cilia similar to those of the gills line the entire branchial chamber, cover all organs which come into
contact with the water, and also line the alimentary tract. They are, as is always true of cilia, in con-
stant motion during life; they act independently of nervous control and in a single plane. Their con-
certed action is in the form of waves—resembling in appearance the passing of a breeze over a field of
grain, or the movement of a bank of oars. The direction which these waves or streams take varies in
theseveralorgans. Butall of the streams taken together are coordinated to accomplish a certain common
end. 2

The mouth of the Lamellibranch lies nearly as far as possible from the external openings, just
behind the anterior adductor muscle. It is thus well protected from the entrance of harmful substances.
It is flanked above and below by the thin narrow lips. The upper lip is continuous with the outer
labial palp on each side, while the lower lip is prolonged into the inner right and left palps. Most of the
ciliary currents of the contiguous faces of the palps and of the lips are directed forward to the mouth.
The outer or noncontiguous faces of both palps and lips as well as the edge of the inner face of the lips
bear cilia which are directed backward and away from the mouth. Thus particles which find their way
between the palps are carried to the mouth. As will soon be seen, very little undesirable matter ever
reaches the mouth or palps, but even here Wallengren (1905) has pointed out how selection and rejection
may be made.

* * * The inner surface of the labial palps, except their outer margins, are made up of minute
vertical ridges, or furrows. These constitute a quite complex mechanism for the sorting of material.
Ee

Upon the ridges as elsewhere occurs a ciliated epithelium. But the ciliary currents are disposed
in a unique manner. Upon the anterior slope of each ridge they are directed backward while those
on the posterior slope lead forward. This seeming conflict is not such in fact, because only one set
of cilia comes into action at a time. The position of the ridges determines which set shall function
atagiven moment. Thus the after slopes are ordinarily brought uppermost, the ciliary currents leading
to the mouth are upon the surface, while the cilia which lead from the mouth lie somewhat underneath
the ridges. So long asno adverse stimuli are received, particles which lie between the palps are thought
to be passed on forward from one ridge to another, to the lips and mouth.

In the event that distasteful matter reaches the palps a reflex erection of the ridges brings upper-
most the cilia leading backward and such material is returned from summit to summit to the edge of
the palps and discharged into the mantle chamber. * * *

FRESH-WATER MUSSELS. 87

The entire epithelium touching the branchial chamber is abundantly supplied with glands which
secrete a mucous substance. The mucus envelops and binds together in strands the material to be
transported by the cilia. This is particularly true of those particles which are of a very distasteful
Natures ayo

Observers have differed widely in their notions of the ability of the mussel to select its food. To
me it is evident that there are, to summarize, four points where such choice is exercised:

(1) The labial palps, at the upper margin.

(2) The labial palps, on the furrowed surfaces.

(3) The mouth.

(4) The incurrent siphon.

As to the last, it is surrounded by a row of pointed, fleshy papille, having a resemblance to plant
structures. These have two sensory functions—tactile and gustatory; for upon being disturbed mechan-
ically they are withdrawn into the shell, while a continued teasing, or a strong chemical stimulus results
in the closing of the shell.

Allen conducted experiments the results of which indicated that a mussel siphons
a liter of water (about 1 quart) in approximately 42 minutes. From other observations
he was led to infer that mussels pass food through the digestive system somewhat auto-
matically or regardless of appetite, but that the secretion of digestive juices and the
utilization of the food ingested may be controlled according to the needs of the mussel.

Allen gives a list of diatoms, desmids and other alge, and miscellaneous food items,
but without quantitative data or appraisal of the relative values of the different sorts
of food and without reference to the presence of plant detritus in the stomachs. Seem-
ingly he supposed, as did many others before him, that mussels subsisted almost exclu-
sively upon living organisms. Data bearing on this question are presented in the
following section.

FOOD OF MUSSELS.
SIGNIFICANCE OF THE PROBLEM.

The fact that the rate of growth of mussels seems so directly proportionate to the
thickness of the shell (p. 129), or, speaking from a physiological point of view, to the
mineral requirements of the mussel—for the shell is chiefly mineral—leads naturally
to the supposition that the limiting factor of growth is not the organic food supply,
but the mineral foodsupply. This is a rather startling inference, since we are accustomed
to view animals in nature as engaged in a fierce competition for food, their numbers and
the luxuriance of growth being proportioned to the abundance of food available; and
the food we ordinarily think of is the organic (animal and vegetable) substance required
rather than the mineral matter. Yet, if it could be assumed that the food requirements
of a floater mussel are of the same nature as those of a pimple-back, then, since in the
same body of water the floater with its shell of paperlike thickness may attain a length
of 334 inches in two seasons, while the pimple-back with thick shell may not in the same
period attain a length of more than about an inch, the conclusion would seem probable
that the thick-shelled species was restricted in growth, not for deficiency of organic
food, but for lack of the materials necessary for the formation of shell. The assumption
proposed, viz, that the food requirement of the different species is virtually identical,
although plausible and substantiated by some evidence, can not be accepted as finally
proved.

It becomes of importance to determine what is the food of fresh-water mussels,
whether the requirements of different species are the same, whether there is serious
competition for organic food between commercial and noncommercial species, and

88 BULLETIN OF THE BUREAU OF FISHERIES.

whether there is a sufficient food supply in water in which it is desired to promote an
abundant growth of mussels.

Three bodies of evidence bearing upon some of these questions are presented in
the following pages. One is a summary of the observations by H. Walton Clark, which
have been published elsewhere in part; another is a table embodying the results of
Shira’s studies of the 60 juvenile mussels taken in Lake Pepin (Shira, unpublished
manuscript); the third comprises previously unpublished observations made in 1916
by Franz Schrader,” formerly scientific assistant in the Bureau of Fisheries. The last
will be given first since the studies were directed more particularly at the questions
just presented.

OBSERVATIONS OF FRANZ SCHRADER ON FOOD OF MUSSELS.
SPECIES STUDIED.

Four species that were thought to be fairly representative were selected for investi-
gation: The river mucket, Lampsilis ligamentina, the Lake Pepin mucket, Lampstlis
luteola, the blue-point, Quadrula plicata, and the spike, Unio gibbosus. The first named
is a typical river mussel, and one of the most important of all from the button manu-
facturer’s point of view—considering the quantity and quality of the shells together.
Lampsilis luteola, a shell of fine quality, is predominantly a mussel of standing bodies
of water, and is found to comprise 31.5 per cent of the entire shell output of Lake Pepin.
Ouadrula plicata, also a good button shell, is evidently equally at home in stagnant
and in flowing water. It is a member of a genus in general slow, ponderous, and heavy-
shelled. Finally, Unio gibbossus is a form of little commercial importance because
of its colored shell but is extremely common in some localities. Thus in Lake Pepin
13 per cent of the shells were found to be of this species, and it was thought that if
competition for food played an important part in mussel ecology, the presence of this
valueless form might be detrimental to the commercial species, especially when occurring
in such numbers as in Lake Pepin.

FOOD CONTENT OF WATERS.

The first step taken was to make a careful examination of the water. For this pur-
pose samples were taken from well-known mussel grounds. A water sampler operating
by means of valves that are closed through releasing the catch by a string was used.
The sample of water taken at from 2 to 4 inches from the bottom was treated with
formalin and the contents allowed to settle in the usual way.

The solid matter thus obtained may be roughly divided into three groups: (1) Min-
eral matter; (2) organic remains predominantly from plants (detritus); (3) plankton,
chiefly green alge and diatoms. The proportions of these were extremely variable,
varying not only with the season but also with changes in the river level. Plankton
varied from less than 1 to more than 20 per cent. The remaining material comprised
chiefly detritus, for, except after thaws or rains, the mineral matter seldom exceeded
5 per cent of the total of solids.

Regarding the plankton, it may be said that relatively few forms made up the
greater bulk. Thus, among green alge there were Scenedesmus, Selenastrum, Pedi-
astrum, Cosmarium, and Volvox, the latter especially in the spring. In August greater

@ Included with his consent.

FRESH-WATER MUSSELS. 89

or lesser fragments of various thread alge, such as Spirogyra, increased in numbers
until they outranked all others in importance. ‘The list of diatoms showed these forms
as important: Coscinodiscus, Synedra, Asterionella, and Navicula. In far smaller
quantities but generally present were Gyrosigma, Tabellaria, Gomphonema, Epithemia,
and a few others that are negligible for practical purposes.

In both quantitative and qualitative constitution no appreciable difference was
noticed between samples from Lake Pepin and those from the Mississippi River at
Homer, Minn.

FOOD DISCRIMINATION UNDER NORMAL CONDITIONS.

Having ascertained the materials available in the water as a possible source of
food, the next step was to determine whether the different mussels showed a preference
or dislike for any of these constituents. This necessitated an examination of the
stomach and intestinal contents of naturally feeding mussels. In every case the con-
stituents of the material obtained from the stomachs corresponded to those found in
a free state in the water. This refers not only to the kind of material found but also to
the percentages, which were discovered always to correspond, at least roughly, to those
obtaining in the water at that period. Lastly, no difference was observed—in stomach
or intestinal contents—among any of the four forms of mussels concerned. ‘Thus,
under normal conditions no discernible degree of discrimination is evinced.

UTILIZATION OF FOOD MATERIALS.

The question of the utilization of these materials was best solved by an examina-
tion of the feces. It was astonishing to note that only about one-half of the green alge
and diatoms were attacked to any degree by the digestive processes. In fact the
green algz, with their often delicate cell walls, on many occasions did not even lose
color. It was the detritus that underwent the greatest changes. The vegetable origin
of this material was easily discerned under the microscope before digestion had taken
place, but in the feces, after digestion, the substance was found almost always to have
undergone a radical change in appearance and in structure. It was evidently attacked
by the digestive processes to a much greater degree than the plankton.

These observations point to a comparatively unimportant réle as played by alge
and diatoms in the food of mussels. Not only are these forms present in very much
smaller amounts than the dead-food materials but also they are not digested as well.

EXPERIMENTS IN FEEDING VEGETABLE MATTER.

Although under normal natural conditions no discrimination of food was observed,
conditions might easily arise which would bring about a radical change in the constit-
uents of this normal food supply. Feeding with different materials was tried, therefore,
to determine any preference that the mussels might have.

The method used was to starve the mussels for four to five days and then feed
them with the material under investigation. In this way the intestine was first cleared
and the state of digestion of the fed material determined without any disturbing con-
tamination from substances previously present in the intestine. As starved mussels
may. lose their sense of discrimination to a certain degree, an equal number of control
mussels feeding and living in a tank with a flow of river water were always experimented
on at the same time. The food was administered from a long pipette into the intak-
ing siphon. It is unnecessary to go into the details here, but it may be mentioned that

go BULLETIN OF THE BUREAU OF FISHERIES.

the utmost care had to be employed so as not to feed particles of food exceeding a
certain size. A neglect of this caution invariably caused violent expulsion of the
whole dose of food, no matter what it was.

THREAD ALGat.—These were accepted by all four species, but only in limited
quantities by the mucket, Lampsilis igamentina. An examination of feces confirmed
the previous observations that green alge are only very incompletely digested.

PALMELLALES.—These soft, slimy, green alge gave no other result save that they
seemed somewhat better digested by the blue-point mussel.

DetrRITUS.—This was artificially prepared by immersing the leaves and soft stalks
of plants that are generally found near the water in some water for a few days until
nitrogenization had set in. They were then macerated with mortar and-pestle and the
resulting pulp strained through bolting cloth. All mussels took this artificial detritus
readily, and the feces showed the characteristic features of digested detritus.

FRESH VEGETABLE MATERIAL.—This was not so readily taken.

VEGETABLE Fat.—Olive oil in the form of an emulsion was accepted by the Lake
Pepin mucket and the river mucket. It was evidently thoroughly absorbed, as no
traces could be found after digestion. The blue-point and the spike were not tried with
this material.

EXPERIMENTS IN FEEDING ANIMAL MATTER.?

FisH Meat (heart of the wall-eyed pike, Stizostedion vitreum).—Two out of three
examples of the Lake Pepin mucket accepted this material readily, the third less so.
The control mussels vacillated, occasionally taking very small quantities. The other
three species evinced strong repulsion, expelling any of the substance taken in in from
1 to 15 seconds. Abnormal reddish feces.

TAILS OF TADPOLES (macerated).—These were refused or quickly expelled by
the river mucket and the Lake Pepin mucket. The other mussels were not tried with
this material.

BLoop OF PICKEREL.—This was refused by all species, even when given in a state
of high dilution.

AnmmaAL Fat.—This was an emulsion of fat obtained from the sheepshead fish,
A plodinotus grunniens. Extremely small doses at long intervals were taken and evi-
dently digested.

In all these cases the food mater.al was generally readily taken (from 1 to 15 seconds)
into the siphon. After a varying period of time (a few seconds), the length of time
necessary for the substance fed to affect the taste organs, disagreeable food was always
expelled again.

The experiments do not point to any undoubted conclusion regarding animal food,
except that they seem to establish the fact that vegetable food is preferred to the animal
substances employed. Probably, under normal conditions, small quantities of the
latter are taken in with other substances, but it is hardly believed that it ever plays
a large réle.

GENERAL OBSERVATIONS.

Throughout the experiments it was noticed that the Lake Pepin mucket, Lamp-
sus luteola, was not so exact in its requirements as the river mucket, Lampsilis liga-
mentina. ‘The latter was indeed the most delicate feeder of the four species, and the

@ Allen (1914, p. 138) fed mussels upon living Paramecia with apparent success.

FRESH-WATER MUSSELS. gI

greatest care had to be taken in handling it, while just the opposite was true of its near
relative, the Lake Pepin mucket, which fed readily on most of the experimental material
and was not so fastidious regarding the physical state of the food; that is, the size of
food particles and the amount given at one time. This may explain to a certain degree
the success attending the culture of the latter species in ponds, but the question then
arises why the river mucket is not crowded out everywhere by this mussel, since one
species, judging from the shell structure, is as well adapted to live in moving water as
the other. As was observed above, however, Lampsilis luteola is typically an inhab-
itant of water with little or no current, while Lampsilis ligamentina is a true river mussel.
The available data of shell structure and feeding habit evidently offer no explanation.

The blue-point and the spike take a midway position as regards their feeding
habits, although the former is perhaps less exacting than the latter.

Detritus undoubtedly forms the main bulk of the food of fresh-water mussels.
Dissolved substances may also play a part (Churchill, 1915 and 1916), but their réle is
probably a comparatively unimportant one when compared with the solid food matter.
This must be especially true: of streams with relatively pure water, in which mussels
have been found to thrive just as well or better than those carrying large quantities of
dissolved matter.

In view of the universal presence of plants in or near waters productive of mussels
there is little likelihood of a shortage of food, for detritus will always be forthcoming.
There can be only a very little competition among mussels as far as food is concerned,
and the noncommercial species are not objectionable from this standpoint.

OBSERVATIONS OF H. WALTON CLARK ON FOOD OF MUSSELS.¢

In general it may be said that the food of fresh-water mussels, as indicated by their
stomach contents, includes about everything obtainable and not positively harmful,
organic or inorganic substances, living or dead matter, if not too large or too active for
the mussels to take in. As the mussel has no means of mastication it can not use long
objects such as filaments of algae and the like.

In the course of general biological investigations and of mussel surveys opportunity
was had to study the stomach contents of mussels from widely separated areas and
under widely different conditions. One of the striking features of the case is that the
size and apparent health of mussels bear no direct relation to the apparent nutritive-
ness of the material in the stomach. Thickness of shell is partly a matter of heredity;
thick-shelled species of Lampsilis are found in fairly good currents where nutritious food
material is scarce; thin-shelled Anodontas are usually found in quiet places where the
food supply is rich. Moreover, generally speaking, Lampsilis of any species in a quiet
lake where food in the form of plankton is abundant, are thinner shelled and smaller
than those of rivers.

Although, generally speaking, thickness of shell seems to be almost always in
inverse ratio to richness of food, that relation itself may be partly accidental. In mus-
sels the secretion of shell is in relation to current or to mineral content of the water.

The stomach contents of some large heavy pocketbooks, Lampsilis ventricosa,
from the mussel beds in Yellow River, Ind., where this species reaches maximum size,

@ For additional data see Clark and Wilson (1912) and Evermann and Clark (1918).

g2 BULLETIN OF THE BUREAU OF FISHERIES.

consisted chiefly of the yellow mud of the river bottom, with organisms of any sort few
and far between. In general, mud® is an abundant element in the stomachs of all mus-
sels; so much so that the color and general appearance of the mass of the stomach con-
tents of all river mussels examined was that of the bottom soil. In ponds full of dif-
fused plankton alge the plants may be present in sufficient quantities to at least fleck
the ‘‘ground color’’ with a pronounced green or blue green. Studies of the stomach
contents of the mussels in the reservoir of the Feeder Canal at Fort Wayne, in 1908,
revealed the presence of many flagellates, such as Trachelomonas and Phacus, together
with such minute plants as Scenedesmus, Pediastrum, Botryococcus, such diatoms as ~
Gomphonema, Navicula, and the like, a few desmids (Cosmarium), fragments of Cera-
tium hirundinella, casts of the rotifer Anurea cochlearis, and small fragments of
confervoid alge. In the main current of the St. Joseph, St. Mary, and Maumee
Rivers there was much mud with about the same organisms scattered sparsely through
it. A mucket, Lampsilis ligamentina, taken in the Auglaize River, contained what
appeared to be bacteria. Mussels in Lake Amelia, near St. Paul, Minn., contained an
abundance of that peculiar organism Dinobryon sertularia. The mussels of Lost Lake
and Lake Maxinkuckee, Ind., contained enough plankton organisms of all the minuter
sorts to give the stomach contents a greenish cast or to mottle it considerably with greenish
flecks. Not to enter into too great detail, they contained such organisms as Microcystis
aeruginosa, Pediastrum boryanum, and P. duplex, Calastrum microporum, Botryococcus
braunii, Scenedesmus, Melosiva crenulata, Coconema cymbijorme, Navicula, Epithemia
argus, Fragilaria, Cocconeis pediculus, and Lyngbya @stuarii. Melosira and Spirulina
represented the longest filaments taken. Anurea cochlearis was common but represented
only by lorica, and Chydorus was the largest and most active organism taken.

Observations believed to be of both interest and importance were made in the Mis-
sissippi in the late summer and autumn of 1919. The river had remained high and
swift until about the beginning of September, when it fell rapidly. With its fall the
great body of marginal water lost the velocity of its flow, and great areas behind wing
dams, lagoons, and mouths of sloughs became extensive areas of calm. In these a rich
and varied plankton, consisting chiefly of holophytic sorts (Euglena, Pandorina, rotifers,
Platydorina, and a bottom benthos of diatoms), rapidly developed in considerable quan-
tities. The stomachs of the mussels in the bottom of these areas of calm contained
numerous organisms of the plankton and benthos such as Anurea cochlearis, Pandorina,
Mycrocystis, Scenedesmus, Phacus, and various diatoms; the stomach contents bore
general resemblance to those of the mussels of the Feeder Canal reservoir.

Opportunity was taken to examine the stomach contents of some young mussels
which were obtained at the same time. In a slough sand-shell, Lampsilis fallaciosa,
19.1 mm. long, all that could be recognized was one colony of Clathrocystis. Another,
18.9 mm. long, contained chiefly brown, gritty mud in which were several Scenedesmus
caudatus, Phacus pleuronectes, 1 Coscinodiscus, a few very minute Melosiras, and some
rough spherical cysts. A third example, 19.6 mm. long, contained much brown flocculent
organic mud, a large colony of Microcystis, 1 Scenedesmus caudatus, the diatom Cyclotella
compta, and many of the green rough cysts.

The stomachs of some very small Lampsilis anodontoides and L. luteola, reared in
troughs at Fairport and apparently thriving, contained only a fine brown flocculent

@ The mud is probably mixed with much decomposing organic matter.

FRESH-WATER MUSSELS. 93

mud, with rarely an occasional diatom. A young L. anodontoides from Smiths Creek bar
in the Mississippi contained fragments of diatom shells indicating that it had been feeding
on them to an unusual extent. Although Pleurosigma covered the mud of that region,
forming an almost unbroken brown scum, it is noteworthy that it was only rarely found in
the stomachs of the young mussels, it being apparently too large to enter the mouth.

As regards the entire subject of mussel food and feeding there are some general
observations it may be pertinent to make at this point.

At one time it was thought that extremely dense beds of mussels in the bottom of
lakes might act as reducers of an excessive accumulation of plankton. They might
indeed take care of many sunken and decaying plankton organisms, but under favor-
able conditions plankton can develop more rapidly than anything can eat it.

The finding of what appears to be bacteria in the stomachs of mussels of the Auglaize
River and the observation made in tanks at the Biological Station at Fairport—that
turbid water in which there were mussels cleared up rapidly, the mussels collecting the
silt and other materials in suspension—raise the question as to whether mussel beds are
not or can not be of use in the purification and sanitation of rivers. If oysters grown
in polluted waters may harbor typhoid bacilli and so communicate the disease to those
who eat them, there seems to be no good reason why mussels, which are not eaten, may
not serve to arrest and devour those as well as other pathogenic organisms.

Since mussels are very inactive animals, the rate of metabolism may be expected
to be low and the food requirements correspondingly small. The problem of obtaining
nourishment for mussels is then one of the least of our troubles. Doubtless younger,
more active mussels require a richer diet, and the first problem of mussel propagation,
that of finding a suitable host, is fundamentally one of finding suitable nutrition for a
creature remarkable for its fastidiousness in this regard. It may be that a critical
problem is the finding of suitable nourishment for the first month or so of free life, but
beyond this the only problem, so far as food supply is concerned, appears to be the
avoidance of actually poisonous or harmful substances.

OBSERVATIONS OF A. F. SHIRA ON FOOD OF JUVENILE MUSSELS.

The following table (1) embodies a record of the stomach contents of 60 juvenile
mussels, distributed among 6 species, taken in Lake Pepin during 1914. The material
was studied with the use of a rafter counting cell, but since only a very small quantity
of food could be obtained from each mussel the calculation of percentages can be only
approximate.

TABLE 1.—Foop OF Srx SPECIES OF JUVENILE MUSSELS TAKEN IN LAKE PEPIN, SEPTEMBER, OCTOBER,
AND NOVEMBER, I9g14.

Juveniles examined. | Length ohvenes (milli- Percentage of food.
Organic
pans In-
i ree . princi- | organic :
Species. Number. Mink Maxt Average.| pally | remains Diatoms.
: * vege- (silt,
table etc.).
matter).
Lampsilis luteola.........sssssseeseneeeeens 12 5.0 15-4 9.5 89 6 2
Lampsilis ventricosa...........++-eeee eee 10 4.8 13-4 8.8 90 5 2
Lampsilis alata......... Soud 8 8.2 ai.5 13-7 96 I z
Mampsilis|graciliss... viccsccecesccerccsse= 10 6.6 19. 6 13-5 95 I I
Quadrula plicata,’. .......cccsteeenecsseases 8 6.4 IIo 74 96| Trace. I
Anodonta aumibectllissicccsscesccsccccucees os 12 6.2 19-5 12.7 91 4 2

75412°—22———7

94 BULLETIN OF THE BUREAU OF FISHERIES.
HABITAT.

The pearly mussels, as inhabitants of fresh water, are found in diverse habitats, in
lakes and in rivers, in shallow and in deeper waters, in cold and in warm waters, in mud,
in sand, and among rocks. Yet they do not occur in all lakes and rivers, nor in all parts
of the lakes and rivers in which they do live; and the several species of mussels, when
living together, are not always found in the same relative abundance. It may, therefore,
be supposed that fresh-water mussels, like other animals, are adapted rather definitely
to particular conditions of environment; that some find congenial environment in still
or sluggish water, while others thrive best in strong currents; that a mud bottom supports
certain species,.while a firmer soil is required by others.

Adult mussels in some cases thrive, or continue to live at least, in environments
where the young would perish, for delicately balanced conditions are required by very
young mussels of many species, and only where these conditions exist can a mussel bed
originate or perpetuate itself. On the degree of stability of the conditions favorable to
the growth of the young the permanency of the bed must depend, since, when replenish-
ment fails, the bed can continue only as long as the life of the adult mussels it contains.
As any mussel has rather limited powers of independent locomotion, the place where it
lives (or prematurely dies) is probably, as a general rule, near where it falls when it
drops from its fish host; yet the early juvenile can be carried by the current, and doubtless
this means of transportation may sometimes aid the young mussel in finding a suitable
habitat. An adult niggerhead mussel lived in apparently healthy condition in a balanced
aquarium at the Fairport station for nearly nine months; yet in nature this species is
found only in strong currents, the favored environment of its fish host, the river herring,

The relationship of fresh-water mussels to the environment may be treated with
reference to body of water, bottom, depth, light, current, water content, vegetation,

and animal associates.
BODY OF WATER.

The various geographic types of fresh water in which mussels occur are rivers, lakes,
ponds, sloughs, swamps, marshes, and canals. In so far as distinctive conditions char-
acterize these various types of waters, each may have its characteristic mussel fauna.
It may be said in general, that wherever conditions suitable for a particular species of
animal prevail, that species will be found, except as it may have been naturally excluded
through features of geologic history or other factors governing the distribution of animals;
in the case of fresh-water mussels, however, emphasis must be placed upon a qualifica-
tion of this general statement. Though all conditions in a body of water may be other-
wise suitable, mussels can not naturally occur where conditions do not permit the entry
and survival of the species of fish which serve as hosts.

STREAMS.

Mussels have undoubtedly reached their greatest development, as to numbers, both
of species and of individuals, in flowing water. From the commercial standpoint, also,
the quality of shells from streams is almost invariably superior. In general, where other
conditions are favorable to mussels, larger bodies of flowing water are more productive
than the smaller. Brooks do not usually contain mussels. Morphologically, mussels
adapted to life in strong currents are differentiated from those adapted to still water by

Buty. U. S. B. F., 1919-20. PLATE VI.

Fic. 1.—Upper waters of Grand River. Habitat of mussels in shallow swift water

Fic. 2—Upper waters of Grand River. Habitat of mussels in sluggish water.

Buu. U. S. B. F., 1919-20. PLATE VII.

Fic. 1.—Black River, Ark., a very productive mussel stream.

Fic. 2.—Red River, near Campti, La., a turbid stream with caving banks and shifting bottom, quite unfavorable
for mussels.

Bui. U. S. B. F., 1919-20. PLATE VILL.

Fic. 1.—Lake Pepin, an expansion of the Mississippi River between Wisconsin and Minnesota,
a favorable habitat for fresh-water mussels.

Fic. 2.—North Fork of Kentucky River, near Jackson, Ky., with sand bottom and conditions unfavorable for mussels.
(Danglade. )

Fic. 3.—Tea Table shoals, another portion of the Kentucky River; the shores indicate stability, the water is
moderately deep, and the environment is favorable for mussels.

BuLy. U.S. Bi Be. 1ron9o—20: PATE Xe

Tic. 1.—An undredged portion of the Kankakee River where valuable mussels flourish.

lic. 2.—A dredged portion of the Kankakee River rendered (temporarily, at least) unfit for fresh-water
mussels,

Buu. U. 8. B. F., 1919-20. PLATE X.

Fic. r.—Lower portion of Grand River, Mich., where mussels thrive under natural conditions.

Fic. 2.—Lower portion of Grand River where conditions have been rendered unsuitable for mussels by
canalization in interest of navigation.

Buty. U. S. B. F., 1919-20. PLATE XI.

Fic. 1.—Auglaize River near Defiance, Ohio, showing Fic. 2.—Maumee River, Defiance Ohio. The river
islets and pools containing dense beds of mussels. bed a broad valley with limestone bottom, broken
into numerous pools and channels with little islands

—an excellent growth of fresh-water mussels.

Fic. 3.—The draining of the I’eeder Canal near Fort Fic. 4.—Parts of the Miami and Erie Canal afford
Wayne, Ind., revealed a remarkably dense popula- excellent environments for mussels.
tion of fresh-water mussels.

Fic. s.—Construction of wing dams in the upper Mississippi River often renders conditions unfavorable for mussels that
previously throve in such sections of the river.

FRESH-WATER MUSSELS. 95

the stronger development of the hinge teeth which aid in keeping the two valves of the
shell in perfect apposition.

Since a river presents from source to mouth conditions of varying suitability for any
form of animal life, there will usually be found in some measure a longitudinal succession
of mussels. Shelford (1913, p. 122) gives a table showing the longitudinal sequence of
eight species of mussels in the Calumet Deep River.

If one goes down a river from its headwaters, making collections of mussels at
various points, many species may be found at each place, but some species first encoun-
tered may disappear before the upper waters are passed. Others appear here or there
and perhaps disappear as one proceeds still farther down. The mussel fauna of the
different sections of the stream are characteristic, although one or more species may be
so adaptable as to live throughout the entire course of the stream.

This longitudinal succession of species is well illustrated by Table 2, which shows
the distribution of mussels in the Grand River, Mich.

TABLE 2.—LONGITUDINAL DISTRIBUTION OF MUSSELS IN GRAND RIVER, MICH.

| Observations made at and below—

Belg (2 3

Scientific name. Common name. o a. a

SW pe beio limped a

vvy! =| E =

— 3 Ul nD g = a} oO ust

Pox] o te) B es) i] e a

3.8] 2 x | 5 5 Pee ied

Sey SNH NEP aE Stalls

x. Quadrula coccinea............0-.-05 “Flat niggerhead”’ x x x x x x | x x

a. Strophitus edentulus................ Squaw-foot,.......... x x x x x onal) x

3. Anodonta grandis................... ldatens ss jdis sab. x x x x x x Box x

4. Lampsilis ventricosa................ Packet Hooke. s<.5)sjj0 060% «cise eins nis x x > an nese x x x x

5. Quadrula rubiginosa................ Flat niggerhead.................- x x Kise Mats cl acninare x x x

6. Anodontoides ferussacianus.........| Small floater. ..................5. x x > an BS os] HERBST x x x

PUAN PSUS ATIS A Nat ete cee tie ota ok Rainbow-shell................... x ee an er 22, [Poapo.| con ee x x
Goes VID VALE As COND eSSAee role ces oaisiee | nein anise aisles aime wisiaislo. siefhjasieisia c= x >a eal Wee aa like 0] bBaas | Res Asd Biden!

Ol Lanipsilisiinteolal 5.5 2th. 2: ee hatimicket (0s {5-2 sheladnea. cee = x x
ro. Alasmidonta calceola...............+ Slipner-shell ie creceiccisieeiisieinis sien x x Soest

11. Unio gibbosus,......... ho-sacodre as Spiel tre-suet Santis aee altos |senbite x x

iz. Symphynota costata...............- Kluted shelly fics scccwe sence ong: x x
Tar Mam psiis eli psHorsiS.,... gases cule ks | tee oak eee ne saate cles acsllene ameter es x pecan

14. Quadrula undulata.................. SEPTEE TIGA PON Ae woticie cade eee x x

1s. Lampsilis ligamentina.............. WTC SO. Ee Garig beim o quince etic) facisa ac] EObod x
16. Alasmidonta marginata............. IVR eg Sandon en SongonOaDOe 44 lagetmd DeBEBe kines] fee 4 eBeaal bHSocc Imes sul | Adnan

17. Quadrula tuberculata............... Flat purple pimple-back.........|......[...0.-]-.0008 x

RBee MAIN PStis rectal. sac em sineersininie/ialas ero Black sand-shell................- orl Boned baeant =

TOL AULOSINS ALATA Ach Stic. ntie s tceites ne Hatchet-back, pink heel-splitter.. Bly. deRA Mo Agere x

20. Quadrula pustulosa................. Wihitenwarty-hacks 1.5 socuueeaarfomtceisi<| eae saleeceis 0 x

2x. Lampsilis gracilis... .........-...... Me sacdelal Wy Aga a Joga sobubod Opc.ndt | Sema acne, he ‘ x

22. Obliquaria reflexa.................-- Three-horned warty-back........]......J....../.0.-8 a x

23-2 Obovaria ellipsis! sif2 55. 20: S818 ERC ony-m il 5g oth ie octeis sch [davies clipes «a[esteecis me x

24. Plagiola elegans................ ...| Deer-toe ..... =

2s. Quadrula lachrymosa.......... ...| Maple-leaf =

26. Symphynota complanata...........| White heel-splitter...............]......].....-J.c000- x
BRO tal eames cies cbetaeiesisicierete d ecle mica] Sao eieiete a) icicierelareiaiale ats o/ojejaiaratn nye cle 10 14 22

i] i}
@ Observations by R. E. Coker in 1909.
SumMary oF TABLE.

uae See Fe CaP MECC Ota rere en eee St ore in ot eide a Saleinai oo ceimnnibin b Siecc oleh a vieaen aja scale sas Ralsiaaaliielevvidedediaeews'aa 26
Other species occurring above Portland...................22.02-2005 6
Species occurring throughout river... 2... 6.00. s eee eee 10
Species found only at or below Portland.................. 10
Species not found below Grand Rapids........ GROAN 4
Opeciesionnconty HelowiGratid: RADICS A420 be dante aostatiscen cbone clenicle nicia sine bk cnindinas Ss pleieide setae aisle fas <teicte 6

It will be observed at once that a far greater number of species is found in the lower
part of the stream. Thus, while only 1o of the 26 species observed in the river were
found near the headwater lakes, 22 species were met in the section of the river between

96 BULLETIN OF THE BUREAU OF FISHERIES.

Grand Rapids and the mouth at Grand Haven. It might be thought that this was due
to the fact that there would be fewer obstacles to the passage of mussels downstream
than to their distribution in an upstream direction. It seems sufficient, however, to
assume that the unequal distribution is due rather to the greater variety of conditions of
depth and of fish associates presented in the lower portion of the river. Shallow water
only is found in the upper river, except as artificial pools have been formed in recent
years by the construction of dams, while in the lower river deep water prevails in its
channel and all lesser depths are found between the channel and the shores. The very
breadth of the lower part of the river affords also a greater area for fish and mussels.

A difference of up-river and down-river habitat is presented by the distribution of two
closely related species, the three-ridge, Quadrula undulata, and the blue-point, Quadrula
plicata; the former, a more compressed and rougher form, is found in the more rapid
waters of upstream habitats, while the latter, being thicker and less ridged, occurs in the
deeper waters of the lower parts of a river system.” (See Clark and Wilson, 1912, and
Wilson and Clark, 1912.)

In some rivers mussels are almost entirely lacking for long distances, asin the main
course of the Missouri River for hundreds of miles above its mouth, where the absence
of mussels is apparently due to the rapidly shifting bottom of sand. The Red River,
with its heavy load of silt and its habit of suddenly cutting into its banks and changing
its course, is manifestly unsuited for mussels, and examination of its bottom in many
places by Isely (1914) and Howard revealed extremely few mussels (P1.VII, fig.2). There
is also a virtual absence of mussels in the Mississippi River, except close alongshore, below
the mouth of the Missouri River. Examination of the Musselshell River in Montana by
J. B. Southall in 1919 revealed the presence in numbers of only a single species of mussel,
and this a species (Lampsilis luteola) characteristic of lakes, which lived in the portions
of the river deep enough to remain as isolated pools during the periods of dry weather.
In the east fork of the Chicago River, Baker (1910) found only 3 species, and these were
mussels characteristic of pond habitats, which were able to survive the dry seasons in
the small ponds left isolated in the deeper parts of the river channel.

The James River, in North and South Dakota, though having very few fish, was found
to possess a comparatively varied and abundant mussel fauna in the still waters between
shallow riffles; but there was evidence that the mussels were derived from fish infected
in other waters, that ascended the stream in times of flood (Coker and Southall, 1915).

The suitability of any section of a stream for the growth of mussels arises from a
diversity of causes, including the nature of the rock or soil through which the stream is
flowing, the character of the drainage waters entering the river at or above the section,
the gradient of the stream bed with its effect upon depth and currents, and the species
of fish which frequent the region.

Barriers in the course of a stream such as natural falls, or artificial dams, if impassa-
ble to fish, may have an effect upon the distribution of mussels. Wilson and Danglade
(1914) found no mussels of the genus Quadrula above the Falls of St. Anthony in the
Mississippi River, although several species of this genus are very common in the river
in the large rivers, and passes gradually, in the upstream direction, into a less obese (compressed) form in the headwaters; (2)
with the decrease in obesity often an increase in size (length) is correlated; (3) a few shells which have, in the larger rivers, a pe-

culiar sculpture of large tubercles, lose these tubercles in the headwaters.’ He ascertains also that these laws do not apply to all

species.

FRESH-WATER MUSSELS. $ 97

below that barrier. Wilson and Clark (1914) found only 4 species of mussels in the
Cumberland River above the Cumberland Falls (one of these probably planted), while 19
species were taken in the pool immediately below the falls, but in this case the conditions
prevailing in the river above the falls appeared distinctly unfavorable for fresh-water
mussels. Animpassable dam formed after mussels were generally distributed throughout
a stream would have little significance with reference to the distribution of mussels the
hosts of which subsequently thrived both above and below the dam. ‘The effect, how-
ever, of a dam in changing a region of rapids into a pool, might cause the mussel fauna of
swift waters to give place to a fauna of slack-water habitat.

Studies of rivers in cross section indicate that there may be quite definite distribu-
tion of life with reference to the banks. Shelford (1913) has discussed a horizontal
arrangement of animals that is best illustrated in the cross sections of curves where there
is a horizontal gradation in rate of current and in size of material in the bed of the stream.
In the strong current only the coarsest materials are dropped, while the finest silt is
deposited where the flow is most retarded. The depth of water is doubtless one factor
governing the horizontal distribution of mussels, but the nature of the bottom material
is of first importance. Howard (Survey of Andalusia Chute, Mississippi River, report in
preparation) found in a branch of the Mississippi, following a comparatively straight
course (not on rapids) and averaging 1,200 feet in width, that mussels were uniformly
restricted to a border 200 feet from the shore line. (See table below.) Some mussels
were found almost anywhere along this border, but occurring in beds at points where the
channel touched the shore and where bottom conditions were favorable; depth seemed
to be a minor factor as affecting the distribution.

The following table (3) indicates the results of a sample series of unit hauls taken at
stated distances from the water’s edge and so represents the distribution in a cross
section of the river. It is not typical because of the narrowness of the bed on the left
bank, but it illustrates in a general way the distribution found throughout the survey.

TABLE 3.—DISTRIBUTION OF MUSSELS IN ANDALUSIA CHUTE, MississipP1 RIVER.

Middle
From right bank. of From left bank.
Tiver.
Distance, in feet, from water’s edge......... 35 85 100 200 300 400 300 200 110 60 20
Number of mussels per unit haul........... 13 3 ° ° ° ° ° ° ° r2 32

Where there are rapids with bowlder or cobblestone bottom across a river of this
size, it is known that mussels are not limited to such a border but are found at all points
across the stream.

LAKES.

The mussels from some lakes are large and heavy-shelled, while in others they are
small, thin-shelled, and stunted. These extremes represent the varied conditions
which lakes present in respect to mussel life.

Lakes that have a free circulation of water seem to be favorable; such are those
that are interposed in the course of ariver. A favorable feature in such cases, no doubt,
is the direct and free connection with streams that are well supplied with mussels.
Examples are Lakes Pepin and Pokegama, Minn., and the former is noteworthy for the
abundance of mussels produced. Though at first sight Lake Pepin might be considered

98 BULLETIN OF THE BUREAU OF FISHERIES.

no more than an expansion of the Mississippi River, further observation shows it to be
a true lake in many of its characters, as in clearness of the water, depth, growth of vege-
tation, and virtual absence of current. In both of the lakes mentioned, a characteristic
lacustrine species, the fat mucket, or Lake Pepin mucket, Lampsilis luteola, which is
thin-shelled and worthless in ordinary inclosed lakes, attains so fine a commercial quality
of shell as to appear almost as a distinct variety. Caddo Lake, La., which is interpolated
in the course of a stream, possesses a rich mussel fauna and has been the scene of active
pearl fishery (Shira, 1913). The small Rice Lake near La Crosse, Wis., which is, in
effect, an expansion of a thoroughfare connecting the Black River, near its mouth, with
the Mississippi River, also supports a varied and luxuriant mussel fauna. Where lakes
are freely connected with rivers, as are those first mentioned, or as are others with short
open outlets to the rivers, the lakes and rivers have many species of mussels in common.

In Lake Pepin, Shira (report in manuscript) found that the distribution of the mus-
sels is confined wholly to the shore line and the flats within a maximum depth of 25 feet;
no mussels at all were taken in the deep central part of the lake. In certain places the
mussels were quite densely distributed, forming very well-defined beds, but as these
beds were generally connected by areas of lesser population, a more or less continuous
mussel bed was found to occur on each side of the lake. The largest and most extensive
beds were located on a gravel bottom, or a mixture of gravel and sand. Several good
though less extensive beds occurred on bottoms containing a considerable percentage
of mud. ,

The upper end of the lake evidently serves as a settling basin for the silt poured in
from the river proper, and for a distance of about 2 miles below the entrance of the river
the lake is comparatively shallow with a soft oozy bottom. In this section of the lake
very few mussels are found.

Shira records 32 species of mussels (report in manuscript). Ten of the most abund-
ant species with the percentage of occurrence are given as follows:

Per cent.
ata eket wy loaHpseles VuclCOUa mnie mots eiere chore ccc scte case es ele lobe wien avetaferetal sfe afoiei shelve etatel este iain tet ts ae eager aitaas
SSR HOt HUG Od oe nn aocpbite boxer vido ao Ob aaso eee aon oos daoonaacocoserae saoQunor soc 13.0
Blue-point, Omadralis plscata 2 gui fy pete cio) mes hat shcilesehehaanip = Pia tolete avait iat athe eet tes eer re mas,
Pigstoe, Ora raider ade oan: cinjace Sate ta alo apetel sb ter ajo nvapebaes 3) einia dele) sim atrial pada) =a ntn! patene to oll otele lee 10. 0
Pinksheel-splitter, Lampstlis alata. ent. site se ctese eee sae oe cere erie taste ne ieee et ee 8.3
Pockethook,<Lampstlas VEWtricOsds ..<\Gen se Mave viel etalon apebare)alevo) Ae] o) evelate fetal tials ete ei eee rete trot Pehle 5.6
Slop-bucket, Anodonta corpulenta............ Seas ian Cannes Scie os aa SoR id wan cara oon apes 5-5
Squaw-foot, Strophitus edentulus...... 0.0.0.0 cc cn cece ence centres eee reece eee enter et ence ee eas 4.3
White heel-splitter, Symphynota complanata. ......... 0. ccc eee cece eee eee eee eee eee eens Zag
Black:sand-shell) Wampsilssmectasiwicns (esis selene ote ilepel s eiet et te Sh ot spare lela edie Seeker teksti sia eta ea

In small lakes of considerable depth and without circulation, except as effected by
winds and changes of temperature, animal life generally is absent or greatly restricted
in the deeper portions, and mussels, when present, are confined to zones near the shores
(Headlee and Simonton, 1904). Muttkowski (1918) in Lake Mendota found the optimum
conditions for mussels at depths of 6 to 9 feet on sand bottom, but there was not an
extensive mussel population in the lake as a whole.

The restriction of mussels to the border zones is indeed generally characteristic
of the lakes of the Middle Western States, and even in this environment where the cir-
culation effects of wave action may be felt, the mussels are stunted in growth. In their
report on the mussel fauna of Lake Maxinkuckee, Evermann and Clark (1918, p. 251),

FRESH-WATER MUSSELS. 99

summarize as follows the results of observations of mussels in lakes of Indiana and else-
where: ;

Generally speaking, lakes and pondsare not so well suited to the growth and development of mussels
as rivers are; the species of lake or pond mussels are comparatively few and the individuals usually
somewhat dwarfed. Of about 84 species of mussels reported for the State of Indiana, only about 24 are
found in lakes, and not all of these in any one lake, several of them but rarelyinany. Of the 24 species
occasionally found in Indiana lakes, but 5 are reported only in lakes, and only 3 or 4 of the species com-
mon to both lakes and rivers seem to prefer lakes.

Characteristic species of mussels of inclosed lakes of upper Central States are named
in the following table (4), and it may be remarked that the fat mucket and the floater
are easily predominant over all others.

TABLE 4.—CHARACTERISTIC MUSSELS OF LAKES OF UPPER CENTRAL STATES.

Species. Michigan.¢ |Minnesota.>| Indiana.¢

Fat mucket, Lampsilis luteola..........
Floater, Anodonta grandis..............
Pocketbook, Lampsilis ventricosa.. 250 ne
Sofia waloot SeropMitws CCE C111GS cece eieje e c1a1e cfniein o oleielnje vinreis n.eic|e aisle ojs\cin\a m e[mimeipin nln ain)mn[n.sinin.e's
Small floater, Anodontoides ferussacianus. .
Bers Quadrula rubiginosa......

Spike, Unio gibbosus. ........
sdeneca Lampsilis subrostrata. .
Rainbow-shell, Lampsilisiris. ... aa
Slop-bucket, Anodonta corpulenta.. 220... cee cence e ee cce erate cecereteccerens
Paper-shell) Atiodotita txt becilis: 5555.00 oes nianielein> wlninleinivinin nlee'eie cian a ainieminime pine = 200
Paper-shell, Anodonta pepiniana......... . 2-02 -eee eee eee cece eer e cence nee e te ceneeecnees

x
x
x
x
x
x
x
x
=

@ Coker, R. E. (unpublished notes).
+6 Wilson and Danglade (1914).
¢ Clark and Wilson (1912); Wilson and Clark (1912); and Evermann and Clark (1918).

While, as has been previously indicated, the plains streams, such as the Red River
or the Missouri, with their ever-changing banks and bottoms and silt-laden currents,
present conditions entirely unfavorable to mussels, yet the oxbow or cut-off lakes adja-
cent to them may offer favorable habitats for several species of mussels (Isely, 1914, and
Howard, unpublished notes).

The sand shores of the Great Lakes to a depth of 8 feet are virtually barren of ani-
mal life (Shelford, 1918, p. 26). Fresh-water mussels are found in these lakes, chiefly,
it appears, in the shallower bays, where they sometimes manifest a vigorous growth.
They have not been used commercially to any extent, and probably few possess shells
of a size and quality rendering them suitable for button manufacture.

In a biological examination of Lake Michigan in the Traverse Bay region, Ward
(1896) encountered 9 species of mussels, all of species generally possessing relatively
thin shells, while Reighard (1894) reported 20 species and subspecies from Lake St.
Clair, of which the following 8 were described as abundant:

Pink heel-splitter, Lampsilis alata(Say). = |....-- Lampsilis nasutus (Say).

Thin niggerhead, Quadrula coccinea (Conrad). Black sand-shell, Lampsilis recta (Lamarck).
Spike, Unio gibbosus (Barnes). Pocketbook, Lampsilis ventricosa (Barnes).
Mucket, Lampsilis ligamentina (Lamarck). Floater, Anodonta grandis (Say).

A more extensive list of mussels from Lake Erie and the Detroit River is given by
Walker (1913), the list including 39 species of 15 genera. Since the great majority of
the species named are those that normally possess thin and fragile shells, it may be

100 BULLETIN OF THE BUREAU OF FISHERIES.

supposed that the conditions in these waters are not favorable to the production of
good shells. Certain species‘are mentioned, however, which, in other regions at least,
possess shells of commercial quality. Principal among these are the following:

Maple-leaf, Quadrula lachrymosa (Lea). Long solid, Quadrula subrotunda (Lea).
Pimple-back, Quadrula pustulosa (Lea). Hickory-nut, Obovaria ellipsis (Lea).
Pig-toe, Quadrula undata (Barnes). Black sand-shell, Lampsilis recta sageri (Conrad).

Clark, collecting on the shores of Lake Erie at Put in Bay, found dead shells all
dwarfed in form but representing 14 species, of which the more common were as follows:

Three-ridge, Quadrula undulata. Pink heel-splitter, Lampsilis alata.
Spike, Unio gibbosus. Black sand-shell, Lampsilis recta.
Round hickory-nut, Obovaria circulus. Fat mucket, Lampsilis luteola.
Paper-shell, Lampsilis gracilis. Pocketbook, Lampsilis ventricosa.

PONDS, SLOUGHS, MARSHES, AND SWAMPS.

These types of environment are grouped together, since their mussel fauna is gener-
ally similar. The mussels are thin-shelled as a rule, since light weight is favorable for life
in mud or soft bottoms and mass is not essential in the absence of current. Some possess
narrow bodies and keel-like shells that fit them for locomotion through soft soil, and a
few of the narrow-bodied species, where other conditions are suitable, have relatively
heavy shells. Such are the pink heel-splitter, Lampsilis alata, and the white heel-
splitter, Symphynota complanata.

The heavier mussels characteristic of rivers are sometimes found in sloughs, but in
these the characters of flowing and still water are in a measure combined, since strong
currents may prevail at seasons of high water. Sloughs, as parts of river systems and
subject to being stocked from them, have mussel fauna to a certain extent related to
that of the river; that is, the still-water species of the river are to be found in the sloughs.
Marshes and swamps may have mussels at places where they contain pond or streamlike
openings. In general the marsh and swamp environment is not favorable to mussels.

In ponds that are more or less isolated the thin-shelled mussels of the toothless
type, as Anodonta grandis (floater) and Anodontoides ferussacianus, are characteristic.
Lampsilis parva, one of the tiniest of fresh-water mussels, scarcely exceeding an inch
in length, is sometimes found in such environments. A characteristic pond-dwelling
species is the mussel Unio tetralasmus, which will survive in ponds that become dry in
summer. Examples of this species of mussel have been found alive buried in the bottom
three months after the water had disappeared on the surface (Isely, 1914, p. 18).

ARTIFICIAL PONDS AND CANALS.

Artificial ponds may present a favorable environment for many species of fresh-
‘water mussels if the water supply is suitable, and some species are likely to become
accidentally introduced with fish that are brought into the pond. The ponds of the
Fisheries Biological Station at Fairport, Iowa, are supplied with water pumped from
the Mississippi River. The first species of mussel to appear in the ponds was the large
thin-shelled slop-bucket, Anodonta corpulenta, some examples of which had attained a
length of 3 to 3% inches when they were first discovered at the expiration of the second
season of the pond, 17 months (May, 1910, to October, 1911) after the date of introduc-

FRESH-WATER MUSSELS. IOI

ing water and fish into the newly excavated pond. Eighteen species which have been
accidentally introduced are listed on page 165 below.

Few of these mussels are of commercial value, but it has been attempted to intro-
duce several useful species by artificial infection upon fish, and success has been at-
tained with the Lake Pepin mucket, a lacustrine mussel of high commercial value,
which thrives well in the ponds and has attained a size and quality of shell suitable for
commercial purposes at the age of 4% years.

In canals mussels frequently thrive (PI. XI, figs. 3 and 4). A mill race from a well-
stocked stream seems to present a favorable environment for them. Clark and Wilson
(1912, pp. 19-22) describe a luxuriant development of mussels in a canal at Fort
Wayne, Ind., as follows:

Toward the upper end of the canal, in a place where the bottom was 15 feet wide, the mussels were
counted for a stretch of ro feet along the canal bed and the following species noted: Quadrula rubiginosa,
11; Q. cylindrica, 1; O. undulata, 86; Anodonta grandis, 6; Ptychobranchus phaseolus, 1; Lampsilis ligamen-
tina, 5; L. luteola,6. The width taken was the total width of the bottom of the canal and was consider-
ably wider than the space occupied by the mussels.

About a mile farther down the canal a space of ro feet square was measured off in the bottom of the
canal, and the following species were found: Quadrula rubiginosa, 6; QO. undulata, 60, all rather small;
Pleurobema clava, 1; Alasmidonta truncata, 2; Symphynota complanata, 2; S. costata, 5; Anodonta grandis,
15; Obovaria circulus, 4; Lampsilis ligamentina, 5; L. luteola, 1; L. ventricosa, 4. This gave a little over
one shell per square foot. In 1908, in a square meter of bottom near the Rod and Gun Club, the follow-
ing species were noted: Quadrula rubiginosa, 9; Q. undulata, 36; Symphynota complanata, 1; Anodonta
grandis, 17; Obovaria circulus, 11; Lampsilis iris, 2; L. ligamentina, 2; L. luteola, 3, giving a total of 81
per square meter. In addition to these shells there were many small Spheriums, the ground being
paved with them, 34 Campelomas, and 23 Pleuroceras. The square meter referred to above repre-
sents, as nearly as could be judged, an average number rather than either extreme.

It would appear from a general comparison of the aspect of mussels in lakes, ponds,
and rivers that the effect of currents or circulation upon the growth of mussels is variable
according to the relative proportions of organic and mineral foods present. In rivers,
where the circulation of water is constant, mussels may grow to large size and possess
thick shells, but when circulation is reduced, as in inclosed bodies of water, the mussels
may be small and relatively thin-shelled, or they may attain a large size with thin shells
(suggesting relative deficiency of mineral food), or else, with heavier shells, they may “
dwarfed in size (suggesting a relative deficiency of organic food).

BOTTOM.

Most mussels are normally embedded in the bottom from one-half to three-quarters
of their bulk.¢ That they may thus establish themselves, a firm but not impenetrable
soil is required. The character of the bottom is, therefore, of especial significance to
fresh-water mussels, though it has important relations to all bottom-dwelling animals.
With regard to the bottom, consideration must be given both to its topography and
to the materials of which it is composed. Major inequalities in topography, such as
waterfalls and rapids, are discussed elsewhere. Minor inequalities are of importance
because of the effects upon currents, sedimentation, light conditions, growth of food,

@ The cases of deep embedding mentioned by Wilson and Danglade (1913), where they give a depth of x foot or more for living
mussels in Shell River (p. rs), and the report ofa fisherman of 2 to 3 feet at Lake Bemidji, seem to be cases of “digging in’’ because
ofdrought. Unio tetralasmus (Isely, 1914) and Quadrula plicata (Howard, 1914) seem to have a remarkable power of resistance
under these conditions.

102 BULLETIN OF THE BUREAU OF FISHERIES.

and protective conditions; stability of soil is important for the establishment of the
juveniles, for otherwise they will be overwhelmed. For some species objects for attach-
ment, to which the byssus of the juvenile may be fastened, may also be necessary.
Most of the varieties of bottom soil encountered are composed of one of the following
materials, or of mixtures of two or more of them: Silt, mud, marl, clay, sand, gravel,
pebbles, cobbles, bowlders, and ledge rock.

In rivers, sandy bottoms are regions of change comparable to sand-dune areas on
land where immobile forms are killed. Sand bottoms occur extensively in many rivers
and they may be veritable deserts. Rivers like the Missouri are devoid of mussels for
hundreds of miles partly because of a preponderance of bottom of shifting sand. Mussels
when found on sand bars in rivers are in transit seeking more stable conditions. Although
comprising regions of instability in rivers where decided currents prevail, bottoms of
sand may offer more favorable conditions in lakes where they furnish a permanent
habitat for mussels. ;

A greater variety of bottoms favorable for mussels, as well as a more indiscriminate
disposition of them, prevails in rivers than in the other bodies of water considered. In
many lakes there is a more definite sorting of materials, leading especially to a segregation
of the finest sediment in the deeper portions of the lake to form a bottom that is very
soft and generally unsuitable for the Unionide; mussels possessing much mass would
sink too deeply and have the gills too much clogged with silt to survive (Headlee and
Simonton, 1904, p. 176). Where such conditions prevail the mussels are found near
shore.

Headlee (1906, p. 315) summarizes observations and experiments in certain lakes
of Indiana in the following words:

The work of 1903 and 1904 shows conclusively that the mussels of Winona, Pike, and Center Lakes
can not exist on the fine black mud bottom—they become choked with mud and apparently smother—
and that the light-weight forms and the forms exposing great surface in proportion to weight can rest
on top of comparatively soft mud and can, therefore, live farthest out on the deep-water edge of the
bed. Because the mussels can not occupy any region where the pure black mud is present, they are
confined by it to isolated beds and narrow bands of shore line.

I believe that the whole evidence of the distributional and experimental work of 1903 and 1904
points clearly to the character of the bottom as the great basal influence in the distribution of mussels in
small lakes generally.

The species he dealt with were the fat mucket, Lampsiis luteola, Lampsilis sub-
rostrata, Quadrula rubiginosa, Anodonta grandis, and other small species with light shells.
While his conclusion accords generally with the observations of the writers in other
waters, the exclusion of mussels from mud bottoms can not be taken as an invariable
rule. In the Grand River, at Grand Rapids, Mich., for example, one of the authors has
observed such a heavy-shelled mussel as the three-ridge, Quadrula undulata, living in
considerable numbers along with the light floater (Anodonta) in very soft mud. Also,
in Mississippi Slough, in the Wisconsin lowlands along the Mississippi River opposite
Homer, Minn., the blue-point, Quadrula plicata, the pimple-back, Q. pustulosa, and the
pig-toe, QO. wndata, have been found in considerable numbers on a soft-mud bottom
along with the heel-splitters, Symphynota complanata and Lampsilis alata, and the
slopbucket, Anodonta corpulenta.

FRESH-WATER MUSSELS. 103

Baker (1918, p. 117) gives a summary of results of studies of mussels with reference
to bottom and depth in Oneida Lake, N. Y., in the following words:

The greatest number of individuals occurred on a clay or sandy-clay bottom. Twice as many
mussels occurred in water deeper than 6 feet than within the 6-foot contour. These features are
expressed in Table No. 27, the figures being averages per unit area of g square feet.

TABLE NO. 27.—AVERAGE NUMBER OF MUSSELS ON BOTTOM.

OM LAC AU COLA CIE DOLLO IM ertnerratbete a tarts settee eye ta a <carcleit ciepdei ere erevoicieivie: state ates sie aleie cea hes ns 6. 14
SPL a 5 hen be Aine BNA Bn She tase eee ee ee RL AY A Oe es SA a no 6. 39
Clavgandisan div, clays tiie separ ptoties eaciy sels cla ot Mie sen AMI TAL Rlaine Reis cee et CANT 13.00
ITEC Die ateo ee eS Con a EeL Coe EE OROe eee T ae to Ss treme rar tartan CRCT tS tn tc tee rr ra anes 10. 26
DW itthirtG-foGtiCOnto turns ect fer pae Nera e let canto clech ect a cfavecshe oft cctetdin lal sycieacop ia, sya aaiic cAI cs a haneephnc otaySiays 7-84
ESI EO TOOL COM COM tray tote aeteet or Pa raat age ico mice ease ao regeyn foe atte ange a= Shenstoaeiayse tala = cesta: ajar cyaiiears 16. 85

The above table shows that mussels are more abundant on the mud bottom in deep water (8 to 14
feet) than on sand, gravel, bowlder, or clay in shallow water (1 to 6 feet). These are the only studies of
this character known to me.

In that lake one species, Anodonta implicata, is reported from one kind of bottom
only, in sand between bowlders; while another species, Lampsilis luteola Lamarck, is
said to be common on all varieties of bottom, except gravel (Baker, 1918, pp. 161, 162).

Muttkowski (1918) found that sand bottoms marked the favored environments
of fresh-water mussels in Lake Mendota, Wis.

In Lake Pepin most of the adult mussels are found on a bottom of gravel or a
mixture of gravel and sand. Bottoms composed largely of mud but made firm by a
mixture of sand or gravel or both, yield a good supply of mussels; such areas are of
much less extent in the lake than bottoms of gravel or gravel and sand. Of 1,397
juvenile mussels comprising 16 species collected in Lake Pepin in 1914, practically 95 per
cent were taken on a sand bottom; about 4 per cent, principally Anodonta imbecillis,
were found on a mud bottom; and the remaining 1 per cent on gravel or a mixture of
sand, gravel, and mud (Shira, report in manuscript).

In ponds and sloughs there is less choice of bottoms than in lakes, and mud bot-
toms usually prevail; for such conditions Lampsilis parva, Lampsilis subrostrata, the
light-shelled Anodontas, and similar species are especially adapted.

When we consider the relation between various mussel species and the bottom in
rivers, we find the matter complicated by several considerations. This much, however,
may be said definitely: No mussels can sufvive in a shifting bottom, nor upon a bottom
of solid bare rock. Between the extremes, beginning with clean sand or soft miry silt
and ending with coarse gravel and bowlders or stiff clay, there is a great variety of
bottoms utilized to a greater or less extent as habitats for various species of mussels.

There are, of course, more or less definite relations between bottom and other
features. Soft, muddy bottom is always associated with a current that is feeble at
least near the bottom, or with the checking of the current; gravel bottom is usually
associated with swift current; and clean sand or gravel is associated with clear water.
Certain of the ‘“‘mud-loving”’ mussels, such as the Anodontas, may be really lovers of
quiet places and their association with mud rather an accident. Some of those supposed
to be partial to sandy or gravelly bottom may simply prefer clear to turbid water. or
may thrive best in a swift current.

104 BULLETIN OF THE BUREAU OF FISHERIES.

Several species, including most of the Anodontas, Symphynota complanata, Arcidens
conjragosus, and others, are confined chiefly to one sort of bottom. A great many,
however, seem indifferent to the character of the bottom, provided other conditions are
favorable. Mussels may also apparently thrive where one would naturally think condi-
tions unfavorable and where they might not survive if artificially planted. Thus in the
crescent-shaped bayous along the Kankakee Quadrula undulata, and in sloughs of the
Mississippi a closely related mussel, both heavy-shelled species, are found thriving on the
top of deep, soft, silty mud which would not seem stiff enough to bear their weight.

In the Grand River, Mich., various species of mussels were found upon ‘“‘clean”’
sand bottoms, but always sparsely. Quadrula undulata and Lampsilis ellipsiformis and
ventricosa seemed best adapted to life in accumulations of drift. In sewage and waste-
polluted waters at Lansing, Mich., Lampsilis ligamentina, ventricosa, and ellipsiformis,
Quadrula coccinea, Symphynota costata, and Alasmidonta marginata were found in appar-
ently healthy condition. The Lampsilis ellipsiformis obtained there, of especially large
size, bore innumerable (but worthless) small pearls. (Coker, unpublished notes.)

In the Mississippi River near Fairport, Iowa, bottoms of unmixed mud and pure
sand were found to be much less occupied by many of the species than mixtures of gravel
and sand or of sand and mud, which supported both a far greater number of individuals
and a somewhat greater variety of species. The preference for certain bottoms is most
conspicuous when the proportion of the total catch of mussels found on the favored
bottoms is viewed in connection with the proportions of these bottoms in the total area
surveyed. Table 5 shows the total number of mussels taken from the different types of
bottom in a survey of Andalusia Chute, Mississippi River (Howard, report in preparation) :

TABLE 5.—MUSSELS COLLECTED IN SURVEY OF ANDALUSIA CHUTE, WITH REFERENCE TO CHARACTER

OF Bottom.

Approxi-

mate per-
nA Number of | Number of

Composition of bottom. centage et Sritiaetal Secrest!

of bottom.
IMA GI A aha cterressiacaattre Carrel cUe O's eevee alae ate ets infaleltie eiteliee ainels Casts ME ale & cep ata ele eins watage tere totes a) 44 17
Mud and sand....... RU AbSE Ec sIas HOO QIOSEED Sanna has Taecgcn prc tiadons 4 158 20
Mud and ledge rock x 17 7
Sand -octiniest’ . nt 71 87 23
Sand and gravel. . 2G 9 289 28
Sandjand nebblest cece seers 5 Late ee ter h aanilee Senile weet cetcle: deinen iets eset thatatl amet etdesete % 29 12
Gravel (pttre)scsce nese. 5 con eeuioasebeneneees ate Jefe chet bebe Seer 2 5 3
Gravel, cobbles, and rock..................- 3 AOR OAS OBSDE Tac cid oj oode sem: non Adc 2 34 14
Gravelianidtentid ces o-ecetriersie cele sielslctetsta ei= RE SESEASSerCreRetet cHeEBAcAdaaac 1 P| Gor ocosnnceed beoscdsoohos
Pep ples ws pee he «tee nae w ceaw ne ee etaicfe eetie tote Nate Meals cas vieteinisteclaicttctats\aielstalteaan s/dtietatats Gee SAs aR eod Bene taciids
RC ic orc nace tele ale ves tetOertatatocierctalefeletctayetempectele sitincte nevis sine we eitstere mentale Ciel ais aeennione sie i am Doc GET Gee cits Reb so008

The niggerhead mussel, Quadrula ebenus, in some streams, at least, is said to show a
decided preference for firm bottoms, as of gravel or blue clay, but few observations have
yet been made upon these mussels in streams having considerable areas of clay bottom.
In the Grand River, Mich., the pink heel-splitter, Lampsilis alata, was found living in a
ledge of very tough slippery blue clay (Coker, unpublished notes). So firm was the clay
that a mussel could be extricated from it only by the exertion of considerable muscular
effort. Several other species of mussel were in the vicinity, but none were embedded in

FRESH-WATER MUSSELS. 105

the clay except one example of the three-ridge, Quadrula undulata, and that was in a
spot where the clay was mixed with mud and was distinctly softer. Some spikes, Unio
gibbosus, were found lying on the blue clay but not embedded; it seemed evident that
they were unable to penetrate so tough a bottom.

The character of the soil has an effect upon the amount of materials carried in
suspension in the water. If the amount is too great, as over soft mud or over extremely
fine sand, under some conditions the mussel becomes smothered, or having no chance
to feed, is starved. Too much decomposing organic matter in the soil is said to cause
enough acidity to attack and erode the shell. For several reasons, therefore, areas of
rapid silt deposition, or soft-mud bottoms, are quite unfavorable to mussels. Mussels
are usually found in rivers in places where the bottom is swept clean by the current,
even though in flood time the water may be heavily laden with silt in suspension.

The selection by some species of bottoms of gravel, pebbles, and bowlders as most
favored habitats can readily be understood from the foregoing remarks; but there are
still other favorable features of rough bottoms. The very stability of the larger-sized
materials protects the bottom from washing, and may save the mussels from being
smothered or carried away. It is of advantage to mussels to be surrounded by numerous
other animals, especially by the smaller ones, which furnish attraction to fishes and thus
promote the reproduction of the mussel. Many of these small animals live attached to
stones, thus giving added value to gravelly and rocky bottom. In gravels, too, the
youngest mussels may be protected through inaccessibility to enemies, and as they
grow older the resemblance to small pieces of stone among which they lie may be the
cause of escape from enemies. As previously indicated (p. 97), where bowlder rock or
cobblestone bottoms occur in regions of rapids, mussels are commonly found abundantly
and occur over the entire river.

The following table (6) embodies the experience of several observers regarding the
preferences exhibited by 62 common species of fresh-water mussels for bottoms of differ-
ent characters. In view of the intergradation of the several types of bottom and the
almost unlimited variety of mixtures of sand, gravel, mud, and clay, the classification of
the bottoms for the purpose of a table must of necessity be rough, and the characterization
of mixed bottoms may in some cases be affected by the personal equation of the observer.
Young mussels may have bottom requirements somewhat different from those of adults.

EXPLANATION OF TABLE 6.

The letters refer to the experience of the several observers (including the present authors and three
previous writers), as follows: A, Baker (1898); B, Call (1900); C, Clark; D, Howard; E, Scammon (1906);
F, Shira; G, Coker.

The use of large capitals indicates that, according to the observer whose letter is in large capitals,
a certain type of bottom is preferred by the particular species of mussel. Wherever a small capital is
used, the observer corresponding to the letter has indicated the type of bottom as favorable for the
particular species of mussel, but not necessarily preferred to other favorable bottom.

The observations of Shira refer largely to lake conditions (Lake Pepin, Lake Pokegama, and Caddo
Lake).

The observations of Coker refer primarily to shallow rivers (Grand River, Mich.).

The habitats indicated by Howard are based chiefly on the observed preferences of juvenile mussels
in rivers, streams, ponds, and slues to the exclusion of true lakes.

106 BULLETIN OF THE BUREAU OF FISHERIES.
TABLE 6.—HABITATS OF CERTAIN FRESH-WATER MUSSELS, CLASSIFIED ACCORDING TO CHARACTER
oF Bottom.
= = Z = je s
5 FI = Slee aid
é «| 3 | 2 \58 BE
wn bs] 2 wB
Scientific name. Common name. E oy E Z 2 Siz
: a 2] £ = a -|@
f 3 s 2 4 a jo lofl 3g gs] 5] s
g e 2 = |/alsa 3 e| 2/8
a a 16) a a | 2 |a a A}O/O
x. Alasmidonta calceola. ....| Slipper-shell A Cc
2. Alasmidonta marginata...| Elk-toe
3. Anodonta corpulenta..... Slop-bucket
4. Anodonta grandis. .......| Floater
5. Anodonta imbecillis. ..... Paper-shell E aes
6. Anodonta suborbiculata. .|..... (fe ere neanh sd) posptasee hecarecd Der oD
7. Anodontoides ferussacia- |.............-++.+5+
nus.
8. Arcidens confragosus..... Rock pocketbook.
9. Cyprogenia irrorata Fan-shell..........
ro. Dromus dromas. . Dromedary mussel]
11. Hemilastena ambigua....|.......-...--..-.---
12. Lampsilis alata........ heel-splitter.
13. Lampsilis anodontoides..} Yellow sand-shell.
14. Lampsilis capax.......... Pocketbook......-
1s. Lampsilis ellipsiformis....]...........-.-+.-+5-
16. Lampsilis fallaciosa......| Slough sand-shell.
17. Lampsilis glans. -...---.-|....-2-----<------=-* Re atc ne oe oe
18. Lampsilis gracilis. . ..-] Paper-shell.......- ABDEF}| C ]....) G
19. Lampsilis higginsii. ......] Higgin’seye...... Cuts;
20. Lampsilis iris........-..-- Rainbow-shell.. ..
21. Lampsilis levissima...... Paper-shell.......-.
22. Lampsilis ligamentina....}| Mucket..........-
23. Lampsilis ligamentina| Southern mucket..
gibba.
24. Lampsilis luteola......... Fat mucket.......
25. Lampsilis multiradiata...]............-.2+++5+
26. Lampsilis parva... ..0.+--|o...sesns eee e nee eee
27. Lampsilis purpurata...... BPurply.ccncste ae
28. Lampsilis recta..........- Black sand-shell. .
29. Lampsilis subrostrata....]........--.+0--0e +5
30. Lampsilis ventricosa...... Pockethook......-.
31. Margaritana monodonta..| Spectacle-case.....
32. Obliquaria reflexa........ Three-horned
warty-back.
33. Obovaria ellipsis..... -| Hickory-nut. .
34. Plagiola donaciformis.....]..........-.
3s. Plagiola elegams..........| Deer-toe
36. Plagiola securis........... Butterfly
37. Pleurobema zsopus....... Bullhead..........
38. Ptychobranchus phaseo- | Kidney-shell......
lus.
39. Quadrula coccinea........ Flat niggerhead...
4o. Quadrula cylindraca...... Rabbit’s foot......}........
41. Quadrula ebenus......... Niggerhead.......|........
42. Quadrula granifera.......| Purple warty-back
43. Quadrula heros. .......... Washboard.......}........
44. Quadrula lachrymosa....-. Mapleleaf..... be
4s. Quadrula metanevra..... Monkey-face
46. Quadrula obliqua......... Ohio River pig-toe
47. Quadrula plicata......... Blue-point........
48. Quadrula pustulata....... Pimple-back......
49. Quadrula pustulosa.......}..... GOs ncaesaceres
50. Quadrula rubiginosa......|........2.2..-20000s
st. Quadrula trapezoides..... Bank-climber.....
52. Quadrula tuberculata..... Purple warty-back| "0G OM Siceenca VEC) ilecen cee }centeires|eicieme
53. Quadrulata undata....... Pig-toe. 5. .(--
54. Quadrula undulata.......| Three-ridge .
55. Strophitus edentulus.. ...| Squaw-foot. .
56. Symphynota complanata.| White heel-s
57. Symiphynota compressa. .|]...........-.-
58. Symphynota costata...... Fluted shell.
59. Tritogonia tuberculata...} Buckhorn.....
60, Truncilla sulcata......... Cat’s paw.......
6x. Unio crassidens........... Elephant’s ear
62. Unio gibbosus............ Lady-finger.......

are adapted) and gravel, including sand and gravel.

It appears from this and the following table that the preferred bottom for the
majority of species is mud (but not deep, soft mud, to which type of bottom few species
Sand ranks next and clay last;
but few species of mussels exhibit a preference for sand or sandy clay, and only two are

FRESH-WATER MUSSELS. 107

recorded (by one observer) as finding the most favorable environment in a bottom of
clay unmixed with sand.

Table 6 may be simplified by reducing the types of bottom to four general classes,
sand, gravel, mud, and clay, and by eliminating all but the leading commercial species.
The results are indicated in Table 7 following:

TABLE 7.—PREFERRED HapiTats OF LEADING ECONOMIC FRESH-WATER MUSSELS, ACCORDING TO
CHARACTER OF BOTTOM.

[X indicates preference as noted by majority and x by minority of observers.]

Scientific name. Common name. Sand.¢} Gravel.b | Mud.¢ | Clay.4
Lampsilis anodontoides soley ellow, sand shells Poe scietejsnce aol scl aaysmaemtanvicscastt. (asad l|Pemesaes
Lampsilis fallaciosa . Rl ESIOUP HI SANG Snel it itsstsmeies cenle nines | sce menl meer lee Onell emt mine
Lampsilis recta. ... . .| Black sand-shell. x
Lampsilis ligamentina.... ea oekeGe yet anc a x
Lampsilis ligamentina gibba................0.0s000- Southern mucket.......... Sen CSCC [leit Salted Cc eA mane 4
Lampsilis luteola............. Rhine lem steteincncs ects (Rat winckets. crores asneab. Bele DKS lt dawcekte loka! J) Kececeee
Lampsilis ventricosa........ SEES a: GUE aee, Pockethooke 3: 222 ser: eae oe aki ee, lh eee SPT ERED PS occss ce
Obovaria ellipsis... CHS, My Ree cela siete Hickory-nut. 5520.00.20 Hee) (ee. Cae] | ster <0 al asemicee Saceaaes
Plagiola securis.... sas; Ebb ccaeule = tele Butterfly....... aisa0 Rats] cae adess o Spe Rea apace on mes
Quadrula coccinea. aoae Bpesp poneadeetce Flat niggerhead . cee Ope x
Quadrula ebenus... E SHS rogoagant dor foes Niggerhead..... Boke Pee recent ee, Gael Ie ee a Pcs 44
Quadrula heros.... ...| Washboard AE x
Quadrula lachrym .| Maple-leaf..... a

Quadrula metanevr: .| Monkey-face
i -| Ohio River pi

Quadrula plicata .| Blue-point......
Quadrula pustulosa ...| Pimple-back.... oo) Serie eee, le RS SSE Eee
Quadrula rubiginosa,....... nosopbepcoodeos| Keane cnocd ae Eapodnaas5aceneS soon x
Quadrula undata........... a icbete neice cnet Ponte nr tec iceacececetos nee Sb ox ALE Ge eee
Quadrula undulata......... eretanteaeer alae (Rhreestid ve wa cen. cdana ce Bier Vegas ictans ice | on Oe |p eee a lecesee cele
UMtIO CEASSICLETISS oy Se aateh ates daleis slaini eh oe siaieaae cnet Elephant’s ear,............ Pedder eeo sacl ecoéeectcan| (2S) 0 Reaendca
LENG} PAD DOSTIS sees aiet cto iatats.cuciele terete ys bie) sions eicte ein clap epae ILA SLRs tHe an SEB Or Ese ob tte opal nos aictic) ko ese mn Ne San Bescnaeeetore
@ Sand alone. © Mud alone.
> Including sand and gravel, mud and gravel, and rocks. 4 Including sand and clay, mud and clay.
DEPTH.

The distribution of many animais of the water is known to be influenced by depth,
the effect of which may be felt, among other ways, through pressure, light, temperature,
dissolved gases, and freedom from wave action, or exposure thereto. In an indirect way,
too, the effect of depth is experienced by any animal through the influence of these
conditions upon food and enemies.

The increase of pressure is approximately 1 atmosphere for each 10 meters (33
feet) in depth, but fresh-water mussels are, so far as known, restricted to shallow waters
where pressures must be insignificant. The Spheriids are the only mollusks found
below the 25-meter line in Lake Michigan (Shelford, 1913). Maury (1916, p. 32), (see
Baker, 1918, p. 155), reporting the results of dredging in Cayuga Lake, N. Y., says:
“These dredgings proved conclusively that Mollusca after 25 feet become very scarce.
* * * Jn the greater depths no signs of Mollusca or of plants were found.” In
clear water minor depths do not markedly affect the light, but if the water is turbid, a
common condition in the environment of fresh-water mussels, the penetration of light
is very much diminished (see p. 114), and mussels if affected by light may, therefore,
be expected to live at greater depths in clear lakes than in turbid streams. Temperature
changes due to depth alone are so inconsiderable for shallow water as doubtless to have
little effect upon the distribution of mussels, except where freezing to the bottom may
occur.

108 BULLETIN OF THE BUREAU OF FISHERIES.

The depth of water below which waves would reach them is apparently a factor in
determining the habitat of many species of mussels in lakes (Headlee, 1906, p. 308—
Winona Lake; Muttkowski, 1918—Lake Mendota). In large bodies of water like Lake
Michigan the action of the waves is said to extend to 8 meters below the surface. The
zone of wave action is a region in lakes comparable to the rapids and riffles of streams,
where there is maximum circulation and aeration and a solid bottom suitable for
such mussels as can withstand the violent action of waves and undertow currents.
The species occupying this zone are given by Headlee for Winona Lake as the spike,
Unio gibbosus, and the fat mucket, L. luteola. Baker (1916) says of this habitat in
Oneida Lake:

The shore may be free from vegetation. It receives the full force of the winds and waves from the
open lake. The water is from 1 to 3 feet in depth and the bottom is heavily and thickly covered with
stones and bowlders, many of the latter being of large size. Animal life is abundant, the clams living
between the stones and on the sand between the stones.

The mussels he reported are as follows: Elliptio complanatus, common; Lampsutis
luteola, rare; Lampsilis radiata, common; Lampsilis iris, rare; Margaritana margar-
tifera, rare; Anodonta cataracta, common; Anodonta implicata, common; Anodonta
grandis, common; Strophitus edentulus, rare. Some of these are very thin shelled and
doubtless survive the force of the waves only through the protection afforded by the
large rocks. No doubt the thorough aeration of the water, resulting from wave action,
is a favorable factor in this zone

On the shores of Lake Pepin one of the authors has often picked up live mussels
that had been thrown up by heavy wave action. The mussels thus most frequently
encountered were Unio gibbosus, Lampsilis alata, Anodonta corpulenta, Strophitus eden-
tulus, Lampsilis ventricosa, and Lampsilis luteola in about the order named. They were
usually immature examples. Occasionally after a storm had subsided one could see
mussels that had not been entirely stranded on the beach near shore and in the act of
making their way back again into deeper water. Headlee and Simonton (1904, p. 175)
recorded similar observations.

While the data available are sufficient only to suggest how depth may affect the
hapitat selection of mussels, it is of interest to note some of the observations on this
relation. A maximum depth of 22 feet for mussels in Winona Lake is given by Headlee
(1906), who ascribes the control of distribution to bottom characters chiefly. Baker
(1918) found thatin Oneida Lake twice as many mussels occurred in water deeper than
6 feet as within the 6-foot contour. (See quotation, p. 103, above.) He records three
species as limited to a depth of 1% to 8 feet, three as living at varying depths between
1% and 18 feet, and one subspecies as occurring only between 8 and 18 feet, the greatest
depth which he explored. He reports an interesting case of bathymetric distribution of
two races, Lampsilis radiata, occurring at 114 to 3 feet, and a subspecies, Lampsilis radiata
oneidensis, living only at 8 to 18 feet, the two forms showing a distinct difference in
habitat. For Lake Mendota the optimum depth for mussels of the genera Anodonta
and Lampsilis is given as from 2 to 3 meters (6 to 10 feet) (Muttkowski, 1918, p. 477);
they were, however, found abundantly between 3 and 5 meters and rarely at greater
depths than 7 meters (23 feet).

Wilson and Danglade (1914), in reporting a reconnoissance of mussel resources in
Minnesota waters, give depths of the lakes, but without detailed data on the distribution

FRESH-WATER MUSSELS. 109

of the mussels. In Lake Maxinkuckee, Evermann and Clark (1918, p. 255) say: ‘‘Mussels
are to be found almost anywhere in water 2 to 5 or 6 feet deep where the bottom is
more or less sandy or marly.’’ Headlee (1906, p. 306) found that the mussel zone
generally extended from the shore line to where the bottom changes from sand, gravel,
or marl to very soft mud, a region in Winona Lake covered by from 4 inches to 9 feet
of water. He did find, however, some mussels on sandy, bottom in 22 feet of water.
He made some experiments in retaining mussels at various depths and in a crate placed
in 85 feet of water; only 1 of 10 specimens died in six days of exposure. After 12 days
several specimens were found badly choked with mud.

In Lake Pepin mussels are plentifully found at depths ranging from 8 to 20 feet,
but the majority are taken at depths ranging from 12 to 18 feet. Relative to the juvenile
mussels, out of a total of 1,397 collected in 1914, 1,283, or 91.8 per cent, were taken ata
depth of 3 to 8 feet; 2.6 per cent at 8 to 12 feet; 2.3 per cent at 12 to 16 feet; 0.4 per
cent at 16 to 20feet; and 2.9 per cent at 20 to 25 feet. A. mbecillvs was the only juvenile
found in any abundance at a depth greater than 15 feet, and 41 of the 79 individuals of
this species collected were taken at 25 feet (Shira, report in manuscript).

A marked distribution with regard to depth has been observed in the artificial
ponds at Fairport, Iowa. Here the species, Lampsilis luteola, is seldom found below a
depth of 3 feet. When held in crates below this depth it does not thrive, although in its
natural habitat, Lake Pepin, this species is abundant at a depth of 8 to 20 feet and has
been taken at a depth of 25 feet.

In rivers and smaller streams mussels seem to be found commonly at lesser depths
than in lakes, but unfortunately we have very few reports of observations in the deeper
parts of large rivers. In the Illinois River, Danglade (1914) mentions a small bed 2 to 3
acres in extent above the mouth of Spoon River, where the bottom was of mud, the
current about 2 miles per hour, and the depth of water 8 feet. At Chillicothe he found
a good bed at a depth of 12 tor5feet. The survey of Andalusia Chute, Mississippi River
(Howard, report in preparation), carried on during relatively high-water stages in 1915,
revealed no mussels in the deeper portion of the river over 12 feet in depth, and the
greater number of mussels were found at depths less than ro feet. Local informants at
Madison, Ark., stated that the niggerhead, Quadrula ebenus, was found in water 20 to 50
feet deep; it was also said that in flood season it was captured from a depth of 75 feet.
There has been no opportunity, however, to verify these statements.

With regard to a collection of 183 juveniles of the Quadrula group from 12 stations
in the Mississippi River, Howard (1914, p. 34) reported depths from o to 8 feet. Wilson
and Clark (1914) reported a rich find (19 species) in the Rock Castle River off the Cum-
berland, in water having a maximum depth of 1% feet. In the Grand River, Mich.,
the senior author has found mussels (muckets, Lampsilis ligamentina, three-ridge,
Quadrula undulata, and others) in conspicuous abundance in swift water less than a foot
in depth. Boepple (Boepple and Coker, 1912) found mussels abundant and of fine
commercial quality in water from 1 to 3 feet in depth in the Holston and Clinch Rivers
of Tennessee. In Caddo Lake, Tex., Shira (1913) found an abundance of mussels in
4 to 8 inches of water, and in many places there was scarcely enough water to cover the
shells. This lake was very shallow over large areas. In fact, mussels are frequently

_found in very shallow water where the conditions of the bed of the stream and other
75412°—22——8

IIo BULLETIN OF THE BUREAU OF FISHERIES.

factors are favorable. In various parts of the country considerable commercial quan-
tities of mussels are collected by hand from shallow waters. At one such place, Lyons,
Mich., the mucket, Lampsilis ligamentina comprised 80 per cent of the collection, although
the three-ridge, Quadrula undulata, the pocketbook, Lampsilis ventricosa, the spike,
Unio gibbosus, and the black sand-shell, Lampsilis recta, were quite common. Among
other species that were frequently found in very shallow water (1 to 2 feet in depth) in
that stream were the following: Lampsilis luteola, wis, and ellipstformis, Quadrula
coccinea and rubiginosa, Strophitus edentulus, Symphynota compressa and costata, Alasmt-
donta marginata, Anodontoides ferussacianus, and Anodonta grandis. In fact, the only
species that were not found in water less than 6 feet in depth in the Grand River were
the three-horned warty-back, Obliquaria reflexa, the hickory-nut, Obovaria ellipsis, the
deer-toe, Plagiola elegans, and the white heel-splitter, Symphynota complanata.

LIGHT.

The small floater, Anodonta imbecillis Say, in sunlight will draw in its siphons when
ashadow passes over. Wenrick (1916) has demonstrated experimentally with measured
{llumination, that a fresh-water mussel, Anodonta cataracta Say, is ‘very sensitive to
decrease in intensity of light. Observations in the Washington laboratory indicate that
the yellow sand-shell, Lampsilis anodontoides, will close when a black cloth is placed
over the aquarium, but will open when exposed either to daylight or to the light of a
bright electriclamp. These reactions may be for protection of the animal from approach-
ing enemies, but it is probable also that the distribution of mussels is largely influenced
by light conditions. Mussels are seldom found in vegetation which is dense enough to
exclude the light to a great extent. This is especially true with regard to plants like the
water lily which have floating leaves. Some relations to vegetation are brought out
in a study of the habitats in Oneida Lake (Baker, 1916).

An exceptional case is reported by Wilson and Danglade (1914, p. 15) where the
mussels were found in densest aggregation submerged deeply in the bottom and below
a covering of vegetation. Their account is of sufficient interest to be quoted in full:

The bottom of the river where these shells are obtained is covered with alge and water weeds to the
depth of 12 to 18 inches, and the thicker the vegetation the more plentiful the mussels beneath it. Two
men were actively working the Shell River at Twin Lakes near Menahga at the time of our visit, and we
watched them rake off the alge and weeds and then dig into the underlying gravel and sand for the
mussels. The latter are often buried to the depth of a foot or more. This is, at the least, a novel con-
dition and one which, so far as is known, has not been reported from any other locality.

Certain species of mussels, the mucket, pocketbook, black sand-shell, and others
are sometimes pink-nacred and sometimes white-nacred, and with the two former, at
least, the outside covering of the shell has a reddish cast in pink-nacred examples.
With such species it is a matter of common observation that pink-nacred shells and
brightly colored exteriors are more frequently found in shallow clear water where the
mussels are exposed to bright light. Thus the black sand-shells of the upper part of the
Grand River, Mich., have a deep purple nacre, while white shells of the same species
predominate in the more turbid Mississippi. The spike, Unio gibbosus, is usually purple-
nacred, but uncommon examples that are nearly white are found in turbid rivers. Clark

@ Grier (1920a) presents the result of an extensive study of the nacreous color of mussels. He notes a tendency to lighter or
bluish nacreous color in the lower portion of stream courses. He has evidence of some correlation between color and sex.

FRESH-WATER MUSSELS. IIl

and Wilson (1912) describe the Maumee River as rather muddy most of the time, and it
is interesting to find that they report that two-thirds of the spikes, Unio gibbosus, in that
river were white-nacred and that the black sand-shells were usually white-nacred.

The reputed migration of certain mussels toward shore in time of flood may be an
accommodation to light conditions associated with turbidity of water under such con-
ditions. We have virtually no data on the distribution of mussels with respect to
permanently shaded areas or with regard to the reactions to daily changes in light.

CURRENT.

The luxuriant development of certain mussels in streams where the current is
strong, in contrast with their growth in sluggish portions of rivers and lakes, bears
witness to the significance of current as a favorable factor of environment for fresh-
water mussels. Current is a characteristic feature of streams, and the rate of flow is
largely determined by the gradient of the channel. Currents producing a circulation
of water occur also in lakes, where they are caused chiefly by wind and to a less extent
by changes of temperature. In some lakes the circulation extends from top to bottom,
but in small deep lakes only a partial surface circulation commonly prevails (Birge and
Juday, 1911). Undertow currents are also developed where there is wave action, and
under some conditions convection currents must exist in natural bodies of water, but
we have little data on this.

Shelford (1913) emphasizes the relation of water animals to current as follows:

The distribution of dissolved salts and gases is dependent upon the circulation of the water, as
their diffusion is too slow to keep them evenly distributed. The water of streams has been found to
be supersaturated with oxygen [citing Birge and Juday, 1911]. Oxygen is taken up by water near the
surface. Nitrogen and carbon dioxide are produced especially near the bottom, and if the water did
not circulate they would be too abundant in some places and deficient in others for animals to live

BLOG) neesunn ie
2 nie current in streams differs from that in lakes in that it.is for the most part in one direction
while the lake currents often alternate. There are backward flows and eddies at various points in
streams in front of and behind every object encountered in the current. As we pass across a stream
we find the current swiftest near the surface in the middle and least swift at the bottom near the sides

MOD) AS goin
. ae factors of greatest importance in governing the distribution of animals in streams are current
and kind of bottom. They influence carbon dioxide, light, oxygen content, vegetation, etc. (p. 66).

Since mussels are bottom dwellers and largely stationary in habit, one can appreciate
how dependent they must be upon circulation of the water to bring renewed supplies
of organic food, mineral matter in solution, and oxygen, and to remove the poisonous
products of metabolism that are produced in their own bodies and in those of other
organisms living about. Mussels, of course, cause by their respirative currents cir-
culation of the water immediately about them, but this is not sufficient to prevent
an early exhaustion of food supply unless broader currents prevail.

It must be emphasized, too, that flowing water carries more matter in suspension
than still water. It has been seen (p. 91) that the food of mussels consists to a con-
siderable extent of the finely divided solid matter; but such materials, however abun-
dant on the bottom, are not available to the mussel until they are taken up in the water
and carried to the mussel. The effects of the current, then, both in lifting solid matter
from the bottom and in holding it in suspension play a foremost part in its relation

112 BULLETIN OF THE BUREAU OF FISHERIES.

to the welfare of mussels. The power of water to move solid matter on the bottom
increases very rapidly with the rate of flow.

The capacity of water to move solid matter from a condition of rest on the bottom of a stream
varies with the sixth power of the velocity of the stream. If the velocity is doubled, the increase
in the force which is capable of putting the particle in motion is multiplied 64 times. (New York
report of Metropolitan Sewerage Commission, 1912, p. 41.)

Fish frequent areas near the current but maintain themselves in eddies or in places
where the current is relatively slack, as at the bottom and near the shores (Shelford, 1913).
In view of the essential part that fish play in the distribution of mussels, the habits
of the fish may be a very significant factor in the distribution of mussels with reference
to current. It has been suggested by Evermann and Clark (1918, p. 252) that currents
may promote the reproduction of mussels by making fertilization of the egg more
certain and by decreasing the chance for inbreeding through the conveyance of sperm
from mussels farther upstream. In still waters the chance for fertilization of eggs
may be less favorable.

The relations of mussels to temperature have not been fully investigated, but it
seems certain that flowing water must protect mussels from excessively high tempera-
tures and thus permit many species to live in much shallower water in streams than
in ponds or lakes.

The tendency of mussels to locate apart from the main channel and nearer the
banks of the streams has previously been mentioned (p. 97). While this distribution
may be partly due to the fact that there the full force of the current is avoided while
many of its benefits are received, nevertheless it must not be overlooked that many
species of mussels thrive in rapid shallow streams and that such regions of swift water
in the Mississippi River, as the former “rapids” at Keokuk or the existing “rapids”
above Davenport, have been among the most prolific mussel grounds of the entire river.
In these circumstances, however, the rocky nature of the bottom affords the mussels
protection against some effects of the current. Evidently the barrenness of the main
channel in most cases is due rather to the nature of the bottom combined with the force
of flow than to the strength of current alone.

On page 99 there have been listed the species of mussels which are characteristic
of lakes and ponds, regions of comparatively still water. The more common mussels
of rivers may be classified according to apparent adaptation to sluggish water, strong
current, and rapids (Table 8). These general comments should be made: In a firm
bottom, such as furnishes good anchorage, a mussel may dwell in a current swifter
than is characteristic of its common habitats; where rocks furnish shelter, mussels
below them may be in rather slow water despite the current around them; deep water
may be fairly sluggish under a swift surface current.

EXPLANATION OF TABLE 8.

The symbols are those used in Table 6, C representing Clark; D, Howard; F, Shira; and G, Coker.
The large capital denotes preference in the opinion of the observer, for a particular condition of current.
The small capital denotes that the condition is favorable but not, so far as is known, preferred to other
conditions. When no large capital occurs on a line, no preference is indicated; and when a particular
letter appears in small capital throughout a line, the observer denoted by the letter has no evidence
upon which to base an opinion of discrimination on the part of the particular mussel between the
different conditions of current regarded as favorable.

FRESH-WATER MUSSELS. 113

TABLE 8.—CLASSIFICATION OF COMMON FRESH-WATER MUSSELS IN RELATION TO CURRENT.

. . Strong or
Scientific name. Common name. Little or rio F Hix of goed one ae

x. Alasmidonta calceola.... Slipper-shell

2. Alasmidonta marginata. . Elk-toe.....

3. Anodonta corpulenta.... Slop-bucket.

4. Anodonta grandis..............- ..| Floater......

5. Anodonta imbecillis............... .| Paper-shell..

6. Anodonta suborbiculata..........-..+0-+. {e000 dost:

PmASIOR OME DIGES ft CLUSSACIASINIS pe falarclelote ral aiai| Pinte cfetetarstctetsiatn’cieeinmi= a) piererehoreschereietala)sintalele'«

8. Arcidens confragosus............. ..| Rock pocketbook

9. Cyprogenia irrorata.... rie Pete SELIM Suet ete carehicietate cinvokesche tote tater

to, Dromus dromas...,......-.-+++- ..| Dromedary mussel

1x. Hemilastenia ambigua........... Pel nicte ten hick «saWhisielelerale = aitelsfewidieivcreisiseeine

Xa) gbanipsilisialatas. sence «astiseais ..| Pink heel-splitter

13. Lampsilis anodontoides.......... ..| Yellow sand-shell

14. Lampsilis capax.........-..++.+5 Fen | RSAC S DOCKEE DOO Mitts eters slate ielsysintetetaicievsicteioiaie
15. Lampsilis ellipsiformis........... 3d] bd ote seen be eDe dcdaad bone Aaenbsosade
16. Lampsilis fallaciosa.............. Slough sand-shell
Ti Lanipsilis glans: \.-js sm nen ee bullase on cacao Re AC AACO CUR DOSmOcCcaAnbagecuris (s
18. Lampsilis gracilis...............+ ..| Paper-shell,
19. Lampsilis higginsii....--....... SMEARS piste eV ee cisnye acca tectelats nce nietetetere)|pidttctettne stetctcters
Ow Pest SIIS ATISS © cles) sasislsispnie/aie = Biiairhow-shellite § sees voces cena caetes a efeie
a1. Lampsilis levissima............. TA Paper-shellGees Pe eyras ee ae cece ceelactee

22. Lampsilis ligamentina......... Balpivtitclcetios cin. i-isicleclnese cistoctantvieicrelcrevareierad

23. Lampsilis ligamentina gibba... Southern mucket

24. Lampsilis luteola.............. Tilers h a naa enae Beer abe ene ODOR OUUEE
25. Lampsilis multiradiata........
26. Lampsilis parva.............+-
27. Lampsilis purpurata,..........
28. ball psiis recta str mie sieleiea ish
29. Lampsilis subrostrata.
30. Lampsilis ventricosa.
31. Margaritana monodont:
32. Obliquaria reflexa.....
33. Obovaria ellipsis’ .

Pocketbook.

Spectacle-case..
Three-horned warty-back
Hickory-nut

Peer A pio lt LOT CHORITLIS Sele cise ect teteisic isle sietzinitial| ante eicieicints

35. Plagiola elegams...... ..| Deer-toe. .

30. Plapiola Sectris sy cspies aaensie UIRBULLeEH O earn emus ser ciate ates

37. Pleurobema esopus........... Bulihead.....

38. Ptychobranchus phaseolus... . te psd ey=ShellE ae crcinisiniclsier<icisia > sian wisi ele

39. Quadrula coccinea,.......... ».|| Platimiggerhead=). 20.3282. ae.

qo. Quadrula cylindrica......... ..| Rabbit’s-foot.....

4t. Quadrula ebenus............ a2 PNipeerhead| Parts ik. seniehinteteren. .scee

42. Quadrula granifera. . =| burpleswarty-back.. cr caecrep scues cian

43. Quadrula heros.............. eeiiWashboarG! serbe tase ot fe ceak cea.

44. Quadrula lachrymosa.... ..| Maple-leaf....

45. Quadrula metanevra.... PleMoukey-ldcess: Ga catere nee teecet ses cldat

46. Quadrula obliqua........ ie | LOHIOsRay en) pig-tOe sitar alone cee clas is ae el eeeiora cle

47. Quadrula plicata.......... PTB ie potntein, ceiset, onthe Sete teeta ate

48. Quadrula pustulata,....... sol) iene Sova’ Wesag hc oconecmosnaee 4

49. Quadrula pustulosa........ Beira ees ais GIONS on on OHORAE Doc Suraaris

so. Quadrula rubiginosa....... Bas eA eae on oats GERD ae TRE ae

51. Quadrula trapezoides...... fan Ppaticcolimber/ i scetd ieee sae

52. Quadrula tuberculata.... . nose) Ptirple warty-back. .6.5.5 ccm wcces

53. Quadrula undata.......... bee GEIR=EGELA TOR ise teen clad sant cakke

54. Quadrula undulata........ Raia Me neee TI Pe eerie niidal ace iiieeicle

55. Strophitus edentulus...... Bebe | POGtawlOObres te emsamcimm cnccnisicies A Si
56. Symphynota complanata, . .| White heel-splitter............... we EDD cteresahs) sists | sieteretaretelsteieie
57. Symphynota compressa. ... Srictt | Gn CE RORCE JOA SoC DEC Oca asEU tno dat are
58. Symphynota costata...... sae [ROUTE SINGLE occie ntuialns icinih mains

59. Tritogonia tuberculata... See, | PBMC RMOLiiess socal cet eaiceh 2 <

Gomebrinicilla, sileatay = sama octal. niscelstuir bra siete Calls) DAW. y cje/ciniaie, since

6r. Unio crassidens.......... ..| Elephant’s ear...

62. Unio gibbosus............. BR Le hoists Rosen aanoe

WATER CONTENT.

The matter that is carried in all natural waters in varying quantities and proportions
consists of suspended matter, both dead and living, minerals and other ordinarily solid
substances in solution, and dissolved gases. All of these classes of substances are utilized
by fresh-water mussels in one way or another, and the quantity of any of them in the
water has a direct bearing upon the suitability of waters for mussels.

Ii4 BULLETIN OF THE BUREAU OF FISHERIES.

SUSPENDED MATTER.

The solids carried in suspension by water consist of mineral and organic substances.
The particles of mineral matter brought in by surface drainage or derived from bottom
and shores, apart from that which is in solution, range in size from coarse to very minute.
The carrying power of the water varies with the sixth power of the velocity, although
in the case of the most minutely divided substances other factors than rate of flow
come into play.

Mussels are affected in various ways by the matter in suspension. It has been
reported that some mussels stop feeding when the water is excessively turbid, as after
a storm. In this way they would avoid taking into their stomachs large amounts of
indigestible mineral. They have, however, the power of ejecting undesirable matter;
this may enable them to continue feeding even though the water is moderately turbid
In streams like the Mississippi, mussels could hardly survive without feeding during
the long periods of turbidity that prevail. Excessive precipitation of silt may smother
or even bury the mussel (Headlee and Simonton, 1904, p. 176). The turbidity of water
over deeper beds materially restricts the amount of light reaching the mussel, and it is
possible that this has an untoward effect. Data regarding the turbidity of several
streams are given in Table 9, page116. The turbidity of representative mussel-producing
streams varies from 37 to 188, except that the Des Moines River at Keosauqua has a
turbidity rating of 542—a striking exception. The Missouri and Red Rivers (non-
productive) and portions of the Mississippi River which do not yield commercial mussels
have turbidity ratings from 556 to 1,931.

Organic materials, both living and dead, are abundantly suspended in most natural
waters, and form a large part of the food of mussels. (See p. 91.) The living bodies
are the microscopic plants and animals which make up what is called the plankton.
The dead organic materials are the remains or fragments of plants and animals in a
state of decomposition, and such also form a part of the food supply.

Some of the plankton originates in the lake or stream in which the mussels are
living. Another and perhaps the greater part is brought in by the tributary streams.
Similar statements may be made regarding the dead organic matter, with the addition
that some of this may be brought in by surface drainage from the bordering lands.

MINERALS IN SOLUTION.

To what extent mussels derive the mineral matter necessary for the sustenance of
life and the formation of shells directly from the water or through the solid food con-
sumed can not be said, but even that part which is derived from solid food must have
been obtained by the smaller organism from the water or the soil. Churchill (1915 and
1916), from experiments conducted at the Fairport Station, has shown that fresh-water
mussels possess the ability to make use of nutriment which is in solution in the water.
While he demonstrated this for such nutritive substances as fat, protein, and starch,
there are yet wanting, as he has pointed out, analyses of the natural water in which
mussels live to prove that such organic substances are present in the waters in quantities
sufficient to play an important part in the nutrition of mussels. There are, however,
abundant analyses to prove the presence of dissolved minerals.

The requirements of mussels in mineral food may be ascertained by analysis of
the soft bodies and shells. Such analysis shows that while the shell is about 95 per cent

FRESH-WATER MUSSELS. 115

calcium carbonate, and 3% per cent organic matter, it also contains other minerals in
very small proportions, less than 1 per cent each, such as silica, manganese, iron, alumi-
num, and phosphoric acid. It does not follow that because these minerals, other than
calcium, occur in minute proportions, they are any the less essential to the welfare of
the mussel; iron forms a very small proportion of the human body, but man can not
live without it. So these minerals may, then, be just as essential to the formation of
good shell as calcium, but with the possible exception of manganese it is probable that
all natural waters contain a sufficient quantity of the minerals to satisfy the needs of
mussels. Nevertheless an interesting and important problem may be found in a com-
parative study of the mineral content of different waters which yield shells of diverse
qualities. It is even possible that an excessive proportion of certain minerals in water
tends to the formation of shells that are brittle, discolored, or otherwise inferior.

The sundried meats of mussels from the Mississippi River when analyzed have
been found to contain, besides moisture (about 7.6 per cent), protein (calculated from
nitrogen), 44 per cent; glycogen, about 9 per cent, ether extract (presumably fats),
a little less than 3 per cent; and undetermined organic material, 13 per cent. The
remainder is mineral matter (chiefly phosphoric acid), 9 per cent; calcium (calcium
oxide), 8 per cent; silica, 34% per cent; manganese, about one-half of 1 per cent; and
such other minerals in small proportions as sodium, potassium, iron, and magnesium
(Coker, 1919, p. 62, analysis by U. S. Bureau of Chemistry). ;

As previously indicated, nearly all natural waters, at least those fed largely with
surface drainage, probably contain certain quantities of the required minerals, but it
would be going beyond the bounds of present knowledge to say whether or not the
abundant growth of mussels in certain streams and the variable qualities of shells
produced in different streams are related to the proportions of minerals present other
than calcium. Certain it is that a deficiency of lime is very unfavorable. The soft
waters of the Atlantic slope support very few mussels and these are small in size and
possess thin shells which are usually badly eroded. The thinness of the shells is asso-
ciated with the deficiency of calcium in the water, and the erosion is an indirect result
of the same cause, since the free carbonic acid, which attacks and consumes the shells
wherever the protective horny covering has been broken by abrasion, would, in harder
waters, be combined with the calcium in solution to form the bicarbonate.

Circulation, of course, plays a great part in making available to mussels the dissolved
content of the water. It may be due not so much to low calcium content as to inadequate
circulation that small lakes and ponds in States of the Middle West generally yield
mussels with thin or dwarfed shells.

The waters of many streams of the United States have been subjected to analysis
by the United States Geological Survey (Dole, 1909). The summarized analyses for
several streams, or parts of streams, productive of mussel resources, and for 10 others
that are not productive of commercial shells, are given in Table 9 below. It appears
that, within broad limits, the variations in content of silica, iron, magnesium, sodium,
and potassium are not significant as affecting productiveness (unless, as may be the
case, the quality of the shell produced is affected). Particular attention may be directed
to the columns of turbidity, calcium, carbonate radicle, and nitrate radicle. The
nonproductive streams, or parts of streams, listed are generally either very high in
turbidity or very low in calcium, bicarbonate, and nitrate. The Shenandoah, among

116

BULLETIN OF THE BUREAU OF FISHERIES.

nonproductive streams, is an interesting exception. So far as can be seen, its analysis
conforms essentially to the standard of productiveness in mussels as revealed by streams

of the Mississippi Basin.

It is possible, then, that the Shenandoah, and perhaps a few

other streams of the Atlantic or Pacific slopes, might support fresh-water mussels of

commercial value should the proper species be introduced.

TABLE 9.—CONTENTS OF WATERS OF CERTAIN PRODUCTIVE MUSSEL STREAMS AND
DUCTIVE STREAMS.

OTHER NONPRO-

«as Suspended] Coefficient; Total Silica Calcium Magne-
Turbidity!" mnatter. [of fineness.jiron (Fe).| (SiOz). [I (F®)) “(ca). | Sum
PRODUCTIVE RIVERS.
Wabash, Vincennes, Ind............... 172 193 TO! [iterates 13-0 ©. 24 61-0 22.0
(hms; pia Salle Sie n Gees ones ele 159 136 ABON Uma crise 12.0 2m 50.0 22.0
Illinois, Kampsville, Ill... ............. 188 145 BO iedeaee eects 12.0 27 47-0 20.0
Hox) Ottawa dil ae ee eee ee Ske 94 87 Sei ee oadoes Ir.o -20 60.0 32-0
Sangamon, Springfield, Il.............. 74 39 fB0s| Ss 5 cede ate 16.0 «32 52.0 24-0
Cumberland, Nashville, Tenn.......... 126 94 ay 7 el Baosotsbris 20.0 +42 26.0 3-6
Cumberland, Kuttawa, Ky............. 176 165 SONG dcgesees 18.0 =30 28.0 4:3
Des Moines, Keosauqua, Iowa.......... 542 642 TSOON | etelelste stele 22.0 -36 58.0 21-0
Grand, Grand Rapids, Mich............ 37 43 1-61 1-1 14.0 -07 56.0 19-0
Cedar, Cedar Rapids, Iowa............. 64 61 SOTA cease cne 14.0 +09 48.0 16.0
Maumee, Toledo, Ohio................. 143 112 +95 3-4 17-0 +27 57-0 16.0
Mississippi, Moline, Ill................. 117 106 SC ial blapeicisacd 16.0 +39 33-0 13-0
Mississippi, Quincy, Ill................. 173 119 ach W Ago dae ae 18.0 -46 36.0 16.0
NONPRODUCTIVE RIVERS.
James, Richmond, Va.......... 90 71 +96 3-9 18.0 “5 14-0 3-0
Potomac, Cumberland, Md 28 29 I-59 3-0 8.2 14 24-0 4-6
Wrateree, Caniden; SUC. een 5. s 259 214 STON ace ee eet 25-0 - 28 6.3 1.8
Shenandoah, Millville, W. Va.......... 31 39 1.64 “9 15-0 +08 32-0 8.2
Mississippi, Chester, Ill................. 858 CU bearer eas .8 22.0 =39 44.0 16.0
Mississippi, Memphis, Tenn............ 556 519 bCH lege panne’ 24-0 61 36.0 12-0
Red) Shreveport, Las.) ...c 0. tenes 790 870 Ppogetlseodoct ae 30:0 II 74-0 17-0
MISsOlini Rese. MGs. 7. <scisececieee cis slel 1,931 1,890 Te) Sante senor 29-0 -5I 52.0 16.0
Savannah, Augusta, Ga..............65 172 142 S7i AP Beto dase 23-0 +44 57 -8
Hudson, Hudson, N. Y................ 13 16 1.26 “7 II-o -1I5 21.0 3-8
Cape Fear, Wilmington, N.C.......... 73 2I +92 1-3 9-9 -78 5-0 I-5
Sse Carbonate | Bicarbo- | Sulphate | Nitrate Ghiodue Total
an sale radicle |nate radicle| radicle radicle (ch, dissolved
(Na+K). (COs). (HCOs). (SO,). (NOs) P solids
PRODUCTIVE RIVERS.

Wabash, Vincennes, Ind................ 25-0 0.0 230 55-0 6.4 36.0 336
Hingis. ba Salle Wis ae ot TOc Oem n cera 203 50.0 6.6 13-0 278
irae enn ce Dle) BOSE Berea enc cot tc] el ee ceapneene 202 42-0 4-3 15-0 267

OR OEER Wels UM oie ences aicielern ciel oeteiche vv Hy s)!| Meee saa 275 61.0 4:9 7-9 33
Sangamon, Springfield, Ill.............. 16501 '53..g2 cea 247 37-0 3-4 7S 335
Cumberland, Nashville, Tenn 9-6 ae} 92 14.0 I.2 2.1 119
Cumberland, Kuttawa, Ky.. 7-8 +9 100 9-7 1.8 3-0 124
Des Moines, Keosauqua, Iowa. . 17-0 +O 216 71-0 3:3 4.8 312
Grand, Grand Rapids, Mich..... I0.0 8.5 214 33-0 2-3 Er 258
Cedar, Cedar Rapids, Iowa.............. 12-0 re} 2 30-0 Ker 3-4 228
Maumee, Toledo, Ohio.................. 24-0 2-5 173 48.0 4-5 40.0 298
Mississippi, Moline, Ill.................. TOS ON | tee eeeimcnsre 152 24.0 1-8 3-7 179
Mississippi, Quincy, Ill................. TINO}| 9a eatjaseeene 175 25-0 2.2 a4 203

NONPRODUCTIVE RIVERS.

James, Richmond, Va.................- 6.7 =o 60 71 +3 23 890
Potomac, Cumberland, Md. 9-0 are} 36 58.0 +9 6.4 130
Wateree, Camilen(iSiCoas ee. fern 0 Beal i) 34 4:2 +4 2.8 73
Shenandoah, Millville, W. Va........... 6.7 1.3 132 6.2 2.6 3-0 140
Mississippi, Chester, Ill................. Pee GH bre rigoenonee 174 56.0 2-7 9-8 a69
Mississippi, Memphis, Tenn............. 19-0 -O 129 43-0 1-7 8.6 202
Red)\Shreveport; Lat .i0). fabs. eee 90.0 4-6 135 140.0 4 121.0 561
Missouri, Ruegg, Mo............000ee00 36.0 -o 178 104.0 2-9 12-0 346
Savannah, Augusta, Ga..........:50.... 12.0 .o 30 6.0 -6 2.1 60
Hudson, Hudson, N. Y................. 7-9 +o 73 16.0 -8 4-0 108
Cape Fear, Wilmington, N.C........... 7-2 +o 25 3-2 +2 5-8 57

a After U. S. Geological Survey.

FRESH-WATER MUSSELS. 117
DISSOLVED GASES.

Air is inconspicuous, yet nothing is more important to man. Without it he dies;
and his comfort, health, and normal development depend upon the purity of the air
by which he is surrounded. This is because of the absolute necessity for oxygen, and
the deleterious effect of too much carbonic-acid gas. The gases dissolved in water
are as invisible as air, but the mussels are as dependent upon the free oxygen in solution
in the water as man is dependent upon the oxygen of the air. The water of streams
and lakes dissolves air at the surface from the atmosphere and derives it from the
physiological action of plants in light. Cold water will hold more free oxygen than
warm, but the absorption of oxygen at the surface is favored by increased evaporation,
with warm dry air and the prevalence of winds (W. E. Adeney, in Report of the Metro-
politan Sewerage Commission of New York, 1912, p. 81). Falls, rapids, and swift
currents promote the absorption of oxygen, and circulation currents lead to its better
distribution into the deeper parts and throughout the whole body of water. Even
without the aid of circulation currents, a measure of distribution of oxygen dissolved
at the surface is effected by diffusion and ‘‘streaming”’’ of the gas within the water
(W. E. Adeney, loc. cit., p. 82).

Carbon dioxide (CO,), commonly called carbonic-acid gas, which is given off as a
waste product of mussels and other animals, and which is also formed by the decom-
position of animal and vegetable matter, is helpful in small quantities, but is poisonous
to animals when present in too great quantities (Shelford, 1913, p. 59; 1918, pp. 39, 40;
and 1919, p. 106). It is used up by green plants in sunlight and is also given off to the
atmosphere at the surface of the water. The same conditions that are favorable to the
absorption of oxygen are also favorable to the loss of CO,.

Carbon dioxide is of especial significance sometimes because of its tendency to
unite with calcium carbonate to form the bicarbonate, which is soluble in water. Since
the shell of a fresh-water mussel is composed principally of calcium carbonate it is liable
to be attacked by free carbon dioxide in the water and taken up into solution. The
horny covering of the shell is a protection against the action of the gas, but if that
becomes broken or worn off in spots, as frequently occurs, the shell is exposed to the
destructive effect of the acid. This leads to little harm in hard waters where the CO,
may unite with the calcium carbonate derived from rocks or soils, but in soft waters, or
in any waters where there is an excess of gas over dissolved calcium, the shells are
partially or completely destroyed by corrosion. On many rivers ‘‘baldhead’’ shells
are commonly encountered, and sometimes the shells are full of pits or even eaten clean
through in the older parts.

Nitrogen, though an important element in the composition of mussels, can not be
used by them in the form of a gas, and its presence in water (unless in excess) is pre-
sumably a matter of indifference to them, just as the nitrogen which composes the
bulk of the atmosphere is uninjurious to men and not directly utilized by them (Shelford,
1918, p. 36). Other gases found in water are ammonia, methane (CH,) and other
hydrocarbons, and hydrogen sulphide (H,S), which are formed in certain processes
of decomposition (Needham and Lloyd, 1916, p. 47). These are of importance only
when occurring in sufficient quantity to be injurious.

118 BULLETIN OF THE BUREAU OF FISHERIES.

Mussels and other animals grow more plentifully in regions of water where, with
other conditions favorable, there is a proper gas content—abundant free oxygen and
limited amounts of carbon dioxide. Such places are near zones of wave action in
lakes and in rapids in streams, where the influence of green plants is felt, and where water

circulation is good.
VEGETATION.

In many lakes and streams in protected locations rooted plants occur in more or
sess abundance. If this vegetation is of open character, not producing a heavy shade, it
frequently harbors an extensive mussel fauna (Baker, 1916, pp. 94 and 95). This kind
of habitat is especially favorable to many fishes,* and to this fact in part may be attrib-
uted the presence of mussels, since the young mussels upon leaving the fish, having
small power of locomotion, will remain where they fall if the habitat is at all suitable.
Since mussels are found in abundance where there is no vegetation, as in rivers like the
Mississippi, and generally are conspicuously absent from dense growths, it would seem
that the association with rooted plants is largely incidental. There is other direct
evidence to indicate that mussels of such habitats are those that are parasites upon
species of fish that have a preference for such an environment.

Shira’s observations in Lake Pepin (unpublished manuscript) indicated a certain
association of juvenile mussels and vegetation, since 94 per cent of the juvenile mussels
taken in a survey conducted in 1914 were taken in situations where more or less vegeta-
tion was encountered. On the other hand, he found juveniles at as many stations
without vegetation as with it. As the result of many observations he concluded that a
dense growth of vegetation was distinctly unfavorable to the survival of young mussels,
and he suggests that the association of juvenile mussels with vegetation may be partly
due to the fact that environments marked by the presence of aquatic plants are attractive
to fish. He also observed that a given area of bottom supportive of mussels might
display a heavy growth of aquatic plants one year but be practically or entirely free
of them in another year. The same author has observed relatively dense growths of
vegetation on mussel beds in Lake Pokegama.

It has frequently been observed in lakes that mussels live abundantly in patches of
Chara, a low-growing green plant usually containing a considerable proportion of
calcium carbonate. In the Grand River, Mich., Coker noted that mussel collecting was
invariably poor in the midst of abundant rooted plants. The principal species found
in such localities were the floaters (Anodonta grandis), the fat mucket (Lampsilis luteola),
and the pink heel-splitter (Lampsilis alata). The mucket (Lampsilis ligamentina), and
other species were likely to be found in the vicinity of rooted aquatic plants.

As quoted on page 110, above, Wilson and Danglade (1914, p. 15) described the
finding of mussels beneath layers of algae and weeds in Minnesota streams.

It must be remarked that rooted plants are not the only ones that contribute to the
oxygen supply and to the depletion of the carbon dioxide of the water. There are
thread alge and innumerable microscopic floating plants which play an important if
not the most important part in oxygenation of the water, and these are widely dis-
tributed in all zones to which sunlight penetrates.

a “Tittle fishes and the greater number of mature fishes keep’ more or less closely to the shelter of shores and vegetation’’
(Needham and Lloyd, 1916, p. 23).

FRESH-WATER MUSSELS. 119
ANIMAL ASSOCIATES.

In the previous discussion of the Naiades in relation to the physical environment,
there has been shown to be an adaptation by certain species to particular physiographic
situations, as to pond, lake, river, swift or quiet water, hard or soft bottom, ete. In
any habitat each mussel is in association with other mussels of the same or other species
and with animals and plants of various classes, all more or less adapted to the same
environment. Such an association of organisms forms a community, the members of
which interact more or less upon one another and upon their environment. The con-
sideration of these communities with reference to their members and to the environment
often reveals important relations. Because of the mutual relations existing, a dis-
turbance or destruction of any one element, by affecting a balanced condition, may
cause a marked disturbance of the whole community. (See Shelford, 1913, p. 17.)
Some of the relations between mussels and their associates may be described as com-
petition, symbiosis and commensalism, parasitism, and preying. A description of a
typical habitat with its inhabitants will illustrate the variety of life associated with
mussels. For Oneida Lake, N. Y., Baker (1916, p. 94) gives an account of a particular
sort of habitat which he designates the bulrush-waterwillow type, where there is not
great exposure to waves, where the bottom.is more or less covered with stones and
bowlders, but with sandy spots here and there, where the depth varies from 1 to a
feet, and where the vegetation consists of bulrushes, waterwillows, and pickerelweed.

The principal differences between this habitat and the bowlder type are the less exposed situation,
the density of the vegetation, the deeper water, and the sandier bottom. Such a habitat is particularly
favorable for black bass, sunfish, rock bass, and others, because of the hiding and breeding places
provided by the thick vegetation, the attachment for eggs by the roots and stems of plants, and the
excellent feeding ground, by the abundance of animal life, insect, crustacean, and molluscan. ‘The
largest number of molluscan species, 39, occur in this type of habitat, including upwards of 15 which
are known to be eaten by bottom-feeding fish. [The following numbers of species are listed: Mussels,
rr, including several species of Anodonta and Lampsilis; univalves, 16; crustaceans, 1 (crayfish);
Spheriids, 10; leeches, 5; insects, 4.]

A typical association of mussels and other species in Andalusia Chute, Mississippi
River, near Fairport, Iowa, is as follows (Howard, unpublished notes):

Bottom—gravel, rock, and sand.

Water—depth 51% to 74 feet. Current at surface estimated 2 miles.

Haul—2>50 feet in length, with crowfoot drag 10 feet wide and with dredge 18 inches wide.

Distance from edge of water—2o0 feet.

Mussels—Lambpsilis gracilis, 3; Plagiola elegans, 1; P. donaciformis, 3; Quadrula ebenus, 1; Q.
meianevra, 3; QO. pustulosa, t; QO. undata, 2; Strophitus edentulus, 1; and Unio gibbosus, 3. ‘Total, 18.

Bivalve—Musculium transversum Say, 1.

Bryozoa—Plumatella polymorpha Kraepelin, 1 colony.

Snail—Vivipara subpurpurea Say, 36; Pleurocera elevatum, Say tr.

Flatworm—Planarian.

Leech—Placobdella parasitica Say.

Insects—Stonefly, Perla sp. (larva); mayfly, Chirotenetes, 1 (larva); Heptagenia, 14 (larve);
Polymitarcys, 2; dragonfly, Gomphus externus, 5, Argia, 3 (larvae), Neurocordulia, 1; caddisfly, Hydro-
psyche, 70 (larvee); beetle, Parnids, 2 (adult).

Crustacea—Crayfish, Cambarus.

In communities of animals and plants, as the individuals increase in numbers there
may develop the keen competition for food which has been designated as the struggle

120 BULLETIN OF THE BUREAU OF FISHERIES.

for existence of the animate world. Since mussels feed upon suspended matter, living
or dead, which they filter from the water, and since water once filtered must be less
richly supplied with food for other mussels, an actual competition for food undoubtedly
exists. Clark and Wilson (1912, pp. 19-20) give an account of a measured area of 1
square meter (10.76 square feet) in which they counted 81 mussels and 57 other mollusks,
making a total of 138 individuals, or about 13 per square foot; and there were present,
of course, many other animals, some of which took the same kind of food as the mussels.
This recorded determination of numbers per given area illustrates the possibilities of
competition. As indicated on pages 91 and 93, above, a detrimental competition for
organic food probably does not occur ordinarily with mussels.

Symbiosis and commensalism exist in such communities. A few supposed instances
affecting mussels are afforded by small forms that live within the shells in the mantle
cavity of the mussel where they receive food and protection. A small bristle worm,
Chetogaster limnei, frequently observed in the mantle cavity of mussels, is supposed
by some to be merely a commensal, but it may be considered a predacious species since
it has been seen with juvenile mussels within its digestive tract (Howard, paper read at
meeting of American Fisheries Society, 1918). The leech, Placobdella montijera, enters
living mussels, but is not known to feed upon them (Moore, 1912, p. 89).

Bryozoa and other sessile forms are found attached to the exposed portions of
live-mussel shells. Doubtless there are many cases of commensalism to be revealed
by closer study of mussels in their natural habitat.

An interesting symbiotic relation exists between a mussel and the bitterling, a
small European fish, which lays eggs in the mantle cavity of a fresh-water mussel which
in turn infects the fish with glochidia (Olt, 1893). A different relation, which shows
some reciprocity, however, is that of the fresh-water drum (A plodinotus grunniens)
of the Mississippi Basin, that eats fresh-water mussels but pays for the privilege,
in part at least, by nourishing the young of several species parasitically encysted
on its gills. (Surber, 1913, p. 105, and Howard, 1914, pp. 37 and 40.) The same is
true of other fish that eat mussels, as the catfishes.

Parasitism is a phenomenon of community relations, and it is of double significance
in the case of mussels, because not only have the mussels parasites to prey upon them,
but they with few exceptions depend for existence upon the opportunity to become
parasites of fish or, in one case, of an amphibian. A rather close relationship of fish
to the mussel community is essential, and there may be a particular interrelation of
given species of fish and of mussels. Questions arise as to when and how this special
and intimate relationship came about and to what extent the habits of host and
mussel interlock in such cases as the gar pikes and the sand-shells (Howard, rg9r4a),
the river herring and the niggerhead, the shovel-nose sturgeon and the hickory-nut,
the catfiches and the warty-back, the mud puppy and the little salamander mussel.
In the last-named case, the peculiar habit of the mussel which lives beneath flat stones
conforms evidently to the habits of the host, for the mud puppy is well known to
frequent such situations.

One feature of certain mussels that possibly serves to decoy fish is the elaborate
development of the mantle flap in gravid females of the pocketbook mussel, Lampsilis
ventricosa, and others. (See p. 85.) These flaps in their form and coloration, includ-
ing an eyespot, resemble a small fish, and the motion of these in the current still further

FRESH-WATER MUSSELS. I2I

enhances the resemblance. The enlarged marsupia distended with glochidia lie close
to these flaps, one on each side. It has been suggested that a fish darting at this
tempting bait may cause the extrusion of the glochidia and then become infected.
(See Wilson and Clark, 1912, pp. 13, 14.) The unwelcome members in the associations
to which mussels belong are discussed in the following section on “Parasites and
Enemies.”

PARASITES AND ENEMIES.
PARASITES.

Long green alge are occasionally found attached to the exposed tips of the shells
of mussels, and these may cause some erosion of the shells. Marly concretions, com-
posed of intermingled low alge and lime often form knoblike lumps on shells in lakes.

Among the most common of mussel parasites are water mites which dwell in the
gill cavity and lay their eggs within the flesh of the mussel, in the inner surface of the
mantle, in the foot, or in the gills. These water mites, which belong to the genus Atax,
vary in size and color and to some extent in shape (Wolcott, 1899). One is black with
a white Y-like marking on its back; others may be reddish. The largest and most
degenerate is of a honey color with white treelike markings, but because of its incon-
spicuous coloration it is often overlooked. The different species of Atax are hard to
distinguish without special preparation and study. Under magnification these water
mites look somewhat like spiders. Small pearls are sometimes formed about Atax eggs.

Leeches are occasionally seen on the inner surface of the mantle of some mussels,
especially in Anodontas (floaters) in ponds. They probably feed on the mucus of the
mussel. ;

A small organism closely resembling a minute leech in general shape and appear-
ance is occasional in the axils of the gills of mussels in some lakes. This is Cotylaspis
insignis, one of the trematodes or flukes (Leidy, 1904, p. 110). One mussel may
harbor a dozen or mote of these parasites. Rather similar to Cotylaspis insignis but
considerably larger and pink instead of yellowish, is the trematode Aspidogaster con-
chicola. It is more complex than Cotylaspis insignis and is usually found in the peri-
cardial cavity of the host mussels, although in severe infection it may overflow into
other organs.

Distomids, both free and encysted, are found in mussels. The distomid occurs
in almost any muscular part of the body but most frequently in the foot or along the
edges of the mantle. Sometimes pearls are formed around distomid cysts. The free
distomids are usually found on the mantle surface next to the shell; they are chiefly
confined to the flesh along the hinge line but may extend lower down. They are often
associated with small irregular pearls. Sporocysts of distomids are common, especially
in some Quadrulas. Many distomid parasites of mussels appear to be harmless, but
one, Bucephalus polymorphus, destroys their reproductive organs (Kelly, 1899, p. 407;
Wilson and Clark, 1912, pp. 69, 70; Lefevre and Curtis, 1912, p. 121). Am ascarid
worm is occasionally found in the intestine of mussels.

A worm with peculiar hooks on its head was found encysted in the margin of the
mantle of some mussels in a pond near Fairport, Iowa. It was probably a trematode
but has been found only once and never identified.

122 BULLETIN OF THE BUREAU OF FISHERIES.

An oligochate worm, Chetogaster limnei, is occasionally found in mussels. It is
possibly a parasite of snails from which it now and then migrates to mussels. We have
some reason to believe that it devours the other mussel parasites. The crystalline
style, a long translucent gelatinous body which is formed by the mussel within its in-
testine, is often mistaken by clammers for a worm.

Certain protozoa, Conchopthirus curtus and Conchopthirus anodonte, somewhat
resembling in general appearance the slipper animalcule, Paramcecium, are occasionally
met in the mucus of mussels. Attached protozoa, like Vorticella, are also occasionally
found on the edge of the mantle.

Occasionally larval Atax migrate into the space between the mantle and shell
and are covered by nacre, where they may form minute white tracks, or in some cases
apparently small raised ‘“‘blisters” or pimples (Clark and Gillette, 1911). One or
perhaps several species of distomid causes a brick-red or purplish discoloration of the
nacre, mostly in thin-shelled mussels (Anodonta and Strophitus) (Osborn, 1898; Kelly,
1899, p. 406; Wilson and Clark, 1912, p. 66). The marginal cyst distomid sometimes
causes a steel-blue stain of the nacre near the margin (Wilson and Clark, 1912, p. 63).

ENEMIES.

Mussels have numerous enemies, among which may be mentioned the mink, the
muskrat, the raccoon, water birds, turtles, fishes, hogs, and man.

Of the depredation of many of these we know little. Water birds probably kill
but few mussels, and of fishes, catfish and the sheepshead, or fresh-water drum, are
the most noteworthy. These probably feed mainly on the thinner-shelled species.
Small mussels (Lampsilis parva) have been found in the intestines of the turtle, Mala-
clemmys lesueurii. ;

Besides man the muskrat is the most notorious enemy of mussels, and the shell
piles left by them are often conspicuous objects along the shores of lakes and rivers.
Conchologists sometimes rely upon the muskrat’s shell piles to furnish them choice
and rare shells. Evermann and Clark (1918, p. 284) found not a few examples of
Micromya fabalis in muskrat shell piles on the banks of Lake Maxinkuckee, though
collecting in the lake during several seasons failed to reveal a single living specimen.
Clammers prospecting new rivers sometimes use the piles of shells left by the muskrat
as aids indicating where to dredge for shells.

Direct observations of the work of muskrats in Lake Maxinkuckee, Ind., were made
by Clark and reported in ‘““The Unionid of Lake Maxinkuckee” (Evermann and Clark,
1918, pp. 261, 262), as follows:

The greatest enemy of the lake mussels is the muskrat, and its depredations are for the most part
confined to the mussels near shore. The muskrat does not usually begin its mussel diet until rather
late in autumn, when much of the succulent vegetation upon which it feeds has been cut down by
the frost. Some autumns, however, they begin much earlier than others; a scarcity of vegetation or
an abundance of old muskrats may have much to do with this. The rodent usually chooses for its
feeding grounds some object projecting out above the water, such as a pier or the top of a fallen tree.
Near or under such objects one occasionally finds large piles of shells. The muskrat apparently has
no especial preference for one species of mussel above another but naturally subsists most freely on
the most abundant species. These shell piles are excellent places to search for the rarer shells of the
lake.

In the winter after the lake is frozen, great cracks in the ice extend out from shore in various
directions, and this enables the muskrat to extend his depredations some distance from shore in defi-

FRESH-WATER MUSSELS. 124

nite limited directions. During the winter of 1904 a muskrat was observed feeding on mussels along
the broad ice crack that extended from the end of Long Point northeastward across the lake. The
muskrat was about go feet from the shore. It repeatedly dived from the edge of the ice crack and
reappeared with a mussel in its mouth. Upon reaching the surface with its catch it sat down on its
haunches on the edge of the crack and, holding the mussel in its front feet, pried the valves apart
with its teeth and scooped or licked out the contents of the shell. Some of the larger mussels were
too strong for it to open, and a part of these were left lying on the ice. The bottom of the lake near
Long Point, and also over by Norris’s, is well paved by shells that have been killed by muskrats.
Muskrats do not seem to relish the gills of gravid mussels; these parts are occasionally found untouched
where the animal had been feeding.

In spite of all these enemies mussels held their own and throve and flourished
until the appearance of man upon the scene, when depletion of the mussel beds became
noticeable. Man exterminates a good many mussel beds by sewage discharge, by
drainage, through which sand is washed down over the beds, by dredging and construc-
tion of wing dams for navigation, by pearling, but, most of all, by exhaustive clamming
for the shells.

CONDITIONS UNFAVORABLE FOR MUSSELS.

Since mussels are animals of generally sedentary habit, with limited powers of loco-
motion, they are more helpless to escape from unfavorable conditions of environment
thanare fish or other active creatures of the water. This relative helplessness does not
characterize the adult mussel alone, but is even exaggerated for the young stages.
From the time the larval mussel attaches itself to a fish until it is liberated it is entirely
dependent upon the movements of its host for its future home; it may be dropped in a suit-
able environment or in a place wholly unfavorable to its survival. On the other hand,
adult mussels of many species can endure unfavorable conditions for a considerable
period of time. This is found to be especially true of several species of Quadrula.

NATURAL CONDITIONS.

Some natural conditions unfavorable to mussel life aré shifting bottom, turbidity,
sedimentation, floods, and droughts. These conditions pertain usually to streams
rather than to lakes. They have received some consideration in various paragraphs
of this section on “Habitat”; therefore it is only necessary to summarize them in
this connection.

The paucity of mussels in the Missouri River, as well as in the greater part of the
Red River and other streams of the plains, is no doubt due to its exceedingly shifting
bottom. Similar conditions apply in lesser degree in the lower stretches of many
streams. In fact, all rivers, for some distances above their mouths, are as a rule very
deficient in mussels as compared with sections farther up where bottom and other con-
ditions are more favorable. Shifting bottoms not only prevent mussels from securing a
foothold, but may also entirely destroy established beds.

Interrelated with shifting bottom are turbidity and sedimentation. All three factors
and the extent to which they may be operative are largely dependent upon flood condi-
tions. In nearly all large rivers floods commonly plow new channels here and there in
the stream bed, cut away banks to a greater or less extent, and build new shoals or
change the form and dimensions of old ones. Such changes in navigable streams are-

124 BULLETIN OF THE BUREAU OF FISHERIES.

familiar to pilots who find it necessary to ‘ learn the nver’’ each season. Many of these
changes must be catastrophic to mussels in certain localities.

Excessive turbidity with consequent increased sedimentation, when of considerable
duration, is no doubt seriously unfavorable to the well-being of mussels. It has been
stated that mussels do not feed during periods of high turbidity, but no definite data
in support of this can be given. That mussels do not ‘‘bite” well on the crowfoot
hooks during a rising stage of water is a condition recognized by clammers. Whether
the fact that the shells are not generally open and the mussels feeding at this time is due
to the turbidity, or to other changing conditions incidental to the rising water, can not
be stated. If heavy deposits of sediment are unfavorable for adult mussels, they must
be more directly harmful to the young during the early stages of independent life, for
the tiny juveniles may be smothered by deposits that would have less disastrous effect
upon larger mussels.

The effects of droughts are ordinarily felt but little by the mussels of the larger
streams and lakes. The most unfavorable condition arises when, owing to a prolonged
dry season, the water is lowered to such an extent that the mussels fall easy prey both
to muskrats and to clammers and pearlers seeking them in the shallow water. Crows,
too, are known to pluck out and kill Anodontas when the water over them becomes low
and clear.

Inthe small streams, lakes, and sloughs, the mussels may be killed by the partial or
complete drying up of the water. Certain species of mussels are, of course, more resis-
tant to such condition than others. Isley (1914) states that live specimens of Unio
tetralasmus were plowed up in a pond three months after it had become dry. The mus-
sels had burrowed down to zones of moisture.

ARTIFICIAL CONDITIONS.

Among the conditions imposed by man that may be detrimental to mussel life in
our streams may be mentioned the discharge of sewage, industrial wastes, dredging,
and the building of wing dams. (See Pls. IX, X, and XI.)

Disposition of the sewage and wastes of large cities without harmful contamination
of the rivers presents an issue of growing importance. Portions of streams just below
important cities are sometimes veritable cesspools, unsuited to both mussel and fish life.
The Illinois River for a considerable distance below its origin is greatly influenced by
sewage pollution through the Des Plaines River and the drainage canal; from the head
of the stream down to Starved Rock, 42 miles from the source, no mussels are found,
and a normal variety and abundance of fishes is not present above Henry, 77 miles from
' its source (Forbes, 1913, p. 170; Forbes and Richardson, 1919, p. 148). Industrial
wastes from pulp and paper mills, tanneries, gas plants, etc., are injurious to fishes,
and no doubt harmful to mussels as well. Such unfavorable conditions as arise through
the depletion of oxygen supply by the decomposition of sewage are partially or com-
pletely corrected by the intervention of rapids or waterfalls. (See Shelford, 1919,
p- 111, and Baker, 1920.)

River improvement work, such as dredging and the building of wing dams, creates
conditions more or less unfavorable for mussels. Hydraulic dredging may destroy
mussels, either directly by pumping them up, or by shifting the river channel so that

FRESH-WATER MUSSELS. 125

ensuing ‘changes cause new sand bars to form and to bury previously existing beds.
Wing dams constructed for improvement of the Mississippi River, built of rock and
brush and projecting from the shore to the channel, have far-reaching effects upon the
course of the current, upon sedimentation, and upon the formation of sand bars. The
area between the dams may fill up with sand, so that eventually willows are growing
where a mussel bed once flourished. Such changes have been observed in the Mississippi
River near Fairport, Iowa, and at Homer, Minn.

The effect of the construction of dams directly across the channel of a river, as for
water-power development, has been discussed on page 97.

Greater irregularity of stream flow resulting from the clearing of forests greatly
influences the life of mussels. The drying up of ponds inhabited by mussels and the
extreme low stages of water which allow clammers to obtain the mussels by wading, form
disastrous conditions to which mussel beds are occasionally exposed. Extreme low
stages of lakes and streams in summer may lead to mortality of mussels resulting from
high temperature of the water and diminished oxygen supply. (See Strode, 1891;
Sterki, 1892; Farrar, 1892.)

GROWTH AND FORMATION OF SHELL.
MEASUREMENTS OF GROWTH.

Methods of propagation, estimate of results, and measures for protection all depend
in a considerable degree upon knowledge of the rate of growth of mussels. It is impor-
tant to know how many years elapse before a mussel may attain a market size, as well
as at what age it may be expected to begin breeding. Furthermore, these questions
require answers for more than 40 economic species, even if consideration were not given
to the more than 500 additional American species of fresh-water mussel. The rate of
growth is not, however, easily ascertainable for most species.

Mussels of any species may be left under observation for a considerable period in
tanks or troughs, but experiments indicate that normal growth does not occur under
the conditions of life in tanks. Even large ponds do not offer the conditions required
by many species. The data to be offered on this subject are derived principally from
experiments conducted at the Fairport station. Further data on growth of mussels
will be found in Isley’s paper (1914).

Pocketbooks, Lampsilis ventricosa, reared in one of the ponds at the Fairport
station attained a length of 41 to 47 mm. (1.6 to 1.85 inches) in two growing seasons,
and about 65 mm. (2.56 inches) by August of the third season. Examples 45 to 47
mim. long (1.76 to 1.85 inches), and these evidently in the second year of free life, were
measured and planted in the Mississippi River by Lefevre and Curtis in June, 1908,
and recovered by the senior author of this paper in November, 1910, at the close of the
fourth year of growth (Lefevre and Curtis, 1912, p. 180 ff). They had attained lengths
of 81 to 85 mm. (3.18 to 3.35 inches). (See fig. 6, p. 133.)

It is evident, then, that pocketbook mussels under only ordinarily favorable con-
ditions may attain a marketable size by the end of the fourth season of independent
life (at 34% years of age from date of infection). The observations reported in the
following table (10) show that a nearly equal rate of growth applies to the Lake Pepin
mucket, Lampsilis luteola.

75412°—22-—-9

126 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 10.—AVERAGE LENGTH OF Six EXAMPLES OF THE LAKE PEPIN MUCKET, LAMPSILIS LUTEOLA,
REARED IN POND 3D AT Farrport, Iowa.

Time of measurement. Length.

Close of second growing season...
Close of third growing season 4...
Close of fourth growing season... one AD ,
C@lose of Githi prowitig seasor aac cists seteteeieite Dae toiaieictel eteiete base etclereletaienceereteiate oie een tee eee = 3-18
Closeiofisixthigrowing seasons niki ak oi' de aries © Malden cease nte Seisele meth chile tenn cater ema nee ote ; 3-35

@ The records of the original lot for the third year having been lost in the fire, there is substituted a corresponding record for
the third year of mussels of another lot recorded in Pond 8D. The mussels in Pond 3D were from a fall infection and those in
8D from a spring infection; therefore the former are slightly older.

Another species of pocketbook, Lampsilis (Proptera) capax, had attained a length
of 49 mm. (1.93 inches) at the end of the second season, indicating a slightly more
rapid growth for this species than for Lampsilis ventricosa. Thinner-shelled species of
the genus Lampsilis may grow more rapidly. Thus some examples of the paper-shell
Lampsilis (Proptera) levissima, known to be not over 16 months of age (in free life),
had attained lengths of 78 to 81 mm. (over 3 inches). An example of the paper-shell,
Lampsilis (Paraptera) gracilis, grew from 17.6 mm. (0.7 inch) to 107 mm. (4.2 inches)
in 2 years 9 months and 18 days, the rate of growth averaging about 1% inches per
year.

The very thin-shelled mussels of the genus Anodonta grow even more rapidly.
Examples of the floater or slop-bucket, Anodonta corpulenta, taken from a pond at the
Fairport station 16 months after the ponds were constructed, varied in length from
66 to 88 mm. (2.59 to 3.46 inches). Examples of another paper-shell, Anodonta sub-
orbiculata, taken at the same time from another pond of the same age, but which may have
offered less favorable conditions, were 64 to 67 mm. in length (2.52 to 2.63 inches).

With regard to heavy-shelled mussels, such as the niggerhead, pimple-back, and
blue-point, there is much less satisfactory evidence as to growth. They undoubtedly grow
much more slowly than mussels possessing thin shells, yet the rates of growth secured
in such experiments as have been conducted can hardly be assumed to be representative
of the conditions prevailing in nature. The species are not well adapted to life in tanks
or ponds, and there are few places where measured specimens can be placed in rivers
with any assurance that they will remain undisturbed or may be recovered at a later
time. In Lefevre and Curtis’s experiments (1912) an example of the hickory-nut,
Obovaria ellipsis, that was practically full-grown when first measured, gained 5 mm. (one-
fifth of an inch, 0.197) in a little less than 2% years. In the same period an example
of Quadrula solida, somewhat less mature, gained 10 mm. (two-fifths of an inch, 0.394),

In the following table (11) there are indicated sizes, at the close of the second year,
of certain mussels reared accidentally or intentionally in ponds at the Fairport station.
The short-term breeders, at least, were a little less than 1% years of age.

Since these are all mussels of river habit, it can not be assumed that the growth
attained in ponds is representative of the rate of growth in a natural environment.

FRESH-WATER MUSSELS. 127

TABLE 11.—SIzES AT CLOSE OF SECOND YEAR OF CERTAIN MUSSELS REARED IN PONDS, FAIRPORT
Station, Iowa.

Scientific name. Common name. | Length.

Millimeters.| Inches.

Lampsilis ligamentina..............0.-0-s0eeeeeeeeee IMasek eth Oo erect sia cdanisieietele arclefetstoiatciss ctnieraie oteie) sl 20.0 0.79
Lampsilis anodontoides. ... zal) Mellow’ sand-shiell'0i 25 2Uic: Stick ccminee se eeelc es 41-0 1.62
Obliquaria reflexa.......... .| Three-horned warty-back . cee = 16.0 - 63
Obovaria ellipsis........... ..| Hickory-nut............ <a II. 4 “45
Plavinla donaciorsmise ce pmcgsisicicrsciinels cicielaidaie’e vic.sia= [siete ceietlns ieee 20.0 -79
Quadrula plicata........... .-| Blue-point. 13-5 -53
Quadrula pustulosa........ ..| Pimple-back 24-2 - 69
Quadrula undata.............. ol Wea Cale? coeiddone Gcluapricge bamboneson cu mabanccoaeeen 15-8 -62

@ Other observations indicate that the mucket grows more rapidly in streams.
> The yellow sand-shell was only 1 year and 3 months of age.

Some medium-sized examples of several species of Quadrula were placed, after
measurement, in a crate which was anchored in the Mississippi River at Fairport, Sep-
tember 19, 1910. When the crate was recovered and the mussels remeasured, July 31 of
the following year, very little growth was apparent in most of the specimens. The data
for measurements of length in the several examples are given in the following table (12) :

TABLE 12.—INCREASE IN LENGTH OF MUSSELS IN CAGE.

Length, Length, o
Scientific name. Common name. Sept. 19, July 31, sae in

IgIo. I9II. »

Inches. Inches. Inches.
Mhuadriilaiebenius: gf. tas ose eeie epariec Secale INIepernend ie paccwer peceoanee one ceteers I.92 1.98 0. 06
Qutadrula pustitlosas oc ooo os Se bee wis lene eee Pimple-back. . I-74 1.85 Ane:
Quadrila metanevra .../)25. 5 vetoes oes ee wee Monkey-face. . 1.70 1. 86 -16
Ritiadritla PlCACA a tennc lc aniwiae tera eiereiateais =\aternioe Blue-point. . 7 2. 80 3.02 -22
Pundtlatindata ct nccee eee ae oe eee eee Pig-toen aerate ceases es SORE spec ec nnn. I. 41 1.74 +33

In another experiment 76 mussels, representing 19 species, principally the thick-
shelled forms, were placed in a crate with nine compartments which was anchored in the
river about 25 feet from shore. The crate was put out July 31, r911, and recovered No-
vember 14, 1913, when 36 of the original mussels, representing 13 species, were found to
be alive. These mussels generally manifested a higher rate of growth than marked some
of the mussels used in the experiment just described, although the increase in size was
disappointingly small. The period of time between the dates of measurements was 2
years 3 months and 14 days. The mussels were of medium size at the beginning of the
experiment, so that the growth to be expected was that which would characterize the
period of approaching maturity rather than that of early life. The mussels living at
the close of the experiment, with the maximum and minimum gain in length and the
average for the species (when more than two examples were available), are shown in
the following table (13):

TABLE 13.—GROWTH OF 36 MUSSELS IN CRATE FROM JULY 31, 1911, TO Nov. 14, 1913.

Increase in length.

Scientific name. Common name. Examples.
Maximum.| Minimum.| Average,

Number. Inches. Inches. Inches.
Quadsulalebennts Fei acisiomian sails <n Niggerhend a pi.i-cjumie ak iscsi mtysielate'= 7 ©. 64 0. 38 ©. 463
Quadrula pustulosa.............. ..| Pimple-back 5 50 +20 376
Quadcilapustilatae. 7 oniseeaath coca teoeen GO cen oeiacigeee se cece wee I poet) EB adoabourd pacsqnacacse
Quadrula metanevra Monkey-face 2 46 LAT |aletieteserne elt
Muadrulanlicataite se ccincuneesauecse Blige paint 652,25 de wats asia ste i 7 80 +32 517
Quadrula undata.)\). 0b. i sae. PEIE-LOG, eins chet ele seis eteleeiene eRe eT 2 49 Okt thon coaman
Obovaria ellipsis................-...-- Hickory-nut 4 72 +20 455
Obliquaria reflexa................0-05- Three-horned warty-back I ail bee hare one Honodkacc:e
Tritogonia tuberculata................. PBtiCR ORNS isco = cs easel on I 94(9 | Acecacosn ood Snacontbes->
Lampsilis ligamentina.................] Mucket.............00..0005 2 -84 FN enor arnonoee
Lampsilis recta’. . 2... 0cec0ces Fe I POSTON WSe SetqogAeuel Isoumcnooe nee
Strophitus edentulus a4 2 - 66 BON IMs tates citaieate
mG PID DOSUS... ne rims cee eee nie eeenniaee I all iqoceae ree see otc aCaRee er

128 BULLETIN OF THE BUREAU OF FISHERIES.

It must be borne in mind that the conditions of life for mussels in an inclosed crate,
and relatively closely crowded together, are probably not nearly so favorable for growth
for the majority of mussels as are those of the natural river bottom, where the mussel
has a fair chance to assume its desired position and secures the full benefit of the food-
laden current. Doubtless the maximum rate of growth shown in the crate is more
nearly normal than the average rate. Our impression is that thick-shelled mussels, such
as the niggerheads, pig-toes, and pimple-backs, after they are half grown, increase
in size ordinarily at the rate of a quarter of an inch a year or less. If this be true, it
would require four years or more for a niggerhead mussel, under ordinarily favorable
conditions, to increase from a length of 2 inches to a length of 3 inches. Assuming that
the rate of growth is more rapid in early life, it may be inferred that niggerheads or
pimple-backs 3 inches in length are 10 or 12 years of age. Additional experiments
conducted under proper conditions are clearly wanted.

A marked contrast in rate of growth is thus afforded by the species of Quadrula (and
others having generally similar character of shell), on the one hand, and those of Lamp-
silis, on the other. This was strikingly shown, in connection with the last experiment
described, by two examples of the yellow sand-shell, Lampsilis anodontoides, which were
not put into the crate but which must have found their way in by chance when still
small enough to pass through the screen wire of 14-inch mesh. Although the crate was
out only a little over two years, these two sand-shells were respectively 3.30 and 4.12
inches in length. Being elongate in form, they may have entered the crate when a
little more than an inch in length.

Table 14 embodies the result of measurements of length and counts of rings on
yellow sand-shells, Lampsilis anodontordes, from the St. Francis River, at Madison, Ark.

TABLE 14.—CLASSIFICATION OF 40 YELLOW SAND-SHELLS FROM ST. FRANCIS RIVER, ARK., ACCORDING
To LENGTH AND AGE.

| Age as indicated by interruption rings on Age as indicated by interruption rings on

Num- surface of shell. Num- surface of shell.
Length in ber Length in ber) | ee EE Eee
inches. each inches. each
length.| Three | Four | Five Six | older length.| Three | Four | Five Six | older
years. | years. | years. | years. : years. | years. | years. | years. :

@ Shell with stunted appearance.

The observations indicate that mussels of this species in the St. Francis River attain
a length of 4 to 4% inches in 4 years, that they may attain a length of 4 inches in 3 years,
and that 6 years or more are ordinarily required to attain a length of 5 inches.

In summary, the rate of increase in length of fresh-water mussels varies from 1% or 2
inches per year for paper-shells (as Lampsilis levissima) to 4 inch (a little more or a little
less) per year for the niggerhead and related species, while an intermediate rate of 34 or 1
inch per year characterizes the muckets and pocketbooks, and a slightly more rapid rate
the sand-shells. In general the rate of growth is so directly proportioned (in inverse

FRESH-WATER MUSSELS. 129

ratio) to the thickness of shell of the species as strongly to suggest that the limiting
factor of growth ordinarily is not organic food, but the mineral content of the water

(p. 87).
PRESENCE OF SO-CALLED GROWTH RINGS.

The ages of animals may not infrequently be determined, at least approximately, by
the ‘rings of growth,” on teeth, scales, scutes, or otoliths (ear stones), or other hard parts
of the body. A similar criterion of age determination is of course commonly applied to
trees. More recently the rings on the scutes of terrapin and those on the scales and
otoliths of fish have been used for the same purpose.

This method of determining age is generally based upon the belief that the cessation
or the slowing down of growth during the winter season may cause the formation of a
distinguishable line or band on a concentrically growing structure. By counting the
number of winter lines or bands the number of winters through which the animal has
passed is ascertained, or by counting the number of zones between such rings, beginning
with the center zone, the number of seasons of growth is discovered. It is one thing to
know that such rings are formed in winter, but quite another thing to learn just how or
why the rings are formed. It is also of primary importance to determine whether or not
similar rings may be formed upon any other occasion than the occurrence of a season of
winter. In.the case of the fresh-water mussel shell, at least, these questions can be
answered by observations and experiments. (Coker, unpublished notes.)

Some years ago when collecting mussels in lakes in southern Michigan it was ob-
served that the shells of the fat muckets were all marked with several conspicuous rings
which were approximately equally spaced on all the mussels of a bed. It seemed a
natural inference that these dark rings represented winter periods and thus afforded a
means of age determination. At another time, upon examination of mussels which
had been measured and placed in crates in the river two years previously, it was observed
that there were rings apparently corresponding to the two winters which had elapsed
since the date of original measurement, but that there was also another ring which
marked the exact size of the mussel when originally measured. (See text fig. 6.)
Subsequent observations showed that whenever a mussel was measured and replaced in
the water, a ring would be formed on the shell before growth in size was resumed.

These observations led to an effort by microscopic examination of sections of the
shell to determine the significance of rings which apparently could be formed either by a
season of cold weather or by the procedure of taking a mussel from the water, applying a
caliper rule, and returning it to the water. To make clear what was learned from the
study of the sections it is necessary first to explain briefly the mode of formation of shell
which leads to growth in size.

MODE OF FORMATION OF SHELL.

The shell is composed of four distinct layers (text figs. 1, 2, and 3). The outer is the
horny covering called the periostracum.? Immediately beneath this is a calcareous
layer composed of prisms of calcium carbonate set vertically to the surface. This pris-
matic layer is very thin, though thicker than the periostracum, and is likely to remain

@ The fact that the periostracum itself comprises 2 layers of separate origin, while very significant in some respects, is imma-
terial in this connection.

130 BULLETIN OF THE BUREAU OF FISHERIES.

attached to the periostracum when that is peeled off. Beneath the prismatic layer and
composing nearly the entire body of the shell is the nacreous or mother-of-pearl layer,

= whichis made upof almost
A NUH Tis ae
we ‘ ‘

am innumerable thin laminz
Me lying one upon the other
z (gprs and sealer to the inner
Hijo” CaS surface of the shell.
Through the nacre, inter-
secting its laminz,passesa
very thin fourthlayer, the
hypostracum,? secreted
by the muscles (p. 172).
Growth of shell in
thickness is accomplish-

Fic. 1.—Diagrammatic and highly magnified camera lucida drawing of section of ed by the laying down of
SE ee Tait ie: Br cece Wath nial Cana ee Scene. lai, peta
Note the folds of epidermis which give the shell its ‘“‘silky”” appearance. the entire surface of the

mantle. layer after layer is added to the inner surface of the shell, each layer exceed-
ingly thin and generally a little larger than the preceding. Ring after ring is added
to the margin of the shell, but since growth is most
pronounced in the posterior (rear) direction, less
so in a ventral, and still less in the anterior
(forward) direction the rings must be widest be-
hind and narrowest in front. It will be noted
that any mussel shell is marked with innumerable
concentric Jines. Superficially such lines suggest
the annual rings seen on the section of the trunk
of a tree, but the resemblance is entirely mislead-
ing. The shell is added to in layers, but a very
great number of layers are made in a year.
Pfund (1917) has, by refined physical methods,
measured the thickness of the layers or laminz
and determined that the thickness in the examples
he studied lies between 0.4 w and o.6 yw. Transla-
ting these terms into ordinary language, there are
some 50,000 layers to an inch of thickness. A shell
one-quarter of an inch thick would have 12,500 lam-
inz; and if such a shell were 8 years old, more than
1,500 laminze would have been formed each year,
on the average. The outcropping edges of these rc. 2—Section through doublelayered peri-
laminze on the surface of a polished niggerhead shell _—_°stracum and prismatic layer. Nacreous layer
below not shown.

have also been measured and found to be spaced at

the rate of about 9,000 to the inch. Such lines are of course not visible to the naked eye,
and therefore the fine rings in evidence on the surface of the shell can not represent these

@ Not shown in figures herewith,

FRESH-WATER MUSSELS. 131

laminz but must have some other significance. They probably mean nothing more
than slight and frequent but irregular retractions of the margin of the mantle during
the process of shell formation, which have registered themselves in fine wrinkles on
the surface of the shell as it is built. The more conspicuous rings that mark some
shells still await our attention.

Fic. 3.—Sections through prismatic layer of Quadrula ebenus. ‘The sections were made at different levels, the prisms being smaller
and more numerous in the outer portion. 300.

Growth of the shell in length and breadth is accomplished by the secretion of shell
substance of the three layers by cells at or near the margin of the mantle. ‘There are
certain cells of a furrow in the margin of the mantle which form only periostracum,
and there is a certain portion of the mantle near the margin which forms only prismatic
shell substance, while the greater portion of the mantle surface normally forms only
nacre. Now, the important point for our present consideration is this: If, from any
cause, the margin of the mantle is made to withdraw within the shell to such an extent
as to break its continuity with the thin and flexible margin of the shell, then, as the
study of sections indicates, when the deposition of shell is resumed, the new layers

Fic. 4.—Section through the interruption ring on pocketbook mussel, caused by handling mussel
in summer. Simple duplication.

of prismatic substance and periostracum are not continuous with the old, end to end,
but are more or less overlapped by the old. In other words, growth does not begin
again exactly where it left off, but a little distance back therefrom, and the cause of this
is largely mechanical (text fig. 4). The amount of overlapping probably depends
upon the degree of disturbance and the extent to which the mantle has withdrawn
itself. The result isan unwonted duplication of layers. Counting inward from the

132 BULLETIN OF THE BUREAU OF FISHERIES.

outer surface we find not simply one series of periostracum, prismatic, and nacreous
layers, but periostracum and prismatic layers, then periostracum and prismatic again,
and finally the nacreous layer; the outer layers are doubled up.

SIGNIFICANCE OF RINGS.

In a case such as has just been described, where the outer layers are doubled up
as a result of an extreme retraction of the mantle, the effect of seeing a second horny
layer through the outer periostracum and the fairly translucent prismatic layer gives
the appearance of a dark band on the shell. This is the so-called growth ring, which
would be better termed duplication ring or interruption ring,® since its significance is
simply that the continuity of the outer layers is interrupted and the break is repaired
by overlapping. In other words, the periostracum and prismatic layers are ‘‘spliced”’
at this point. A duplication of layers should easily be observable on shells having
fairly light-colored or translucent periostracum but not on shells having a very dark
or opaque covering, and this is found to be the case. Growth rings or interruption
rings are commonly seen on pocketbooks, fat muckets, yellow sand-shells, floaters, and
other shells of light or only medium dark colors, while they are distinguishable with diffi-
culty, if at all, on niggerheads, .
pimple-backs, blue-points, and
other dark-colored shells.
ereerrpess =m ome ZZ EEE If the winter rings are

formed in the same way, and
the breaking of the continuity
Fic. 5.—Section through interruption ring (winter ring) on shell of pocket- of the outer layers is due to
book, Lampsilis ventricosa, showing repeated duplications of periostracum the withdrawal of the mantle
aug pramsHy layers in cold weather, then it would
be expected that several duplications would occur for a single winter. For cold
weather does not ordinarily fall with one blow. Periods of cold and warm weather
alternate for a time before winter sets fairly in, and again in the spring periods of low
and high temperature alternate before winter is entirely passed. Such fluctuations
of temperature are, of course, not so frequent or noticeable in the water as in the air,
but they do occur. It might be expected that the mussel would react to the first sharp
touch of winter by closure and a sharp withdrawal of the mantle but that the deposition
of shell would be resumed after a time, while further interruptions and resumptions
of growth would occur before the full effect of winter was experienced. Again in the
spring there might be alternate interruptions and resumptions of growth. ‘This, at
least, is the story which seems to be told by a section through a winter ring when
examined under the microscope. Text figure 5 shows such a section, where the alterna-
tion of periostracum and prismatic layers is repeated seven times, indicating six inter-
ruptions of growth. As virtually no increase in size occurs between the several inter-
ruptions, the duplicated or repeated layers are simply piled upon one another.

Interruption rings corresponding to seasons of winter differ from those corresponding
to a single severe disturbance of the mussel during the normal period of growth in that
the latter are rings of single duplication (text fig. 4), while the former show several repe-
titions (text fig.5). The winter rings in shells that have been observed are, therefore,
darker, though they may or may not be broader (text fig. 6).

@ See Isely, ror4, p. 18.

FRESH-WATER MUSSELS. 133
ABNORMALITIES IN GROWTH OF SHELL.

Seriously malformed mussels are not infrequently found, and peculiar interest
attaches to these because shellers generally entertain the belief that a mussel with de-
formed shell is most likely to contain a pearl. It seems possible that this belief is not
without some foundation. Pearls probably occur more frequently in parasitized mus-
sels, and many of the observed malformations are undoubtedly due to parasites.

A few distomids upon the mantle of Anodontas along or near the dorsal fold evidently
cause rusty stains in the nacre, abnormal growths on the inner surface of the shell, de-
formities of the hinge teeth, and dark or poorly formed pearls. Another parasite which
infests the reproductive or-
gans may almost completely
destroy the gonads of the fe-
male mussel, and in such case
the female may develop a
shell in the form of a male or
in a form intermediate be-
tween that of the male and
the female. There is evi-
dence that parasites found
encysted in the margin of the
mantle may give rise to stains
on the nacre at the margin of
the shell, that others cause
the not unfamiliar steely or
leaden-colored margins of
shells, while some produce a
pitting of the inner surface

Fic. 6.—A shell of the pocketbook, Lampsilis ventricosa, which was recovered after

of the shell. having been measured and confined in a wire cage in the Mississippi River for

One of the most common two years, four and a half months. The line a, an interruption ring, marks the

i size at the time of measuring. Thelines b and c evidently correspond to the two

and serious defects of other- periods of winter intervening. The inconspicuous sign of a winter interruption

wise valuable commercial preceding the date of measurement does not appear in the drawing. Natural
size. (After Lefevre and Curtis.)

shells is the presence of yel-
low and brown spots or bluish or greenish splotches in the nacre. Regardless of the
texture of the shell, the partially or wholly discolored buttons must be given a very low
grade. The spots are not always found upon the surface but may lie deep within the
nacre, to be brought out in the finished button by the processes of shaping and polishing.
Spotted shells are most common in certain rivers or parts of rivers, particularly where
the current is sluggish as in partly inclosed sloughs. Some of these discolorations are
often observed to be associated with a parasitized condition of the mussels, but it is
not probable that the spots are always due to parasites. The U. S. Bureau of Stand-
ards, in connection with an investigation of the bleaching of discolored shells, has found
that the dark-yellow and brown spots are mud fixed by the nitrogenous organic layer
which binds together the calcium carbonate, and that the pale-yellow color is apparently
due to an organic coloring matter in the organic layers. That bureau also reports that
the color of the pink shells is due to an organic coloring which is not confined to the
organic layer but permeates the whole shell.

134 BULLETIN OF THE BUREAU OF FISHERIES.

A striking form of shell associated with the presence of parasites is that with abbre-
viated gaping anterior margins, the edges being much thickened and in appearance
rolled outward. The explanation appears to be simply that the parasites check the
peripheral growth of the forward portion of the mantle, or perhaps, as the result of irri-
tation, keep the mantle more or less retracted in this portion. The shell being controlled
in growth by that of the mantle, its forward extension is checked, while growth in thick-
ness continues. Meantime the valves of the shell, growing normally in other directions,
are gradually and naturally pushed apart as successive layers are added in the posterior
portions. In consequence, after a time the valves of the shell cease to meet anteriorly
when the posterior margins are apposed. The result is a shell of normal dimensions
behind and below but abbreviated in front, where the edges are disproportionately thick
and gaping.

A very familiar form of abnormality is shown by the shellsin Plate XII. Whena
single shell of this type is first seen one is inclined to suppose that the deformity is the
result of a mechanical injury; but when shells marked by almost identically the same
abnormality are repeatedly found in various places and in different kinds of bottom, it
becomes evident that the explanation of mechanical injury is not applicable. It is prob-
able that a parasite checked the growth of the mantle at a particular point, so that, while
growth of shell continued normally both before and behind, it was so retarded at that
point that a permanently notched outline resulted. The subject of discolored and mal-
formed shells is not introduced, however, with the object of definitely explaining them,
but rather with a view to directing attention to the desirability of further investigations of
the parasites of mussels, as well as of certain features of the environment of mussels, as
regards their effects upon the form and quality of shells.

PLATE XII.

TEtoneit,. Win Sh IS 185 weg =A

Illustrating a peculiar abnormality of not infrequent occurrence among fresh-water mussels.

Burr, U.S: Be BP 1o1r9—20: PLATE XIII.

[See text, page 139, and compare Plate XXI, fig. 1,
showing marsupium occupying outer gills only.
Figures after Lefevre and Curtis.]

Fic. 1.—Niggerhead mussel, Quadrula ebenus;
Mmarsupium occupying all four gills.

5. 2.—Black sand-shell, Lampsilis recta; marsupium
occupying only posterior end of outer gills.

Fic. 3-—Three-homed_ warty-back, Obliquaria reflexa; marsupium
occupying middle region of outer gills.

Fic. 4.—Dromedary mussel,
Dromus dromas; marsupium
occupying only lower border
of outer gills. Anterior end of
gill not included in marsu-
pium but overhangs it.

Fic. 5.—Kidney-shell, Piychobranchus phaseolus; marsupium occupying entire lower
border of outer gills and much folded.

PART 2. LIFE HISTORY AND PROPAGATION OF FRESH-WATER
MUSSELS.

INTRODUCTION.

The life histories of fresh-water mussels present features in striking contrast to those
of other familiar mollusks of our seas and rivers. The American oyster, the clam, the
quahaug, and the sea mussel cast the eggs out to undergo development while floating in
the water. The pearly mussels of rivers and lakes, on the contrary, deposit their eggs
in marsupial pouches which are really modified portions of the gills, and there they are
retained until an advanced stage of development is attained. This particular feature of
breeding habit is not, however, unique to mussels. There are clams in coastal waters
that incubate the eggs in the gills, and the common oyster of Europe displays a similar
habit; but with all these the larve when released are prepared for independent life.
Such is not the case with fresh-water mussels. When the larval mussels are discharged
from the marsupial pouches, the mother has done all that she can for them, but they
still want the services of a nurse or foster parent, as it were. Lacking the structure and
appearance of young mussels, they display a peculiar form designated as glochidium,
and (with few exceptions) they will not continue to live unless they become attached to
some fish, upon which for a certain time they will remain in a condition of parasitism.

During the period of parasitic life the glochidium undergoes a change of internal
reorganization, or metamorphosis, with or without growing in size. After the change
is complete and a form somewhat similar to the adult is attained, the young mussel
leaves the fish to enter upon its independent existence. At this time, or soon thereafter,
some mussels, but not a great number, differ distinctly from the adult form in bearing a
long, adhesive, and elastic thread, or byssus, by which they attach to plants, rocks, or
other anchorage.

The life history, then, comprises the following five stages: (1) The fertilized and
developing egg retained in the marsupial pouches of the mother mussel; (2) the glochid-
ium, which, before liberation, is often retained for a considerable further period in the
gills; (3) the stage of parasitism on fish (or water dogs); (4) the juvenile stage, which may
or may not be marked by the possession of threads for attachment to foreign objects;
and (5) the mussel stage, with the usual periods of adolescence and maturity.

Such in brief is the typical story of the life of a pearly mussel. And yet each
species of mussel, and there are many, has its own characteristic story, which differs in
more or less important respects from those of other species. One kind of mussel will
pass through the stage of parasitism only upon a particular species of fish, while another
kind acquires the aid of certain other fish. The diversity in life histories also manifests
itself in such details as in the season of spawning, in the part of the gills in which the
glochidia are carried, in the duration of the incubation period, in the matter of growth
in size during parasitism, and in many other particulars. There are even some mussels
which, like exceptions that prove the rule, undergo complete development without being
parasites upon fish at any stage. It is advisable, therefore, to treat the several stages

135

136 BULLETIN OF THE BUREAU OF FISHERIES.

of life history at greater length and with such detail as is necessary to establish an
understanding of the conditions necessary for the successful propagation of the various
useful mussels and for the effective conservation of the mussel resources.

HISTORICAL NOTE.

It seems appropriate to remark that the considerable fund of knowledge which has
been gained in very recent years regarding the diversified life histories of fresh-water
mussels has been gained very largely as a result of scientific studies which have been
stimulated by the practical need of conserving an economic resource, and which have
been pursued preliminary to or in connection with the propagation of mussels as a
measure of conservation. To put it in another way, the development of the fresh-
water pearl-button industry has furnished an effective stimulus to biological studies
of high scientific interest and importance, just as the application of science to studies of
commercial mussels has rendered a distinct economic service.

As early as 1695 at least, the glochidium (see text fig. 8, p. 143) was observed in the
gills of European mussels, and was understood to be the larval form of the mussel, although
it was not then called a glochidium. Of the further stages of life history, science, as well
as the public, remained inignorancefor along time. So wide indeed was the gap of knowl-
edge that it became possible for a scientific writer in 1797 to advance’the theory that
the little mollusks noted in the gill pouches were not young mussels, but were parasites
of mussels constituting a genus and species of their own, which the investigator designated
with the Latin name Glochidium parasiticum. ‘This view, known as the Glochidium
theory, though it never won full acceptance, was strongly supported, and an exhaustive
inquiry and report upon the subject by a special committee of the Academy of Sciences
in Paris, completed in 1828, failed to effect its decisive defeat. When, however, in
1832, Carus was fortunate in observing the passage of the eggs from the ovary of the
mussel into the gill pouches, the false theory was definitely overthrown. The name
glochidium, suggested though it was by an erroneous assumption, has persisted ever
since, being now correctly understood to designate not a distinct animal but a typical
stage in the development of the mussels. f

It still remained to determine how and where this peculiar larva became trans-
formed into the familiar adult mussel, and this important gap was abridged by Leydig,
in 1866, when the glochidium was discovered in parasitic condition upon the fin of a fish.

The advance in knowledge of the life history of fresh-water mussels made in the
ensuing decades was slow and inconspicuous, and textbooks, both American and foreign,
continued to reproduce accounts based upon the inadequate observations of the life
histories of European mussels. A period of distinct progress came with the extensive
and admirable investigations conducted by Lefevre and Curtis (1910, 1910a, and 1912)
in association with the Bureau of Fisheries during the years 1905 to 1911. These inves-
tigations served to reveal not only some of the distinctive features of the breeding
habits and life histories of the American mussels as contrasted with the European
species but also the great diversity existing among the many American species, in breed-
ing season, period of incubation, and form of glochidia. The results of the investiga-
tions aggregated a mass of original observation on various phases of the propagation
and life history of fresh-water mussels. Other investigations, notably Ortmann’s (1911,
1912, etc.), have contributed materially to knowledge of the breeding characters and

FRESH-WATER MUSSELS. 137

habits and the development of mussels, while Simpson (1899, 1900, 1914, ete.), Walker
(1913, 1918, etc.), Ortmann (1911, 1912, 1913, etc.), and others have greatly extended
our information regarding classification, distribution, and structure.

With the establishment of the Fisheries Biological Station at Fairport, Iowa, and
the beginning of its scientific work in 1908, the studies pursued by the scientific staff
of that station, in connection with the propagation of mussels, made still further advances.
Chief among the results of the studies conductéd at this station may be mentioned the
discovery that particular species of mussels are restricted in parasitism to one or a few
species of fish, the rearing of young mussels in quantity from artificial infections upon
fish, the demonstration that the glochidia of certain species of mussels may grow mate-
rially in size during the period of life on the fish (being, therefore, true parasites), and the
observation that one noncommercial species of fresh-water mussel normally completes
its life history without a stage of parasitic life.%

Finally it should be remarked that one of the most difficult of all gaps to bridge
was the rearing of young mussels after they leave the fish. Strange as it may seem,
all attempts to keep alive and to rear the young mussels under conditions of control
failed of result. Lefevre and Curtis (1912, pp. 182, 183) recorded the rearing from an
artificial infection of a single young mussel which attained a size of 41 by 30 mm. In
1914, however, Howard was successful in rearing over 200 Lake Pepin muckets from
an artificial infection, when the infected fish were retained in a small floating basket in
the Mississippi River (Howard, 1915). ‘These mussels attained a maximum size of 3.2
cm. in the first season; and in subsequent years many of them were reared to maturity,
the glochidia developed from their eggs were infected upon fish, and a second generation
was reared to an advanced stage. In that year (1914), too, Shira, using watch glasses
and balanced aquaria, reared a few mussels from an artificial infection to a maximum
size of 0.44 cm. in 291 days. In the same year, though from an experiment initiated
by the senior author in the fall of 1913, young mussels were reared in a pond, from an
artificial infection of fish liberated in the pond, to a maximum size in the first season of
3-5 cm. Some of these mussels at the age of 4 years had attained sizes suitable for
commercial use in the manufacture of buttons. The same species, Lampsilis luteola
(Lamarck), known as the Lake Pepin mucket, was used in all of these experiments.
Subsequent experiments on a larger scale conducted both at Fairport and in Lake
Pepin are mentioned on a later page.

AGE AT WHICH BREEDING BEGINS.

The age at which mussels begin to breed varies with the species. There is reason
to believe that the paper-shell, Lampsilis (Proptera) levissima, breeds in the same sum-
mer during which it leaves its host or when just 1 year of age from the egg. Anodonta
imbecillis and Plagiola donaciformis apparently breed in the second summer. The small-
est breeding Quadrula observed was a pig-toe, Quadrula undata, 30 mm. (about 1.2
inches) in length, and 4 or 5 years of age as evidenced by the interruption rings. The
smallest washboard, Quadrula heros, observed in breeding condition was 91 mm. (3.58

@ Vefevre and Curtis (1911) had previously observed and reported the fully developed juvenile mussels in the gills of Strophitus
edeniulus. Later, Howard (1914) while showing that.the glochidia of that species will become parasitic on fish and undergo devel-
opment under the usual conditions, discovered that another species, Anodonta imbecillis, normally develops without the aid of
fish. (See p. 156, below.)

138 BULLETIN OF THE BUREAU OF FISHERIES.

inches) in length and of an estimated age of 8 years. Females of the Lake Pepin mucket,
Lampsilis luteola, reared at the U. S. Fisheries Biological Station, Fairport, Iowa, were
found with mature glochidia in the third season of growth, a period of slightly more
than two years after dropping from the fish. Undoubtedly not all species breed at
such an early age, and it perhaps takes the heavier Quadrulas 6 or 8 years to reach the

breeding age.
OVULATION AND FERTILIZATION.

’ With a few exceptions,” the sexes are separate in American species of fresh-water
mussels. The discharge of eggs (ovulation) has been observed in some instances (Latter,
1891; Ortmann, 1911, p. 298; and Howard, 1914, p. 35). The eggs pass from the
ovaries by way of the oviduct, through the small genital aperture into the cloaca and
suprabranchial chambers, and then into the portions of the gills which are to serve as
brood pouches. The sperm which has been thrown out into the water by one or more
male mussels, doubtless those in the near vicinity of the female, is taken in by the female
with the respiratory current, but whether the eggs are fertilized while on the way to
the brood pouches or after reaching them is unknown, since the process of fertilization
in nature has never been observed. We have no clue either as to the nature of the
stimulus which may excite ovulation or as to how it may be timed so as to take place
when a supply of living sperm is available in the water for the fertilization of the eggs.
Certain it is that the eggs are usually fertilized, although in the brood pouches of any
gravid mussel that may be examined there are found a good many eggs that have failed
to develop, presumably because they have escaped fertilization.

The discharge of sperm in great quantities may not infrequently be observed when
male mussels are retained in aquaria. The writers have observed in a large tank at the
Fairport station a male mussel discharging sperm. During the process it traveled exten-
sively over the bottom, leaving in the sand a long winding furrow which was filled with
a white cloud of sperm. Perhaps the discharge of sperm and its introduction with the
respiratory current into the female constitute the exciting cause of ovulation. Exper-
iments are clearly wanted to determine this question. The arrangement of the eggs
in the several chambers of the brood pouches varies according to the character of the
pouch, and will therefore be more conveniently described in the following section.

BROOD POUCHES OR MARSUPIA.

The gills of mussels, as of other lamellibranch mollusks, are thin flaps that hang
like curtains from each side of the body, a pair on each side. As explained in another
place (p. 175) each gill, thin as it may appear, is really a double structure, or more cor-
rectly is a sheet folded upon itself just as a map, larger than the page of a book in which
it is bound, is folded on itself. There is this difference; the map may be unfolded at
will, but the gill may not, because the two sections are attached together by many par-
allel partitions which divide the narrow space between the sheets into a lot of long
slender tubes. It is into these tubes that the eggs are deposited, and when filled with
eggs or glochidia the several tubes are greatly distended (text fig. 7). The entire gills
or the parts of the gills bearing the eggs then appear not as thin sheets but as thick

@ The known exceptions are, occasionally, Quadrula rubiginosa and pyramidata, and Lampsilis parva, and, usually, Anodonta
imbecilis and henryana (Sterki, 1898), and Symphynota compressa and viridis (Ortmann, 1911, p-. 308).

FRESH-WATER MUSSELS 139

pads. In this condition the marsupial pouches might be compared to pods filled with
closely packed beans, the individual beans representing not single eggs but separate
masses of eggs.

When the tubes of a mature female mussel are empty the gills may be as flat as
those of the males, or they may appear as sacks with thin translucent walls. The lat-
ter condition generally characterizes the long-term breeders, in which the portions of
the gill intended to receive the eggs are permanently enlarged.

The marsupia are conspicuously colored in some species, but in Ginter species
the coloration is not necessarily attributable to the same cause. In the niggerhead,
Quadrula ebenus, the pig-toe, Quadrula undata, and other species, the bright-red appear-
ance of the marsupia is due to the deeply colored eggs showing through the thin walls
of the marsupia. In the yellow sand-shell, Lampsilis
anodontoides, the pocketbook, Lampsilis ventricosa,
and the Lake Pepin mucket, Lampsilis luteola, the a5 Z ou
pigment lying in the outer walls of the ovisacs takes a iy Zi \
the form of dark bands on the lower portion of the
marsupium, the pigmentation becoming more dense
and conspicuous when the mussels are gravid. In the
young Lampsilis ellipsijormis that we have seen the
pigmentation is more intense and more general, ex-
tending even to the upper portion of the marsupia,
but there restricted to the partitions separating the
ovisacs. The color in the black sand-shell, Lampsilis
recta, and the Missouri niggerhead, Obovaria ellipsis, is
white or cream, in contrast to the yellowish color of
the remainder of the ovisacs.

The extent to which the gills are specialized or
modified to receive and retain the eggs while they are Fic. 7.—Horizontal section of a water tube of a
developing into the glochidia has been largely utilized pagiapernianes pepe ace ts a eed
in the classification of mussels. All of the North glochidia. (After Lefevre and Curtis.)
American species belong to the groups in which the
brood pouch or marsupium comprises either all four gills or only the outer gills.
This group, in turn, is divided into the following seven divisions, according to the spe-
cializations involved (Simpson, 1900, p. 514):

1. Marsupium occupying all four gills, as in the niggerhead mussel, Quadrula ebenus, and perhaps
all Quadrulas (Pl. XIII, fig. r).

2. Marsupium occupying the entire outer gills, as in the heel-splitter, Symphynota complanata (P1.
XXI, fig. 1).

3. Marsupium occupying the entire outer gills, but differing from the second in that the egg masses
lie transversely in the gills, as in the squaw-foot, Strophitus edentulus.”

4. Marsupium occupying only the posterior end of the outer gills, as in the black sand-shell, Lamp-
silis recta, etc. (Pl. XIII, fig. 2).

5. Marsupium occupying a specialized portion in the middle region of the outer gills, as in the
three-horned warty-back, Obliquaria reflexa (P1. XIII, fig. 3).

6. Marsupium occupying the entire lower border of the outer gills in the form of peculiar folds, as
in the kidney-shell, Ptychobranchus phaseolus (P1. XIII, fig. 5).

7. Marsupium occupying the lower border only of the outer gills, but not folded, as in the drome-
dary mussel, Dromus dromas (Pl. XIII, fig. 4).

Most of the commercial species belong to the first and fourth types.

140 BULLETIN OF THE BUREAU OF FISHERIES.

With such species as have all four gills, or the entire outer gills serving as marsupia,
the sexes are scarcely, if at all, distinguishable from an examination of the shell; but
when a distinct portion of the outer gill is used as a brood pouch there is usually a pro-
nounced inflation of the shell over the region of the marsupia, so that the female mussel
is clearly marked on the exterior. (See also Grier, 1920.)

It is to be remarked that the eggs packed into the water tubes or marsupial cham-
bers do not usually remain free of each other, but become either attached together by
their adhesive membranes or else embedded in a common mucilaginous substance. When
the eggs or glochidia are removed from the gills they do not separate from one another
unless fully ripe, but remain in large masses which conform to the shape of the tubes
from which they have been removed? (Pl. XIV, figs. 8-11). It occurs frequently
when gravid mussels are disturbed that the eggs, in whatever stage of development they
may be, are aborted or discharged into the water. This not infrequently happens in
aquaria, and doubtless may occur in nature. Abortion is presumed to be due to a de-
ficiency of dissolved oxygen in the water; the mussel, beginning to suffocate, discharges
the eggs in order to employ its gills more effectively for respiration.

SEASONS OF DEPOSITION OF EGGS.

We must distinguish with fresh-water mussels the seasons when eggs are matured,
passed out of the body, and deposited in the marsupial pouches from the season when
the developed glochidia are cast out into the water. The term ‘‘spawning season’”’
might be misleading, because it is commonly used to refer to the occasion when the
glochidia are discharged to the exterior, and this may be weeks, months, or some-
times nearly a year after the eggs are actually extruded from the reproductive organs
and the young are launched into existence. In general, the deposition of eggs—the
actual spawning process, scientifically speaking—occurs with the long-term breeding
class (see below) in the latter part of the summer or early fall. In the short-term
breeding class spawning usually takes place in June, July, or August, although in one
or two species it is known to occur as early as April. One mussel, the washboard,
deposits eggs only in the late summer and early fall, August to October.

It is the experience of the Fisheries Biological Station at Fairport that the spawn-
ing seasons of mussels fluctuate to some degree in different years, no doubt because the
ripening of mussels is affected by varying conditions of water temperature. There are
also, of course, some differences of breeding season corresponding to differing climatic
conditions in more northern or more southern waters.

SEASONS OF INCUBATION OF EGGS.

Generally speaking, fresh-water mussels may be divided into two classes with re-
spect to their breeding seasons—the long-term breeders and the short-term breeders.

In the case of the long-term breeders the eggs are fertilized during the middle or
latter part of the summer and, passing into the brood pouches, develop into glochidia,
which are usually matured by fall or early winter. The glochidia may pass the entire
winter in the brood pouches, to be expelled during the following spring and early summer.
As might be expected, there is some overlapping of successive breeding seasons; females

4 Exceptions to this rule are noted by Ortmann (ror1, p. 299). In such cases (the genera Anodonta, Anodontoides, Sym-
phynota, and Alasmidonta) the eggs or glochidia are entirely separate from one another and flow out freely when the ovisac is
opened.

FRESH-WATER MUSSELS. 141

that have discharged the glochidia quite early in the summer may already have the
brood pouches filled with eggs for the next season, while other mussels of the same spe-
cies are still retaining the glochidia developed from eggs of the past year. ‘This fact is
obviously favorable to the work of artificial propagation, rendering it possible to obtain
glochidia of certain species of mussels at any time during the year. Thus in Lake Pepin,
a widened portion of the Mississippi River between Minnesota and Wisconsin, where the
Lake Pepin mucket or fat mucket is being propagated on a large scale by the Bureau,
a sufficient number of gravid mussels can be obtained for carrying on the operations from
the time they are commenced in May until they are terminated in October or November.

In the case of the short-term breeders the breeding activities are restricted to a
season of about five months, from April to August, inclusive. The period of incubation
for any individual mussel of this class is undoubtedly very much shorter, although tem-
perature or other conditions may cause the period of incubation to be lengthened or
shortened.

In Tables 15 and 16 there are listed the more common species of mussels with indi-
cation of the months in which females have been found with mature glochidia. The
lack of a record of gravidity may, of course, be due in some cases not to an actual gap
in the breeding season but to the want of opportunity for sufficient observation of the
species during a particular month. (See also Ortmann, 1909; Lefevre and Curtis, 1912;
and Utterback, 1916.)

The commercial and noncommercial species are grouped in different tables, not
only because the records are more complete for the former but because those who are
concerned with the conduct or regulation of the mussel fishery will be interested almost
exclusively in the mussels of direct economic importance.

TABLE 15.—THE More ImportTaANT COMMERCIAL MUSSELS, WITH INDICATION OF MONTHS DURING
WuicH FEMALES HAvE BEEN FouND WITH MATURE GLOCHIDIA.

Scientific name. Common name. al2/ el RIS a) 2 Pilald|3si|¢g
Slalal<¢/S/4/S]/</alolaja
| | |
Cyprogenia irrorata...............- an-shell. Seve sani ie seu snivniesssteieal oa aacd SER eae Boao Woe) encd likiad bene (EON) 2 ee,
Dromus dromas.............. een promMedary MUSSEL. oe ciccciscoceess eel ewee|boee Sealbann nod J eeoal oad bee re || BS leno
Lampsilis anodontoides ...| Yellow pane Sher Brystceicie SSeS SSeS esd leads aU oS ole <1 Soils
Lampsilis fallaciosa. --.-........... Slotighisarid-shell arse heats cen csece|tonalcces|eene SSeS ee sls ele lo Gillie
Lampsilis higginsii................. Fiigpin'sievey.cie oon sxe Bric |e 4 EOE se reread) le. 8 Spre Ce ot loa
Lampsilisligamentina........ ere POLITICA Cn ers Cerete/ceirtorts eicracie Spee les SoS ap > lie sill all S <
amostlisilutealas (oj o..: cnc cacees || Mat mutcket 50. oii cisisjecss 5 lhe. cil [ies] esa ee 9 | fib (ee. cal (n> ll ip
Lampsilis recta... .. Soe] ceo | excel Wi ose | oe Mee ca ese A Se
Lampsilis ventricosa...............| Pocketbook....... Saeko Peele cxsetace ince | excl) am
Obliquaria reflexa x |x | xX) x} X |----}.. el. elses
Obovaria ellipsis. . bal less he cd Mlotscl ft, 6} eS fabs] est hes
Plagiola securis. Sree |§28-\| Be. fea ies Apes |) elie <5 a
Pleurobema zsopus Rey SL PUN ee ee Se teed nes seeped eed seed en oe ied gles |biad Good BAS
Ptychobranchus phaseolus......... Kidney-shell Sapeed oeoee Te etealicen|tsae 5e5e abe Baad le 4 Sa ESN ES
Quadrula cylindrica................ Rabbit's foot............ Sod end no oclaaor Poe > Salli al hone De ooed
Quadrula ebenus.................. INipperhend totes toss nce conacemelemecleccsloene xxi || oe ix lie nco4
Qiiadrilasheros oo 0- scscecs= scones Washboard............. boyfie <1 1 4 Bae eked Pek aes ears | bake || ca ee
Quadrula lachrymosa.............. Maple-leaf.....2 54.52.25. Sone | eon eallex: e| pocs tee ome
Quadrula metanevra............... Monkey-face............ re pee |) es IRs lend head
Quadrula obliqua............. ...! Ohio River pig-toe...... Sel) B54) Soul Gel Ss Sl hes
Quadrula perplicata Round Lake.......... BOOG Neo 1) ese) he.sal Gocd Oana
Quadrula plicata...... Blue-point............ x ls |e ix eee
Quadrula pustulata................ Pimple-back.......... Tae (22-< | lve sells bone
Quadrula pustulosa--.............. d socd| esilles'f esi|soae
Quadrula rubiginosa Ce selesel) 6.9 dcne
Qaadrila\sohday. 22S seh ieee. Foi tao ele ond broad
Quadrula undata pena NS. ne ca setb aobdoocUpmonr: Coddor ane c| heed [ead pees bacd 6 Ab <ol> <a Mies
Quadrula undulata ax eri
Symphynota complanata pe sulhesule
Tritogonia tub c : ee |x | ox
Unio crassidens... :| Elephant ’s ear. By fo ce| le <
Unio gibbosus... . -| Lady-finger..... xx

75412°—22——10

142 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 16.—SOME NONCOMMERCIAL MUSSELS, WITH INDICATION OF MontTHS DuRING WuicH FEMALES
Have BEEN Founp witH GLOCHIDIA.

Scientific name. Common name.

Jan
| Feb
Mar,
Apr
May.
June
| July.
Aug
=
| Oct
| Nov
| Dec.

Alasmidonta pena
Anodonta cataracta. .

‘Anodonta corpulenta .
Anodonta grandis. .

x
‘Anodonta imbecillis x
Anodonta implicata . nos
Anodonta stewartiana............. ieieiel tivistel| me
Anodonta suborbiculata............ Paperahell eer sccvene cease oeeet > Sallie ol [GaSe

Arcidens confragosus... Rock Bocket book :
Gonidea angulata....
Hemilastena ambigua
Lampsilis alata......
Lampsilis borealis. ...
Lampsilis capax............0.s000-
Lampsilis gracilis..................
Lampsilisiris..........
Lampsilis ellipsiformis.
Lampsilis lavissima
Lampsilis lienosa. .
Lampsilis parva. . “Baan!
Lampsilis subrostrata. . ae A one esac
Ramrpsilis\ Cexqsensistc.. sce cee cae lacc cee ee tne boron ee ieee macmiameae BGA HbAd badd Gace
Lampsilis ventricosa satura. Bnd bees Geee ceca
Plagiola donaciformis. . a5 dl tinde

KHKAM

KA:

Plagiola elegans..........

Ptychobranchus phaseoltis..2 52+ .0|) Midney-shell! sec. enci ces. oes oscil sce|seee|Soeelaneelseee|eeeeleen.
Quadrula cooperiana...

Quadrula granifera................- Purple warty-back eacenaitcte elec recall see leeerel comedies
Strophitus edentulus............... Satiaw-footicc.csentan. meee wane aie ae

Symphynota costata..............- Fluted'shelly ve incacveceses ccs cowan ictal leicicle

Symphynota compressa.......--+.-[--.-.sseeeeceee

Truncilla arczformis, Sugar-spoon. .

‘Truncilla capszformi: Oyster mussel

Unio tetralasmus

It will be observed that, generally speaking, the several species of Quadrula and
Unio, as well as Pleurobema e@sopus (bullhead), Tritogonia tuberculata (buckhorn), and
Obliquaria reflexa (three-horned warty-back) are short-term breeders, while the species
of Lampsilis, as well as Obovaria ellipsis (hickory-nut), and Symphynota complanata
(white heel-splitter), Plagiola securis (butterfly), and others are long-term breeders.
Most interesting is the case of the washboard, Quadrula heros, which, from its taxonomic
position, would be expected to have the short summer breeding season, but which at
least simulates the long-term breeders. The glochidia become mature from early
autumn to winter, apparently varying with the latitude, but so far as known are not
held for a long period after maturity. They react like the short-term summer breeders
when removed from the water in that they quickly abort the contained glochidia. It
-may be either that its relationship has been incorrectly appraised or that it represents a
transition stage from the short-term to the long-term breeding class. Certainly it is
the one species of mussel subjected to close study which has never been found to have
either eggs or glochidia in its gills during the summer months.

Finally, it may be remarked that the terms “short-term” and ‘‘long-term,” as
applied to the breeding season, are perhaps inappropriate and misleading. So far as
we know, in all species (except the washboard, in one respect) the development of the
egg into the glochidium follows promptly on ovulation, occupies a period of a very few
weeks, and occurs during warm weather. The short-term breeders are those which
throw out the glochidia at once, while the long-term breeders carry them over until the
following year. It seems to be a general rule that the short-term breeders pass through
all phases of reproductive activity on a rising temperature, while the long-term breeders

FRESH-WATER MUSSELS. 143

begin their breeding activities on falling temperatures of one season, but discharge the
glochidia on rising temperatures of the following season.

Several experiments have shown that the glochidia taken from long-term breeders
in the fall of the year may be successfully infected upon fish and that the young mussels
will undergo development. It appears, however, that these “‘green’’ or newly formed
glochidia require a longer period of parasitism than those which have been nursed by the
parent through the winter season (Corwin, 1920).

The origin and purpose of the retention of glochidia during the winter season re-
mains a mystery. This may be an instance of nature’s remarkable adaptations, per-
mitting the development of the egg to occur during the warmer months of summer, and
the glochidia to be discharged for attachment upon fish in the spring when there is a
general tendency toward an upstream movement of fishes. It is distinctly interesting
to note that the long-term breeders (mucket, sand-shells, etc.), as a general rule are
mussels of much more rapid growth than the short-term breeders (niggerhead, pimple-
back, ete.), although the young of the former are delayed for nearly a year in becoming
attached to fish and completing their metamorphosis.

It is important to point out one fact which is clearly established by data in Table
15, page 141. There is no month of the year in which a considerable number of commer-
cial mussels are not gravid with glochidia. This fact deserves careful consideration in
connection with measures of conservation, since it makes impracticable the protection
of mussels by ‘‘closed seasons” of months based upon the times of breeding.

GLOCHIDIUM.

The larval mussel or glochidium, when completely developed and ready to emerge
from the egg membrane and before attaching itself to
a fish, has apparently an extremely simple organization.
The soft mass of flesh possesses neither gills nor foot nor
other developed organ characteristic of the adult mussel,
but it bears a thin shell composed of two parts which
are much like the bowls of tiny spoons hinged together
at the top (text fig. 8). The two parts or valves of the
shell can be drawn together by a single adductor muscle,
but, when the muscle is relaxed, they gape widely apart
as shown in the illustration. There are also on the
inner surface of each side of the body several pairs of
“sensory” cells with hairlike projections. It has been SN s/s
assumed that the cells were sensory in function, and ic. 8—Glochidium of Quadrula heros with
recently L. B. Arey, working at the Fairport station, een eee ri = ee ake
determined after detailed experiments upon several thevalves. Inner and outer sensory hair
species of Lampsilis and Proptera that there is a well- ie OHS AG Teale ee Soo eine ay
developed sense of touch centralized in the hair cells. He regards the tactile response
as entirely adequate to insure attachment of the glochidium.

In at least three genera of American mussels (several species of Unio, Anodonta,
and Quadrula) the glochidium possesses a peculiar larval thread of uncertain signifi-
cance (text fig.8). This thread, so generally mentioned in textbooks based upon studies
of European mussels, is not found on the great majority of American species. We

144 BULLETIN OF THE BUREAU OF FISHERIES.

have observed it on glochidia of the following species: The washboard, Quadrula heros,
the blue-point, Q. plicata, the pig-toe, 0. undata, the bullhead, Plewrobema @sopus, the
spike, Unio gibbosus, the slop-bucket, Anodonta corpulenta, and the river pearl mussel,
Margaritana margaritijera. The squaw-foot, Strophitus edentulus, has a modified larval
thread (Lefevre and Curtis, 1912, p. 173).

That the structure of the glochidium is less simple than appears to the ordinary
observer is shown by the fact that, in the fully developed glochidium, close microscopic
study will reveal the rudiments of foot, mouth, intestine, heart, and other organs which
will not, however, assume their destined form and functions until after the period of
parasitism. The shell of the glochidium is firm but somewhat brittle owing to the car-
bonate of lime of which it is partly composed. If the lime is dissolved out with acid,
the remaining shell, composed only of cuticle, preserves its general form, although it
becomes wrinkled and collapsible.

The number of glochidia borne in the brood pouches of a fully grown female mussel
according to the counts and computations made by various observers, varies in the
different species from about 75,000 to 3,000,000. An example of the paper-shell, Lamp-
stlis gracilis, yielded by computation 2,225,000 glochidia. The mussel was 7.4 cm.
(about 3 inches) in length. Several examples of the Lake Pepin mucket yielded glo-
chidia in the following numbers, the length of the mussel being indicated in parentheses:
(6.1 em.) 79,000; (7 em.) 74,000; (7.4 cm.) 125,000; (8.5 cm.) 129,000.

The glochidia of mussels are very diverse in size and form, although for any given
species the dimensions and shape of the glochidium have been regarded as fairly con-
stant (Surber, 1912 and 1915). Differences in sizes of glochidia within the species are
noted by Ortmann (1912 and 1919)* and Howard (1914, p. 8). The matter requires
investigation. As regards their form, glochidia are separable into three well-known types:
(1) the “hooked” type, (2) the ‘““hookless” or “‘apron’’ type, and (3) the ‘‘ax-head”’ type.

(1) The “hooked” type (Pl. XIV, figs. 1 and 2) possesses a rather long stout hinged
hook at the ventral margin of each triangular or shield-shaped valve. These glochidia
are usually larger than those of the other two types and the shell is considerably heavier.
The hooks are provided with spines which no doubt assist the glochidium in retaining
its hold upon the host. As ali hooked glochidia generally (though not invariably) attach
to the exterior and exposed parts of the fish, the fins and scales, the advantage of the
heavier shell and stout hooks may readily be seen. This type of glochidium is possessed
by mussels of the genera Anodonta, Strophitus, and Symphynota (floaters, squaw-foot,
and white heel-splitter, etc.). (See also text figs. 9 and 12.)

(2) The shells of glochidia of the ‘‘hookless’’ type (Pl. XIV, figs. 3, 4, and 5), while
lighter than those of the hooked type, are nevertheless of sufficient strength to with-
stand considerable rough handling. So far as we now know, all the glochidia of this
type are gill parasites with the exception of the washboard, Owadrula heros, which
has been successfully carried through the metamorphosis on both gills and fins. The
hookless glochidia vary rather widely in shape and in size (text figs. 9 to 12); among
the smallest is that of the spectacle-case, Margaritana monodonta (0.05 by 0.052 mm).;
while one of the largest is that of the purple pimple-back, Ouadrula gramifera (0.290 by
0.355 mm.). Placed side by side, about 500 of the smallest or about 80 of the largest

a Ortmann gives many cases of small discrepancies between his measurements and those of others, based no doubt upon the
different sources of material. In several cases he has observed differences in sizes of glochidia from different individuals. See
papers in the Nautilus, Vol. XXVIII, 1914, and Vol. XXIX, 1915. In oneinstance he reports glochidia of two sizes from one indi-
vidual (1912, p. 353). See also Surber, 1912, p. 4.

Bury. U. S. B. F., 1919-20.

PLATE XIV.

(Figures from Lefevre and Curtis, ror2.]

Fics. rand 2.—Hooked glochidium of Symphynota costata.

Fics. 3, 4, and 5.—Hookless glochidium of Lam psilis subro-
strata.

Fics. 6 and 7.—Ax-head glochidium of Lampsilis (Prop-
tera) alata.

Fic. 8.—Conglutinates (masses of glochidia) from the three-
horned warty-back, Obliquaria reflexa.

Fic. 9.—Portion of conglutinate of Obliquaria reflexa,
magnified. Glochidia still within egg membranes which
are closely pressed and adhering together.

Fic. 1o.—Conglutinates (masses of glochidia) from the
mucket, Lampsilis ligamentina.

Fic. 11.—Portion of conglutinate of Lampsilis liaamentina
magnified. Glochidiainclosed in membranes are embedded
in a mucilaginous matrix.

Burnes: Baebes rorg—20s

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KARAS

1.—Gill ef a black bass infected with glochidia of
mucket, Lampsilis ligamentina.

VITT, ETI Co

fil

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Fic. 3.—Three gill filaments of rock bass, with glochidia of
mucket.

Fic. 2.—Part of fig. 1, enlarged.

Fic. 4.—Stages in formation of cyst surrounding a glochidium of the mucket.

Taken at 15 minutes, 30 minutes, 1 hour,
and 3 hours, respectively, after infection.

lic. 6.—Young Lake Pepin muckets at
ages of 1, 2, 3, and 4 months, respec-
Fic. 5. Young muckets, one week after liberation from the fish, showing new tively. Natural size.
growth of shell, cilia on foot, and positions assumed in crawling. Enlarged.

(Pigs. 1-5 after Lefevre and Curtis. }

FRESH-WATER MUSSELS. 145

BOS Coe
try 20002

m oO
Fic. 9.—Glochidia of common fresh-water mussels. (After Surber, 1912 and 1915.)

a, Alasmidonta calceola. 9, Anodontoides ferussacianus k, Parris anodontoides.

6, Alasmidonta marginata. subcylindraceus. 1, Lampsilis breviculus brittsi.
c, Anodonta cor pulenta. h, Arcidens confragosus. m, Lampsilis fallaciosa.

d, Anodonta grandis. i, Cyprogenia irrorata. n, Lampsilis gracilis.

e, Anodonta imbecillis. J, Dromus dromas. o, Lampsilis higginsii.

J, Anodonta suborbiculata.

146

BULLETIN OF THE BUREAU OF FISHERIES.

q t

Fic. 10.—Glochidia of common fresh-water mussels. (After Surber, r912 and 191s.)
a, Lampsilis ‘ris.
b, Lampsilis lienosa unicostata.
c, Lambpsilis ligamentina.
d, Lampsilis luteola.
e, Lampsilis multiradiata.
Sf, Lambsilis parva.
og, Lampsilis picta.

h, Lampsilis recta.

i, Lampsilis subrostrata.

j, Lampsilis trabalis.

k, Lampsilis ventricosa.

1, Lampsilis ventricosa satura.
m, Margaritana monodonta.

n, Obliquaria reflexa.

o, Obovaria circulus.

, Obovaria ellipsis.

q, Obovaria retusa.

r, Plagiola donaciformis.
s, Plagiola elegans.

t, Plagiola securis.

u, Pleurobema esopus.

FRESH-WATER MUSSELS. 147

Fic. 11.—Glochidia of common fresh-water mussels. (After Surber, 1912 and rors.)

aandb, Proptera alata. 1, Quadrula granifera. n, Quadrula plicata.
c, Proptera capax. J, Quadrula heros. o, Quadrula pustulata.
d, Proptera laevissima. k, Quadrula lachrymosa. P, Quadrula pustulosa.
e and/, Proptera purpurata. 1, Quadrula metanevra. g, Quadrula solida.
g, Quadrula coccinea. m, Quadrula obliqua. r, Quadrula undata.

h, Quadrula cbenus.

148 BULLETIN OF THE BUREAU OF FISHERIES.

Ceres

f

Fic. 12.—Glochidia of common fresh-water mussels. (After Surber, ror2 and sors.)

a, Strophitus edentulus. d, Symphynota costata. g, Unio crassidens.
b, Symphynota complanata. e, Truncilla sulcata. h, Unio gibbosus.
c, Symphynota compressa. J, Tritogonia tuberculata.

would make a line 1 inch in length. Hookless glochidia are possessed by practically all
of the more important commercial mussels; in fact, as far as we know, this type of glo-
chidium characterizes all the genera and species not mentioned in the paragraphs im-
mediately preceding and following.

(3) The ‘‘ax-head”’ type (PI. XIV, figs. 6 and 7) is considered more closely related to
the hookless than to the hooked type, although glochidia of this type, except those of
a single species, Lampsilis (Proptera) levissima (Coker and Surber, 1911), possess four
hooklike prongs, one at each lower corner of the shell. These pointed projections of
the shell are not comparable to the pivoted hooks of glochidia of the hooked type. The
ax-head type of glochidium occurs with the following species: Lampsilis (Proptera)
alata, levissima, purpurata, and capax. (See also text fig. 11, a to f.)

When the glochidia are fully developed they are ready to break out from the egg
membrane and to be liberated from the gills of the mussel, although as previously indi-
cated many species of mussels retain the developed glochidia in their gills for many
months. A characteristic feature of the mature and healthy glochidium is the active
snapping together and opening of the shell. This action can be stimulated by adding a
drop of fish blood or a few grains of salt to the water in which the glochidia are held.

STAGE OF PARASITISM.

After the fully matured glochidium has been expelled from the brood pouch of the
mother, its continued development is dependent upon its coming in contact with the
gills or fins of a suitable fish host and attaching to them. If it fails to make this attach-

leer, Wi Sy 180 1, uopno—70) PLATE XVI.

Fic. 1.—Filaments of gill of fresh-water drum with heavy natural infection of
Plagiola donaciformis, Estimated total number of glochidia carried by fish
4,800.

Fic. 2.—Glochidia of washboard mussel, Quadrula heros, on Fic. 3.—Section through ‘vacated cysts on gill filaments;
fin of fresh-water drum, Cyst very much enlarged. Quadrula ebenus on river herring,

Buiy., U. S. B. F., 1919-20. PLATE, XVID.

Fic. 2.—A young mussel, Sympbhynota
costata, six days aiter completing the
stage of parasitism. (Lefevre and
Curtis.)

Fic. 1.—Glochidium of Symphynota costata 1n process of transformation
during stage of parasitism. (Lefevre and Curtis.)

Fic. 3.—A young squaw-foot mussel, Sirophilus edentulus, which had Fic. 4.—A young mucket, Lampsilis
completed metamorphosis without parasitism; showing two adduc- ligamentina, a week aiter the close of
tor mussels, foot, gills, and rudiments of other organs of adult mussel. the parasitic period. (Lefevre and '
(Lefevre and Curtis.) Curtis.) ‘

FRESH-WATER MUSSELS. 149

ment it will die within a few days’ time. In other words, the glochidium must pass the
life of a virtual parasite on the fish while undergoing its metamorphosis into the free-
living juvenile stage. In the light of our present knowledge, this is true of all the fresh-
water mussels (Unionide) except the squaw-foot, Strophitus edentulus, and one of the
small floaters, Anodonta imbecillis. The former species may complete its metamorphosis
either with or without parasitism (Lefevre and Curtis, 1911 and 1912, p. 171; and
Howard, 1914, p. 44), while the latter, as it appears, never endures a condition of para-
sitism (Howard, 1914, p. 44).

On coming in contact with the gill filament or fin of the fish the glochidium attaches
itself by firmly clamping its valves to the tissue of the host. A certain portion of the
tissue of the fish thus becomes inclosed within the mantle space of the glochidium, and this
quickly disintegrates and is taken into the cells of the glochidium and consumed as food
(Lefevre and Curtis, 1912, p. 169). Within a very short time the tissue of the fish
commences to grow over the glochidium, presumably in an effort to heal the slight
wound caused by the ‘‘bite”’ of the glochidium, or perhaps as the result of a positive
stimulus imparted by the glochidium. L. B. Arey (report in preparation) successfully
induced encystment by attaching tothe
filaments of excised gills of fish minute

metallic clamps the size of glochidia or ie TR
smaller. The growth of tissue continues = :
until the larval mussel is completely Lae

inclosed within a protective covering,” T<\* 2 bi dey
known as the cyst (PI. XVI, fig. 2). % © Set iN
The several stages of encystment are “AA AAAI pp

clearly represented in the series of fig- mod : ; o

Fic. 13—Glochidium of pink heel-splitter, Lampsilis (Proptera)
uresreproducedfromLefevreand Curtis alata, in condition of parasitism on gill of sheepshead, showing
(191 2) (Pl. D,GV fe fig. 4), and the process as of the juvenile mussel beyond the bounds of the glochidial
may becompleted within 24 or 36 hours.
The appearance of a gill bearing a considerable number of glochidia is shown by
figure 1 of Plate XV, while figure 2 is an enlarged view of a few of the gill filaments of
a black bass carrying glochidia of the mucket.

It is not our purpose to go in detail into the changes which occur in the glochidium
during the period of its parasitism. They are principally changes of internal structure
which scarcely affect the external appearance. Nevertheless, at the conclusion of para-
sitic life the young mussel is a very different sort of an organism from the simply organized
glochidium which has been described on page 143. Generally it has not increased in size,
but the single muscle which held the valves of the glochidial shell together has given place
to two adductor muscles as in the adult; the mouth and the intestine are formed,
the gills and foot are represented by rudiments which are prepared to function. The
larval mussel is, in fact, ready to begin its independent life and to take care of itself. All
of the changes which occur during parasitism require the expenditure of energy and the
use of body-building material, and as the glochidium enters upon the parasitic life with
no considerable store of food material, it is reasonable to assume that it derives at least
a small amount of nutritive material from the fish. Since no growth in size generally
occurs, the drain upon the fish therefore must be comparatively slight. There are, how-
ever, a few species (none of the commercial mussels, so far as we know) in which, during
the period of metamorphosis, the larval mussel grows to a comparatively large size

150 BULLETIN OF THE BUREAU OF FISHERIES.

(text fig. 13), and, in such cases, the mussel must be generously nourished by the fish.
(See Coker and Surber, 1911.)

The duration of the parasitic period varies greatly with the season of the year during
which it occurs, and with other conditions which are not fully understood. The results
of some recent experiments indicate that glochidia of long-term breeders have a rela-
tively long infection period when they are infected upon fish shortly after maturing
and a relatively short period when infected after they have remained in the marsupial
pouches over winter; that is, young glochidia complete metamorphosis in parasitism
more slowly than old glo-
chidia. The temperature of
the water seems to be one
of the factors governing the
duration of the parasitic
period, and doubtless the
Fic. 14—A dorsal view of a juvenile pink heel-splitter showing glochidial shell still vitality of the host fish is

eC) another; but there is diver-
sity even among glochidia of the same species when infected on the same fish. Lefevre
and Curtis (1912, p. 168), for example, show under such circumstances variations from
9 to 13 days, and even from 13 to 24 days. The following instances (Table 17) from
records at the Fairport station are illustrative:

TABLE 17.—INFECTIONS SHOwING DuRaTION or Parasttic PERIOD.

. Average
‘Soetiee of 1 SiNses of fish Date of sie we wakes tem
pecies of mussel. pecies of fish. aikettical! infection | Perature
in days. uring
period.
BRO Wopers CHEE ties te June 5,1919 13
ai arc tare CO ia steraieln ect ttcto alee niStn ise ulale pinicivipininpetntntm nicl June 20, 1919 12
Als toleke Pa ratovers Elio iveleesnisia oie oe riane oki tehabetces July 3,1919 Ir
eee hace ey Jac: >Seegecnnonosdnobaaaracces July 9,1919 13
ap eee KOO. bee clas cick garsie'y «ates Bete ghiaa metbie: siditiciche July 23,1919 Iz
ratvnctctans June 5.1919 13
aoe cluieinis.s cis oiceticin cletee ate etote ha wsiatele June 20, 1919 13
saan Seniod appa scnndscccllosmeueibe a July 14,1919 10
SSC Ae CA pease Snee Cer meceon Ise ee dovxtoe- II
Sonat HMO PO ROL BCG erecntos lec oF el Misekes s+ 12
MA CTA ee ctcctcte einiete wc 8 56 aint July a 1919 to
DRE acne snscadotnee taooben sy roar ab Breee ao- 1a
See eects db odio ciclela Poctente] oleae db. PASARS 12
Sue a meeds Aug. ak 1919 12

| Aug. pe 1919 10 |.
June 5, 1919 15 |.
odo 30, 1919 I3 i}

dolomieu Are
Stizostedion vitrewm . 2... ic. erence cceela snes Oseees = 20
Perca MavesceniS. ects s+ ociem cie'cicie = ene enl-iape Aug. 18, 1914

3 eee do eee Ae ....| Sept. 26, 1914 (2)

.| Stizostedion vitreum..... ....| Sept. 16, 1914 (@)

Quadra pustulosa . ..| Ameiurus melas............ ....| Aug. 21,1912 6to8

SR Gio One GbCOOREBH GS snced ao ..| Ictalurus punctatus...... wsee--| July 7, 1912 gtorr

RS Ue ei Paak Saduldtotel tec noite cosee ener do dean ettstehreistet takkhe Join ered | AMR a Ors rr to12
aa Licata, woe cmos cite Sahl eeministe retort] MAVEDISOSECIUS lA POSLOMIUS 2 foie) ctorop« amie! neret-tre July 12,1918 II
EAM PSilis fALACIOSA.A «Heute, o sila ence dete fons ee OSE eatla Kis Ae to hore dee July 13, 1918 14 to 18
Lampsilis anodontoides............. Wien deen secede ny BBO. ute cooper cots sce July 7, 1919 14 to 21
Qitadrula heros. concen steeds. heme ser ee Aplodinotus Primmiens! oo. 0h lodca eae se Oct. 7.1912 193

@ Still carrying infection, Apr. 14, 1915.

In about one week after attachment, as arule, the wall of the cyst begins to assume a looser texture,
the intercellular spaces becoming infiltrated with lymph, and from this time on to the end of the parasitic
period there is little further change in its structure.

Before liberation of the young mussel, the valves open from time to time and the foot is extended.
By the movements of the latter the cyst is eventually ruptured, its walls gradually slough away, and the
mussel thus freed falls to the bottom (Lefevre and Curtis, 1912, p. 171).

FRESH-WATER MUSSELS. 151

Before taking up the history of the mussels in independent juvenile life, we must
discuss the very significant facts which have been discovered concerning the special
relation between mussel species and fish species, and refer also to the rare instances known
of mussels which complete their development without the aid of fish.

HOSTS OF FRESH-WATER MUSSELS.

As has previously been indicated in a general way, mussels do not attach to fish
indiscriminately, but for each species there is a restricted choice of hosts. Some are
more catholic in their tastes than others, yet for any mussel there is a limited number
of species of fish upon which it will attach and complete its metamorphosis. The Lake
Pepin mucket has nine known hosts, while the niggerhead has apparently but one;
the yellow sand-shell is restricted to gars, and the pimple-back to catfishes. It is, of
course, employing language in a loose sense to refer to this selection of hosts in terms of
taste or choice; it is a matter of physiological reaction. When fish and glochidia are
artificially brought together, glochidia will sometimes attach to the wrong fish, but in
such cases they soon drop off, or even if partial or complete encystment ensues, the glochi-
dium does not develop normally and after a time cyst and glochidium are sloughed off
and lost. It seems evident, then, that successful encystment and development depend
upon appropriate reactions on the part of both glochidium and fish, and that failure
ensues upon the lack of afavorable reaction on the part of either parasite or host. The
reaction may depend in part upon the condition of the individual glochidium or fish, but
primarily it depends upon the species of mussel and the species of fish.

It is evident that the artificial propagation of mussels can not be conducted success-
fully and economically unless we have accurate knowledge of what species of fish serve
as hosts for the several species of mussels. Such knowledge has been gained by following
two methods of inquiry, the observational and the experimental.

By the observational method, fish taken in the rivers are subjected to careful
examination for the presence of glochidia on the gills or fins. Preliminary to and
attendant on such studies, glochidia have been taken from as many species of mussels as
could be found in gravid condition, these have been studied with the microscope, meas-
ured, and figured, so that in most cases the species of mussel can be identified in the
glochidium stage as well as in the adult. (See text figs. 9 to 12.) This method of deter-
mining the natural hosts is exceedingly laborious. Infection in nature is a matter of
chance, and only a small proportion of fish bear infections. If it were otherwise, artificial
propagation might not be necessary. One must, therefore, examine large numbers of fish
from different localities and at different seasons, and even then the glochidia of some
species may not be encountered, or they may not be found upon all the hosts to which
they are adapted. During the calendar year 1913, for example, 3,671 fish of 46 species
were examined for natural infections principally during the warmer months from April
to October. Of these, 324, or 8.9 per cent, were found to be infected with glochidia of
some species, but only 104 of these, or less than 3 per cent, were infected with glochidia
of commercial species of mussels. The fishes infected with commercial mussels belonged
to 12 species, and the glochidia represented 20 species. The average number of glochidia
of a given species on infected fish ran from 1 to 416, with a mean of 125.%

@In August, 1912, 5 examples of the river herring were taken and found to bear glochidia of niggerhead mussels in numbers
ranging from 1,895 to 3,740 per fish (Surber, 1913, p. 110). Similarly, heavy infections are frequently found on the fresh-water
drum, but the glochidia are not usually those of commercial mussels.

152 BULLETIN OF THE BUREAU OF FISHERIES.

The experimental method is simpler in some respects. It consists in submitting
various species of fish to infection with the glochidia of a given species of mussel and
observing whether or not the glochidia attach. Since glochidia will sometimes attach to
fish which are not their natural hosts, it is necessary to hold the fish under observation
until the mussels have completed the metamorphosis and dropped off. It is, however,
impracticable to have on hand all the species of fish at the particular time when the
glochidia of a given species of mussel may be available. Furthermore, the failure of an
artificial infection to go through successfully on fish held in confinement may be due,
not to the want of a natural affinity between mussel and fish, but to the fact that the
fish does not retain its full vitality in close confinement, or to some other defect in the
experimental conditions. Neither of the two methods for the study of infections may,
then, be relied upon exclusively for the determination of the natural hosts of fresh-water
mussels. On the contrary, it has been found necessary to carry on the two lines of study
hand in hand, according to the plan which was adopted at the beginning of the scientific
work of the station. In this way, though our knowledge of the hosts of mussels is as
yet incomplete, there has been obtained a considerable body of information most of
which is summarized in the following table (18),% listing 17 species of mussel and 30
hosts (29 fishes and 1 amphibian), and indicating those which serve as hosts for each

species of mussel.
EXPLANATION OF TABLE 18.
N. Found on the gills in natural infection.
Nf. Found on the fins in natural infection.
n. Record of natural infection but of doubtful significance.
A. Carried through on gills after artificial infection.
Af. Carried through on fins after artificial infection.
a. Results of artificial infection unsatisfactory or not uniform.
o. Tested and found unsuitable.
T. Tested; development occurred; host perhaps suitable, but experiment not carried to conclusion.

TABLE 18.—COMMERCIAL MUSSELS AND THEIR Hosts.

d b R & -Ilo Jo L s | o
3 ele] if 1 sie [2 18 lS lzcl4
ussels. g/d] 3 y/ele ig ja 5 Bj
g/eleleie lao! [flel8 (2 loelod ale
4 | A g)* ./ 83] o] el 8 # |aeleul 8
Sia] o] -|4d/ss| 4]oa) Alo s/e:| sess) es] 2
2) 8/4) o) 28/22) 8/3) ¢|/ 28) 8) Sgleeisa 3
{3} 9) e)/s41s5) o)s8] 2/8 13 °)23/8s/ es] §
Scientific name. Common name. 3 5 E e 5 gs 3 5 b EI 3 ria 2 58
Rlals|s 2H | PSE Pies | |e el (i
det fied [et Viet” SEY ea see et ero ee
Lampsilis anodontoides...| Yellow sand-shell....... On eOules A
Lampsilisfallaciosa....... Slough sand-shell.......}.....
Lampsilis higginsii. . BA serrate Open scot paecd penne:
Lampsilisligamenti ..| Mucket.... °o
Lampsilis luteola . . . .| Fat mucket . °
Lampsilis recta........ ..| Black sand-shell At
Lampsilis ventricosa...... Pocketbook... ..
Obovaria ellipsis.......... Missouri niggerhead.
Plagiola securis............ Butterflynd J Aseas seve oases
Quadrula ebenus......... Niggerhead...... °
Quadrula heros........... Washboard..+... A
Quadrula metanevra...... Monkey-face..2.....0.0¢{be...
Quadrula plicata.......... Blue-point....... a
Quadrula pustulata....... Wrarty-back. i fecips src |eeeate
Quadrula pustulosa.......]..... (Gh gecdetos INAS PAS arava ie ers deters | Seca ete | heracoll eteuanall raters |EQONG] | crates eal eras Ree
Qtradrilajsolid amen ine cc) aetna nets eiies Bel fase seni enc Bo
Quadrula undata.......... Lp C20 Honenacmocogsqaddd eorad |jaoollon na Pane) neod bowed) Gnoe trad (ines meerel oribcci paca cand saacc hece

@ A great many data regarding the hosts of noncommercial species of mussels had been accumulated, but unfortunately most
of the records applying to such species were destroyed with the burning of the laboratory in December, ro9r7.

FRESH-WATER MUSSELS. 153

TABLE 18.—COMMERCIAL MUSSELS AND THEIR Hosts—Continued.

|

large-
mud

Mussels.

white ||
black

small-

orange-
mouth black bass.

perch.

puppy.
P. chrysochloris, river

herring.

annularis,
crappie.

crappie.

bass.

sturgeon.

Scientific name. Common name.

spotted sunfish.

L. pallidus, bluegill.
sparoides,
chrysops, striped

salmoides,
mouth biack bass.

L. olivaris, yellow cat.
N. maculosus,

P. flavescens, yellow
S. platorhynchus, sand
S. gyrinus, mad Tom.

L. humilis,
M. dolomieu,

Pp
15h
R

M.
S. canadense, sauger
| S. vitreum, walleye.

Lampsilis anodontoides .| Yellow sand-shell.....

Lampsilis fallaciosa...... Slough sand-shell..... es
Lampsilis higginsii...... Higgin’seye.......... Bers
Lampsilisligamentina...| Mucket............... Ree
Lampsilisluteola........ atmucketmsaness./-r- a
Lampsilis recta......... Black sand-shell...... BB
Lampsilis ventricosa....| Pocketbook........... Dace!
Obovaria ellipsis. ....... Missouri niggerhead...|_...
Plagiola securis.......... aiittertl yee scent ce Bae
Quadrula ebenus. . ..| Niggerhead........... ae
Quadrula heros....%..... Washboard........... rere
Quadrula metanevra....| Monkey-face.......... node
Quadrula plicata........ Blue-point............ Tack

Quadrula pustulata
Quadrula pustulosa
Quadrula solida. ..
Quadrula undata........

Tt will be observed that the number of hosts corresponding to a particular species
of mussel (as so far determined) varies from one to thirteen. It is of interest to give
the number of known hosts for each species of fresh-water mussel, as determined both
by observation of natural infections and by the experimental method, and this is done
in Table 19. ;

e
TABLE 19.—NUMBER OF SPECIES OF FISH KNOWN TO SERVE AS Hosts FOR CERTAIN SPECIES OF
MUSSELS.
Mussels.
Natural Artificial
infection. | infection. Common. Total.
Scientific name. ~ Common name. |

Lampsilis anodontoides.................... Yellow sand-shell............... I 3 I 3
Lampsilisfallaciosa.................-ee00es Slough sand-shell............... I I I I
MATHS WIS HIS PUTISIA yaya ehelejeinicie.e cle einieleiaya a. PR p pin Sieve: Mite ccitten cites + ot kpeets I ° ° I
Mamrpstlis ligamentina.-cc-cecccee ccs PMLLICK EL Sess ents Se ccetan\cteces 7 6 4 9
HMeaMOStis iiCeOlA sel iicls sislaiste «inipiaieisinisieiaisele Matimnicketty sew dtccvts raereatsent 3 9 3 9
GAIT SUIS LECEAMamecrdte a emitmteterta cites hte mene Black sand-shell................ 2 ° ° 2
TANI PSLIS WeNtTICOSA sf pers aieeisieisieieaincieisie.oles Pocket books 5.) xdsite< crac totiacits 2 5 I 6
Qbovariaiellipsise ee cece eee = = Missouri niggerhead............. I I I I
Plagiolatsecttris fs) jets sac an caste cae oeiyaina's Bitterfly yin bcp decnisteeae eae site I t I I
Otddrilavebentishis. tbe thn eee rite Wrpperhieadmoncrim cone scluctinec ce I I I x
Qiiadrnlasherosiee ie ia erceee nna pWeashi board). ici: Mok erties 8 9 4 13
Quadrnilasmetanevrar se ssecsnne cece Monkey-faces <8. oii. s. ccm ecnsns 2 ° ° a
Quadritla’ plicata jie obs ca eisriaieialensiee Blie-potntes . ais. ee scion weit eewiee 5 6 2 9
Quadrula pustulata NULL -DaCKonn carr netratectense ct I ° ° I
Quadrilasoustilosaty. saney- ie eedeaes|ecene OSE a obra screseye cast Save hetaate tel 2 3 2 3
Qiuddrialasolidaemeemunren scence cnet eeertltecticn aces cticlsecicts vetcineicemeciens I ° ° I
Quadmnilanindatassiceateanaauteceaaceea: Pig-toer as. sa nsnut awe cede (?) ° ° (2)

Table 20 lists the common species of fish showing the number of species of mussels
which each fish has been observed to carry as parasites. The greatest number is six,
for the bluegill, Lepomis pallidus, the white crappie, Pomoxis annwaris, and the sauger,
Stizostedion canadense.

154

BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 20.—NUMBER OF SPECIES OF COMMERCIAL MUSSELS KNOWN TO BE CARRIED AS PARASITES

BY CERTAIN FISHES.

Fishes
Natural Artificial
infection. | infection. | CO™™02 Total.
Scientific name. Common name.

‘Ameiurgis melas: 5225 55.) .«seake nies Bullhead orn sap cny ae vice omy tate I 2 I 2
Ameiurus nebulosus. met teste Cle sdase ce Bee cue ° 2 ° 2
Anguilla chrysypa............... Bp tt Or Ree Ce a I ° ° I
Aplodinotus grunniens,......... .| Sheepshead.......... 2 2 2 2
Dorosoma cepedianum.......... Gizzard shad........ I ° ° Ir
SOR MNCIHS. nciteg ete aoe Sariccns Aan SB BEDE I ° ° ba
Eupomotis gibbosus............. ..| Red-ear sunfish. ... I ° ° I
Ictalurus punctatus. .. z«| sspottedicat-- snc. . 2 2 I Zi
Lepisosteus Osseus............... ..| Long-nosed gar ... I I I I
Lepisosteus platostomus......... ..| Short-nosed gar... . I 3 I 3
Lepisosteus tristoechus.......... .| Alligator gar......... ° It ° I
Lepomis cyanellus............. ..| Blue-spotted sunfish. 2 I ° 3
Lepomis euryorus.. . ae | eotineasin een tte cial. ° I ° I
Lepomis humilis. ... .| Orange-spotted sunfish. (@) ° ° (?)

Lepomis pallidus. Biegler eae 5 3 * 2 6
Leptops olivaris............... Wellowicats 2255 Sb... I Tt I I
Micropterus dolomieu......... ..| Smallmouth black bass.......... I 2 ° 3
Micropterus salmoides. ..| Largemouth black bass......... 2 4 2 4
Necturus maculosus @. .| Mud puppy.. (?) ° ° (?)

Pomolobus chrysochlori River herring. . I I I I
Perca flavescens... Yellow perch 2 4 2 4
Pomoxis annularis White crappi 5 5 4 6
Pomoxis sparoides Black crappi ° 4 ° 4
Roccus chrysops. Striped bass 2 2 I 3
Scaghiceaehii platorhynchus. . ...| Sand sturgeon I I I I
Schilbeodes gyrinus............. al | Wiad Mompeees sccm: mercedes 4 I ° ° I
Stizostedion canadense........ ....| Sauger 4 2 ° 6
Stizostedion vitreum..............-.....-0+ Walleye I I I I

@ An amphibian.

It is necessary to point to some significant practical conclusions from the data pre-
sented. Since mussels are “choice” as to their hosts, the chances for the successful
attachment of glochidia in nature are greatly diminished. ‘The glochidia when dis-
charged from a parent mussel are lost if no fish are at hand to receive them or if the
fish that pass are not of one of the very limited number of species which are useful to
the glochidia of that particular mussel.

There must necessarily be some definite ecologic relation between the mussel and
the fish. The bottom that is inhabited by the hickory-nut mussel must be one that is
frequented by the sand sturgeon during the breeding season of that mussel. Again, if
one were looking for the river herring, it would be reasonable to expect to find them,
during June at least, in places where niggerhead beds are known to exist. It is evi-
dent that no species of mussel could exist unless its host were of such habit as to be at
the right places at the right times in a sufficient number of cases to penmit first, of the
infection occurring, and second, of the young dropping where they can survive.

What the factors are that bting mussels and fish into proper association we can not
say. In the case of one species of mussel (the pocketbook) at least, it is known that the
gravid mussel protrudes from its shell a portion of its mantle as a long brightly marked
flap that waves in the water, assuming the appearance of an insect larva or other at-
tractive bait (p. 85). Again we have the sheepshead fish (fresh-water drum) which is
known to feed upon small mollusks, mussels, and the spheriids and univalves that live
on mussel beds, and which thus exposes itself to easy infection; sheepshead, indeed, are
almost invariably found to be loaded with glochidia. The behavior of the pocketbook
is believed to be exceptional, and the sheepshead is one of a very few species of fish

FRESH-WATER MUSSELS. 155

known to feed directly upon mussels. It is certain, however, that the fresh-water mussel
beds harbor quantities of other small animal life, such as insect larve, snails, and
worms, and are gardens for the food of fishes (p. 119); in this, probably, lies the prin-
cipal clue to the association of fish and mussels.

Finally, an economic consideration should be emphasized. The conservation of the
fishes is as important to the preservation of the fresh-water mussel resources and the
industries dependent upon them as is the propagation and protection of mussels. The
disappearance, or the radical diminution in number, of certain species of fish would re-
sult in the complete or virtual disappearance of corresponding species of mussel. On
the other hand, if the growth of mussels in more or less dense beds produces conditions
which are favorable to the growth of fish food, and observations do so indicate, then
the disappearance of the fresh-water mussels would result in the diminution of the
food supply for fishes, and the conservation of mussels is important for the preserva-
tion of our resources in fish.

PARASITISM AND IMMUNITY.

It is worth while to inquire as to the effect of the glochidia upon fish. Are they
parasites in the same sense as tapeworms or round worms? Do they sap the vitality of
the fish, and are they accordingly to be regarded as in the nature of a disease? While
the relation of the glochidium to the fish can not be fully stated in the present stage of
investigation, it can be said that the principal effect upon the fish, at first, at least, is the
slight laceration of the gills caused by the attachment of the glochidium. ‘The fish
quickly heals over this wound to inclose the glochidium and form a small cyst, and
after that there is in nearly all cases no evidence of further irritation or of material
detriment to the surrounding tissues, except as the cyst and glochidium are sloughed
off at the expiration of the proper period.

The fish feels the attachment of the glochidia; it shows that by the flirting move-
ments which are made as infection begins, and it is known that excessive infections of
young fish, at least, may cause the gills to become so lacerated and inflamed as to pro-
duce the death of the fish (Lefevre and Curtis, 1912, p. 165). The use of small fish is
avoided in experiments and operations conducted at Fairport, and as care is taken to
avoid excessive infections it can be said that of thousands of fish artificially infected
and kept under observation in experimental work at that place there has been no case
of death or evidently diminished vitality with evidence to implicate the glochidia as
cause.

After the microscopic lesion of the gill is healed over, which usually occurs in the
course of a day, the commercial species of mussels generafly make little demand upon
the fish. No doubt they derive some nourishment from the fish, but this must be very
slight, since the young mussels, after spending two or three weeks in undergoing meta-
morphosis, are found to be of the same size as before they attached to the fish. The
demands upon the energies of the fish caused by the glochidia are probably not greater
than those arising from a few extra movements.

It has recently been learned that some fish acquire a certain immunity to glochidia,
thus being protected against too frequent repetition of infections. Reuling (1919) has

@ The mussels which grow in size while in parasitism (p. 149) are not commercial species.

156 BULLETIN OF THE BUREAU OF FISHERIES.

found that some of the very large bass, having doubtless experienced some previous
natural infections, become immune after one heavy artificial infection, while small bass,
without previous infections presumably, require two or three artificial infections before
showing immunity. When immunity is acquired, the fish can not be successfully infected
with glochidia of any species of mussel. The period of duration of immunity is not
known.

An earlier significant discovery had been made by C. B. Wilson (1916, p. 341). His
observations and experiments showed that the fish which are most susceptible to glo-
chidia are those which are subject to parasite copepods (fish lice); that there is a definite
connection or fellowship of copepods and mussel parasites, so that knowing the species of
mussel for which a given species of fish serves as host, one may often predict what species
of copepod fish of that species will carry; and finally, that the presence of glochidia on an
individual fish renders that fish practically or completely immune to the attacks of the
fish lice, and vice versa. These conclusions may be stated in another way: While
glochidia and copepods have essentially identical taste in fish hosts, the presence of the
one is antagonistic to the other.

These observations indicate that artificial infection of fish with glochidia may have a
positively beneficial effect upon the fish in giving it protection against a class of parasites
which are pernicious in effect; for copepods are relatively large parasites which sap the
vitality of fish and have been known to cause serious mortalities.

The case of the sheepshead or fresh-water drum, A plodinotus grunniens, may be sig-
nificant. Sheepshead are found to be almost invariably loaded with glochidia upon the
gills, carrying infections which would be regarded as highly excessive if caused artificially
(Pl. XVI, fig. 1). They are, no doubt, greatly exposed to infection in consequence of
the habit of feeding upon molluscs, which they are well fitted to crush with their strong
grinding teeth. By carrying successfully glochidia, which they secure while devouring
the parent mussel, they are aiding in the propagation of the mussel which may serve them
as food. Indeed, the sheepshead unwittingly engages in growing its own food supply.
Now, of the fish which have been examined in numbers, the sheepshead is the one species
of fish (besides those of the sucker family, which carry neither glochidia nor copepoda)
which has never been found to have copepods on the gills. Its immunity from copepods
is now easily understood, and it may be presumed that this immunity is worth the cost
of almost continually carrying heavy infections of glochidia.

METAMORPHOSIS WITHOUT PARASITISM.

So generally, almost universally indeed, are fresh-water mussels dependent upon fish
for the completion of their development, that peculiar interest attaches to the two ex-
ceptions which have so far been encountered. Lefevre and Curtis (1911) discovered that
glochidia of one species, the squaw-foot, Strophitus edentulus Rafinesque, may undergo
metamorphosis into the juvenile stage without the aid of the fish (Pl. XVII, fig. 3). In
this mussel, as in others, the eggs when deposited in the gills are packed in a formless
mucilaginous matrix, but in the course of the development of the glochidia, the matrix
becomes changed into the form of many cylindrical cords, in each of which a few glo-
chidia are embedded. ‘There is evidently in this case a special provision for the nour-
ishment of the embryo from materials supplied by the mother, so that metamorphosis

FRESH-WATER MUSSELS. 157

of the glochidium is accomplished at the expense of the parent rather than of a fish.
Howard (1915) subsequently found that the glochidia of this species could be made to
attach to fish and would undergo metamorphosis in the usual way on this fish. He also
discovered that the glochidia of another species, a small floater, Anodonta imbecillis,
developed into the juvenile mussel within the gills of the parent, and that they would not
remain attached to fish.

It is significant that there are just a few species of mussels which diverge in two
directions from the general rule that fresh-water mussels undergo metamorphosis only in
parasitism and without evident growth in size during the process. On the one hand,
we have the cases just cited of change of form accomplished without parasitism, and on
the other the instances mentioned on page 149 of two or three species in which the larval
mussel increases many times in growth while still encysted upon the fish. The tendency
manifested by two species is toward independence of fishes or other hosts, while the
tendency revealed by a few others is toward a much greater dependence upon fishes.
The vast majority of species, including all the mussels having shells of commercial value,
occupy the middle ground of limited dependence upon fish; they must live upon the
fish, but they require little from them. ‘The hope has been cherished that in time a
means would be found of supplying artificially to the glochidia of the common species of
useful mussels the food materials and other conditions necessary for the metamorphosis.
so that it might become possible to rear mussels without the use of fish. $6 far, how-
ever, failure has marked every attempt to accomplish this purpose.

JUVENILE STAGE.

At the close of the period of parasite life, the young mussel is no longer a glochidium,
and while it possesses the rudiments of the principal organs of the adult, it has yet to
undergo many changes of structure—or better perhaps, a progressive development in
structure—before it fully assumes the adult form and manner of life (Pl. XV, figs. 5 and 6;
Pl. XVII, fig. 4). To the intermediate stages, or series of stages, between parasitism and
the development of functional sex organs the term juvenile may properly be applied.
The siphons or respiratory tubes, the labial palps, outer gills, and sex glands are among
the conspicuous features of structure acquired during this stage.

With many and probably most of the common species of mussels, the early juve-
nile mussel is no larger than the glochidium—in the case of the Lake Pepin mucket slightly
less than one one-hundredth inch in length and slightly more than one one-hundredth inch
in height. Its thin mussel shell underlies the glochidial shell, and is scarcely visible until
after several days of growth. The most conspicuous feature of the young mussel at this
time is the foot, which may be protruded from the shell as a relatively long, slender, and
active organ of locomotion. The following description applies primarily to the Lake
Pepin mucket: The foot is somewhat cleft at the apex to give a bilobed appearance and
it is clothed with cilia or minute living paddles, which are in rapid motion while the foot
is extended. The foot has also the power of adhesion to surfaces as smooth as glass; by
means of it the young mussel can move about rapidly or effect temporary attachments to
foreign objects. It is not long before the peculiar characters of the juvenile foot are lost,
for during the first month of independent life this organ becomes changed into the char-
acteristic form of the foot of the adult mussel.

75412°—22——_11

158 BULLETIN OF THE BUREAU OF FISHERIES.

At a very early stage a special organ of attachment is formed in some species, espe-
cially among the Lampsilinie (Sterki, 1891, 1891a; Frierson, 1903, 1905; and Lefevre and
Curtis, 1912). This is the byssus, a sticky hyaline thread produced by a byssus gland
formed in the middle line of the rear portion of the lower side of the foot. In the wash-
board, Quadrula heros, a very few days after leaving the fish there is apparent a tough
mucuslike secretion by means of which the juvenile mussel may anchor itself. The
byssus may serve to anchor the mussel by attachment to foreign objects, but its func-
tion needs to be more definitely ascertained. Juvenile mussels are sometimes captured
in considerable numbers, owing to the sticky thread becoming attached or entangled on
the crowfoot hooks or lines or on aquatic vegetation drawn into the boat. While such
observations suggest the function of keeping the mussel from being carried away by
the current, nevertheless the organ is well developed in young Lake Pepin. muckets
which are observed to bury themselves deeply in the bottom. The byssus is retained a
varying length of time in different species and in different individuals of the same species.
The byssus has been seen in young muckets, Lampsilis ligamentina, late in the second
year of free life and rarely in adults of Plagiola donaciformis. ‘The species of mussel
observed with byssus are listed below.

SPECIES OF MUSSELS THE JUVENILES OF WHICH ARE KNOWN TO HAVE A BYSSUS.

Lampsilis alata, pink heel-splitter. L. luteola, Lake Pepin mucket.
L. anodontoides, yellow sand-shell. L. recta, black sand-shell.

L. capax, pocketbook. L. ventricosa, pocketbook.

L. ellipsiformis. Obovaria ellipsis, hickory-nut.
L. fallaciosa, slough sand-shell. Plagiola donaciformis.

L. gracilis, paper-shell. P. elegans, deer-toe.

L. iris, rainbow-shell. Quadrula ebenus, niggerhead.
L. levissima, paper-shell. Q. plicata, blue-point.

L. ligamentina, mucket.

The shell formed during the first month (more or less) of development possesses
certain peculiar characteristics—besides having a relatively low lime content and being
transparent, it bears on its surface certain relatively high ridges, knobs, etc. (Pl. XX).
The cause or the meaning of these nicely formed ridges is unknown, but the pattern of
sculpture of the early juvenile shell is characteristic for the species. Though all the
remainder of the shell be perfectly smooth, the ‘‘umbonal sculpture,” as it is called, can
be made out in well preserved adult shells of most species, and their markings are given
significance in the classification of mussels.

We need not concern ourselves here with the details of development of the internal
organs, except to say that a considerable elaboration of structure must ensue before
the mussel is prepared to assume its culminating function—the reproduction of its
kind. The first act of breeding marks the close of the juvenile period, and this occurs
in the Lake Pepin mucket two years after the beginning of the juvenile stage, or early
in the third summer of life counting from the deposition of the egg in the gill of the
mother. In some species of mussels, those of small adult size, or those possessing very
thin shells, sexual maturity comes at an earlier age, but in most species of mussels it
undoubtedly occurs later. (See p. 137.)

The maximum sizes, at various ages, attained by Lake Pepin muckets under obser-
vation, are shown in the following table:

FRESH-WATER MUSSELS. 159

TABLE 21.—MAxXIMUM SIZE OF YouNG LaKE PEPIN MucKETS AT VARIOUS AGES.

Age. Length. Age. Length.
Millimeters.| Inches. Millimeters.| Inches.
Beginning of juvenile stage.......... 0. 25 HOF GS GaAyS: «Ao aceis sss a aisieleview erele'eincis 13-0 0.5!
SEES Shyscach sadade SaridaeSUn00dee “5 202) |i 5 THOMCHS Ul ir reniiceaasiebiee aiyecelsis 32-3 I. 27
SICAYS Ui cele eet tliat stale eale oe 4-2 17 || End of second growing season........ 58.3 2.30

This species displays perhaps the most rapid growth of any commercial mussel,
although it is surpassed in this respect by some of the noncommercial floaters and
paper-shells. The maximum size attained in the second year by mussels of several
other species reared at the Fairport station is given in Table 22.

TABLE 22.—SIZE AND AGE OF MUSSELS REARED AT FatrRvoRT STATION.

o Approxi-
Species. Length. mate age! Remarks.
Mitlimeters.| Inches. Years.
Lampsilis ligamentina, mucket...... 2.2... .0 6.00.0 e cee ee cece eee 20.0 ©. 79 2 Accidentally reared.
Lampsilis anodontoides, yellow sand-shell ..................--. 41.0 1.62 1% | Intentionally reared.
Obliquaria reflexa, three horned warty-back. . . Sono 16.0 63 2 Accidentally reared.
Plagiola donaciformis............. ae 20.0 -79 2 Do.
Quadrula plicata, blue-point oh 13-5 53 2 Do.
Quadrula undata, pig-toe.... sie 15.8 ~ 63 cr Do.
Obovaria ellipsis, hickory-nut... 22... 60.0 e cece eee eee e eee II-4 -45 ai )| Do.

Much remains to be learned regarding the habits and habitats of the juvenile mus-
sels of many species. The study is somewhat difficult, because mussels in the juvenile
stage are usually hard to find. This is the experience of all collectors, although rich
finds of larval mussels are occasionally made in particular locations (Howard, 1914,
pp. 34 and 47). In 1914 Shira collected 1,394 juveniles representing 16 species in Lake
Pepin, and 92.9 per cent were taken upon sand bottom where there was scattering vege-
tation. This figure can not, however, be taken as an index of preference for that par-
ticular sort of habitat, since 86.2 per cent were taken at one station. Isely (1911, p. 78)
made a collection of 32 juveniles comprising 9 species, 6 of which were represented in
the Lake Pepin collections, but Isely’s specimens were all taken in fairly swift water,
1 to 2 feet deep, and from a bottom of coarse gravel. In rearing young mussels, prin-
cipally Lake Pepin muckets, in ponds at Fairport, the best success has been attained
on prepared bottom of sand; yet when Howard reared Lake Pepin muckets in a crate
floating in the river, silt accumulated to a considerable depth, and the juvenile mussels
were sometimes found deeply submerged in the soft mud; nevertheless, more than 200
young mussels survived the season in a very small crate, and excellent growth was made.

After the byssus is shed the young mussels often bury themselves in the bottom -
more deeply than do adults. They are inclined to travel considerably at this stage,
but the rate of movement and the distances covered are less than might be thought
from observation of the conspicuous and apparently fresh tracks behind the young mus-
sels. It has been found that the tracks will retain the appearance of freshness for sev-
eral days; hence the trail which one might at first suppose to have been made in a few
hours may represent a journey covering a considerable period of time. Clark observed
a young mussel which made forward movement every 10 seconds, each movement being

160 BULLETIN OF THE BUREAU OF FISHERIES.

followed by a brief rest period. A young hickory-nut mussel was observed to travel
o.1 meter (about 4 inches) in 29 minutes. The rate of travel of sand-shells is much more
rapid.

Because of their small size and delicate shell the early juvenile mussels are doubt-
less the prey of numerous enemies. Turbellarian and chetopod worms are known to
devour them. No doubt they are sometimes eaten by fish and aquatic animals, such as
are accounted enemies of larger mussels, yet there has been found little evidence of
serious depredations upon young mussels by such animals. Perhaps the most serious
natural mortality among juvenile mussels occurs from falling upon unfavorable bottoms
or from the effects of currents, especially in times of flood, which may draw the rela-
tively helpless mussels into environments in which they have small chance for survival.
It may be expected, too, that the repeated dragging of crowfoot bars over favorable
mussel bottoms works damage to juveniles both by injuries directly inflicted and by
pulling them from the bottom and exposing them to the action of currents from which
they had previously found protection.

ARTIFICIAL PROPAGATION.
PRINCIPLE OF OPERATION.

As the previous account of the life history of fresh-water mussels has shown, the
mussel not only deposits great numbers of eggs but nurtures them in brood pouches
within the protection of her shell. There is not, as in fish, a great wastage of eggs and
larve in the very earliest stage of development. There exists, therefore, no necessity
for artificial aid to effect fertilization; that is, to bring the male and female reproductive
elements together. Nature’s own provisions have adequately provided for the bringing
of enormous numbers of each generation of offspring to the glochidium stage. It is
after this stage is attained that the greatest mortality occurs; the great abundance of
glochidia produced by each female is, indeed, evidence that enormous losses are to
occur subsequently, and observation indicates that the critical stages are, first, when the
glochidia are liberated from the parent to await a host, and, second, when the juvenile
mussels are dropped from the fish that serves as host.

The artificial propagation of mussels as now practiced aims to carry the young
mussels through the first great crisis. Its object is to insure to a large number of
glochidia the opportunity to effect attachment to a suitable fish. Under present
conditions the operations can be conducted extensively and economically only in the
field. The procedure in brief is to take fish in the immediate vicinity of the places to
be stocked, infect them with glochidia of the desired species of mussels, and liberate
them immediately. Artificial propagation, then, as applied to fresh-water mussels, is
a very different sort of operation from that employed in the propagation of fish,
although it is no less directly adapted to the conditions and needs of the objects to be
propagated.

METHODS.

In each field the operations are conducted under the immediate direction of a qual-
ified person who may be either a permanent or temporary employee of the Bureau work-
ing under the Fairport station. The fishing crew is comprised of three or four local
fishermen, or laborers, temporarily employed.

FRESH-WATER MUSSELS. 161

The equipment for seining and handling the fish consists of a motor boat, one or
two flat-bottomed rowboats, seines or other nets, including small dip nets, tanks,
buckets, etc. The motor boat is used to cover the various fishing grounds as rapidly
as possible to distribute the infected fishes, and to move the outfit from place to place
as it becomes advisable or necessary to extend the field of operations. The rowboat is
employed in the actual work of seining and handling the fish. If the fish are taken in
very large numbers it is convenient to have one or two tanks, similar to the ordinary
4-foot galvanized stock tanks and equipped with handles. Under ordinary conditions,
tubs serve very well, especially if the fish have to be transported by hand for some dis-
tance, as is the case when the fish are taken in rescue work from land-locked ponds or
lakes. At times, when the field of operations is at some distance from a place where
living and sleeping accommodations can be secured, a camping outfit, or a house boat, is
used for quartering the crew. The head of the party must be provided with a dissecting
microscope, a magnifying hand lens, and simple dissecting instruments.

Before an infection can be made, it is first necessary to obtain a supply of glochidia
of the desired species of mussels. In localities where commercial shelling is actively prac-
ticed this can be done by visiting the shellers’ boats and examining the catch for freshly-
taken gravid mussels. If it is desired to use the glochidia at once, the brood pouches
are immediately cut from the females and placed in water; but if it is desired to use them
over a period of several days, the gravid shells are purchased and the glochidia removed
as needed. In locations where shells are scarce, or where little or no commercial shelling
is done, it is sometimes necessary to hire a sheller to procure the mussels.

The fish are next sought by means of seines or nets, and when secured are sorted and
transferred to the tanks or tubs; the fish that are not required for purposes of mussel
propagation are immediately liberated in suitable waters. When the containers are
comfortably filled with fish, overcrowding being avoided, the brood pouches of one or
more mussels, as necessary, are cut out and opened with scissors or scalpel and the
glochidia are teased out in a small pail or other container from which they are poured into
the tanks with the fish. Figures 1 to 4, Plate XVIII, show the seining and infection
operations in the field.

The experienced operator can usually tell at a glance whether or not the glochidia
are sufficiently ripe for infection. If they freely separate when removed from the brood
pouches and placed in a dish of water, it is usually a sign that a sufficient degree of ripe-
ness has been obtained. If, however, they adhere in a conglutinate mass and can be
separated only with difficulty, it is certain indication that they are unsuitable for
infection; examination with a hand lens in such case will show also that the glochidia
are still inclosed in the egg membrane, thus revealing theirimmaturity. If the glochidia
are fully developed, one can readily determine if they are alive and active by dropping
a few particles of salt or a couple of drops of fish blood into a small dish containing some
of the glochidia. Itisasign of maturity and vitality if the valves begin to snap together
as the salt or blood diffuses through the water.

After being removed from the brood pouches the life of the glochidia is usually
rather short, but it is possible to keep them alive a day or two if the water in which they
are retained is changed at frequent intervals and not permitted to become too warm.

The operator is guided by his experience as to the quantity of glochidia to be placed
with a given lot of fish and as to the length of the infection period. The water may be

162 BULLETIN OF THE BUREAU OF FISHERIES.

stirred from time to time in order to keep the glochidia in somewhat even suspension,
but in most cases the movements of the fish themselves insure a circulation of the water
and a general distribution of the glochidia. At intervals individual fish are taken by
hand or small dip net, and the gills examined with a lens; when, in the opinion of the
operator, a sufficient degree of infection has occurred, the fish are placed at once in
open waters, or transferred to other containers for conveyance to a place suitable for
their liberation. The rapidity with which infection takes place depends upon a variety
of conditions, such as temperatures of water, kind and size of fish, and activity of glochi-
dia. Ordinarily a period of from 5 to 25 minutes is sufficient to insure an optimum
infection. The infection time is usually shorter in warm water than in cold. As basis
for approximate computation of the number of glochidia planted, several average-sized
specimens of each species of fish infected are killed and the gills removed for subsequent
counts of the glochidia attached. The counting is done by the foreman with the aid of a
microscope and usually in the evening after the close of the field operations of the day.
The number of glochidia per fish of each species having been determined by the count of
representative examples, and the numbers of fish of the species being known, the entire
number of glochidia planted on a given lot of fish is easily computed. The data in detail
are promptly recorded on form cards provided for the purpose. The count of total
glochidia planted is of course only approximate, but the method of count and computation
described is as accurate as the conditions of operation permit, and it is as precise as the
methods of count generally practiced in fish-cultural operations. In the long run, the
actual errors on one side and the other must approximately balance.

That degree of infection which employs the fish to best advantage in mussel propa-
gation, without doing appreciable injury to the host, is termed the “‘optimum infection.”
It varies with the species of mussel and with the kind and the size of the fish. Table 23
gives illustrative instances.

TABLE 23.—OPTIMUM INFECTION FOR CERTAIN SPECIES OF MUSSEL ON SEVERAL SPECIES OF FISH.

Species of mussel. Fish host. |
Number of
5 cate
rasan a: ize in on fish
Scientific name. Common name. Species. aches

Lampsilis luteola....................005 Lake Pepin mucket 8 2,000
Ooo sabe we ws emcee Screen ae aed cemeioe do 8 2,000

DIO fate imo le cte:clelatie a kv, - tafe PSC ee | See do. 8 2,500

LOE eee ee eee ci crise ao ice do. 5 500

DOW, seco neces shanks Bog bose do 5 4oo

BVO 5 ais ctocsiaginie ts oc dere cau cisae tema tCeee do 6 I, 500
Lampsilis anodontoides. .. ...| Yellow sand-shell . 16 2,000
Lampsilis ligamentina. ... aes pCKetie nnn ec Be 8 2,000
Lampsilis pustulosa.................... Pimple-hack: 2.222 cee eee 14 I, 200

Incidental to the field work in mussel propagation, valuable results are frequently
gained in the reclamation of fish from the overflowed lands bordering the various rivers.
All fishes rescued in connection with propagation work, whether suitable or unsuitable
for infection, are liberated in the open waters, and under such circumstances the value
of the fish thus saved in large measure recompenses for the cost of the mussel propaga-
tion work.

The operations of mussel propagation as just described serve to carry the young
mussels through the most critical stage of the life history—to give to thousands the

Butt. U. S. B. F., 1919-20. PLATE XVIII.

Fic. 2.—Seining fish in Lake Pepin for mussel propagation. Fic. 3.—Transferring fish to infection tank. Foreman in
boat is pouring the glochidia from a can into the tank.

Fic. 4.—Sorting the fish for infection with glochidia,

Buty. U. S. B. F., 1919-20. PLATE XIX.

Fic. 1.—A floating crate containing four baskets in which fish infected with glochidia were placed and young mussels reared.
(Compare Pl. V, fig. 3.)

Fic. 2.—Lifting one of the baskets from the crate for examination and cleaning.

FRESH-WATER MUSSELS. 163

chance of life that would ordinarily fall only to dozens. As previously pointed out
(p. 151), an extensive series of observations of fish reveals the fact that but few are
naturally infected with mussels and these usually in slight degree. The chance that a
large proportion of the glochidia discharged by any mussel will become attached to a
proper host is slight, and it is only because nature is prodigal in the production of glochi-
dia that the various species of mussels can maintain their numbers under natural condi-
tions. With the disturbance of natural conditions by the active pursuit of a commercial
shell fishery, nature’s fair balance is destroyed, and some compensatory artificial aid to
the propagation of mussels is rendered necessary.

It is not presumed that all the vicissitudes of mussel life are removed by the bringing
together of fish and mussel. Nature undoubtedly exacts heavy tolls at other stages.
Many of the young mussels on being liberated from the fish will fall in unfavorable
environments and meet an early death, while those that survive the earliest stage of
independent life may still be subjected to numerous enemies throughout the juvenile
period at least. Nevertheless, glochidia of certain species can be planted in such large
numbers and at such slight cost that, after making due allowance for an extraordinary
subsequent loss, substantial returns can be expected. ‘That such results do obtain is
indicated both by experiments to be later described (p. 166) and by common experience

MUSSEL CULTURE.

The rearing of young mussels in tanks, in ponds, or (if under conditions of control)
in the river, may properly be termed “mussel culture,” as distinguished from ‘‘ mussel
propagation,’ which, as we have seen, consists in bringing about the attachment of
glochidia to fish and liberating the fish in public waters. For several years experiments
in mussel culture have been carried on by the Bureau of Fisheries at Fairport and else-
where, with a view both to securing information regarding the life history of mussels
and to testing experimentally the possibilities of culture as a public measure of conserva-
tion or as a field for private enterprise. At first little success attended these efforts.
It was found that the mussels could readily be carried through the parasitic stage, but
that soon after leaving the fish hosts they perished. Apparently there was something
inimical to the young mussels in the artificial conditions of aquaria, tanks, or ponds,
although these might be supplied with running water derived from the natural habitat
of mussels.

The first reported rearing of mussels under control was accomplished with the
Lake Pepin mucket in a crate floating in the Mississippi River (Howard, 1915). Ex-
periments initiated by the senior author in the ponds at Fairport, Iowa, about the same
time were also successful with the same species. Subsequently broods of the Lake Pepin
mucket have been reared from year to year by various methods. Less consistent results
have been obtained with the following river mussels: The pocketbook, Lampsilis ventri-
cosa, the pimple-back, Quadrula pustulosa, and until recently the yellow sand-shell,
Lampsis anodontoides, and the mucket, Lampsilis ligamentina. Apparently the condi-
tions required for rearing the Lake Pepin mucket are less difficult to meet under control
than is the case with the other species mentioned. The reason is, doubtless, that Lamp-
stlis luteola, being a lake-dwelling species as well as an inhabitant of rivers. is adapted to
more varied conditions.

The methods employed in rearing mussels may be designated as follows: (1) The
floating crate with closed bottom (chiefly used in rivers); (2) the floating crate with open

164 BULLETIN OF THE BUREAU OF FISHERIES.

bottom (chiefly used in ponds) ; (3) the bottom crate; (4) pen with wooden or box bottom ;
(5) concrete ponds; (6) earth ponds; (7) troughs of sheet metal, wood, or concrete tanks,
and aquaria.

(1) The floating crate with closed bottom was devised to meet the special conditions
of a large river where the level is subject to considerable change, where excessive turbidity
frequently prevails, and where there is a decided current. To prevent the washing away
of the microscopic mussels, while permitting the passage of water and food through the
crate, the crates are constructed of fine-meshed (100 mesh to the inch) wire cloth on a
wooden frame. The form of the crates and the manner of using them may be under-
stood from the illustrations (Pl. XIX, figs. 1 and 2). They are described in more detail
in a forthcoming paper by A. D. Howard. A plant of young mussels is obtained by
placing infected fish in the crate and removing them after they are freed of the mussels.
The results with the floating crate have been quite satisfactory with the Lake Pepin
mucket, and a few yellow sand-shells have also been obtained in them. Other river
mussels have failed to develop beyond early stages. Good results with river mussels
would be expected, but it is found that even with the crate floating in the river, the
conditions within it are not those of the natural habitat of the mussel on the clean
current-swept bottom of the river. No one has yet devised a container to employ under
such conditions that would fully answer the requirements.

(2) The floating crate with open bottom has been used in artificial earth ponds.
The bottom is actually closed to fish, though open to juvenile mussels, since it is made of
coarse-mesh wire cloth (114-inch mesh). The infected fish are kept inclosed until freed of
glochidia, which fall through the wire to the bottom of the pond. To obtain the mussels
when developed, the water is temporarily drawn from the pond. Good results have
been obtained with the Lake Pepin mucket only.

(3) The bottom crate has been used in studies of growth of larger mussels, by
Lefevre and Curtis (1912, p. 180), Coker, and others, and in experiments in pear! culture
by Herrick (Coker, 1913). It has recently been adapted for the purpose of retaining
infected fish and securing plants of early postparasitic stages of mussels. The crate
rests on the bottom of the pond. It may have either a solid bottom or one of screen
wire which, of course, sinks a little way into the mud covering the bottom of the pond.

(4) The pen of galvanized netting with wooden floor is adapted to quiet water
without current. The pen, having walls of wire cloth that extend from the bottom to a
safe distance above the surface of the water, allows the fish to seek their own range of
depth and permits the mussels that fall from the fish to remain close to the bottom of the
pond or lake, as is natural for them. The mussels are collected by raising the wooden
bottom at the end of the growing season. Excellent results have been obtained in Lake
Pepin with the Lake Pepin mucket. In the most successful experiment more than
11,000 living young were secured in one crop in a pen 12 feet square. These were
liberated from 79 fish which had been artificially infected (Corwin, 1920).

(5) Concrete ponds having vertical sides have been planted in the usual way and
the fish removed with a seine after the mussels have been shed. Some 50 examples
of a river-inhabiting species, the pimple-back, Ouadrula pustulosa, were reared to the
age of 4 years in one experiment, but other trials with this species have failed. The
usual consistent results have been secured with the Lake Pepin mucket.

(6) Earth ponds with devices for control of depth and water supply have been
stocked with mussels by introducing infected fish. As a rule the fish are not removed

FRESH-WATER MUSSELS. 165

until the end of the season when the pond is drawn. The Lake Pepin mucket in con-
siderable numbers have been reared in earth ponds. A few pocketbook mussels, L.
ventricosa, were obtained after a recorded plant in a pond of modified type, having earth
bottom but wooden sides. Mussels of several other species have been found in ponds
from accidental plantings. The sporadic occurrences of young mussels in the first ponds
and in the reservoir constructed at the Biological Station at Fairport, Iowa, are of
interest as showing how, through parasitism upon fish, many species of mussel will
quickly invade new waters. It is significant that none of the species which have intro-
duced themselves abundantly into these ponds are commercially valuable. Apparently
the commercially useless mussels are more easily and abundantly distributed by natural
means than the useful ones. A list of the species noted, with additional data, is com-
prised in the following table (cf. Pl. XX):

TABLE 24.—MuSSELS RECORDED FROM PONDS AT THE FAIRPORT STATION.

Scientific name. Common name. Number or frequency. [eee
|

Anodonta corpulenta Cooper...........-..-..++- Tab Szel eae sehoocBacr sap ataacecteene:
Anodonta suborbiculata Say ..| Paper-shell. ae 67-4
Anodonta imbecillis Say.............-2-...-.-+-|-.--- do;..-. 2-48
Arcidens confragosus Say ©. . ..| Rock pocketboo! | 39-49
Lampsilis ligamentina Lam.... iG. (ite So ap ea ee es ee Baer 6-20
Lampsilis (Eroptem) alata Say..... ...| Pink heel-splitter.... 69-5
Lampsilis (Proptera) capax Green. . ..| Pocketbook. . 49-5
Lampsilis (Proptera) levissima Lea ..| Paper-shell... ae hy. ~a,ae 27-90
Yjamipsilis sttbrostrata Say G20. 2 eee ee re eee e nese ciscce Bee d eile 8. 48
Lampsilis gracilis Barnes...............2......- Paner-shelloe.oa 5 iss. cease neste ae = 9- 1-71
Lampsilis parva Barnes@...... Seite icra | ee ere ole wialo cisiaisin oleleia aheiaetetetalais | EC hcn eaten 5- 7-27
Obliquaria reflexa Rafinesqu ..| Three-horned warty-back...... hee 16
Plagiola donaciformis Lea. BE Ht 0 >= 3 9° pn ee ee Soom 2. 6-20
Quadrula plicata Say..... ..| Blue-point 13-5
Quadrula undata Barnes...............0.2.5.-5 Pig-toe..... 15-8
Strophitus edentulus Say @....... .| Squaw-foot 62.1
Symphynota complanata Barnes. ....| White heel-splitter 64-91
Obovariaellipsis Teal... b ie. 2 ssc cbed weeds nen Bickory-nuts 2 Fs joss5 Shee ty. So 5. e 11.4

@ Uncommon in the river.

(7) Experiments have also been made with various containers of small dimensions
which are usually supplied with running water. Such are the glass aquarium and the
tank or trough which may be made of wood, concrete, or sheet metal. Of these the one
most used for experimental rearing of mussels at Fairport, Iowa, has been the trough of
sheet metal painted with asphaltum. A special arrangement for water supply is em-
ployed. The water is not taken directly from the main reservoir, but is drawn from the
surface of a pond containing vegetation; in some cases it is also strained through cloth.
In this way water is obtained that is very clear and probably free to a large extent from
such small animals of the bottom as would prey upon the young mussels. The Lake
Pepin mucket, the river mucket, and the yellow sand-shell have been reared through the
first year in such troughs. The experiments are of such importance as to merit detailed
description. The following account is based upon a report of F. H. Reuling, who first
assisted in the experiments and later was charged with their conduct. (See also Reuling,
1919.)

The experiments were conducted in a series of eight galvanized iron troughs, placed
at a sufficiently low level to receive a gravity supply of waterfrom pond 1D. This pond
was supplied by gravity from the reservoir which received its supply direct from the
Mississippi River through the pumping plant. The water in pond 1D remained com-
paratively clear throughout the season, and this was one of the primary considerations

166 BULLETIN OF THE BUREAU OF FISHERIES.

iv locating the troughs. The troughs were 12 feet long, 1 foot wide, and 8 inches deep,
painted with asphaltum, and each had its independent inflow from a common screened
supply pipe in the pond. The bottom of each trough was covered with fine sand to a
depth of about one-half inch.

Records were kept of the progress of the larval mussels through the process of devel-
opment, and when they had reached that stage when they were ready to drop from the
fish, counts on the fish gave a close approximation of the number dropped in the trough.

The results of the experiments the first season were quite meager, as only 7 young
of the Lake Pepin mucket, Lampsilis /uteola, varying from 6 mm. to 17.8 mm. in length,
and 4 of the mucket, L. /igamentina, with an average length of 2.6 mm., were reared.
However, in case of the mucket the results were very encouraging, as it marked the first
instance of juveniles of this species being artificially reared to this size.

During the season of 1918 greater results were obtained with the Lake Pepin mucket,
the young mussels being successfully reared in four troughs. In one trough a count of
746 was obtained, The experiments with /igamentina yielded negative results, though
a lack of glochidia for infection greatly handicapped the work with this species.

The results in 1919 were still more gratifying. Young Lake Pepin muckets were
obtained in each of five troughs planted with this species. In one trough 2,008 were
counted at the end of the season, these little mussels varying in length from 9 mm. to
17.5 mm., the growth comparing very favorably with that made by the young of this
species in their natural habitat. Ina trough devoted to the river mucket, L. /igamentina,
a total of 565 were reared. These little mussels varied in length from 5 mm. to 8.5 mm.
In a trough planted with the yellow sand-shell a count of 2,006 was obtained at the end
of the season, the young mussels varying in length from 5.5 mm. to 12mm. ‘The result
of this experiment is highly interesting, in that it is the first record of the artificial rearing
of this very valuable species in any quantity.

The 746 young /ufeola reared during the summer of 1918 were carried over the winter
in a shallow crate bottom 5 feet square and 8 inches deep, submerged in one of the earth
ponds. During the summer of 1919 an inventory of the crate bottom gave a count of
238 young mussels, a survival percentage of about 32 per cent.

The method of artificial rearing of young mussels, as detailed above, denotes a
distinct departure from the methods previously used and gives the operator complete
control of conditions throughout. The results of the experiments have been such as to
justify the employment of the method on a much larger scale in future, and plans are
under way for materially increasing the facilities and equipment. Certain phases of the
work need further study and amplification. Additional information on the possible
enemies of the young mussels in the troughs is needed; a study of their food should be
made; it should be learned if artificial feeding is practicable; and further experiments
should be made to determine the most favorable bottom material for the troughs,
whether fine sand alone, or sand with a slight admixture of silt, etc. The present indi-
cations are that fine sand is the most desirable bottom material.

In summary of the topic of the culture of fresh-water mussels, it may be stated that
the results of many experiments conducted under diverse conditions demonstrate that
the valuable Lake Pepin mucket can be reared in quantities, under conditions of control.
Sufficient success has been attained with other species to warrant confidence that, with
them also, methods of securing constant results will be found.

1919-20. PLATE XX,

» &@e @&

e ©

Juveniles of 20 species of mussels found in the artificial ponds at the U.

Fisheries Biological

Station within two years from the time of construction of the ponds. Reading from left to right
these are:

one-half. (Photographed by J. B. Southall.)

Top row: Anodonta imbecillis, Anodonta corpulenta, Anodonta suborbiculata, Arcidens confragosus.
Second row: Strophitus edentulus,Symphynota complanata, Lampsilis alata, Lamp silis laevt
Third row: Lampsilis capax, Lampsilis gracilis, Lampsilis ventricosa, Lampsilis luteola
Fourth row: Lampsilis subrostrata, Lampsilis parva, Lampsilis ligamentina, Obovaria ellipss
Fifth row: Plagiola donactformis, Obliquaria reflexa, Quadrula plicata, Quadrula undata

All reproduced natural size excepting the two right-hand figures in top row which are reduced

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PART 3. STRUCTURE OF FRESH-WATER MUSSELS.
INTRODUCTION.

A general description of the structure of fresh-water mussels may assist those
without special knowledge of the anatomy of mussels to follow intelligently the account
of the natural history, propagation, and development which it has been the primary
purpose of this report to give. It may also serve as a helpful introduction to persons
with limited technical knowledge who wish to make original observations or experi-
ments concerning the habits and growth of mussels. It has been the special purpose
of the authors to point out the more conspicuous gaps in our knowledge of the behavior
of mussels and their relations to the environment. Many of these gaps can readily be
bridged by any who will take the trouble to observe painstakingly and repeatedly the
conditions under which fresh-water mussels live in the streams, lakes, or ponds in one’s
own neighborhood. The species subjected to observation or exyeriment should, of
course be definitely known, but identifications of species can always be obtained of
_ Government agencies or from independent specialists in the study of mollusks.

In most localities some species of mussels are easily obtainable and observable
in nature or in aquaria. In rivers of the Atlantic States, generally, the common mussel
is the Unio complanatus. The more familiar forms in lakes and alongshore in streams
of the Mississippi Valley and the Great Lakes drainage are the fat mucket Lampsilis
luteola,* and some of the floaters of the genus Anodonta. Closely related to the fat
mucket is the mucket, Lampsilis ligamentina, which is common in the Mississippi and
its tributaries as well as in many streams discharging into the Great Lakes. Asa rep-
resentative type in the simplicity of its form and of the sculpture and markings of its
shell, the mucket serves as the basis of the following general description, except
as explicit qualifications are made. With more or less modification, the account may
be applied to whatever species is most readily available. The functions of the organs
described will generally be briefly indicated.

Let it be understood first that a living mussel is commonly partly embedded in the
bottom, with the forward end directed obliquely downward and the rear end upward.
The ‘“‘mouth” as understood by fishermen is in reality the double siphonal opening
in the hinder part of the mussel; the true mouth, through which food is taken into the
body, is a very small and scarcely discernible opening in the part of the soft body which
is farthest away from the exposed end of the mussel.

The fresh-water mussels differ markedly in structure from the oyster or the pearl
oysters which pertain to a different order of lamellibranchs. They are likewise far
removed from the sea mussels, which lie in a third order. Their nearer relatives are
the sea clams and the small Cyrenians of the rivers; the sea clams and the little clams
(Cyrenians) of the rivers are more closely allied to each other than to fresh-water
mussels. The pearly fresh-water mussels or Naiades comprise two great families,

* The best commercial type of the mussels of this species is also known as the “ Lake Pepin mucket.”
‘ 167

168 BULLETIN OF THE BUREAU OF FISHERIES.

the Unionide, with which the present paper is concerned, and the Mutelide of South
America and Africa. The Mutelide differ from the Unionide in some particulars of
structure, especially in the form of teeth on the shell and in the form of larva, which
is a Jasidiwm, instead of a glochidium such as has been described above.

THE SHELL.

The shell is composed of two parts very similar in exterior aspect, but generally
differing from each other in interior form. Each portion is called a valve, and the
two valves are hinged together.

EXTERNAL FEATURES.

In form the shell is roughly elliptical, evenly rounded in front, but more or less
angular behind. ‘The lower or ventral margin is generally evenly rounded, but may be
arched inward just behind the middle, especially in shells of females. The dorsal or hinge
margin is rather straight except for the rounded prominence on each valve just in front
of the middle of the back; this knob, or arched portion of each valve, is called the
umbo. Where the umbones of opposite valves approximate each other they are more
or less elevated above the surrounding shell surface to form the beaks. The beaks in
many species, though not in the mucket, are beautifully sculptured with coarse or fine
ridges in the form of single or double loops. With the river mucket, beak sculpture
is entirely wanting, while it can be seen clearly in Symphynota complanata (Pl. XX, 2d
row, 2d fig.). Almost every species, if good specimens are available, show some form of
beak sculpture;* commonly, however, in older specimens the beaks are so much eroded
that the ridges are hardly, if at all, apparent.

In some streams scarcely a single example can be found with the beaks preserved;
in other waters erosion occurs less commonly and the beak markings can be observed
even in some of the large examples.

In some cases the resting periods of winter have left distinct marks by color or
otherwise on the shell, so that rings or zones corresponding to the growth of each year
are recognizable. The rings of annual growth are not, however, generally recognizable
on shells having a dark-colored exterior surface. It is also observed that such rings
may result from other causes than the interruption of growth by the severity of winter.
(See p. 132.)

A conspicuous feature of the shell is the prominent ridge, which extends from the
beaks backward and downward to the posterior ventral angle of the shell. A somewhat
similar ridge characterizes almost every species of mussels.

The exterior color of the shell is a most variable character. Generally speaking,
the body color is a greenish straw, relieved by narrow green rays, very narrow on the
beaks and widening out toward the lower margin. These rays are a nearly constant
character in the mucket, but vary in number, in width, in brightness of color, and in
being continuous or interrupted. The periostracum, or horny covering, of shells grow-
ing in clear streams is generally much more brightly rayed than that of those in turbid

@ The beak sculpture of young specimens is a very important diagnostic character or means of distinguishing species which
may closely resemble each other in general form. Compare the yellow and the slough sand-shells, Lampsilis anodontoides and
Lampsilis fallaciosa, or the pocketbooks, Lampsilts ventricosa and Lampsilis (Proptera) capax, which are occasionally distinguished
by this feature alone. ‘The beak is, of course, the beginning of the shell—the oldest portion.

FRESH-WATER MUSSELS. 169

ones. Young shells are more brightly rayed than old, the rays generally fading some-
what or wholly disappearing with age. In different localities, and even in the same
bed, the colors are various, the shells may be nearly uniformly straw-colored or largely
green; again, a red or rusty-brown color may predominate. The red color without
is commonly associated with a pink nacre within. The shell may be smooth and glossy
or roughened by fine lines; a silky appearance may be caused by innumerable fine
lamine or folds projecting out from the surface of the periostracum. The silky surface
is characteristic of some species, as the hickory-nut, Obovaria ellipsis.

Looking now at the top or hinge of the shell there is seen just back of the beaks a
long, narrow, tough, leathery, elastic band, the ligament, an important part of the hinge
mechanism. Just in front of the beak is a small region between the shell valves, which
is occupied by a similar horny material. This is called the anterior lunule, but in the
mucket it is scarcely developed, being about one-half inch long and very narrow in a
specimen of 3 inches total length. A posterior lunule may be found just back of the
ligament. The compressed form of the shell is noticeable in this view. Roughly speak-
ing, the thickness of a mucket from side to side is about one-third of the length, while
the width—or height, more correctly—is about two-thirds of the length.

INTERNAL FEATURES.

The interior surface of the shell is smooth, white, and lustrous, and usually somewhat
iridescent in the extreme posterior portion. In color it is white or pinkish in the mucket,
but in other species it may be salmon or purple. Often the proper color is obscured by
yellow, greenish, rusty, or salmon-colored stains, resulting from disease, injury, or in-
clusion of mud in the nacre. The body of the shell is mainly calcareous, being composed
chiefly of a compound of calcium of somewhat the same chemical composition as marble
or limestone, but differing in physical structure from either. An account of the struc-
ture of shell is given in another place (p. 129).

The conspicuous features of the interior aspect of the shell are the general con-
cavity of each valve; the deeper beak cavities; the dorsal margin roughened by ridges
or protuberances known as the “teeth;” two rounded, impressed, and roughened sur-
faces, one near each end, the adductor muscle cicatrices; and a curved impressed line
parallel to the margin of the shell, extending between the two scars just mentioned.
This last is the pallial line and marks the attachment of certain muscles of the mantle.

The two valves, it is noted, are practically identical except for the teeth, which
instead of being equal in the two valves, correspond to each other in such a way that
the teeth of one valve fit into the spaces between the teeth of the opposite valve. The
two valves are thereby interlocked so that they can not slide over each other. Heavier
teeth characterize the mussels that are adapted to live in strong currents, while weak
teeth or the total lack of them mark the species that must live in quiet waters. The
teeth in each valve are of two forms; at the anterior or front end are the stout, rough,
and somewhat conical cardinal or pseudocardinal teeth; while behind these, and more
or less separated from them, are long, narrow, bladelike ridges, the lateral teeth. On the
right valve there is one lateral tooth which exactly fits into the deep narrow furrow
between the two slenderer lateral teeth of the left valve. The two valves are practically
exact mirror images.of each other except for the teeth; accordingly, in species such as the

170 BULLETIN OF THE BUREAU OF FISHERIES.

Anodontas, which are without teeth, the bilateral symmetry is complete. In some
marine bivalves the two shells are essentially different, as in the oyster, where one is
concave while the other is flattened and smaller.

The ligament is composed of two parts; the dark outer layer is inelastic and con-
tinuous with the periostracum of the shell; while the inner part, comprising the bulk
of the ligament, is elastic and bears somewhat inappropriately the name of cartilage.
The elastic cartilage is confined between the inelastic layer above and the firm hinge of
the shell below. It is compressed when the shell is closed. The natural or relaxed
condition of the shell is, therefore, open; that is to say, with the valves separated below
by about one-half inch. Consequently, the shell is kept closed in life only by an exertion
on the part of the animal. This is accomplished by means of two stout bands of muscle
fibers, constituting the anterior and posterior adductor muscles, which extend from one
valve to the other near each end of the shell. These are firmly attached to the shell
at each end, the places of attachment being the conspicuous rounded impressions pre-
viously noticed.

The hinge mechanism is completed by the lunule previously referred to. This is
a thin horny covering occupying the space between the valves in front of the beak.
Unlike the ligament behind, it is stretched when the shell is open. The lunule doubtless
has no especial significance except to serve as a protective covering and to make a firm
union of the two valves.

Besides the two adductor impressions and the pallial line, some smaller muscle im-
pressions are apparent. Such are those of the muscles which draw back the foot, or
the anterior and posterior retractor muscles. These are small impressions, two in each
valve, just above the big adductor impressions and in this mussel (Lampsilis ligamentina)
confluent with the latter. The impression of the protractor, or the muscle which aids
in protruding the foot, is usually quite distinct and just beneath the anterior adductor
impression. Deep in the beak cavity and on the under surface of the cardinal teeth,
or the bridge between cardinal and lateral teeth, are small pits which are the points of
attachment of numerous small muscles that serve to elevate the foot. These last are
the dorsal muscle scars referred to in systematic descriptions. (See Pl. XXI, fig. 1.)

DIVERSITY IN FORM.

Many modifications of the above description would have to be made for other species
of mussels. The shell may be pear-shaped as in the niggerhead (Quadrula ebenus), or
nearly circular as in Quadrula circulus; it may be very much inflated as in Lampsiis
capax or in L. ventricosa (the pocketbook), or exceedingly compressed as in Symphynota
compressa. In some the shell is not only greatly flattened from side to side but also
extends upward in wings before and behind the beaks. Such species are given locally
such descriptive names as pancakes, hatchet-backs (Lampsis alata), or heel-splitters
(Symphynota complanata). Some shells are proportionately very heavy, while others,
included mostly in the genus Anodonta, the paper-shells or floaters, are so thin as to be
useless for any present economic purpose. The Anodontas, adapted to live in lakes or
close alongshore in streams, are further characterized by the entire absence of teeth.

Variations in thickness or in uniformity of thickness are important from the stand-
point of the button makers, and so also are variations in the surface sculpture. Some

FRESH-WATER MUSSELS. I7I

forms are covered with protuberances or knobs in regular or irregular pattern, thus ac-
quiring such common names as warty-backs or pimple-backs; while others have strong
ridges running obliquely across the shell, as the three-ridge, Quadrula undulata, the
blue-point, QO. plicata, and the washboard, Quadrula heros. One species, Unio spinosus,
of Alabama, bears long sharp spines on the shell. Diversity of interior color has pre-
viously been alluded to. No satisfactory explanation of the colors of nacre has yet
been offered. Certain species are almost always white-nacred, as the pimple-back,
maple-leaf, and niggerhead. Others are white or pink, examples of the two colors
living side by side. Some species have usually a deep purple or salmon nacre, but
white-nacred shells of the same species may predominate in particular streams.

Variations in external color are conspicuous in any collection of shells even from
the same mussel bed. Along with shells of uniform color, light or dark, we find shells
of glossy surface and brilliantly rayed; the rays may be continuous or variously inter-
rupted, sometimes composed of small zigzag markings forming striking and fantastic
patterns. In short, the differences in form and color of shell are unlimited and could
not be described, even within the limits of a systematic monograph.

THE SOFT BODY.

For observation of the body the mussel may be carefully opened by severing the
adductor muscles close to one valve, preferably the left, and gently freeing the soft
mantlé from the shell as the knife blade is passed from one end of the shell to the other.
Removing or bending back the upper (left) valve, the body of the mussel is seen to be
almost completely enveloped in a thin mantle corresponding to the interior of the shell
in form and size (PI. XXI, fig. 1).

FORM AND FUNCTIONS OF THE MANTLE.

The mantle is composed of right and left sheets entirely free from each other except
along the back where the two sheets are continuous not only with each other but with
the body as well. The mantle is, in fact, a double fold from the back of the mussel
draped over the body and lining the shell. A thin wing or dorsal extension of the man-
tle covers entirely the surfaces of the cardinal and lateral teeth and underlies the liga-
ment.

The mantle is not of uniform character throughout but shows a broad border thicker
than the central portion and somewhat muscular. This border along its inner line is
attached to the shell through many fine muscle fibers, the attachment of which forms
the pallial line on the shell. The border is muscular and, therefore, contractile; the
lower or right mantle, which has not been separated from the shell, will have its edge
contracted away somewhat from the margin of the valve; generally there is apparent
a thin film of horny material which connects the edge of the mantle with the extreme
edge of the shell. It is not infrequently the case that in separating the surface of the
mantle from the shell a delicate transparent membrane is distinguishable, some parts
of which adhere to the mantle and some parts to the shell. Unless, therefore, a rupture
has occurred, the mantle normally is actually continuous at the margin with the outer
surface of the shell, and probably organically but delicately connected to the inner surface
of the shell over its entire surface.

172 BULLETIN OF THE BUREAU OF FISHERIES.

The relations of the mantle as observed will have greater significance from a state-
ment of its functions. Besides supplementing the gills in respiration and serving along
its border as a sensory organ, a chief function of the mantle is the formation of shell.
The extreme edge of the mantle secretes the horny covering of the shell, as also the liga-
ments and lunule, while the remaining mantle surface secretes the calcareous shell.
For our purpose, accordingly, the mantle is a most significant organ. Diseases or other
influences affecting the mantle frequently show effects in the shape, color, or quality
of the shell, and it is in the mantle, probably, that all free pearls are produced. The
mantle is not, however, the only portion of the mussel capable of forming shell. The
two adductor muscles pass entirely through the mantle, having direct attachment to the
shell. While the shell becomes thicker in other parts by the superposition of layer after
layer of calcareous material from the surface of the mantle, the thickening of the shell
against the muscles is in some measure, apparently, a function of the muscles them-
selves. It is not surprising, therefore, that these muscles also give rise to a large number
of pearl formations, baroques, and slugs, but not, ordinarily, good pearls. No other
parts commonly give origin to pearls, although it is reported that pearls have been.
found within the body. Baroque pearls and slugs are frequently found in the tissue
just beneath the hinge line, but this is actually a part of the mantle.

The shell substance formed by the muscles is called hypostracum, and is largely
horny in nature. Since each muscle occupies a nearly constant relative position regard-
less of the size to which the mussel attains, it is evident that in any adult individual the
muscle traveled in the course of life history from the back to its latest position; the
hypostracum, therefore, does not occupy a single spot but is a tapering vein passing
through the nacre from the beak to the position of the muscle at any given time. Simi-
larly the hypostracum of the pallial line is the margin of a thin stratum of like sub-
stance which extends from the beak or beginning of the shell and divides the nacre
into two portions (p. 130).

The mantle has other functions of great importance. When the muscles are relaxed
and the shell is gaping, the opening between the valves of the shell is largely closed by
the apposed margins of the mantle. Nothing can enter between the valves of the shell
without affecting the highly sensitive border of the mantle and thus giving warning
to the animal, which may then contract its muscles and close the shell instantly. The
nerves of the margin of the mantle are not only sensitive to tactile stimuli, but apparently
are also connected with organs of something like visual function, so that the animal
may close or open its shell under the influence of shadows or bright light.

It is the margins of the mantle that surround and form the two siphonal openings
at the hinder end of the shell, through one of which water and food pass into the shell,
while through the other water passes out, conveying the waste products. The lower
of these two openings particularly is protected by projections of the mantle, in the form
of papillae or fimbriz, which, being very sensitive, give warning of any objectionable
character or content of the water.

OTHER CONSPICUOUS ORGANS.

Without disturbing the upper mantle two internal organs are distinctly evident.
The heart is recognized by its throbbing action. It lies at the back just below the lateral
teeth of the hinge and in front of the posterior adductor muscle. The rate of beating

FRESH-WATER MUSSELS. 173

varies in different species and under different conditions but is generally under 20 pul-
sations per minute. The heart will continue to beat a long time after the shell has been
opened. Near the anterior adductor is a greenish mass of tissue, the so-called liver
or digestive gland, surrounding the white stomach. Through the transparent tissue,
covering the chamber inclosing the heart, another portion of the alimentary tube is
generally distinguishable. This is the rectum or hinder portion of the intestine which
passes directly through the heart to discharge just above the posterior adductor muscle.
The brownish tissue beneath the heart represents the organ of Bojanus, as it is called,
with functions corresponding to a kidney.

To distinguish other organs the mantle must be folded back. The muscular mass of
plowshare form and brownish white in color, constituting the anteroventral border
of the body, is the foot." Several curtainlike flaps are conspicuous. ‘Toward the forward
end are two large earlike flaps, the labial palpi or lipfolds. They are easily torn in folding
the mantle back, but if in good condition, it may seen that each of these palps is contin-
uous, around the front end of the body, with the palp of the opposite side. Immediately
in front of the body they are very narrow and lie one above and the other just below an
exceedingly small opening, the mouth, which can be seen only by very careful exami-
nation.

The other two folds are much larger and rounded below. These are the gills, which
extend from the anterior third of the body to the extreme posterior end. The inner is
slightly the larger. The outer gill is connected above and on the outside to the mantle.
Folding this one back, it is seen that it is attached also to the inner gill above. The inner
gill on the inner side is attached to the body and, behind the body, to the inner gill
of the opposite side. In many species the inner gill is partially free from the body.
These gills, though thin, are really basketlike structures, containing chambers within,
as will be described below.

INTERNAL STRUCTURE.

It is not the province of this paper to enter minutely into the internal anatomy.
But the following epitomized statement of the structure of the animal is given to serve
as a key to the understanding of the functions of the organism as a whole.

The digestive system comprises the mouth, with a short tube or gullet, leading
from the mouth to the stomach; the dark brown digestive gland, or so-called liver,
which surrounds the stomach; and the intestine, which is a long tube that leads down-
ward from the stomach and coils upon itself behind the foot in a complex way, before
bending upward to approach the back and extend posteriorly straight through the heart
as the rectum, which opens just above the posterior adductor muscle. A long, slender
flexible gelatinous rod, the crystalline style, is frequently found in the intestine; it
serves a function in separating food from foreign particles and comprises a store of
enzymes or ferments for use in the processes of digestion (Nelson, 1918).

The excretory system comprises a functional kidney with a bladder which discharges
into the cavity surrounding the heart.

The circulatory system includes, as in higher animals, heart, blood, arteries, and
veins. The blood of a mussel is colorless but maintains a regular circulation from the
heart through certain arteries to many smaller vessels ramifying all through the body,
returning by a main vein to the kidneys, thence to the gills and back through other
veins to the heart to begin its course anew. ‘The blood, however, which passes from

75412°—22——12

174 BULLETIN OF THE BUREAU OF FISHERIES.

the arteries to the mantle, returns, not through the kidneys or the gills, but directly
to the heart.

The mantle and the gills constitute the chief respiratory organs, where the blood
is aerated. The significance of the mode of circulation is evident. The venous blood
returning from the body laden with waste products passes first to the kidney, thence
to the gills to be cleared of impurities and freshened with oxygen, after which it returns
to the heart in purified condition. The blood returning from the mantle requires no
further purification or oxygenation before entering the heart.

Without a distinct brain, the body of the mussel is coordinated through a nervous
system, consisting of three pairs of nerve centers, which are connected together by
nerve cords. ‘Two of these centers or ganglia lie one on each side of the gullet near the
mouth, a second pair is in the foot, while the third lies just beneath the posterior adductor
muscle. From these ganglia fine nerves are sent off to supply the various tissues
and organs.

Though eyes and ears are not present, sensory organs are not entirely wanting.
A small organ near the ganglia beneath the posterior adductor is supposed to serve to
test the purity of the water. Another, the otocyst, is sometimes found near the ganglia
in the foot and possibly serves as a balancing organ, by means of which the mussel
may feel whether it is in horizontal or vertical position. Sensory cells are found along
the border of the mantle, especially near the posterior openings for the passage of water.
(See p. 87.)

The organs of reproduction comprise a large part of the body mass above the foot.
The ova or semen are discharged through small openings on each side of the body into
the chamber above the gills. In the case of the male the sperms are thence passed
out with the respiratory (exhalent) current and set free in the water. They may be
drawn into the female with the water of the inhalent current, to fertilize the ova perhaps
as they are passed down from the suprabranchial chamber into the tubes in the gills
where incubation takes place. In some species the reproductive tissue is brightly
colored—orange, pink, or red.

STRUCTURE AND FUNCTIONS OF THE GILLS.

The gills, as the name would suggest, are primarily breathing organs. Nevertheless,
they have an equal if not a greater function in food gathering, and, furthermore, in
fresh-water mussels and in some other lamellibranchs, the gills have acquired a third
office which is of coordinate importance with the other two. We have seen that the
incubation of the egg takes place in the water tubes of the gills, a part or all of which may
be filled with embryo mussels. The respiratory function of the gills of the female mussel
must be greatly reduced during the period of incubation, and this condition is made
possible by the fact that the mantle of the mussel plays an equal réle with the gills
in respiration. In becoming adapted to this function of protection and perhaps nour-
ishment of the eggs and young, the gills of the female have undergone varied modifica-
tions in different species. In consequence, when gravid females can be examined, the
gills of different mussels are often found to be more strikingly distinct than is the external
form or any other obvious character. This is especially true when microscopic study
of the structure of the gills can be made.

FRESH-WATER MUSSELS. 175

Whether or not, therefore, these differences are a true guide to relationships, the
gills become one of the most convenient organs for distinguishing genera or species and
serve as the most important basis of modern classification.

Some knowledge of the anatomy of the gills is necessary for proper comprehension
of the life process of mussels in breathing, feeding, and reproduction.

The gills consist, as we have seen, of two platelike bodies on each side between the visceral mass
and the mantle. We have thus a right and a left inner gill and a right and a left outer gill. Seen from
the surface, each gill presents a delicate double striation, being marked by faint lines running parallel
with the long axis and by more pronounced lines running at right angles to the long axis of the organ.
Moreover, each gill is double, being formed of two similar plates, the inner and outer lamelle united
with one another below as well as before and behind but free at the top or dorsally. The gill has thus
the form of a long and extremely narrow bag open above. Its cavity is subdivided by vertical bars of
tissue, the interlamellar junctions, which extend between the two lamelle and divide the intervening
space into distinct compartments or water tubes, closed below but freely open along the dorsal edge of the
gill. The vertical striation of the gill is due to the fact that each lamella is made up of a number of
close-set gill filaments; the longitudinal striation, to the circumstance that these filaments are con-
nected by horizontal bars, the interfilamentar junctions. At the thin free, or ventral, edge of the
gill the filaments of the two lamellz are continuous with one another, so that each gill has actually a
single set of V-shaped filaments, the outer limbs of which go to form the outer lamella, their inner limbs
the inner lamella. Between the filaments, and bounded above and below by the interfilamentar
junctions, are minute apertures or ostia, which lead from the mantle cavity through a more or less
irregular series of cavities into the interior of the water tubes. (After Parker and Haswell.)

The gills, then, which appear as thin plates, are really comparable to long baskets
greatly flattened from side to side, the interior_of the basket being subdivided into a
series of deep tubes, all in one row. The surface of the basket, which is perforated by
many pores visible only with a microscope, is covered with very minute paddles like
fine flat hairs. The concerted action of these little paddles, called cilia, keeps driving
the water from without the gill through the minute pores into the water tubes. Through
these tubes the water passes upward into a chamber above the water tubes, called the
suprabranchial chamber, and thence backward and finally out of the shell.

Since the cilia are habitually driving the water through the surface of the gills
into the water tubes, it follows that there must be a regular stream of water entering
the mantle chamber from without through the open valves, as well as an outgoing
stream passing out from the chamber above the gills. These two streams are known
as the inhalent current and the exhalent current, respectively. If a mussel is observed
in undisturbed condition on the bottom of an aquarium (PI. V, figs. 1 and 2), the two
openings between the edges of the mantle are readily seen and the currents may easily
be observed by introducing with a pipette into the water near each opening a little
colored water. The coloring matter placed near the lower inhalent current is drawn
into the shell, but that placed near the upper opening is driven forcibly away. The
two pronounced currents, or rather two aspects of the same current, are, it may be
repeated, formed entirely by the minute paddles surrounding the innumerable pores
of the gill surfaces.

The gills themselves are living strainers in the course of this current, and as the
water passes through them the material which serves as food is filtered out to be passed
on to the mouth; at the same time, the blood in the minute vessels and spaces within
the gill filaments and partitions is being purified and recharged with oxygen. The
matter strained from the water becomes clotted with mucus and is driven along by the
cilia over the surface of the gills to the labial palpi, where it is taken up and if suitable
for food is passed on to the mouth, for the surfaces of the palpi as well as of the gills

176 BULLETIN OF THE BUREAU OF FISHERIES.

are covered by cilia or minute paddles, the combined action of which forms a wonderful
mechanism for conveying the food from any point of the gill surface into the funnel-
shaped mouth. The detailed working of this mechanism and the places and means of
“switching off’’ undesirable matter form too complex a subject to be treated in this
paper. (See Allen, 1914, and Kellogg, 1915.)

The course of the water is better understood after observing the mode of attachment
of the gills. The outer lamella of the outer gill is attached to the mantle throughout
its entire length, while its inner lamella and the outer lamella of the inner gill are attached
together to the body. ‘There is thus above each gill a small suprabranchial chamber
just above the water tubes. Behind the body or visceral mass, however, the inner
lamella of the right and left inner gills are attached together, and there is, therefore,
a single large chamber above the four gills—the cloaca or exhalent chamber. The
water, after passing through the pores of the gill surface, makes its course up the water
tubes and backward by the suprabranchial chamber into the cloaca, to be passed thence
out of the shell.?

It will be understood that the eggs and young borne in the water tubes of the gills,
which become marsupial pockets, are most favorably located for respiration, being
situated, as it were, in the respiratory current of the mother. There is, among the
various species of the Unionide, great variation in the extent to which the gills are
employed as marsupia (p. 139). In certain species the water tubes of all four gills are
filled with eggs, in others only those of the outer gills receive the eggs, while in still
others a portion of each outer gill is set apart asa marsupium. This may be the posterior
half, the posterior third, or a few water tubes in the middle.

It is largely because of the great significance of the gills with their remarkably
diverse functions of food collection, respiration, and gestation that the modifications
both in the external form and in the histologic structure of the gills are important and
serve so well as a basis of classification. Generally speaking, species in which all four
gills serve as marsupia are considered lower or more primitive forms. Those in which
the marsupia are most highly specialized are regarded as most highly developed.

@ The effect of the gills in filtering the water is made clear when one fills two jars with turbid river water after placing in each
sufficient sand for a mussel to become embedded. If one or two mussels are placed in oneof these jars, the water will become
clear in a comparatively short time.

BIBLIOGRAPHY .:¢
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FRIERSON, L. S.
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Grier, N. M.

1920. Sexual dimorphism and some of its correlations in the shells of certain species of Najades.
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HEADLEE, THOMAS J.

1906. Ecological notes on the mussels of Winona, Pike, and Center Lakes of Kosciusko County,
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HEAaADLEE, T. J., and SrMmonrToN, JAMES.

1904. Ecological notes on the mussels of Winona Lake. Proceedings, Indiana Academy of Science,

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Howarp, A. D.

1914. Experiments in propagation of fresh-water mussels of the Quadrula group. Appendix IV,
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4-11. Boston.

FRESH-WATER MUSSELS. 179

, ISELY, FREDERICK B.
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1899. A statistical study of the parasites of the Unionide. Bulletin, Illinois State Laboratory of
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Latrer, O. H.
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1912. Studies on the reproduction and artificial propagation of fresh-water mussels. Bulletin,
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Lemmy, JOSEPH.
1904. Researches in helminthology and parasitology, by Joseph Leidy, M. D., LL. D. (Arranged
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MoorE, J. P. .
rg12. Classification of the leeches of Minnesota. Geological and Natural History Survey of Min-
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1916. ‘The life of inland waters. 438 pages. Comstock Publishing Company, Ithaca.
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180 BULLETIN OF THE BUREAU OF FISHERIES.

OrtMANN, A. E.—Continued. :
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FRESH-WATER MUSSELS. 181

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Wiison, CHARLES BRANCH.
1916. Copepod parasites of fresh-water fishes and their economic relations to mussel glochidia.
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ment 781, 63 pages, 1 pl. Washington.
Witson, CHARLES BRANCH, and DANGLADE, ERNEST.
1914. The mussel fauna of central and northern Minnesota. Appendix V, Report, U. S. Com-
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Wotcott, RoBert H. ’
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me

PERITONEAL MEMBRANES, OVARIES, AND OVIDUCTS OF
SALMONOID FISHES AND THEIR SIGNIFICANCE
IN FISH-CULTURAL PRACTICES

&

By William Converse Kendall
Scientific Assistant, U. S. Bureau of Fisheries

183

CONTENTS.
&

Page.

bites ls (ado een GRU Sb aac doc UoEUaOconenoasnan toaoen anced Sav ono ro OnoagSU OOO CO aS Os p COs OaDE 185
Abdominal ViSCeran etree cee eee etare eae eae hens terete nlc acer leemaeene se croe nae eee eres eecterevorerencverate ts 185
Alimentary tract. |. oe :is:cspie.csftsrats eparsteleraje aia) stays oth oj nyavayorts oye olel Aspe tetera personae ase ste ts tetetsiefasspera= 187

1 (2 ea en Meae cnriae ado cen wear ner cnet nor inermmaon acon tmemiac one cad cosooscomsas 187
St Soe Be SAT ISG Be DEBS ae aeltide Sepia pte don.cdic Poaubounasud SuacmSagnenenienecane oc 187
PaniCKe aS: acme cr sisp pee « > party ge ei ee ER Be © 9 eee Oo ote tae weer oe are ree ee 187
S31) Eo ant thn dione Acris cineca thm eam icra arte atimeran cnn bua cer roo Is 0 187

Air bladder! ¢ “n7T3 4-04 V6. . SLE WELE. CIA REE ES. SE Tee: 187
(SoeGlyys soba snddausobbooconde rate Solo Ae Snlnc mete Si tiacionan Maa rc Og 187
The peritoneum and supporting membranes of the viscera. ............--. 52.20.22 02s sees ees 187
Histological structure and embryonic development............-... 00.0.0 esse eee ee eee 187
The dorsal mesentery of Salmomid@. .. .. 0... .fipe ccc cee eee eee eee en ee eee teen eee 188
Whewentraltmesentery., eyes yoscscts itch) sel ovenereter ererener rela ces lege ee stiie eepte seer nae etek =e Paneer ee Vente 188
Structure and development of genital organs of fishes‘in general.......-............-.--5-5- 188
Observations upon ovaries and ovarian membranes of Salmonide..............-.-.+.-.+e+005- Igt
Oviducts of Salmonidee. -5. scene te tas demiseyeeh- he ane» Ie Ne pete Py Nabe Seis ase nse la «alpina ae erat 194
Peritoneal membranes, ovaries, and oviducts of Coregonide.............-.----- eee eee ee ees 197
Ovaries, ovarian membranes, and oviducts of smelts.......... 22.02.25 eee eee eee eee e eee 197
Siirijert- in Gon een Ae Gns etm nen ohm onenGroanin cc BOE coos poocoOOgeordoan aD Spams HORE oochodn 200
Relationship of salmonoid fishes, ganoids, and elasmobranchs as indicated by the oviducts...... 200
Relation of the anatomical facts to fish-cultural practices. ....... 0.2... 6665s eee eee eee eee 203
Bast of -worksiconstl ted s<:s,.c.c teers eve ae saisie rote se etadere sete = misiese efoto ie ehedesets ialetaterelersistetel nis s/wictsteisisteisiare 206

184

PERITONEAL MEMBRANES, OVARIES, AND OVIDUCTS OF
SALMONOID FISHES AND THEIR SIGNIFICANCE IN FISH-
CULTURAL PRACTICES.

Bd

By WILLIAM CONVERSE KENDALL,
Scientific Assistant, U. S. Bureau of Fisheries.

Bad
INTRODUCTION.

The observations embodied in the present discussion were begun several years ago
and have been carried on intermittently to the present time. The study has been
attended by various difficulties. It has been almost impossible to obtain perfectly
preserved specimens in which the internal organs had not been more or less deranged
or mutilated. The membranes in question, being very delicate, are easily torn or broken
in handling prior to or during dissection and are liable to disintegrate unless well pre-
served. These facts and others, together with erroneous ideas derived from published
references to these structures, have occasioned many uncertainties which have taken a
long time to clear up. Since the ovaries undergo many changes of both external and
internal appearance, as well as of position, at no time in their growth or development
can they be said to be exactly the same as at any other time. After the ova are shed,
“in those species which normally survive the spawning period, the ovaries undergo many
retrogressive changes. Furthermore, the conditions are not always uniform in the same
species. Somewhat different conclusions might be reached from observations upon
examples representing one or two periods of development only than from a more com-
plete series. Therefore it has required many individuals to permit of an exact determi-
nation of conditions. In fact it was only after careful dissection of more than a hundred
American smelts that one which seemed to conform to the conditions in the European
smelt, as described by Huxley (1883), was found. Probably the failure of the anato-
mists, to whom reference is made in this paper, to recognize the conditions which are
herein described, is attributable to some such facts as the foregoing.

As this paper is primarily intended for fish-culturists and those unfamiliar with
anatomy, definitions of the principal abdominal structures precede the discussion.
Although desirable, it has been impossible to entirely eliminate scientific phraseology.

At the end of this paper is given an alphabetical list of the authors and works con-
sulted. In the text of this discussion these works are referred to by author and date of
publication.

ABDOMINAL VISCERA.

The abdominal viscera comprise the greater portion of the alimentary tract, secre-
tory, excretory, and reproductive organs, together with certain nervous and vascular
connections. The present discussion is principally concerned with the supporting and

185

BULLETIN OF THE BUREAU OF FISHERIES.

186

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MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 187

investing membranes (peritoneal membranes) associated with the digestive and repro-
ductive systems. i ?

ALIMENTARY TRACT.—In the Salmonide the alimentary tract forms a loop within
the anterior half of the abdominal cavity or ccelome, so that three portions are recog-
nized: The stomach (fig. 1 »), a thick-walled arm extending backward to the point
where it makes a sharp bend and as the pyloric arm (fig. 1 0), more or less covered by
the mass of pyloric appendages or ceca (fig. 1 p), extending forward to the posterior
surface of the liver, where another sharp bend occurs and from which the intestine
(fig. 1 g) extends back to the vent.

LivErR.—tThe liver (fig. 2 7) is relatively massive and fills nearly the whole anterior
end of the abdominal cavity, on each side more or less overlying the other anterior
viscera.

Kipneys.—tThe kidneys lie immediately below and in contact with the dorsal surface
and extend from the anterior septum or diaphragm (fig. 1 k) to the region of the vent.

PANCREAS.—The pancreas is an elongated lobulated digestive gland, more or less
embedded in fat, lying on the upper surface of the stomach and often more or less upon
the upper surface of the intestine posteriorly to the stomach.

SPLEEN.—The spleen (fig. 1 m) is a dark-colored lymphoid or fluid gland of varia-
ble size, irregularly a three-surfaced pyramid, situated close behind the posterior curve
of the stomach.

AIR BLADDER.—Immediately below the kidney mass, in contact and approximately
coextensive with it, is the air bladder.

Gonaps.—The reproductive glands of the Salmonidze are paired, more or less
symmetrical organs, one on each side of the abdominal cavity.

THE PERITONEUM AND SUPPORTING MEMBRANES OF THE VISCERA.

The peritoneum is a serous membrane lining the adbominal cavity and sending
out various folds which support and more or less attach to each other the visceral
organs. Anteriorly, in conjunction with other tissues, it forms a partition analogous
to the diaphragm of higher vertebrates, separating the adbominal cavity from that
part of the ccelome containing the heart, gill, esophagus, etc. (fig. 1 k). A fold extend-
ing to the digestive organs, infolding and forming suspensory membranes, or filamentous
and ligamentous attachments, is called the mesentery (fig. 1 s and 2).

HISTOLOGICAL STRUCTURE AND EMBRYONIC DEVELOPMENT.—According to Bridge
(1904), the peritoneum histologically consists of a stratum of connective tissue, support-
ing on its free surface an epithelial stratum (ccelomic epithelium). Primarily, the invest-
ing peritoneum is continued both dorsally and ventrally into bilaminar suspensory folds,
the dorsal and ventral mesenteries, which extend to the mid-dorsal or mid-ventral line
of the abdominal cavity. The two layers then separate and become continuous with
the parietal layer of peritoneum lining the whole of the inner surface of the body wall.
Embryologically, the two mesenteries owe their formation to the fusion above and
below of the mesenteron of the contiguous walls of two laterally and primarily distinct
ccelomic cavities. The dorsal mesentery in the adult is occasionally complete, as in the
myxinoid Cylostomata and in a few teleosts, but much more frequently is reduced by
absorption to anterior and posterior rudiments, or to a series of isolated bands, or even,

.

188 BULLETIN OF THE BUREAU OF FISHERIES.

as in the lamprey (Petromyzon), to a few filaments accompanying the intestinal blood
vessels.

THE DORSAL MESENTERY OF SALMONIDH.—In adult Salmonide the supporting
membrane of the alimentary tract diverges from near the longitudinal median line of
the peritoneal covering of the air bladder and is attached to the upper surface of the
canal as follows: From the diaphragm (fig 1 k) and along the mesial line of the air
bladder (fig. 1 v), a fold (fig. 1 s) is sent out to the upper surface of the stomach on
which it ends near the posterior bend or sometimes extends to the spleen (fig. 1 m).
The pyloric arm has no supporting membrane, but is connected to the cardiac arm of
the stomach by filamentous bands, though sometimes anteriorly there may be a trace
of membrane. Again, beginning near the diaphragm is another fold (fig. 1 ¢), which,
attached to the backward prolongation of the intestine, extends nearly to the vent in
the female and quite to the vent in the male.

THE VENTRAL MESENTERY.—Concerning fishes in general, Bridge writes that the
ventral mesentery is rarely present and, if present, is never complete. In Lepidosteus
a ventral mesentery is said to be present in connection with that part of the intestine
which contains the spiral valve. In Protopterus, and also in Neoceratodus, there is a
well-developed ventral mesentery in relation with the greater part of the length of the
intestine, although in the former Dipnoid its continuity is interrupted by one or two
vacuities, and in the latter the mesentery is incomplete posteriorly. A ventral mes-
entery is also present in the intestinal region of some of the Murenide among teleosts,
but no mention is made of it in Salmonide.

I have examined four species of Oncorhyncus (O. kisutch, O. gorbuscha, O.
tschawytscha, and O. nerka); several species of Salmo (S. salar, S. sebago, S. trutta,
S. gairdnerii, and 8. shasta) ; and several Salvelinus (S. stagnalis, S. aureolus, S. oquassa,
S. marstoni, S. malma, S. kundsha, and 8. fontinalis), all of which possess a certain
extent of ventral mesentery (fig, 1 ~). Its anterior ventral insertion is a little be-
hind the base of the ventral fins, and the corresponding intestinal insertion somewhat
in advance of the ventral insertion, thus presenting a vertical concave edge toward
the front. This mesentery in its ventral and intestinal attachments extends to the
posterior end of the abdominal cavity. According to Felix (1906) the embryo salmon
has a complete ventral mesentery. fe

By these vertical dorsal and ventral mesenteries and the intestine to which both
are attached, about one-third of the abdominal cavity is posteriorly divided into two
lateral longitudinal chambers, with a posterior communicating aperture of varying
length, but always short, in the dorsal mesentery above the intestine of the female.

STRUCTURE AND DEVELOPMENT OF GENITAL ORGANS OF FISHES IN GENERAL.

The suspensory portion of the ovarian membrane is known as the mesovarium,
or mesoarium, and that of the spermary as the mesorchium. Morphologists state that
the gonads of the majority of teleosts are completely enveloped by the peritoneal mem-
brane and that the ova and sperm of oviparous forms are conveyed to the exterior of
the body cavity by closed canals or tubes composed of the same enveloping membrane
extending from the gonad to the genital pore (fig. 2 h). The previous state of
knowledge regarding especially the ovarian membranes of Salmonide is well indicated
by the following review of the opinions or statements of principal writers.

e ~

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 189

One authority (Wiedersheim, Parker, 1897) states that the male and female gonads
of teleosts closely correspond with one another as regards position and the arrangement
of their ducts. Dorsal and ventral folds of the peritoneum are developed in connection
with the elongated ovary, and these in most cases meet along its outer side, so as to
inclose a portion of the coelome, and thus convert the ovary into a hollow sac, blind
anteriorly, on the inner folded walls of which the ova arise; this sac is continued back-
ward to form the oviduct, which is generally short and fuses with its fellow to form a
tube or “‘ovipositor’’; or the ducts may communicate with the urogenital sinus.

The same authority describes the development of the ovary as originating in at
first undifferentiated cells of coelomic or peritoneal epithelium on the dorsal side of
the body cavity at either side of the mesentery in which the adjacent mesoblastic stroma
penetrates. Into the stroma of an ovary thus formed, the cells of germinal epithelium
grow in the form of clustered masses; some of which cells increase in size more than
others, giving rise to ova, while the smaller cells form investment of follicle around each
and serve as nutritive material. ;

From the foregoing it is understood that the ovaries of most teleosts are derived
from folds of the peritoneum, usually one on each side of the body cavity, and, as a
rule, are closed sacs consisting of an outer enveloping membrane and inner lamin of
ovigerous stroma. Each egg is inclosed in a follicle from which, as it ripens, it breaks
out into the inner or central cavity of the ovary and makes its exit from the fish by the
way of a tube, or oviduct, of the same membrane and the genital pore.

Some exceptions to this arrangement have been noted. Something over 90 years
ago, Rathke (1824) described the ovarian membranes of certain salmonoid fishes, and
nearly 60 years later Huxley (1883) reviewed Rathke’s work, from which he quotes as
follows: y

In certain fishes the oviducts have entirely disappeared; this is the case in the eel, the sturgeon,
Cobitis tenia, and in the lamprey. In others, however, such as the higher kinds of salmonoids, there
extends back behind each ovary a narrow band which may_be regarded as the remains of an oviduct. In
all these fishes, therefore, the central abdominal cavity must take the place of an oviduct, as it receives
the eggs when they are detached, and allows them to make their exit by a single opening at its posterior
extremity.

Still quoting from Rathke, Huxley continued to the effect that, while a proper
oviduct is absent from the Salmonidz, there is an analogue of that structure, consisting
of a flat, narrow band, commonly arising at the upper and posterior end of a platelike
ovary, gradually diminishing in width backward, and finally becoming lost toward the
end of the abdominal cavity. It was stated that in the salmon proper it disappears
upon the air bladder opposite the commencement of the last fifth of the abdominal
cavity; in the fresh-water trout on the sides of the intestine not far from the anus; in
the whitefishes (Coregoni) on the intestine close to its end.

In describing the ovary of the European smelt Osmerus eperlanus, which was at that
time regarded as a member of the salmon family, Huxley stated that in all essentials of
the structure of the ovigerous portion or body it agreed with that of the other Salmonidz.
It was said to have the form of a half-oval plate, with the curved edge ventral and the
straight edge dorsal. To the latter a narrow mesovarial fold of the peritoneum was
said to extend “from that part of the dorsal wall of the abdominal cavity which corre-
sponds with the ventral surface of the air bladder”’ and the line of attachment to be

75412°—22—13,

190 BULLETIN OF THE BUREAU OF FISHERIES.

parallel with that of the mesentery and a little distance from it. The ovary, described
as a broad, thin plate, was stated to have its inner surface covered by the peritoneum,
which is continued over the ventral edge, ending about a third or fourth of the height
of the outer face by a well-defined margin and its outer face ‘‘to give rise to a great
number of ovigerous lamelle of broadly triangular form, which are disposed transversely
to the length of the organ and perpendicularly to the body.’’ Huxley went on to say
that superficially the ovary appears to be laminated only above the reflected membrane,
but that transverse section revealed that the ovigerous lamine pass under the band to
the ventral wall and that their outer edges are attached to the band.

In the Salmonide, then, according to both Rathke and Huxley, ovigerous lamine
without peritoneal covering occupy the outer surface of the pendent mesovarial fold,
thus constituting the ovary, from which as they ripen and burst from their investing
follicles, the ova fall into the abdominal cavity. As will be seen later, the foregoing
observations pertain to only one stage, that of a collapsed and retracted ovary.

Prior to Huxley’s description of the oviduct of the smelt, no salmonoid was sup-
posed to have such a structure. In the smelt, according to Huxley, the mesovarial fold
continues backward from the posterior end of the ovary to the oviducal apertures,
while laterally it passes into the peritoneal lining of the lateral wall of the abdomen,
ending in a free concave edge immediately behind and on the outer side of the posterior
extremity of the ovary. It thus forms the ventral boundary of a passage which opens
in front by a wide ostium into the abdominal cavity. As the posterior end of the right
ovary lies very far behind that of the left ovary, it follows, Huxley says, that the right
ostium is equally far behind the left. The mesentery, he continues, terminates by a
free posteriorly concave edge just opposite the level of the posterior end of the right
ovary; and, behind this free concave edge of the mesentery, the left and right passages
unite in a short but wide common chamber which opens externally in the middle line
behind the anus and in front of the urinary outlet.

It appears that it must be to this structure in the smelt that all subsequent writers
refer when mentioning oviducts of Salmonide, many regarding the smelt as a member
of this family.

This idea that the salmonoids have no oviducts and that the ova are deposited
free in the abdominal cavity has been handed down to the present day in all literature
pertaining to the subject. Owen (1866) said that the salmon is an example in which
the ova are discharged by dehiscence into the abdominal cavity and escape by the peri-
toneal outlets, as in the eel and lamprey, and that the free surface of the stroma of the
ova is exposed.

Gegenbaur (1878) said that in the Salmonide the eggs are passed into the abdominal
cavity and are evacuated through the abdominal pore.

Gitinther (1880) wrote that in some families of fishes the ovaries are without closed
covering and without oviduct, as in Salmonide, Galaxide, Notopteride, Murenide,
and others. He stated that the surface of such an open ovary—as, for instance, that of
the salmon— is transversely plaited, the ova being developed in capsules in the stroma
of the lamine; after rupture of the capsules, the mature ova drop into the abdominal
cavity and are expelled by the porus genitalis.

Day (1887) makes practically the same statement, saying that the ovaries are svym-
metrical organs and destitute of a closed covering, while their internal surface is lined

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. I9gI

with stroma and transversely plaited. Here, he said, the development of the eggs takes
place, each of which is invested by a fine membrane, by which they hang suspended to
the ovary, the length of the pedicle decreasing as the egg augments in size. But as the
ovaries are destitute of oviducts it necessarily occurs, he continues, that when the invest-
ing membrane bursts, the ovum falls into the abdominal cavity, from whence it is extruded
through the abdominal pore.

Jordan and Gilbert (1882) and Jordan and Evermann (1896) make similar state-
ments: ‘Ova falling into the cavity of the abdomen before exclusion.”’

In discussing the brown trout (Salmo fario) as an example of ‘‘subclass III Teleos-
tomi’’ Parker and Haswell (1897) state that the ovaries extend the full length of the
abdominal cavity and are covered with peritoneum on their inner or mesial faces only,
and that, when ripe, the numerous ova are discharged from their outer faces into the
abdominal cavity. They then go on to say that there are no oviducts, but that the
anterior wall of the urogenital sinus is pierced by a pair of genital pores through which
the ova make their way to the exterior.

A previously cited authority (Wiedersheim, Parker, 1897) wrote that the ovary of
some teleosts is solid and that the ova are shed into the body cavity. The oviducts of
the smelt (Osmerus) and capelin (Mallotus) were referred to as peritoneal funnels having
open ccelomic apertures close to the ovaries, into which the ova pass. In the case of
other Salmonide, the Mureenide, and Cobitis, it was stated that these peritoneal funnels
are shorter and even absent, the ova then being shed into the urogenital sinus through
paired or single genital pores.

After describing the genital structures of the Salmonide, Bridge (1904) states that
in all instances the eggs are set free from the ovaries into the ccelome, whence they escape
through the peritoneal funnels or genital pores. The foregoing statements reveal the
influence of Rathke and Huxley upon all subsequent interpretations of the structures.

The only teleosts besides Salmonide mentioned by Rathke as possessing no oviducts
were two species of loach (Cobitis barbatula and C. tenia) and the eel. Regarding these
Huxley says that in Cobitis barbatula the single ovary has an oviduct of the same charac-
ter as other Cyprinoid fishes, but that he had not examined C. tenia, about which, in
other parts of his memoir, Rathke’s statements were full and precise.

Inasmuch as one of the species of the loach was found to have an oviduct, it is quite
possible that the other has also. If such is the case, according to Rathke, the only
supposedly oviductless species, besides the Salmonidz, left without such a duct is the
eel. However, a few other fishes have since been stated to be oviductless.

The salmonoids, according to the authorities mentioned, appear to occupy almost!
a unique place among teleosts; but in the discussion which follows I hope to show that
their position is not as anomalous as from the foregoing it would seem to be.

OBSERVATIONS UPON OVARIES AND OVARIAN MEMBRANES OF SALMONIDZ.

The two ovaries in each of the salmonoids which I have examined are never exactly
symmetrical in form or of the same length. They have a general primary shape which
is maintained, but in their growth and enlargement such modifications of shape and posi-
tion as occur are largely determined by contiguous internal organs and the abdominal
walls. Each ovary is suspended by a membrane (fig. 2 c) originating in the dorsal

BULLETIN OF THE BUREAU OF FISHERIES.

192

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MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 193

peritoneum at the side of the air bladder. This membrane covers the surface of the
ovary which faces the longitudinal axis of the body cavity. From its posterior end a
membranous band, which is a continuation of the mesovarium and ovarian covering
extends toward the posterior end of the abdominal cavity. Up to this point the condi-
tions are as stated by the anatomists previously cited.

An immature ovary shows that its membrane not only covers the mesial or inward
surface as described, but envelops the entire organ. The edge of the membrane, which
was stated to mark the termination of the covering at or near the lower margin of a

Fic. 3.—Upper view of left ovary, with most of ova removed, showing cross septa and membrane extending up over the
forward end. A, mesovarium from which ovary is turned downward to show upper view.

Fic. 4.—Dorsal view of a section of same ovary as in fig. 3 from the region of B, BB representing the same cross septum as
B in figs. 3 and 5. Some ova have been removed, others are shown still in the follicles. A, mesovarium.

Fic. 5.—Cross septum (B) in upright position. In natural position, mesovarium (A ) would incline to right, and upper edge
of septeum (B) to left. Impressions of ova shown in septum.

Figs. 3 to 5 drawn by Mrs. Effie B. Decker.

platelike ovary, passes up over the outer surface and is in contact with the membrane
of the inward surface. At this time the ovary has much the same general external ap-
pearance as that of the other isospondylous teleosts. At a later period, beginning at the
posterior end of the ovary, the edge of the membrane of the outer surface to some extent
parts from the membrane of the inward surface, leaving a narrow area of ova without
attached membranous cover. The area thus uncovered gradually widens and extends
forward as the ovary increases in size. Even at maturity the egg surface is to a certain
extent infolded in membrane (fig, 2 a), due to the fact that the suspensory meso-
varium does not hang vertically but, from its origin at the side of the air bladder slants
inward toward the axis of the body cavity, and the egg surface is tipped over so that its

194 BULLETIN OF THE BUREAU OF FISHERIES.

face is against the mesovarium. This position brings what has been termed the upper
edge of the ovary downward, so that it is actually considerably lower than the supposed
lower edge (fig. 2 d),so far as there is any edge. In other words, even the ovary is not
platelike, but the supposed plate is folded in such a manner that it may be said ina
general way to be boat-shaped with a decided list to starboard or port according to
whether it is the left or right ovary. Posteriorly the exposed egg surface is usually
proportionally wider and sometimes actually wider than at the anterior end. In fact,
the anterior end is permanently covered to some extent by membrane, or to continue the
boat simile, it is decked over forward (fig. 3). Furthermore, the ovigerous stroma,
which has been stated to be arranged in vertical lamine, transversally and somewhat
diagonally connects the two sides, dividing it into transverse compartments (figs. 3 B,
4 BB and 5 B).
OVIDUCTS OF SALMONIDZ.

As relates to the vestigial or rudimentary’ oviduct in the form of a narrow band to
which the previously quoted anatomists have referred, it is necessary to say that it
varies in extent according to the species and does not terminate as described by Rathke,
but, without close examination, in an immature, or spent, fish it might be so interpreted.

In a silver salmon (O. kisutch), which was unripe; but approaching breeding condi-
tion, the lesser backward extent of the ovary resulted in a relatively longer band than was
evident in ripe fish, by which the general arrangement is more clearly defined. This band
(fig. 6 e) arises from the posterior end of the ovary whence backward it is an extension
of the ovarian covering and the mesovarium. The line of attachment of the mes-
ovarium (fig. 6c) to the air bladder extends obliquely inward and backward toward
the median line of the air bladder until it attains a point near the termination of the
mesentery at the anterior end of the communicating aperture above the intestine
previously mentioned (fig. 6 w). Here the mesovarium, as such, apparently ends.
Fusing with the mesentery at a corresponding point- on the upper surface of the
intestine, the mesovarian membrane joins the membrane of the opposite side, form-
ing a single band, which is attached to and extends along the intestine backward.
The outer edge of this band, at the posterior end of the ovary, in unripe or imma-
ture fish at least, appears to fold over onto the band forming a sort of hem to the edge
(fig. 6 f), later becoming the outer edge of the trough, which is supported by the lateral
walls of the narrow posterior portion of the abdominal cavity. This outer edge pursues a
similar direction to the air-bladder attachment of the mesovarium to the point where the
mesentery and mesovarium terminate, whence it takes a course parallel with the middle or
line of attachment of the band to the intestine. Its outer edge remains free, and the
fold, though becoming narrower, is continued to within a short distance from the genital
pore, where it seems to vanish. The membranous band is deflected to either side and
becomes attached to the lateral abdominal wall (fig. 6 g). Thus from each ovary
a troughlike oviduct passage is formed as far as the termination of the mesentery
of the intestine, the two passages then merging into one which, not far from the outlet,
spreads out and joins the lateral wall on each side. This terminal structure would ap-
pear to be a reduced homologue of the so-called funnel described by Huxley in the case
of the smelt.

1 Wiedersheim (Parker), 1897, p. 360, referring to these structures, says: ‘It is uncertain whether the latter is the primitive
arrangement among teleosts, or whether the peritoneal funnels represent reduced oviducts.”’

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 195

As the ova approach maturity,! the left ovary is nearly or quite always the longer,
and it extends, tapering, to the posterior end of the abdominal cavity (fig. 7 a). About
at the point where the mesovarium as a suspensory membrane ends and forms the

7

Fic. 6.—Drawing by Mrs. Effie B. Decker from a specimen of Oncorhynchus kisutch, 26 inches long, from Ankon Slough,
Alaska, July 10, 1917, collected by Ernest P. Walker, salmon inspector. Dorsal view of the posterior end of the abdominal cavity,
the abdominal wall somewhat spread out. In natural position this portion of the abdominal cavity is very narrow, and the
walls closely approximate. ‘The intestine is laterally flattened and compressed so that it does not show beyond the edges of the
superimposed membrane, and the edges of the membrane are turned upward, forming a trough. a, Left ovary; b, right ovary;
c, upper severed edge of mesovarium; d, outer edge of ovarian membranous covering; e, fold or free border of the posterior exten-
sion of ovarian membrane, which joins with the other on median line of intestine forming an oviducal channel or trough;
f, oviducal channel, combimation of e from both sides; g, lateral deflection and junction of oviducal membrane with abdominal
wall; k, genital pore; g, intestine; t, severed dorsal intestinal mesentery; w, posterior end of severed mesentery.

beginning of the trough mentioned (fig. 7 w), the posterior extension of the ovary
has no membranous attachment to the trough, but has a free fold or flap of mesovarial
or ovarian membrane along its upper inner side which narrows posteriorly to the end

1 As observed in one specimen each of Atlantic and humpback salmon.

196 BULLETIN OF THE BUREAU OF FISHERIES.

of the ovary where it again completely infolds the organ (fig. 7 c). This flap and the
inner side of the ovary probably lie in the trough on the top of the intestine, and the
greatly narrowed or pointed end of the ovary rests on the bilateral expansion formed
by the deflection of theedge of the trough to the abdominal wall (fig. 7 9).

c.)

Lome en mew ne n=

t

“MOA

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iy

TT

1

!

'

'

‘

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Fic. 7.—Drawing by F. E. Prior, from dissection of a specimen 234 inches long, from the Penobscot River, Me. Dorsal
view of a spread-out section of posterior portion of abdominal viscera and membranes of nearly ripe Atlantic salmon (Salmo
salar). a, Left ovary, b,right ovary, turned away from mesovarium showing eggs not covered by ovarian membrane; c, mesovaria
laid back from normal position on surface of otherwise uncovered eggs; d, outer edge of ovarian membrane; e, fold or free borders
of mesovaria which unite posteriorly to form the oviducal channel; f, oviducal channel continuation of e; g, posterior lateral
expansion of oviducal channel, each side of which unites with peritoneum of the lateral walls of the abdominal cavity; h, genital
pore; i, eggs not covered by ovarian membrane; g, intestine; ¢, dorsal intestinal mesentery; w, posterior end of intestinal mesen-

tery with confluent mesovaria.

The right ovary (fig. 7 6), always somewhat shorter, seldom extends in this manner
much behind the common opening above the intestine, and accordingly it may or may
not have some extent of membranous flap as just described. The ova apparently run
along the fold on the inner side of the ovary, and hence into and along the trough

mentioned.

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 197

These backward extensions of the ovaries are formed by the maturing and enlarging
ova filling the previously crowded interlamina spaces at the posterior end of the ovary
(fig. 3), thus stretching it longitudinally.

PERITONEAL MEMBRANES, OVARIES, AND OVIDUCTS OF COREGONID.

A number of specimens of each of the genera Coregonus and Leucichthys were
examined.

The arrangement of the visceral organs was similar to that of the Salmonidz, but no
ventral mesentery was observed. The ovaries and oviducts were much as in Salmonide.

OVARIES, OVARIAN MEMBRANES, AND OVIDUCTS OF SMELTS.

As has been seen, according to Huxley, the smelts were supposed to have free
ovaries and oviducal funnels, while the salmonids were stated to have free ovaries and
only narrow bands, or vestigial homologues of oviducts. My examination of many smelts
reveals that, while Huxley was correct concerning the oviducal structures, his interpre-
tation of the ovary was not in accord with all of the facts. He probably accurately
described what he saw under certain limited conditions. I previously remarked that at
no time in their development can the ovaries be said to be exactly the same as at any
other time. This is particularly true as concerns the ovaries of the smelt (Osmerus
mordax). If the ovary of a spent fish, or one from which the eggs have been removed
or washed out, as Huxley stated of his example, is examined, the condition is likely to
be as represented by Huxley. The ovary then is in a collapsed, flabby condition, or
more or less shrunken state. When the ovaries are full-grown, just before spawning time,
but before any ova have been discharged into the oviducts, they exhibit an entirely
different appearance. As described of Salmonide, the air bladder is attached to each
side of the dorsal portion of the abdominal cavity and is covered by the closely adhering
peritoneal membrane, in which the mesovarium of each ovary originates.

Posteriorly the intestine is dorsally situated, and the mesentery is there so narrow
that the intestine appears to be almost adherent to the peritoneum of the air bladder.

Huxley correctly described the anterior origin of the oviducal membrane at the
posterior end of each ovary and the relative situation of each ovary, the right or smaller
ovary being posterior to the left or larger ovary.

The oviducal membranes, as in the case of the salmonids, finally unite in a common
channel above the intestine. Both of these oviducal membranes, when not containing
ova, posteriorly, lie against the membrane of the air bladder which forms the roof of the
so-called funnel.

The gravid ovaries practically fill all the space in the abdominal cavity not occupied
by other viscera. Upon opening the fish from throat to vent along the median line of
the belly and laying the lateral walls aside, at first glance there appears to be one single
mass of eggs in front of which is the liver; posteriorly a small portion of the intestine
may be visible. The greater portion of the egg mass is the anteriorly situated left ovary
which extends from the liver to some distance beyond the base of the ventral fins (fig.
8a). Closely juxtaposed to the posterior end of the left ovary is the right ovary
(fig. 9 b) which extends nearly to the vent. The dividing line, which is often difficult
to discern, beginning perhaps a little in advance of the ventral fins, extends ob-
liquely from the right side (left as observed) backward to the left side (right as

198 BULLETIN OF THE BUREAU OF FISHERIES.

observed). Both ovaries are ventrally convex from side to side, and concave above,
thus forming a broad, more or less triangular, continuous groove in which anteriorly the
stomach lies. The intestine, at first above the stomach, finally lies in the grooves of the
left and right ovaries. These grooves are formed by the left ovary curving over so that
its so-called lower edge is in contact, or nearly so, with the dorsal surface of the abdom-
inal cavity on the right side, and the left ovary curving in like manner in the reverse
direction.

Except in shape and relative position the ovaries are much like those of the salmonids
previously described. They are nearly covered by a very delicate membrane which is so
thin that it is easily broken or rubbed off, so that one may be easily deceived into
believing that there is no membrane and that the eggs are free in the abdominal cavity.

The mesovarium (fig. 9 c) arises near the lateral edge of the air bladder, and, in
the case of the anterior ovary, its line of attachment gradually passes obliquely inward
to its attachment to the intestine. The mesovarium of the posterior ovary has a
proportionally longer intestinal attachment.

As in the Salmonide, the dorsal mesentery (fig. 10 7) ends some distance from
the posterior end of the intestine (fig. 10 w), and the mesovarial membranes unite to
form the floor of the common opening above the intestine. The outer edges continue
attached to the lateral walls of the abdominal cavity (figs. 9 gand 10g). Thus the mes-
ovarian membranes, originating on the outer side of each ovary and deflecting to
the abdominal walls, form the floors of the respective oviducts, while the peritoneum
of the air bladder, the abdominal walls, and the mesentery form the other boundaries.

As in the case of the Salmonidz, the portion of each ovary uninvested with adherent
membrane consists of a narrow dorsal area which is tipped in against the mesovarium.
In these passages, formed by the investing membranes, the ova pass backward into the
oviducts. If they are set free into the abdominal cavity, there appears to be no con-
ceivable way by which they can be extruded. The smelt appears to have no ventral
mesentery, unless a close adhesion to the ventral or abdominal surface near the vent
is such.

As previously stated, the gravid ovaries are situated one behind the other and
almost entirely fill the abdominal cavity, save the comparatively small space occupied
by other viscera. Before the ova of the left ovary have entered the oviduct, the gravid
right ovary presses the left oviducal membrane (fig. 9 g) against the air bladder
and left abdominal wall.

The ova of the right ovary ripen, enter the oviduct, and are deposited first. As
the right ovary is emptied and its oviduct (fig. 10 g) is filled, the ova of the left
ovary enter its oviduct and the empty and collapsed right ovary is compressed between
the distended left oviduct and the right abdominal wall. The left ovary and its dis-
tended oviduct, together with the distended right oviduct, then have the appearance
of a single mass of eggs, but, by careful manipulation, a longitudinal line of separation
may be detected. As the right oviduct is emptied the left becomes entirely filled and
with the remaining ova in the Ieft ovary has the appearance of a single continuous
ovary. Probably this was the condition which deceived Bloch, causing him to think
that the smelt had but one ovary. When both ovaries are emptied and collapsed, the
left is considerably anterior to the right and may have the appearance as described by
Huxley; that is, a semioval plate, laminated on the outside and having a marginal
membrane of about one-third its width.

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 199

a gy at

Z satel

Fic. 8.—Semidiagrammatic drawing made by Walter H. Rich, from dissection by William C. Kendall. Specimen from
Sebago Lake,Me. Ventral view of ovaries and oviducts of smelt (Osmerus mordax). a, Left or anterior ovary; b, right or posterior
ovary; g, lateral expansions of mesovaria and ovarian membranes joining peritoneum of abdominal walls to form oviducts;
h, genital pore; /, liver; g, intestine; 7, anus.

OAL Ay

a 4 g rk

Fic. 9.—Left view of ovaries and membranes of same as fig. 8. a, Left ovary; b, left side of right ovary bending up on left
side so that its lower portion is dorsally situated; c, left mesovarium; d, outer edge of ovarian membrane; g, posterior lateral
expansion of mesovarium and ovarian membrane forming left oviduct; h, genital pore; g, intestine; r, anus; w, posterior end
of intestinal mesentery with confluent mesovaria.

4 * a

x i “

Any #¢ 2 mao

Fic. 1o.—Right view of same as fig. 9. a, Left ovary bending up under stomach and intestine forming a groove in which
the viscera extend; b, right ovary; c, mesovarium of right ovary; d, outer edge of ovarian membrane, between which and the
mesovarium the egg surface not covered by membrane other than the mesovarium is situated; g, right posterior expansion of
the mesovarium and ovarian membranes forming the short right oviducts or practically the right side of the common oviduct
posterior to w; hk, genital pore; 7, liver; », upper or cardiac arm of stomach; 0, lower or pyloric arm of stomach; g, intestine;
tT, anus; ¢, intestinal mesentery; v, air bladder; w, posterior end of intestinal mesentery with confluent mesovaria.

200 BULLETIN OF THE BUREAU OF FISHERIES.
SUMMARY.

The Salmonidz have a ventral mesentery extending from near the ventral fin
region to the posterior end of the abdominal cavity. The Coregonide and Osmeride
appear to have no ventral mesentery.

The ovaries of the three families mentioned (Salmonide, Coregonide, and Osmeridz),
are structurally similar, consisting of a membranous covering continuous with the
mesovarium and almost completely enveloping the ovigerous stroma.

A practically complete envelopment is formed by the position of the ovary and the
mesovarium. ‘The ovary is usually so inclined that the otherwise uncovered portion
is protected by the mesovarium.' The prolongation backward of the mesovariums and
ovarian investments form the oviducts, which in the Salmonide and Coregonidz are trough-
like, open above, the inner wall consisting of the mesovarium and the free outer wall
(fig. 7 f) supported by the abdominal wall. Near the outlet, the two troughs unite
into one above the intestine at the point of termination of thedorsal mesentery. Atashort
distance from the genital orifice each outer wall of the common channel is deflected and
is attached to the respective wall of the abdomen.

The smelt differs from the other forms mentioned only in the position of the ovaries
and in the extent of the lateraly deflected portion of the oviducts.

RELATIONSHIP OF SALMONOID FISHES, GANOIDS, AND ELASMOBRANCHS AS
INDICATED BY THE OVIDUCTS.

A discussion of the origin and development of the oviduct in its relation to the
nephridial system, concerning which morphologists still entertain different views, is
not pertinent to this paper, but a brief consideration of the oviducts of other fishes
may have some bearing upon the question of how widely the salmonoids differ from
the other forms respecting these structures. Huxley wrote that, whatever their mor-
phological nature, the arrangement of the membranes in the smelt in a physiological
sense was, obviously, comparable to that of Fallopian tubes, and that everyone
who was familiar with the anatomy of the female reproductive organs of the ganoids
would at once perceive that these passages are the homologues of the oviducts of
Acipenser, Polyodon, Polypterus, and Amia.

Huxley observed no difference in structure or essential anatomical relation of the
oviducts of the smelt and the ganoids mentioned. In the structure and relations of its
oviduct, he regarded Osmerus as forming the third term of a series of modifications,

1Intwo humpback salmon there appeared to be more or less free egg surface on the upper outer side of the left ovary, as though
the ovary had been unduly stretched by the growing ova, and the surface usually inclined inward had been crowded so as to seem
somewhat outward. The most marked instance was as follows:

The left ovary is about 250 mm. long, and about 45 mm. in vertical height near the posterior end of the lobe of the liver,
extending to the outlet. ‘The mesovarium is attached to the upper edge—the ovarian membrane comes up on the outside a
little over one-third the width of ovary, making the exposed egg area comparatively wide.

About at the point of anterior attachment of the ventral mesentery, the ovary passes up to the top of the intestine. Thenits
vertical heightis2smm. ‘The end of the ovary within its almost completely infolding membrane lies in the trough with the free
egg surface nearly dorsal.

‘The dorsal mesentery ends about 60 mm. from the posterior end of ovary. A little anterior to this, the mesovarium leaves
the dorsal attachment and extends free on the inner side of the top of the ovary, lying in the trough (due to the prolongation of
the ovary backward).

The right ovary is nearly 190 mm. long and 42 mm. wide, at about the anterior end of spleen. At this place is the only free
egg space to be seen without tipping the ovary. This space is semiovalin shape. ‘These membranes are 14 mm. in narrowest
place. The outer edge of membrane at posterior end runs diagonally across to mesentery and extends downward to form the
side of the dorso-intestinal trough.

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 201

tending toward the separation of the ureteric from the oviducal ducts, two terms of
which were presented by the ganoids, and the arrangement of the parts which obtain
in the ordinary Salmonide a fourth term. Huxley stated as follows:

The abortion of the oviducts, commenced in Osmerus, is completed in Salmo, and all that remains
of the primitive arrangement is the fold described by Rathke and the so-called abdominal pore, which,
it will be observed, is the homologue of half of the urogenital opening of the ganoids and has nothing to
do with the abdominal pores of these fish and of the selachians.

He also says that, as is well known, Lepidosteus presents an example of a ganoid
with oviducts like those of the higher Teleostei; in Osmerus, on the other hand, we have
a teleostean with oviducts like those of the ordinary Ganoidei. It is tolerably obvious,
he continues, that, therefore, the characters of the female reproductive organs can lend
no support to any attempt to draw a sharp line of demarcation between the ganoids and
the teleosteans.

Bridge (1904) distinguishes two types of genital ducts in fishes: (1) Those which
are obviously derived from some part of the kidney system; and (2) those which are
special ducts and appear to have no connection with kidney ducts. The elasmobranchs
offer a typical example of the first, and the Teleostei afford an equally typical example
of the other. Representatives of certain other orders, among which are Acipenser,
Polyodon, and Amia (Amiatus), are regarded as more or less transitional.

Whatever may have been their embryological origin, it is quite clear that in the
adult teleost the ovaries and oviducts have no relation to organs other than that of
peritoneal attachment. These fishes, according to previously cited authorities, present
two types of ovaries, free and closed, and three oviducal adaptations, closed peritoneal
tubes, peritoneal funnels, and no oviducts at all except the ovipore.

The closed ovary is said to develop in two ways from the genital ridge: (1) By the
upturning and attachment above of the lower edge of the genital ridge, thus infolding
the genital cells; and (2) by the formation of a groove on the surface of the ridge, the
genital cells becoming infolded by the conjunction of the two edges of the groove.

The so-called free ovary, accordingly, was supposed to be formed by the genital
cells developing on the outer side of the ridge and the lower edge folding up only slightly
or not at all.

In each instance of closed ovary the closed oviduct is formed by a backward exten-
sion of the ovarian peritoneal membrane, the process of its formation being somewhat
different, according to whether the ovary is of the upturning or groove development.
In either case an extension backward of the mesovarium is involved. In the case of the
free ovary, the oviduct, if any, is developed wholly from the backward extension of the
mesovarium. In the case of the closed ovary, according to Goodrich (1909), the oviduct
begins as a parovarial or endovarial channel blind in front. _In the case of the free
ovary, if there is any oviduct, it is said to begin as the wide mouth of a funnel near the
posterior end of the ovary or at some distance behind it.

In the case of the ganoids previously mentioned, there is obviously a veritable
funnel formed by the folding of the peritoneal membrane on itself, which is well exem-
plified by that of Amia (Amiatus), as shown by Huxley.

According to the same authority, the smelt differs from the ganoids in having the
outer edge of the peritoneal fold attached to the abdominal wall, yet it is still called a
“funnel” and considered homologous with the oviducal funnels of ganoids.

202 BULLETIN OF THE BUREAU OF FISHERIES.

There is this difference between the oviducal membrane of the smelt and the funnel
of the ganoids mentioned, that in the smelt the membrane turns outward to become
attached to the abdominal wall (fig. 8 g), while in the other form it folds inward and is
attached to the mesovarial membrane (fig. 11). In the latter a funnel is formed; in
the former, only a half-funnel, which is not a homologue of the ganoidean funnels, but
is homologous with the oviducts of other Isospondyli, even (some at least) of those with
closed oviducts. Any phylogenetic significance
of the smelt oviduct then would appear to per-
tain only to teleosts and to have no relation to
the ganoids.

The Isospondyli comprise forms which are
~ stated to have closed ovaries and true oviducts
as well as those which have free ovaries with
funnel-like oviducts or only vestigial oviducts.

Besides the previously mentioned species,
specimens of Pomolobus pseudoharengus, P.
mediocris, Dorosoma cepedianum, and Hyodon
tergisus have been carefully examined. The
following two examples will serve to show that
the Isospondyli, other than Salmonide, as rep-
resented by the specimens examined, are not
radically different in their general structure
from the Salmonide, but considerably differ-
ent from other orders having closed ovaries.

The clupeoids are supposed to have closed
ovaries and oviducts. In the alewife (Pomolo-
bus pseudoharengus), the ovary of a large adult,
taken July 4, therefore some time after the
breeding season, is long and narrow, extending
well back in the abdominal cavity. The mes-
ovarium is narrow, the ovary lying close to the
air bladder. Anteriorly the line of attachment
of the outer edge of the enveloping membrane

, is close to the junction of the inner attachment
Fic. 11.—Left ovary and oviduct of bowfin (A miatus cal- 5

vus), after Huxley. 643. ov.l., left ovary; m.o.l., left of the mesovarium to the Ovary, along the outer
mesovarium; od. l., left oviduct; od. a., opening of ovi- side of the air bladder, and there is a pro-

duct into the bladder. “ b & a
jection forward of the ovary, which is com-
pletely inclosed in membrane with no air-bladder attachment of the mesovarium.
Posteriorly the lines of attachment diverge slightly, so that the inner line continues
along the air bladder, but the outer one becomes attached nearer to the lateral abdom-
inal wall at the side of the air bladder. The mesovarium is so narrow that it is scarcely
perceptible except as a fold lying in the outside of the ovary, but the membranous
attachment is wider and free from ovigerous lamin, leaving a noticeable space of free
eggs; that is, without otlier covering than the peritoneum of the air bladder. This
free-ova portion constitutes the beginning of the oviduct within and on one side of the
ovary. The remainder of the oviduct consists of the extension of the mesovarium and

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 203

outer attached edge of the ovarium membrane forming a channel with a very narrow
roof of dorsal peritoneum. The two oviducts unite near the outlet. ‘This alewife has a
ventral mesentery of about the same relative extent as in the salmonids.

The hyodons are stated (Jordan and Evermann, 1896, p. 412) to have no oviducts,
the eggs falling into the abdominal cavity before extrusion. An example of Hyodon
lergisus in breeding condition showed that the ovaries are completely inclosed in mem-
brane which, continuing from the mesovarium junction with the ovary, passes down
its inner surfaces and up over the outer surface and upper edge, then downward again
on the inner surface to the mesovarial attachment. The fusion of the outer edge of
the ovarian covering with the mesovarium at its junction with the ovary appears to be
complete as far back as the common opening in the dorsal mesentery. In this speci-
men the remainder of its backward extent seems to be still attached by fascialike, adhe-
sive membrane similar to the adhesions of the viscera in general to the abdominal wall
and to each other. At the termination of the mesentery posteriorly in the common
opening an interovarian channel is formed by the continuation of the ovarian mem-
branes. The membranes of the inner surface of each ovary fuse along the median longi-
tudinal line of the upper surface of the intestine, forming the floor of a common ovi-
ducal channel, the outer sides of which are formed by the ovarian membranes of each
ovary, beginning on the inner surface as a projecting fold. At this point the intestine
and canal somewhat abruptly turn downward to the outlet. Another mesovariumlike
membrane on each side begins forward, originating close to the mesovarium, and is
attached to the upper surface of the ovary. It appears to continue backward beyond
where the dorsal attachment of the true mesovarium ends and, by adhesion to the outer
edge of the oviducal canal on each side, respectively, forms a closed oviduct. Except-
ing in this secondary membrane, this oviducal structure is very similar to that which
has been described in connection with the Salmonide.

Since the intestine, with the superimposed oviducal canal, for the most of its extent
is dorsally situated, it is quite evident that any ova falling into the abdominal cavity
can not be extruded.

RELATION OF THE ANATOMICAL FACTS TO FISH-CULTURAL PRACTICES.

Boulenger (1904, p. 568) says of the Salmonide:

The large size of the eggs, their lack of adhesiveness, and the fact that the ova fall into the abdom-
inal cavity, out of which they may be easily squeezed, renders artificial impregnation particularly easy
and the species of Salmo have always occupied the first place in the annals of fish culture.

The error of this statement has been shown in the foregoing pages. It has been
seen that the mature ovary is inclosed in a delicate membrane, which is a continuation
of the peritoneal fold called the mesovarium. From the posterior end of each ovary an
open membranous trough extends inward and backward to the median line of the upper
surface of the intestine at the posterior termination of the dorsal mesentery, whence, by
a fusion with each other mesially, a single oviducal trough, open above, which conveys
the ova to the genital pore, is formed on the upper surface of the intestine.

Inasmuch as the ova do not naturally fall into the abdominal cavity and can not be
extruded if they are displaced into it, it follows that their adventitious presence there
can not be of advantage to the fish. Fish-cultural methcds afford several means of

204 BULLETIN OF THE BUREAU OF FISHERIES.

displacing eggs into the abdominal cavity. There is abundant evidence that present
fish-cultural methods cause such displacements. They may be occasioned by dipping
the fish head first into a scoop net, which causes considerable flopping by the fish; or
by grasping the fisu py the tail and holding her head downward until her struggles
cease. If the fish is ripe, or partly ripe, the mass of eggs sags visibly toward the head,
and it would seem inevitable that any free eggs would settle into the forward end of
the abdominal cavity outside of the ova-containing membrane. It is, however, after
the stripping process has begun that the danger of displacement is greatest, and par-
ticularly after some eggs have been expressed and the tense condition of the supporting
abdominal wall is relaxed. It is largely due to displacement that the repeated strip-
ping process fails to secure all of the ripe eggs, and even should the fish subsequently
emit retained eggs, it is manifestly impossible for her to rid herself of displaced eggs.

Another disadvantage from which the fish may suffer is rupture of the membranes
and injury to the ovaries by forcible pressure, so that the eggs falling into the abdominal
cavity are not secured. The ovary thus injured may not recover its natural function
and may thereby become sterile.

I have dissected various salmonids which have had deformed or distorted ovaries
and others with postnuptial reduced ovaries containing hardened eggs of the previous
or some preceding season, and have observed several instances of rainbow trout which
had been stripped some months previously, containing masses of collapsed eggs adhering
to each other, the viscera and abdominal walls, and others more recently stripped, in
which the ovaries still contained eggs, in follicles, more or less crushed, and in one
instance of which the posterior end of the ovary still containing eggs had been broken
off and was loose in the abdominal cavity. Several samples of ruptured ovaries have
been observed. In one example of landlocked salmon, several eggs had been pressed
into the under side of the lobe of the liver so that they showed through on the outside.
These facts can be ascribed to nothing except forcible attempts to strip the fish.

Some of these fish were artificially reared trout from a hatchery whence had come
a complaint that the trout were yielding fewer eggs than the normal yield, and con-
cerning which the suggestion was offered that the deterioration was due to inbreeding.

It is a common practice to begin the stripping pressure well forward and to repeat
the movement until all eggs possible have been squeezed out, the last frequently being
accompanied by fecal matter, mucus, and blood, This process is not only liable to
injure the ovaries and membranes, but to express unripe eggs, impossible of fertilization.
In fact, all of the eggs are never secured and some are retained and apparently are not
subsequently naturally extruded.

In A Manual of Fish-Culture, Charles G. Atkins (1900, p. 35) thus describes the
process of taking eggs from the Atlantic salmon:

The spawntaker clad in waterproof clothing and wearing woolen mittens, sits on a stool or box,
and on a box in front of him is a clean tin pan holding about ro quarts, which has been rinsed and
emptied, but not wiped out. A female salmon is dipped up from one of the floating pens and brought
to the operator, who seizes her by the tail with the right hand and holds her up, head downward. If
unripe, the fish is returned to the pens; if ripe, the spawn will be loose and soft and will run down
toward the head, leaving the region of the vent loose and flabby, and the operator, retaining his hold
of the tail with his right hand, places the head of the fish under his left arm with the back uppermost,

the head highest, and the vent immediately over the pan. At first the fish generally struggles violently
and no spawn will flow; but as soon as she yields, the eggs flow in a continuous stream rattling sometimes

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 205

with great force against the bottom of the pan. Shortly the flow slackens and must be encouraged and
forced by pressing and stroking the abdomen with the left hand. It is better to use the face of the
palm or the edge of the hand rather than pinch between the thumb and fingers; the latter action,
especially when working down near the vent, is apt to rupture some of the minor blood vessels, with
the result of internal bleeding, and it is better to leave some of the eggs behind to be taken another
day than to run the risk of such rupture.

In the same publication, George A. Seagle (1900, p. 66) describes a somewhat
more careful method of taking eggs from the rainbow trout as follows:

In taking spawn the manipulation of the fish without injury is a very delicate and exacting task,
full knowledge of which can only be acquired by experience, as it is difficult to squeeze the spawn
from the fish without injuring or even killing it. In taking hold of the fish in the spawning tub the
operator catches it by the head with the right hand, the back of the hand being up, and at the same
time slips the lefthand under the fish and grasps it near the tail, between the anal and caudal fins. If
the fish struggles it must be held firmly, but gently, until it becomes quiet, and when held in the right
position it will struggle only fora moment. A large fish may he held with its head under the right arm.

When the struggle is over the right hand is passed down the abdomen of the fish until a point
midway between the pectoral and ventral fins is reached; then, with the thumb and index finger, the
abdomen is pressed gently, and at the same time the hand is slipped toward the vent. If the eggs
are ready to be taken they will come freely and easily, and if they do not the fish is put back in the
pond until ready to spawn. If the eggs come freely from the first pressure the operation is repeated,
beginning at or near the ventral fin. :

After the first pressure has been given, by holding the head of the fish higher than the tail, all
of the eggs that have fallen from the ovaries and are ready to be expressed will fall into the abdomen,
near the vent, so that it will not be necessary to press the fish again over its vital parts, the eggs having
left that portion of the body. All of the eggs that have fallen into the abdomen below the ventral fin
can be easily ejected without danger of injury to the fish, caused by unnecessary pressure over its
important organs after the eggs have left that part of the body. If these directions are judiciously and
carefully followed, but little, if any, damage will result; and, as an illustration, it may be mentioned
that fish have been kept for 14 years and their full quota of eggs extracted each season during the egg-
producing term, which is normally from 10 to 12 years. The male fish is to be treated very much in
the same manner as the female, except the milt must not be forced out, only that which comes freely
being taken.

At the thirteenth annual meeting of the American Fish Cultural Society, Charles
G. Atkins presented some notes on the landlocked salmon, regarding which, among
other things, he said:

Among the migratory salmon of the Penobscot, ovarian disease is rare; but with the landlocked
salmon of the Schoodic Lakes it is very common. In 1883, by careful observation, we learned that
18 per cent of the female fish were affected with some disease of the ovaries, resulting in defects of the
eggs which were apparent to the eye, in some instances involving the entire litter, but generally a very
small number of eggs. The phenomenon was observed before artificial breeding began at Grand Lake
Stream, and does not appear to be influenced thereby.

Atkins does not state under what circumstances or conditions the phenomenon
was previously observed, but it is, perhaps, significant that following the adoption of
the gradual stripping process at Grand Lake Stream there were no further reports of
“ovarian trouble” or defective eggs among the salmon.

These facts indicate that in the case of those salmonoids which normally survive
the season of reproduction, all care possible should be exercised in the process of manip-
ulation for the purposes of artificial propagation.

The fish should be gently handled and at no time should be permitted to hang and
struggle head downward. Inasmuch as the fish does not naturally emit the eggs at one

75412°—22——14

206 BULLETIN OF THE BUREAU OF FISHERIES.

time, in stripping a fish this fact should be borne in mind, and no forcible attempt
_should be made to express more than those eggs which easily flow under gentle pressure.
It may take several operations to secure all of the eggs, and as the eggs begin to ripen
in the posterior part of the ovary, to obtain them it is not necessary to squeeze the
whole length of the abdomen. In fact, it is liable to injure the eggs or rupture the
ovarian membrane to do so. Experiments indicated that by the usual method of strip-
ping a large percentage of the eggs are obtained in the first operation. The question,
therefore, arises whether the number of good eggs obtained would be reduced by a
gentler operation and whether a second operation is necessary. In any event it would
seem to be a more rational procedure to follow nature and first remove the eggs in the
posterior end of the fish, using no more force than gentle pressure near the vent, witha
movement toward it. If eggs do not flow at first, repeated, short, gentle strokes may.
cause them to, if they are ready to be deposited. Some egg takers hold the fish belly
up at an angle which will permit the eggs to fall into the pan for receiving the eggs.
It would seem to be more in accordance with nature if the fish were held belly down
thus permitting the eggs to flow or roll along the oviduct toward the vent, as others
are emitted. The flow may be aided by gentle stripping motions repeated each time a
little further forward, not going further than the region of the middle of the ventral
fins. When the eggs cease to flow under gentle stripping pressure the operation should
cease. Possibly not as many eggs would be obtained by this method as by the usual
forceful method, but by operating only once or twice with-due care, the danger of both
external and internal injuries is lessened, and the breeder is saved, providing retained
eggs are not harmful. This latter point remains to be ascertained.

LIST OF WORKS CONSULTED.
Atkins, Charles G.
1goo. The Atlantic and landlocked salmons. In A manual of fish-culture, revised edition, pp.
17-60. Washington.
Balfour, Francis M.
1878. On the structure and development of the vertebrate ovary. Quarterly Journal of Micro-
scopical Science, new series, vol. 18, pp. 383-438, Pls. XVII-XIX. London.
1881. A treatise on comparative embryology. Vol. II, 677 pp., illus. London.
Beard, J.
1890. The inter-relationships of the Ichthyopsida: A contribution to the morphology of verte-
brates. Anatomischer Anzeiger, Bd. 5, pp. 146-159 and 179-188. Bardeleben: Jena.
Boulenger, G. A.
1904. ‘Teleostei (systematic part). Jn The Cambridge natural history, vol. 7, pp. 539-727. Mac-
Millan & Co. New York, London. :
Bridge, T. W.
1904. Fishes, exclusive of the systematic account of Teleostei. In 'The Cambridge natural history,
vol. 7, pp. 139-537. MacMillan & Co. New York, London.
Day, Francis.
1887. British and Irish Salmonide. . 298 pp., illus., 12 pls. London.
Felix, W. fi
1895. Uber die Entwickelung des Excretionssystems der Forelle (Vorniere, Urniere, Nachniere).
Verhandlungen der anatomischen Gesellschaft, 9 vers, pp. 147-152. Basel.
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8, pp. 249-466, 8 pls., and 39 figs. Wiesbaden.

MEMBRANES, OVARIES, AND OVIDUCTS OF SALMONOIDS. 207

Felix, W., and Bithler, A.

1906. Die Entwickelung der Keimdriisen und ihrer Ausfiihrungsgange. In Handbuch der Ent-
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fascicle: Cyclostomes and fishes). 518 pp., illus. London.
Ginther, Albert C. L. G.
1880. An introduction to the study of fishes. 720 pp., 320 figs. Edinburgh.
Haller, B.

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9 figs. Jena.
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1902. A manual of zoology. Translated and edited from the fifth German edition by J. S. Kings

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ical Society of London, pp. 132-139, illus. London.

Hyrtl, J.
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Akademie der Wissenschaften zu Wien, Bd. 1, pp. 391-411, 2 pls. Wien.
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1g05. A guide to the study of fishes. 2 vols., 1223 pp., 427 illus. Henry Holt & Co. New York.
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1882 (1883). Synopsis of the fishes of North America. Bulletin, U.S. National Museum No. 16,
lvi+1018 pp. Washington.
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1889. Beitrage zur Kenntniss der Entwickelung der Geschlechtsorgane bei den Knochenfischen.
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2pls. Wiirzburg.

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des Téléostéens. Archives de Biologie, Bd. 2, pp. 497-530, 2 pls. Gand.
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1897. A text book of*zoology, Vol. II, xx+683 pp., illus. New York.

208 BULLETIN OF THE BUREAU OF FISHERIES.

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1820. Uber die weiblichen Geschlechtstheile der Lachse und des Sandaales. Deutsches Archiv
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Parker. Second edition (founded on third German edition), 488 pp., illus. New York.

FURTHER LIMNOLOGICAL OBSERVATIONS ON THE
FINGER LAKES OF NEW YORK

a

By Edward A. Birge and Chancey Juday
Wisconsin Geological and Natural History Survey, Madison, Wis.

CONTENTS.
&

Page.
Jer eco.s Hise to Une k age OSs Eka ane iad TARA SRGINS COED Ot mEaS SoH STISHo Shot ACCOMM amr
‘Lemperatures and wheat budpets... occ c0cs 2 sven 5 eon sk ahs G Aten twa soa eRe MRSS s eee 211
Surface’ and: bottom temperatures: -ic.ce se ante eins ees Ma ewes OMe sie aera mimic 212
UMermMAloVERIGMSH 5c ws cei g cee inrase wR Se ae Cine Mie Te CesT cieee att erates whats RRP ofthe tarcto ene re ito 213
Summer heat MCAMes -2 coe css) Nalc co hw migele whe cence es ce MER TOO eet ts Mein tis ma iepsieieterete 2I5
Distribution, of heats. Sash axis haere Gow oc tele wate e elon Sie = Sree IN ein o8 Sie elo nae eee 218
Direee work ik2.SaF E8845 Jo. SPEER ERS A EIS Rh Rete duke ~ ao ate ee 219
Distributed: Work so< x ayes cep rea pes ogee a es ge pokes oe elem ein © oes eS enaats 221
MUD tC HON NEVES re mclstere site Sn were ain Ore Re ticle oinral eesete tn eke eon a neate ei Ie Slats eee 221
Heat and “work ‘as;-mensured| at ideptt. SS re oc neyo sie ws eeinicie te eee ciate wrens ers 222
Absorption’ of sun’s energy: so iciccn aie sohas «eters ee Fe oe ele See ee ee CNEL ree 223
Workrob the san jin, Gistrip iting eRe se coe erie cece ius eae aise at Rive cibotalere (n'a esata 232
Planktoms..:. 6:5... GSI IAs VRIOTBE. 2 SIS ~ DEI Fs EB ES: SERS oe eee oe 235
INETHOUS cmoeeanraen ROSS CTOs See Meee Re Deel a Oey Ai Bsa AO Uae a ao Sa ooo 235
IAPR an NEV gia Tye ie oetese Mic hh oS Sst hos kone ton ToS SERIE Sos coer 236
Phytoplankton < co.c,cen eco sere is rere winds, eeeicles ice iat tines Mauer eeie i ei ereeie ieee 236
y/o A NUT gic: Tea NG OA AORN OO MSO COS POC Ones SAUso Io Cogs ado as caso baa Sanbooces 236
Nanoplaniktotts ce. scar oxi ttele cicre mialercrom ie sie ierer cl erate Sissi ie al ats eo eer 241
Planktom tables is. sake oi sce om eee se te pret ehe le le ee Orrate Ris mingle abies oe hie Spe aie ee eer 243
Bottom “farinas<stes.s sree e erete es re ont coved croveroms arate Nleretier lorane noi taint chor ele een ate eae 250
Riteratnre poiteds < 5.2. o..s lox vieidisa wou. wang ones ce oesenie semielnla Cee Oe oe anil oes eaten nar 252

210

FURTHER LIMNOLOGICAL OBSERVATIONS ON THE FINGER
LAKES OF NEW YORK.

oh

By EDWARD A. BIRGE and CHANCEY JUDAY,
Wisconsin Geological and Natural History Survey, Madison, Wis.

Bd
INTRODUCTION.

In 1910 and rgr1 the U. S. Bureau of Fisheries enabled the authors of the present
paper to spend some weeks in the study of the Finger Lakes of New York. ‘The results
of this work were published in the Bulletin of this Bureau for 1912 (Birge and Juday,
1914). In this expedition there were applied to the study of the New York lakes
methods that had already been tried on the lakes of Wisconsin, which are much
smaller and shallower than those of New York. The resulting report dealt with the
hydrography of the lakes, their temperatures and heat budgets, their content of dis-
solved gases, and their net plankton. Since that study was made, the Wisconsin
survey has increased the scope of its observations on lakes. In particular there has
been devised and used extensively: a new instrument, the pyrlimnometer, designed for
measuring the transmission of the sun’s radiation through the water of a lake; numer-
ous determinations of the weight of the individual members of the net plankton have
been made; an elaborate study of the nannoplankton, both numerical and quantitative,
has been completed; and it is now possible to make a rough correlation between count
and weight of both net plankton and nannoplankton.

The Bureau of Fisheries authorized a second expedition to the New York lakes
in July and August of 1918, in order to apply these newer methods to them. The
following paper reports the results of the observations.

The authors are indebted to Hobart College, Geneva, for the free use of its labora-
tories during their stay on the lakes, and to Prof. EK. H. Eaton, of the same college, for
unwearied assistance in their work. Much of the success which was reached was due
to this aid. All recorded series of temperatures between 1911 and 1918 were taken
by Prof. Eaton, as also were those taken after August 1, 1918.

This report comes from both of its authors, as was the case with their former paper
on the same subject. Mr. Juday, however, has prepared the part which deals with
the plankton and Mr. Birge that which relates to temperatures and transmission of
radiation. f

TEMPERATURES AND HEAT BUDGETS.

The temperatures of the Finger Lakes were discussed in our former paper (Birge and
Juday, 1914, pp. 546-575), and it is unnecessary to repeat what was said there. Addi-
tional observations have been made and the discussion can be enlarged, therefore, at
certain points.

2Ir

212 BULLETIN OF THE BUREAU OF FISHERIES.

Table 1 shows the dates at which series of temperatures have been taken for use in
computing the summer heat income. A five-year mean of August temperatures may be
obtained for Canandaigua and Cayuga Lakes and a four-year mean for Seneca Lake.
Additional observations are not likely to make essential changes in the results thus

obtained.
SURFACE AND BOTTOM TEMPERATURES.

Observations of the surface in August and early September show in Canandaigua
Lake a mean of 21.4° C., ranging from 20.7 to 21.7°; in Cayuga Lake the mean is 21.1°,
ranging from 19.8 to 22.6°; in Seneca Lake, 20.4°, ranging from 20.0 to 21.1°. These
must not be taken as the maximum surface temperatures, which undoubtedly are likely
to come earlier in the season. Seneca Lake was visited on July 24, 1918, in the after-
noon of a clear, hot day and at the close of a hot and windless period. The surface
temperature in water 40 m. deep was 25.0° C. A heavy shower with violent squalls
occurred later in the afternoon. ‘The surface temperature on July 25 was 20.8° and
there was a marked rise of temperature above that of the 24th at all depths between
5 and 30 m.

TABLE 1.—DaTES OF TEMPERATURE SERIES: SURFACE, BOTTOM, AND MEAN TEMPERATURES.

Lake and date. | Surface. | Bottom. | Mean. Lake and date. Surface. | Bottom. | Mean.
|
CANANDAIGUA LAKE. g CAYUGA LAKE—Ccontinued.
oC, eG. 5G. rG, ce °C.
ANG: OMEGLOR Re cholo ote eid 21.7 5-4 FIO} |) Atos(r6, 11907 tahoe esidaes eae eS 22.6 4-3 9. 44
EG C0 Beane oreo qe EO Oae 20. 7 43 XONO2N || MAUS 405) TOL Gaieiseiaig os eiaistofeis!=tvlas 22.0 4.2 9. 66
Alig. 27; ifor4-2 Shi. xt 21.6 45 IO. II
Aug. 31, 1916..... 21.6 5.0 II. 57 earl renisag siaciseainc acs 21.1 4.2 9. 43
July 27, 1918..... 23.1 cae 9 II. 91
Sept. 1, 1918...... 21.5 5.0 II. 42 SENECA LAKE.
DCA ve ctacaeteiiere eects 21.4 4.8 mew il | [NEES BCPC G seorieecess aon se 20. 2 4.2 7.71
——————S || Sept. 1, 1911.. Ae 20.0 4.0 7-34
CAYUGA LAKE. Sept. 5, 1ro1q.......
Aug. 29, 1918
TT RES oe Or) Cle gop. Soro Ue OO 19. 8 43 9. 24
ne’ Ap) SAE ae Baan Ie 20,0 4.1 8.93 Mean tire. feb rcbsiens
Sentators rear ec eascieetion « 21.4 4.1 9. 65

Bottom temperatures average 4.8° C. in Canandaigua Lake (84 m. deep), ranging from
4.3 to 5.4°; in Cayuga Lake (133 m.) they average 4.2° with a range from 4.1 to 4.3°; in
Seneca Lake (188 m.) the mean is 4.05° and the range from 4.0 to 4.2°. The reading was
4.0° in three of the four series.

In most of these cases the observations were made with a Negretti and Zambra deep-
sea thermometer divided to 0.5°. Such an instrument gives approximate but not very
exact results. In 1918 the attempt was made to ascertain whether the water of Seneca
Lake might not be below 4.0° C. at the bottom. The temperature of maximum density
is lowered by pressure, as pointed out by Hamberg (1911, pp. 306-312). Since the
depth of Seneca Lake is 188 m. the pressure at the bottom is about 19 atmospheres, and
maximum density would be reached between 3.3 and 3.4°.

A special thermometer was used, ranging from — 2.0 to +14.0° and divided to 0.1°.
This instrument read exactly 4.1° when at the temperature of the surface water, 19.3°.
Correction for the expansion of the mercury shows that the true temperature at the
bottom was 3.88° and, therefore, below 4.0°, though decidedly above the temperature

FINGER LAKES OF NEW YORK. 213

of maximum density for the depth. Hamberg (loc. cit.) quotes examples of similar
temperatures from Lakes Ladoga and Mjésen. It is worth noting that the temperature
in both these lakes at the depth of 190 m. was between 3.8 and 3.9°._ The observations of
Huitfeld-Kaas (1905, p. 4) in Mjésen give temperatures at 200 m. which rise as high as
4.1° in November and as low as 3.65 or 3.75° in April and May. At the bottom, 400
m. or more, 3.60 and 3.75° were
found. At this depth the tempera-
ture of maximum density is slightly
above 3.3°. ,

It is very probable that the
temperature of Seneca Lake, record-
ed in 1910 as 4.2°, was really close to
4.0°, and that all readings of 4.0° at
the bottom indicate temperatures as
low as 3.8 or 3.9°. It is not worth
while, however, to apply an estimated
correction to these readings. There
is no reason to believe that the bot-
tom temperature of Cayuga Lake is
below 4.0° in late summer.

THERMAL REGIONS.

Table 2 shows the thermal
regions of the several lakes. The
epilimnion of Canandaigua Lake was
II or 12 m. thick; the thermocline
was 4 to 8 m. thick, averaging 6 m.
In Cayuga Lake the epilimnion was
13 to 15 m. thick and the thermocline
4 to 5 m. thick.

There was more variation in
Seneca Lake. The epilimnion was
15 to 19 m. thick and the thermocline
4to6m. On August 1, 1918, the
epilimnion at Hector Point was only
ro m. thick; on August 29, at Kashong, it was determined at 20 m. But since Kashong
is near the north end of the lake and the readings were taken on the day following a hard
south wind, the epilimnion was no doubt thicker there than observations at the center of
the lake would have shown. In computing gains of heat, therefore, the thickness of
the epilimnion for 1918 was taken as 15 m.

On July 24, 1918, at the north end of the lake in 40 m. of water the epilimnion was
only 7 m. thick. This was at the end of nine days of hot and calm weather and is an
exceptional condition. The thickness of the epilimnion rapidly increased to 14 or 15 m.
in the course of the following week and was subject to considerable fluctuations.

Fic. 1.—Curves of mean temperature to 34m.depth. A, Canandaigua
Lake; B, Cayuga Lake; C,Seneca Lake. (See Tabie 1, p. 212.)

214 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 2.—DISTRIBUTION OF SUMMER HEAT INCOME TO THERMAL REGIONS OF LAKES.

[Note.—Mean is derived from mean temperatures. Extent=vertical thickness of region in meters; R. T.=reduced thickness
of region, i. e., the thickness in meters of the region when reduced to the area of the surface of the lake. It is computed by
dividing the volume of the stratum expressed in meters by the area of the surface of the lake expressed in square meters;
T=gain of heat above 4.0°, i. e., the summer heat income expressed in degrees centigrade; Cal.=gram calories per square
centimeter of lake surface; P. ct.=per cent.]

CANANDAIGUA LAKE.

1910 IgI
Thermal region. i=
Extent. Se ue
Epilimnion............ o-12 10.0 16.8
Thermocline... 12-20 5.6 9.3
Hypolimnion.. 20-84 23.1 2.73
Meanortotal....].......... 38. 7 7.07
1914 1916
Thermal region.
Extent. | R. T. Ts Cal. P. ct. | Extent.\|, (Ro: oe Cal. P. ct.
Epilimnion............ o-Il 9. 34 31.0 15, 830 58.6 o-1I2 10.8 21.2 17, 420 59.3
Thermocline... 11-18 5.01 | .« 14.0 5, O10 9
Hypolimnion.... 18-84 24. 45 6.5 6, 160 7
Meanortotal....}.......... 38.8 10. 96 27, 000
1918 Mean.
‘hiermral regions, © 9 | Seine arr iene eee
Extent. | R. T. T Cal. P.ct. | Extent.| R. T. at Cal. P. ct.
Epilimnion Cheriton o-Ir 9.34 20.7 15, 610 54.3 o-1Ir 9. 34 20.8 15, 660 58.0
Thermocline. II-I5 2.91 16. 2 3, 560 12.4 II-17 7.18 15.9 4,970 18.4
Hypolimnion.. 15-84 26. 25 77 9, 600 33-3 17-84 25. 82 16. 5 6, 350 23.6
Mean or total.....-].......05- 38.5 It. 42 AB ano Me ceims cal oeeisemtiece 42. 34 10. 95 26; 980: |... -5 sane
CAYUGA LAKE,
1910 IgIr
Thermal region.
Extent. | R. T. T, Cal. P.ct. | Extent.) R.T oe Cal. P. ct.
o-Is 11.8 15.5 18, 300 64. 2 o-16 12.5 15.2 19, 00O 71.1
x r 15-22 4.62 10.3 4, 800 16.9 16-21 3-3 9.2 3, 300 12.4
Hypolimnion. 22-133 38.3 I. 41 5,400 18.9 21-133 38.7 1.14 4, 400 16.5
Meanortotal....].......... 54-72 5. 26 28,)500))| aieisiaisivioie's al phere epee 54-5 4.94 26, 700 |.......005
1914 1917
Thermal region.
Extent. | R. T. a Cal. P. ct. | Extent. | R. T. 7. Cal, P. ct.
Epilimnion eo Aspire O-I5 II. 97 21.2 20, 624 66.8 o-13 10. 56 21.0 17,977
Thermocline 15-20 3-35 16.7 4, 266 13.8 13-17 2.76 15.6 3, 201 10.8
Hypolimnion. 20-133 39- 27 55 5,980 19.4 17-133 14. 29 6.1 8, 542 28.8
Meanortotal....].......... 54-59 9. 65 ORB ION ec cares Banit me cieiacidiasra 27. 61 9. 44 2951720)|| c. ccsenisinie
1918 Mean.
Thermal region.
Epilimnion............
Thermocline.
Hypolimnion

Meanortotal....}.......... 54. 61 9. 66 30, 910

FINGER LAKES OF NEW YORK. 215

TABLE 2.—DISTRIBUTION OF SUMMER HEAT INCOME TO THERMAL REGIONS oF LAakES—Continued.
SENECA LAKE.

1910 IQIr
Thermal region.
Extent R. T. ay Cal Pick Tt Cal. P. ct
Epilimnion............ o-12 In5 15.4 17, 700 53.8 15.4 21, 200 71.5
Thermocline..........-. 12-20 6.2 10. 2 6, 400 19.5 8.6 5, 200 17.5
Hypolimnion.......... 20-188 70.9 I. 21 8, 800 ar ©. 47 3) 300 11.0
Meanortotal....].......... 83. 6 3-71 SENOS) Ihopesccoes Sasson sac q sBele 29; JOO !\|'=:2/= «)m ateie lass
I9I4 1918
Thermal region.
Extent, R. T. 4 Cal, Pict Extent.| R.T 45 Cal. P. ct.
Epilimnion.... o-19 16. 92 20.0 27, 000 71.2 ois 13. 60 20.0 22, 420 62.2
Thermocline. Ss 19-25 4. 83 13.9 4, 780 12.6 I5-19 3.32 14.6 3, 510 9.8
Hypolimnion.. 25-188 66. 85 4.9 6, ogo 16.2 19-188 71. 68 5-4 10, 030 27.9
Meam or totale cn ehs cosas. 88.6 8.27 chRiye) | Seipenocdod lccnncosce 88. 6 8.07 50/1000! [omar ssiaias as
Mean.
Thermal region.
Extent R. T. ae Cal. P. ct.
per Oni i0 1 ye eb aSoHae ma BRSaen Nancaon ar se acosemacnde ShoneTeMOncernncnissode oO-I5 13. 60 19.8 21, 410 6.
BPhermmocltie oases cece secre etelsteicreiel micah saetaiardicre cis eleeetainys iotcie's orefeyetatar ere fiyae roar 15-20 4.13 14.8 4, 450 13.1
13 RPC OES aces seta Snob bec hac bEOeOrl oe HOOOCR OB nt: U0 ADACPEeInAe ERS EnoaCsE 20-188 70. 87 5.2 | 8, 160 24.0
MTear Or Oval «crc cie te cota ert area ehcisror aie ale stole tereve wre veVoreyeleiave sicia alors efelw | eiw cie|a'a in/nie'e 88. 6 7-84 | 34,020 |........0-
|

SUMMER HEAT INCOME.

The summer heat income represents the gains in heat of the water of the lake
above the temperature of 4°. This notion was put forward in our paper on the New
York Lakes (Birge and Juday, 1914, p. 562) under the name of ‘wind-distributed
heat.” In the following year (1915, p. 167) I proposed the name “summer heat in-
come” for the same gains of heat, preferring a term which does not imply any theory
as to the method of distributing such heat. For reasons discussed in the same paper
(1915, p. 186) the summer heat income of lakes can be used as an index of their heat
exchanges in much the same way as the annual heat budget. The heat income, like
the heat budget, is stated in gram calories per square centimeter of lake surface. For
the sake of brevity it is ordinarily stated as so many calories without adding in every
case the qualifying terms. The whole question of heat budgets and the methods of
computing them is discussed in the paper already referred to (Birge, 1915).

Table 2 shows the summer heat income of the three lakes concerned. Canandaigua
Lake shows a mean income of nearly 27,000 cal./em.?, ranging from 23,000 to more
than 29,000 cal. Cayuga Lake has an income of about 29,500 cal., ranging from less
than 27,000 to nearly 31,000 cal. The income of Seneca Lake is about 34,000 cal.,
ranging from less than 30,000 to nearly 38,000 cal. The smaller income of Canandaigua
Lake is mainly due to the thinner epilimnion, which, in turn, is due to the smaller size
of the lake and to the protection from wind afforded by its high shores. So far as
area goes, Cayuga Lake is as well off as Seneca and its depth is ample to secure as large
anincome. But while the epilimnion in both lakes is 15 m. thick, its reduced thickness
is nearly 12 per cent less in Cayuga Lake than in Seneca. This fact is due to the large
extent of shallow water at the north end of the lake, which causes a corresponding reduc-

216 BULLETIN OF THE BUREAU OF FISHERIES.

tion in the amount of heat as stated in terms of units of surface area. The upper 20
m. of these lakes contains 75 to 80 per cent of the total quantity of heat, and the reduced
thickness of this stratum in Cayuga Lake is nearly 14 per cent less than in Seneca Lake.
(See Table 3.) The slightly higher temperature of the stratum in Cayuga Lake is not great
enough to compensate for this difference in thickness (cf. Birge and Juday, 1914, p. 574)-

A longer series of years would undoubtedly change the figures stated above. But
it is not probable that such a series would greatly alter them or that it would change
the general relations of the heat income of the several lakes to each other. The smaller
lake has the smaller income, largely because of its thinner epilimnion. Cayuga Lake
has less heat than Seneca, largely because of the smaller ratio between maximum and
mean depth. The differences are not so great but that the series of budgets overlap,
the largest heat income of Canandaigua being larger than the smallest of Cayuga, and
Cayuga’s series overlapping in a similar way that of Seneca. The largest heat income
in the series is that of Seneca in 1914, nearly 38,000 cal.

Table 2 also shows the distribution of heat to the three thermal regions of the
lakes. The epilimnion contains about 60 per cent of the summer heat income, ranging
from 53 to more than 70 per cent. This stratum, together with its thermal depend-
ency, the thermocline, contains from 70 to nearly 90 per cent of the heat. Thus in Seneca
Lake, which may be nearly 200 m. deep, a surface stratum occupying little more than
the upper one-tenth of the depth contains from three-fourths to nine-tenths of the heat
accumulated from the sun during the season.

Table 3 shows the distribution of the summer heat income by 1o m. intervals.
It shows the same facts as Table 2 but in another form. It makes especially clear the
small amount of heat which can be carried to considerable depths. In Canandaigua
Lake, for example, the total quantity of heat transmitted below 50 m. during the season
does not exceed the quantity delivered to the surface in one summer day; and even in
the much larger and deeper Seneca Lake it does not exceed two days’ supply.

TABLE 3.—DISTRIBUTION OF TEMPERATURES AND OF CALORIES OF SUMMER HEAT INCOME.

[Nore.—R. T.=reduced thickness of stratum in meters; T.= temperature in degrees centigrade; Cal. =calories of summer heat
income, i. e., gain of heat above 4°; P. ct.=per cent of heat income in stratum.]

CANANDAIGUA LAKE.

1910 Igir I9I4
Depth in meters. Ros

Lie Cal. P. ct. iy Cal P. ct. AY Cal P..ct
21.2 14, 720 53-3 19.9 13, 610 58.2 21.1 14, 649 56.3
14.3 7370 27.0 14.2 7, 300 31.5 13.6 6, 870 26.4
7.4 2, 190 8.0 6.1 I, 350 5.6 7.4 2, 190 8.4
6.2 1, 260 47 49 510 2.4 6.3 I, 310 5.0
5.8 880 Re 4.6 290 12 54 680 2.6
5.6 580 2-3 45 180 8 48 290 1.r
5-5 280 II 4-35 7° xe; 4.6 110 .4
5-4 7° =3 43 DOA Sciatica 45 20 as
II. 05 27,35° 100. 0 10, 02 23, 330 100, 0 10, 71 26, 110 100.3

1916 1918 Mean.

ae Cal Pict 4 Cal. P. ct. At Cal. ace
21.4 14, 890 50. 7 20. 8 14, 380 50.0 20.9 14, 45° 53-5
14.9 7, 800 26.6 14.9 7, 800 27.1 14.4 7,430 27-5
8.6 3,420 11.6 89 3,150 II.o0 7.8 2, 460 9.1
6.6 1, 480 5.0 6.8 1, 600 5.6 6.1 I, 230 4.6
5.9 93° 3.2 59 93° 3.2 5.5 74° 2.7
55 550 1.9 5.6 57° 2.0 Sa 43° 1.6
5:3 250 .8 5.4 270 1.90 rh 200 y)
5.0 5° 12 5.3 7o aa 48 4° 2
ap Ft AP II. 57 29, 37° 100, 0 II. 42 28, 770 100, I 10.95 26, 980 99.9

FINGER LAKES OF NEW YORK. 217

TABLE 3.—DISTRIBUTION OF TEMPERATURES AND OF CALORIES OF SUMMER Heat INComME—Con.
CAYUGA LAKE.

1910 IQII 1914
Depth in meters. RAT
We Cal. Pacts T Cal Ge a Cal aes
8. 42 19. 2 12, 800 44.8 19.9 13, 400 49. 8 21.3 14, 600 47-3
6. 88 Ory 9, 400 32.9 myax 9, 000 33-5 18.8 10, 200 33.0
6. 27 8.8 3, 000 10. 5 8.2 2, 600 9-7 9.6 3, 500 753
5-79 6.4 I, 400 49 5.6 goo 3-4 6.2 I, 300 42
5.12 5-4 700 2.4 4:7 350 1.3 5.2 600 1.9
4.52 49 400 I.4 4-4 180 +7 4.6 290 -9
4.03 4.6 250 “9 44 140 “5 44 160 5
3. 60 45 190 +6 4:3 130 +5 4.3 9° 3
5. 89 45 290 1.0 4.2 120 +4 4-1 90 55}
4.09 4.4 170 -6 4.2 80 +3 4.1 40 oa
54. Or 9. 24 CMe) lSsqnccecas 8.93 26, 900 Sea 9. 65 30, 870 aca
1917 1918 Mean.
Depth in meters. Bis
aL Cal. eet a Cal. P. ct. T Cal. pects
8. 42 21.3 14, 600 49.2 21.1 14, 400 46. 6 20.6 14, 000 47-5
6. 88 16.1 8, 300 28.0 16.4 8, 500 27.5 17-3 9, 100 31.0
6.27 8.8 3, 000 10.1 9.1 3, 200 I0. 4 9.0 3, 100 10. 5
5. 79 6.9 I, 700 5:7 Gere 1, 800 5.8 6.4 I, 400 48
5.12 eer 880 3.0 6.3 , I, 200 3-9 CAG. || 770 2.6
4-52 49 410 1.4 7 75° 2.4 49 410 1.4
4.03 4.8 320 rae 5.1 449 1.4 46 260 9
3. 60 45 180 .6 47 250 .8 45 160 a5
5. 89 44 210 -7 45 290 “9 43 190 7
4.09 43 120 +4 4-2 80 -3 4.2 90 +3
|
54. 61 9. 44 29,7720 |i caceee este 9. 66 BO, QXLOLIS cknie clara 9. 40 29, 480 |....... Sink
SENECA LAKE.
I9I0 Igit 1914
Depth in meters. ROP.
pt Cal P. ct. “LE Cal. Pacts he Cal. UNS
9.35 19. 6 49-5
4° 15-7 34-5
7.86 8.7 8.3
7.41 6.4 2.7
6. 92 a 1.3
6.49 49 1.0
5. 89 4.8 -6
5.52 4.6 .6
9. 82 45 St
12.14 42 4s
5.76 42
3.22 42 .
Sens 55 soe Ch GRs |) @ eb oeee| ec dopebcl | Ser aky lll Se chil RES GAncaps
1918 Mean.
Depth in meters. 1s ate,
Ate Cal. P. ct. abs Cal Bact.
9.35 20. 5 19.9 14, 900 43.8
8. 40 17.2 xy 10, 960 32.4
7. 86 9.9 9.3 4, 200 12.4
7. 41 6.8 6.3 I, 700 5.90
6. 92 6.0 5-4 94° 2.8
6. 49 5-2 4.6 420 1.2
5. 89 44 45 270 8
5: 52 43 43 180 5
9. 82 42 4.2 260 .8
2. 14 4.1 41 130 -4
5-76 40 40 40 ou
E 4.0 POM bacnkcosap

218 BULLETIN OF THE BUREAU OF FISHERIES.

DISTRIBUTION OF HEAT.

The radiation from the sun which enters a lake is rapidly absorbed by the strata of
water near the surface. Even in very clear lakes only 20 per cent of the total radiation
passes the 1-meter level, and only about 10 per cent passes the 3-meter level. (See p.
228.) All of the warming of the deeper water and most of the warming of that which
lies below the surface meter is due not to insolation but to mixture of warmer water
carried down from near the surface. This mixture of warm surface water with the
cooler water below is effected by the wind for all temperatures above 4°. It involves
work against gravity, since the warmer water is lighter than the cooler. This work may
be measured and may be conveniently stated in gram-centimeters per square centimeter
of lake area. These facts were stated in our paper on the New York Lakes (Birge and
Juday, 1914, p. 562). The principles underlying these ideas were later published as a
special paper (Birge, 1916, pp. 341-391) and were applied to Lake Mendota. It was
there shown that about 1,210 gram-centimeters of work per square centimeter of area
are needed to distribute 18,400 gram-calories of heat per square centimeter of area
through the waters of a lake 24 meters in maximum depth and 12.1 meters in mean depth.
It is understood that in this statement the term “‘work”’ is not used in an exact sense;
since in it are included both the action of the wind in distributing heat, which is properly
work; and also the direct effect of insolation, which does not involve work. (See Birge
and Juday, 1914, p. 574; Birge, 1916, p. 360.) This division of the distribution of heat
between sun and wind is discussed later in the paper. For the present, however, the
matter is discussed as though the entire distribution of heat were due to wind.

TABLE 4.—TEMPERATURE (T) IN DEGREES CENTIGRADE AND GRAM CENTIMETERS (G. CM.) oF WoRK
NECESSARY TO DISTRIBUTE THE SUMMER Heat INCOME.

[Nore.—This table shows the “direct curve of work,” i. e., the work necessary to carry the warmed water from the surface to
e stratum in question. It is stated in gram centimeters per square centimeter of surface of the lake.]

CANANDAIGUA LAKE.

1910 IgII 1914 1916 1918 Mean.

Depth in meters. —

oi G. cm a G. em. T. G. cm. aT G. cm. T, G. cm Ay G. cm.
21.6 236.2 | 20.0 224.0] 21.5 240.8 | 21.5 240.8 | 21.1 224.0] 21.1 224.0
21.0 582.0 | 19.6 505.3 20.7 574.1 21.3 613.0 20.6 568. 1 20.6 568. 1
18.0 630. 7 17.5 589. 5 16.9 539.3 17.8 612. 4 17.0 548. 4 17.5 589. 5
10. 6 199. I 10. 6 199. I 10. 2 176.6 | 12.0 288. 3 12.5 309.6] 11.2 235.5
8.2 100. 4 6.2 25.8 7-4 62.7 9.2 149.8 9.8 19I.9 8.2 100. 4
7.0 60. 8 5-4 13.7 6.9 56.5 8.0 106. I 8.0 106. I 7-1 64.2
6. 2 75-2 4.9 13.9 6.3 83.2 6.6 104.9 6.8 122.8 6.1 69. 3
5.8 57.2} 4.6 6.6 5-4 35.2 5.9 63.8 5-9 63.8 5.5 39.6
5.6 42.0 4-5 4.0 4.8 1Oo/] 5.5 36.0 5.6 42.0 Sa 24.0
5.5 22.3 44 I.2 4.6 a7 5.3 17.4 5-4 19. 8 5.1 12.4
5-4 6.7] 4.5 -4|- 45 -8| 5.0 3-3 5-3 5-8] 4.9 2.9
irate PAC FAC Eo} hae? St: < Hsia dormer bbe iy cee otal ieiacobed fee Bek Ook) Meier [pee HE Gr Bey eee 1,929.9

FINGER LAKES OF NEW YORK. 219

TABLE 4.—TEMPERATURE (T) IN DEGREES CENTIGRADE AND GRAM CENTIMETERS (G. Cm.) oF WORK
NECESSARY TO DISTRIBUTE THE SUMMER Heat INCOME—Continued.

CAYUGA LAKE.

I9I0 IgII 1914 1917 1918 Mean.
Depth in meters.
pt G. cm sib G. cm a G. cm. a. G. cm st G. cm ae | G. cm
|
6 187. 6 20.0 195-4 21.4 229.8 21.8 239.8 | 21.4 237-5 20.8 | 215.3
6 488. 4 19.9 497-1 21.4 598. 2 20. 7 554-9 | 20.8 560. 7 20.5 540.4
4 727-6 | 19.6 745-3 | 20.9 864.4 | 18.8 674-7 | 19.3 718.8 | 19.6 | 745-3
° 603.6 | 14.9 503.4 | 16.7 673.9 | 13.2 363.9 | 13.4 379-r | 14.8 494.6
9 189. 6 9.0 137-9 Ir.o0 264. 2 9. 8 |- 183.8 | 10.0 196. I 9.9 89. 6
8 95.0 6.9 56.0 8.0 105.2 ees 90.7| 8.2 115.3 7.7 90. 7
4 94.9 5.6 30.3 6.2 70.7 6.9 133-3 | 7-1 147-5 6.4 | 92.9
4 41.6 4:7 5.8 5.2 20.8 5-9 53-1 | 6.3 97-9 5.5 41.6
9 17-4 44 5-0 4.6 6.2 49 17-4| 5-7 54.8 4-9 | 17-4
6 9.2 44 2.6 4.4 2.6 4.8 13.1 5.1 26.2 4.6 | 9.2
5 54) 43 2.7 \( (4.3 2.7 4.5 5-4) 47 12.1 4-5 | 4.0
5 10.6 fers asco se eongeell | CECA PR SArE 44 5-3 4.5 10.6 4-3 | os
4 7-2 ees ans Cy el Seria saseer 4.3 4-8 PEER ssa kore hee (PME Ct Be snase.
apceooe PAL SS SbEc CA) Hike aah hndse da) Meat o 2. ppARe on Meas cr 6) Rodan he AL Loh 2 PeSSaso 2, 446.3
SENECA LAKE
IgIo I9II 1914 1918 Mean.
Depth in meters. © |_———7—_ -
A G. cm. 4) G. cm. ae G. cm Ab G. cm x G. cm

19.8 205.9 19. 7 203.5 20.4 220, 2 20.6 226.1 20. I 213.0
19.4 552.8 19. 2 539-4 20. 2 603.0 20. 5 626. 4 19.8 579.6
17.8 718. 2 17.8 718.2 20. 1 959. 4 20. 2 975-5 19. 2 863.0
13.3 457-8 14.0 526.3 18.0 996. 4 14.0 526.3 14.8 609. 4
9-3 194.6 8.0 112.2 13.4 585.5 II. 5 380. 1 10. 6 296.8
7-9 126. 3 6.3 44.9 9.4 237-5 8.2 145. 5 8.0 132.7
6.4 119.6 5.8 67.6 aX 195.0 6.8 161.2 6.3 109. 2
5.5 56.0 4.6 9.3 5-4 49.8 6.0 99.5 5.4 49.8
4-9 24.6 4-4 3.5 47 14.0 5.2 42.1 4.6 10.5
4.8 19.0 4.3 3.8 4:4 3.8 44 3.8 4.5 7-6
4-6 22.0 4.3 5-5 C5eay |esioap gee 4.3 5.5 4.3 4-5

4:5 19.6 Aa lonimeinieier crete Pet nee raia aeete Heh Mee eR sone 4.2

4.2 Agito encircle NOD nuts selene. Cera ae Semgoee 4.1

4.2 |. BnOinseeneiteet Mizell eeaad seed CHD ee anced 4.0

4.2 ZHteh| baROnboo Se AON sonatas BON Mos ye 550 4.0

Sienna |SnOROS 3866) “CHEEKS | Nenahdeopel!! ALICE OH Sboagosee8 | SbECEECM Bodoosaocn

DIRECT WORK.

Table 4 shows the distribution of heat for the lakes under consideration. The
resuits of the computation only are given; the details of the method being quite similar
to those illustrated in the paper before referred to (Birge, 1916) and also in Table 5,
page 220, of this paper. Taking the means only it appears that in Canandaigua Lake
about 1,930 g. cm. of work per square centimeter of the area of the lake are needed to
distribute about 27,000 cal. of heat through the water, the depth of which is 84m. In
Cayuga Lake about 2,450 g. cm. of work distribute 29,500 cal. in water, the maximum
depth of which is 133 m.; in Seneca Lake 2,880 g. cm. distribute 34,000 cal. in water
the maximum depth of which is 188 m.

The amount of work needed to carry the heat to the corresponding stratum of the
several lakes varies with the loss of density of the water due to rise of temperature
and with the quantity of water in the stratum. The latter factor is represented by
the reduced thickness of the stratum. (See Table 3.) The first factor is the more

220 BULLETIN OF THE BUREAU OF FISHERIES.

variable in these lakes, and to it are due most of the striking differences in the work
required to warm the deeper strata. In the 30 to 40 m. stratum of Canandaigua Lake,
for instance, it required about 70 g. cm. to put 1,230 cal. into place. In the corre-
sponding stratum of Cayuga Lake it required 93 g. cm. to place 1,400 cal. The
difference in calories is about 14 per cent, in work over 30 per cent. This is mainly
due to the difference in loss of density. At 6.1°, the temperature of Canandaigua Lake,
this is 35 points,! and at 6.4°, the temperature of Cayuga Lake, it is 46 points, or over
30 per cent greater.

Table 4 shows that a great amount of work is necessary to produce by mixture
the high temperature of the upper strata; it shows also that an almost incredibly small
amount of work is needed to carry considerable heat to great depths if only it involves
but little rise of temperature. Note, for example, Seneca Lake, where 42 cal./em.?
of surface are transported to a mean depth of 55 m. for an expenditure of about 1 g. cm.
On the other hand, in the corresponding stratum of Canandaigua Lake, each gram
centimeter of work transports only about 18 cal. The difference is due to the much
greater rise of temperature in the smaller lake—reaching 5.2° instead of 4.5° in Seneca

Lake.

TABLE 5.—DETAIL FOR SENECA LAKE OF THE Facts oF DISTRIBUTION OF MEAN SUMMER HEaT INCOME.

[Nore.—T.=temperature in degrees centigrade; 1-D=loss of density due to warming; RTXZ=factor, reduced thickness
multiplied by depth. Direct=work done im behalf of stratum in question; Dist.=work done im stratum in question; Cal.=
calories of summer heat income in stratum. All expressed in units per square centimeter of lake surface. See fig. 3, p.
229; also Birge, 1916, P. 349,355-]

Direct work. Dist. work,
Depth
Depth in meters. . : aay i os (a ee eae . i G.cm.} Cal.
G. cm.

0. 001853 a é . 2,874.4] 34,020
1815 a ; . : 2,589-8 | 32,396
1815 5 D . : 2,323-3 | 30,808
1790 - : - : 2,074-5 | 29,253
177° : 1,843-0 | 27,723
1770 . : : : 1,629.4 26, 219
1749 . - 5 or : 1,432.4 24,731
1729 (, B - es Z I, 251-6 23,284

1,086. 7 21,862
937-1 20, 480
802. 5 19,114
682. 7 17,757
577-5 | 16,424
486.6] 15,108
410.1 13,850
345-5 | 12,609
292-5 11, 483
249-2 | 10,487
213-6 | 9,595.
184-3 8, 804
159-7 8,156

78-9 | 5,503

43-2 3,943

13-7 2,229

46 1,260

7 775

“4 512

«2 347

2,874.4 Sol | eee (Etta tac Cote

1 By a “point” is meant a decrease in density of one part per million, The density of water at 6.1 as compared with that
at 4.0° is 0.999965. ‘The loss in density is, therefore, 0.000035 and this represents the loss in weight of the lighter surface water at
6.x°, and, therefore, is one factor in determining the work to be done in pushing it down into deeper and cooler strata. For con-

venience in computation this factor is taken as a positive quantity and a whole number is stated as 35 points. (See Birge, 1916,
D. 391.

FINGER LAKES OF NEW YORK. 221
DISTRIBUTED WORK.

Table 4 deals with the direct curve of work. It gives for each stratum the amount
of work necessary to convey the warmer and lighter water from the surface to the
depth in question, assuming that the lower water has a temperature of 4.0°. In warm-
ing all strata below that at the surface most of the work is performed in the strata
above that for the benefit of which the workis done. If the work for each stratum is thus
distributed to the several strata above it, we derive the curve of distributed work. (See
Birge, 1916, p. 355). This is shown for the mean of each lake in Table 6 and for Seneca
Lake in figure 3. The numbers for each stratum show how many gram centimeters
are necessary to distribute through the stratum the heat retained in it and to convey
through it the heat which goes on to lower strata. The table shows how shallow is
the stratum which receives most of the work of the wind. More than 94 per cent of
this work is expended in conveying the heat through the upper 20 m. of the lake. While
the effect of the wind extends to the bottom, even in Seneca Lake, the work done in
the deeper water is very small, as measured by the fall in density due to increased tem-
perature. In the upper 5 m. are found from 43 to 50 per cent of the work and in this
stratum the largest deductions from the apparent work are to be made for the influence
of direct insolation.

TABLE 6.—DISTRIBUTED WorK, MEAN.

[Note.—This shows work done in each stratum in distributing the heat brought to it, and in carrying on to the next stratum the
heat which passes throughit. This is computed only for the means of the lakes.)

Canandaigua Lake. Cayuga Lake. Seneca Lake.
Depth in meters.
G.cm. |Percent.| G.cm. | Percent.| G.cm. | Per cent.
45-0] 1,245.0 43-4
28.5 826.9 28.8
15-1 457-0 15-9
5-6 185-8 6.5
40 116.5 41
1.2 29-5 1.0
“4 9-1 -3
+2 2.9 «I
oI ToS) lala atalaterti ote
Sietererstecmiate ih | Sveleteicte a ee
eres Se 25874. 4 |..ceesecee

SUBTRACTION CURVES.

Table 7 shows the data for the mean subtraction curves of the three lakes. (See
Birge, 1916, p. 384.) It shows the number of calories which pass through the several
levels of the lakes and the amount of work needed to distribute them through the water
below these levels. Comparison of the data at the surface shows that 12 to 14 cal. of
heat are distributed through the subjacent water by 1 g. cm. of work. At lower levels
the temperature declines and the decrease in density falls off even more rapidly with
the result that an increasingly large number of calories is distributed by 1 g. cm. of
work. At the depth of ro m. the ratio is 25 to 30 cal. to 1 g. cm.; at 20 m. the ratio
rises to 40:1 or 50:1; at 30 m. in Seneca Lake and at 4o m. in the others it has risen
nearly or quite to 100:1. This relation explains how in lakes of great depth a large
quantity of heat is carried in spring to the lower water. The great quantity of work

75412°—22 15

222 BULLETIN OF THE BUREAU OF FISHERIES.

needed for distribution in the upper water as the temperature rises equally makes clear _
the reason why the lower water soon ceases to gain heat as the season advances.

In Seneca Lake work amounting to only 0.4 g. cm. is needed to distribute 512 cal.
to depths below 70 m., while no appreciable amount of work is needed to distribute 347
cal. through the water below80m. ‘The last statement is obviously not strictly accurate,
but it is not worth while to compute the work in those cases where the decrease in den-
sity due to increase of temperature is less than one part per million.

TABLE 7.—SUBTRACTION CURVE MEANS: AMOUNT AND PER CENT OF HEAT IN SUMMER HEAT INCOME
AND OF WorK NECESSARY TO DISTRIBUTE THIS HEAT FOUND AT THE SURFACE AND AT DIFFERENT
DEPTHS OF THE SEVERAL LAKES.

[Note.—Stated in units per square centimeter of the surface of the lakes.]

Canandaigua Lake. Cayuga Lake. Seneca Lake.
Depth in meters.
Cal. ECU s | Gres CE eral Cee Cal. P. ct. |G.cm.| P. ct. Cal. Piet. | Greme| backs

2,446 5 34,020 100.0 2,874 100.0
1,345 . 77-2 | 1,629 56.8
56.3 802 28.0
37-1 345 12-0
24-0 159 5-6
II-7 4B mos
6.7 13 “5
3-9 4 +2
2-6 I +0

I-

I.

HEAT AND WORK AS MEASURED AT DEPTH.

In Table 7 the data are given in terms of the surface of the lake—so many calories,
or gram centimeters, per square centimeter of surface. If the datum plane is taken
as the area of the lake at the depth in question, the number of calories and gram
centimeters at each level will be increased proportionally to the decrease of area as
compared with that of the surface; but the ratio between the amounts of work and of
heat would remain unaltered. This relation is shown in Table 8. Perhaps the most
interesting fact shown by it is the very close agreement between Cayuga and Seneca
Lakes in both heat and work after the surface level is passed. Approximately equal
quantities of heat pass through the 5 to 40 m. levels of both lakes. Cayuga Lake shows
at the surface considerably less heat per unit of area than Seneca has, but this is largely
due to the great area of shallow water at the north end of Cayuga Lake. No such area
is found anywhere in Seneca Lake. The area of Cayuga Lake at 5 m. is about 79 per
cent of the surface area, while that of Seneca Lake at the same depth is 87 per cent of
the surface. The area of the 10 m. level in Cayuga is about 92 per cent of that at 5 m.,
and in Seneca about 93 per cent of the 5 m. level, a very close correspondence, which
shows itself in the heat and work. ‘he large area of shallow water in Cayuga Lake
adds nothing to its effective area in absorbing heat, nor does it seem to diminish the
efficiency of the lake. Canandaigua Lake, however, is plainly less efficient than either
of the others. Its smaller area and higher banks cause this condition, since both factors
lessen the efficiency of the wind. (See Birge and Juday, 1914, Pls. CXIII, CXIV, CXVI.)

FINGER LAKES OF NEW YORK. 223

TABLE 8.—AMOUNT OF HEAT IN SUMMER HEAT INCOME AND WORK NECESSARY TO DISTRIBUTE IT.

{Nore.—Expressed in units per square centimeter of the depth in question; not (as in other tables) in units per square centimeter
of the lake surface.]

Canandaigua Lake. Cayuga Lake. Seneca Lake.
Depth in meters.
Cal G, cm. Cal. G. cm Cal G. cm
1,929 29, 480 2,446 34) 020 2,874
1,150 27) 750 I, 710 | 28, 000 1,740
549 21, 440 892 | 21,900 922
246 14; 530 406 14) 900 410
136 9, 800 220 10, 100 197
56 5,420 76 5,190 56
26 3,440 33 3,150 17
Ir 2,330 17 1,980 6
4 1,640 9 1, 480 1-7
I, 150 5 I,1I0
820 Jeseeeeeees 840
BOOS he icystow 2 420
aa E70 | ele cin tote
| 90
| °

ABSORPTION OF SUN’S ENERGY.

Observations were made in 1918 on Seneca, Cayuga, and Canandaigua Lakes in
order to ascertain the rate at which the energy of the sun’s rays is absorbed by the
water of the lakes. The instrument is described in another paper (Birge, 1921),
and the description will not be repeated. It consists of a receiver containing 20 small
thermal couples which can be lowered into the lake to any desired depth and alternately
exposed to the sun and covered. The electrical effect of the sun’s radiation on the ther-
mal couples is proportional to the energy in its rays, and the resulting electrical cur-
rents are measured by the deflections caused in a d’Arsonval galvanometer. The
galvanometer is kept on shore and is connected with the receiver by an insulated cable
roo m. long.

The observations on the three lakes afford excellent illustrations of the results
obtainable by this instrument, and also of the difficulties which necessarily attend
observations of the kind if made in the course of a short visit, when every opportunity
must be fully used. The general results from each lake are clear and unmistakable,
but in each case the details are affected by special conditions of sky or water.

A part of the observations on Seneca Lake is given in Table 9 in order to show the
nature of the data.

224 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 9.—TRANSMISSION OF SUN’S ENERGY BY THE WATER OF SENECA LAKE Orr HEcTor Pornt,
N. Y., AuG. 1, 1918.

[NoTE.—1.50 to 2.23 p. m., Government time=12.40 to 1.11 sun time. Transparency 6.8 m.]

Depth real Depth
in Read- | Deflec- in Read- | Deflec-
Hour, p. m centi- | 2°: | ing. | tion. | Hour, p.m. centi- | 2€T- | “ing, | tion.
meters. meters.
Io. 27.8 . '
PACE eae ee CPE Cee ° { ee | Sa \ cn Otol lWCH-y Pen emeeeoanoesaadacaccs 2 400 { rege Bae \ 17-1
ris eats bed ee etd 98 25 4 ae ae } obs) ||) ies o soon oagsscoonocodooa 5 500 { eee i \ 11-9
‘ou 13.0| 77-0 , 12.1 20.3
SRSA Oh Oe Cpe nA OMaE Sanat 50 { 300 7760 \ CY BOW) | hee Bae onc ooanncsocsoaacns- 600 ponies ae } 8.3
oa Mees ie aamcir ecb 100 { = : aoe } BUT s-3) || ae Lh ctalcreie ras slateve ete etatelevatetererotape 700 oa rae } 5-9
DiBQ nee Semen Kien wialeis ican 150 { oat ae } Bas Rel| tia acrasive re cccrlere et aWerc evar roots 800 vale x3 \ 4-0
2.00 200 \ see 45:8 i 33+2 ae wee |
Preteen eens \\ 12.2 45-5 Fan pean om sop sabe OOS 900 12-3 15-1 2-9
he aso \{ 12-2 40-6 \ Le 12.2 15-0
Abbdnoce epooansoccosce 5° |) -i2.0 40-2 2 12.2 14-5 |
12.1 | 35-8 \ 12.2 14-4
Do ea 3°91! 32.0] 36-5 SAPD || Fosag te ck centRecrssmsenice eee I,000 12.2 x8 2.2
if | 3 12. -
BOS ate syeialalelewrelete leveled clefurete etetatals 35° i{ 5 : ee } 20-0, aa Showed

NOTES ON ABOVE TABLE.

1. Sky perfectly clear and sun’s radiation steady; no clouds; practically no haze. Light south
air, causing ripples on surface. Some swell from wind of yesterday and of early morning. The
swell caused irregularities of reading in upper water, as it raised and lowered the boat. At 100 cm.
the scale moved over 4 to 5 divisions, and reading had to be estimated under these conditions. This
effect became less as depth increased. Ripples cause a quivering of the reading in the galvanometer
but are too small to cause swings of the scale.

2. In reading the direct sun a shunt coil is included in the circuit in order to keep the reading
within the limits of the scale. This coil is cut out by a switch when the receiver is used in water. The
reading in air must be multiplied by 1.89 to reduce it to the same scale as those in the water. Its value,
therefore, on this occasion is 221 divisions. One division equals 0.059 cal./cm.?/min., so that the sun
was delivering about 1.30 cal./cm.?/min.

3. The observations not reported included a repetition of several of the readings, and a second
reading in the air, which gave a value of 116.2 divisions, or substantially the same as the first reading.

4. The numbers in the columns headed zero, reading, deflection, indicate divisions of the scale of
the galvanometer.

From these readings may be computed the value of the energy delivered by the
sun at different depths of the lake, as is shown in the following table:

TABLE 10.—CALORIES PER SQUARE CENTIMETER PER MINUTE FouND AT VARIOUS DEPTHS OF SENECA
LAKE, AUG. 1, 1918.

Depth in centi- Cal./cm.?/ Depth in centi- Cal./cm.?/ Depth in centi- Cal./cm.*/
meters. | Per cent. min. meters. ecicent min. meters. Per cent. min.
|

100. 0 1.30 12.8 0.17 HOO taaictevie se aioe ai ©. 035
31.8 . 41 10.9 14 fe Disha aeon nee acc r8 . 023
29.0 -38 9.0 12 DOO es clakrera ate eis {3 O17
aI. 4. 28 7-7 © LO |] X{OOO. cesiceiecaccens 1.0 O13

17-4 2 5.4 +07

15.0 20 3.8 . 05

FINGER LAKES OF NEW YORK. 225

TABLE 11.—TRANSMISSION OF SUN’S ENERGY PER METER OF DEPTH.

[Nore.— Per cent of the energy found at the upper surface of each 1 m. stratum which is present at the lower surface of such
stratum.)

: | Trans-
Stratum in meters. mission,
per cent,

Stratum in meters.

Table 11 is given as it stands in order to bring out the various small variations in
percentage which are inherent in the observations. In all cases the fraction of a
division of the galvanometer scale must be estimated and is, therefore, subject to error.
The value taken as zero is not a fixed one and in any observation may be recorded
slightly too low, or more probably a little too high. The motion of the boat, due to
the swell, as stated above, might introduce some errors in this case, especially in the
readings from the upper water. In figure 2 the results are plotted and a smooth curve
a-a is drawn through them. All of the observations are very close to the curve. It
is plain that there was transmitted through each 1 m. stratum of water below the surface
meter about 71 per cent of the energy received at its upper surface. It is not probable
that the higher transmission indicated in the 9 to 10 m. stratum has any significance.
A reading of 2.1 divisions of the scale at 10 m. instead of 2.2 divisions would bring this
interval into line with the others.

Lake water differs widely from pure water in the quantity of energy transmitted.
If we assume a solar energy curve corresponding to a path of the rays in the air of 1.5
atmosphere, with about 0.5 cm. condensable water in the atmosphere, about 47 per
cent of the solar energy will be left after passing through 1 m. of pure water. ‘The water
of Seneca Lake, therefore, cuts off about 25 per cent more than does pure water and adds
one-half to the loss due to pure water. Pure water transmits through the 1 to 2 m.
stratum nearly 80 per cent of the energy reaching its upper level and over 90 per cent
passes through all deeper 1 m. strata, the loss per meter rapidly declining to a minimum
of about 2 per cent of the energy incident on the upper surface of the stratum. At
5 m., therefore, there would remain about 29 per cent of the original energy of the sun
and about 23.4 per cent at 10 m. instead of 5.4 per cent and 1 per cent found in Seneca
Lake. This wide difference between pure water and the lake water is probably due
chiefly to matter suspended in the water of Seneca Lake, since there is very little stain
present in the water. The suspended matter is partly organic but chiefly fine silt
derived from the soft shales that constitute much of the shores.

In pure water the transmission through the 1 to 2 m. stratum is much smaller than
in those below. This is due to the rapid absorption of the rays of the red end of the
spectrum as compared with the slow absorption of the shorter waves. No such effect
seems to be present in the lake, nor is it ordinarily demonstrable in lakes. Sometimes,
but not commonly, the deeper strata of a lake show a transmission 1 or 2 per cent higher
than the 1 to 2 m. stratum, but in general the transmission in that stratum is nearly
the same as in those immediately below. This means that the large nonselective ab-

226 BULLETIN OF THE BUREAU OF FISHERIES.

sorption due to turbidity and the selective absorption due to stain obscure the selective
absorption of the water, as water, after the first meter has been passed. In that meter
of water is absorbed practically all of the energy contained in that part of the spectrum

Per cent 6 10 16 20 25 30

Fic. 2.—Curves of transmission of sun’s radiation, Seneca Lake; Aug. 1, 1918. The vertical axis gives depth and the horizontal
axis gives per cent of the total radiation of thesun. A-A, direct observations; B-B, verticalsun; C-C,meansun. Thesun’s
rays passed through a thickness of roo cm. water of the lake at the depth of 94cm. Dotsare placed corresponding to this depth
on the curve A-A, and from these is plotted the curve B-B, for thesun in the zenith when depth and stratum traversed by
rays are equal. The rays pass through a mean distance of 115 cm. during the warming season in reaching a depth of roo cm.
‘These points are marked on the curve B-B, and from them is plotted the curve C-C or the curve of meansun. (See Table
12, p. 228.)

lying below the A line which is commonly taken as the lower limit of the visible spec-
trum.

The general result of these observations is, therefore, plain. Under the conditions
of the time and place 21 to 22 per cent of the sun’s energy delivered to the surface was

FINGER LAKES OF NEW YORK. 227

present at a depth of 1 m. In the deeper 1 m. strata there was a loss of 28to 29 per
cent of the energy present at the upper surface of the stratum. At 5 m. depth there
remained about 5.4 per cent, and at 10 m. about 1 per cent of the energy delivered to
the surface.

We may infer from such a set of observations the penetration of the sun’s rays
during the whole day or during a longer period, assuming that the turbidity and color of
the water remain unchanged. In such a process it is not hard to secure results which
are correct in general, but it is impossible to secure minute accuracy. Certain, though
not all, of the facts which prevent minute accuracy will be mentioned.

1. Sunlight is a mixture of the direct rays of the sun and of rays reflected from the
sky. The percentage of sky radiation is very variable, being sometimes as low as 8 per
cent of the total radiation and rising nearly to 100 per cent when the sun barely shines
through haze or cloud. The quantity of energy reflected from a unit area of sky is also
variable and differs with the nature of the sky and the proximity of the area to the sun.
The mean percentage of sky radiation reflected from the surface of the water differs
from that of the direct rays, and the mean path in water of the rays from the sky differs
from that of the direct rays. It is practically impossible, under the conditions of ob-
servations on lakes, to determine either the amount or the distribution of the sky radia-
tion. It is, therefore, impossible to make full correction for the elements in the mixture
of direct and diffuse rays at the time of observations.

2. It is also impossible to make such corrections for longer periods, since the aver-
age amount of sky radiation is still quite unknown for most places, and is not accurately
known anywhere.

3. No correction has been made in the observations for radiation reflected from the
surface of the water, but the readings at 1 m., etc., have been compared directly with the
reading in air. The direct sun radiation, at the altitude of the sun when the observa-
tions were made, would lose about 2.1 per cent by reflection. The sky radiation would
lose 17.3 per cent if equal quantities came from equal areas of sky. This loss at the
surface, which can not be known accurately, has been balanced against the opposite
effect of the hemispherical glass cover of the sunshine receiver. There would be about
4 per cent of the sun’s radiation reflected from this in air and about 0.5 per cent in water.

In computing a standard curve of absorption for Seneca Lake, all radiation has
been referred directly to the sun, and the path of the rays in the water has been computed
on that basis, from the following elements:

Time of observations, August 1, 1918, 12.40 to 1.11 sun time.

Corresponding altitude of sun, August 1, 64.1 to 62.3°.

Depth at which sun’s rays pass through 1 m. of water, at first observation, 94.5 cm; at last observa-
tion, 93.7 cm.; mean 94.1 cm.

On the curve of direct observations (A—A, fig. 2) are noted the readings at the dis-
tances corresponding to this path of the rays in water. These periods are plotted and
connected by a new curve, B-B, the curve for vertical sun. In this curve, which assumes
a sun in the zenith, the depth below the surface equals the length of path of the rays in
reaching that depth. This constitutes a standard curve, from which may be derived
the energy which remains at given depths below the surface at any time of the day or
year, provided the altitude of the sun is known and the corresponding length of the
path of its rays in water. It must be assumed also that all radiation comes directly

228 BULLETIN OF THE BUREAU OF FISHERIES.

from the sun, or at least that the value of the sky radiation is the same as at the time
of observation.

The results are stated in Table 12, vertical sun.

The mean distribution of sunshine and cloud at Seneca Lake is not known, but at
Madison, Wis., the mean daily supply from sun and sky during the five months April
1 to August 31 is 398 cal. The mean path of the rays during this period to reach a depth
of 100 cm. below the surface is 115 cm. In this computation allowance is made for
reflection from the surface in excess of 2.1 per cent; all radiation is supposed to come
from the sun; and the form—though not the area—of the solar energy curve is supposed
to be constant.

The points corresponding to this distance of 115 cm. per 100 cm. of depth are noted
on the curve for vertical sun, carried up to their proper place, and a third curve, C—C,
figure 2, is drawn, which is the curve for mean sun (Table 12).

TABLE 12.—TRANSMISSION OF SUN’S Rays BY WATER OF SENECA LAKE, AUG. 1, 1918. (See fig. 2, p. 226.)

Per cent radiation remaining Per cent radiation remaining
at depth indicated. at depth indicated.
Depth in centimeters. Computed per cent. Depth in centimeters. Computed per cent.
Observed Observed
per cent. | Vertical Mean per cent. | Vertical | Mean
sun, sun, sun. sun.
21.4 21.9 20. 7 3.8 44 ek
15.0 15.6 14-3 zarh 3.2 2.3
10.9 Il. 5 9.9 1.8 iG 1.6
77 8.3 6.8 1.3 1.7 1.0
5:4 6.0 4.7 I, 1.0 1.2 7

This curve of mean sun and Table 12 show that in Seneca Lake at 1 m. depth there
is found an average of about 20.7 per cent of the incident radiation and that each 1 m.
stratum below transmits less than 70 per cent of the radiation received by its upper
surface. ‘The water has absorbed 99 per cent of the incident energy at about 9 m. as
compared with about 10 m. for the observed curve and 11 m. or more for the curve of
vertical sun.

The difference in the three curves are not striking in this case; but if the observa-
tions had been made at an hour farther from noon, or later in the season, the difference
would have been correspondingly larger.

It must not be supposed that this mean sun curve represents exactly the mean con-
ditions actually present during the period when the lake is warming. ‘The transparency
of the water is variable and the sun’s penetration varies with it. No account is taken
in this curve of the energy received during cloudy hours. Yet after all deductions are
made it remains true that the curve gives a generally correct picture of the actual direct
delivery of the sun’s radiation to Seneca Lake so far as a single observation can give
this. Hardly more than 20 per cent of the incident energy is delivered to water below
the surface meter. Not over 5 per cent is delivered to a greater depth than 5 m. and not
over 1 per cent below 10 m. Even a considerable increase in transparency would leave
these figures, not unchanged, but of the same order of magnitude.

Observations such as these are ordinarily made at times when the sky radiation is
relatively small—near noon of clear days. When, therefore, such an observation is

FINGER LAKES OF NEW YORK. 229

used as the basis of larger conclusions and when in computing the results all radiation
is assumed to be direct, the effect of the direct rays of the sun in warming the lake is
placed at a maximum. In the preceding paragraph all radiation is supposed to come
directly from the sun. In fact at Madison about 16 per cent of the total radiation

oO __Gen. 50 100 150 200 250 B_s00

Fic. 3.—Work curves of Seneca Lake, mean temperature. ‘The vertical axis shows depth; the horizontal axis shows gram centi-
meters of work per meter of depth and square centimeters of surface of lake. OCC, curve of direct work. About 145 g. cm.
of work, for instance, are necessary to carry the heat of the 9 to rom. stratum from the surface and put it in place. BDE,
curve of distributed work, derived from OCC, showing the amount of work donein each 1 m. stratum. The area OBEFO
(distributed work) is equal to the area OCCFO (direct work). ODD shows the contribution of the sun in distributing the
sun’s energy. The area ODDBO gives the contribution of the sun, and that of the wind is represented by the area ODEFO,

(See Table 16, p. 235.)
received April 1 to August 31 comes during cloudy hours, and about 16 per cent more
comes from the sky during sunny hours. The direct sun, therefore, supplies only about
two-thirds of the radiant energy received by the lake. It may be assumed that during
cloudy hours equal areas of sky supply equal amounts of energy to a surface normal to
the rays. On this basis, and allowing for reflection from water surface, the mean path of

230 BULLETIN OF THE BUREAU OF FISHERIES.

the diffuse radiation in reaching a depth of 100 cm. would be about 126 cm. as compared
with 115 cm. for the direct rays. The mean path for sky radiation during sunny hours
would be between the numbers given above, depending on the relative amount of the
sky radiation coming from areas close to the sun and, therefore, having approximately
the same length of path in the water as the sun’s rays have.

In the absence of knowledge of the amount of sky radiation at Seneca Lake, either
general or on the date of observation, no correction can be made for sky radiation.
Such correction can be made where observations are so numerous that it may safely be
assumed that sky radiation was the mean amount. ‘This is the case with Lake Mendota,
and the best computation that can be made shows that the mean path of all rays to reach
a depth of roo em. in the period of April 15 to August 15 is about 118 cm. No essential
difference, therefore, is made in the results if all radiation is attributed to the sun with
a mean path of 115 cm., as has been done in the previous paragraphs.

The observations on Canandaigua and Cayuga Lakes may be treated much more
briefly. ‘They were taken at the same intervals as on Seneca Lake but to the depth of
5 m., which is ample for the determination of the rate of absorption. The results are
shown in figures 4 and 5, and summarized in Tables 13 and 14.

TABLE 13.—TRANSMISSION OF RapIATION BY WATER OF CayUGA LAKE, SHELDRAKE POINT, JULY 29,
1918, 1.45 TO 2.45 P. M., GOVERNMENT TIME. (See fig. 4.)

[Nove.—Sky with cumulus clouds drifting across; clear between clouds. Transparency of water 6.2m. Transmission per
meter about 66 per cent.]

Per cent radiation remaining at depth | Per cent radiation remaining at depth
indicated. | indicated.
|
Depth in centi- Depth incenti- |
naoterct = Computed per cent. Tete | 2 Computed per cent.
Observed) |, Sa a i aa | | Observed) 95, Bete
r cent. |° Smee . | per cent. observe E
Pe per cent.| Vertical Mean per cent.| Vertical | Mean
sun. sun. | sun. sun.
|
6
Ig-2 | 19- 19. - .
Me eNO ABOMUED otstpnod { aay 9:4 9:9 17-9 BOO. aciniscisteleecedpi leet nel { a \ 55 6.1 49
13-4 \| 3-6
ease cAosune st.cobae II-3 12.8 13-3 11-9 3°4
II-4 Reskaecesnee sriognacr 36 3-6 4r ger
8.1 8.4 9-1 7-6 35
Nein ren ees 5

Fic. 4.—Work curves for Cayuga Lake. (See explanation, fig. 3.)

The observations on Cayuga Lake are rendered somewhat irregular by the fact
that numerous white cumulus clouds were passing over the sky and work had to be
done when the sun was in the spaces between the clouds. Under these conditions the

FINGER LAKES OF NEW YORK. 231

radiation from the sun is sure to be variable; the approach to the sun of a white cloud
momentarily raises the radiation and unnoticed wisps of cloud may reduce it. In
the series it is clear that the mean of the readings at 200 cm. is too low as compared
with all of the others, since the transmission in the 1 to 2 m. stratum should be about
the same as below. The value of 12.8 per cent has been assumed, therefore, for the 200
em. level and a mean transmission of about 66 per cent per meter. Under these condi-
tions about 99 per cent of the sun’s energy would be delivered to the upper 8 m. of
water, somewhat more than 80 per cent going to the first meter, or with mean sun about
82 per cent.

Tt will be noted that corresponding with the smaller transparency of the water, as
compared with Seneca Lake, the transmission of radiation is decidedly lower.

TABLE 14.—TRANSMISSION OF SUN’S ENERGY BY WATER OF CANANDAIGUA LAKE, JULY 27, 1918, 11.37
A. M. TO 12.03 P. M., GOVERNMENT TIME. (See fig. 5.)

[Notr.—Sky hazy. Transparency of water 4.4m. ‘Transmission per meter about 60 per cent.]

Per cent radiation remaining Per cent radiation remaining
at depth indicated. at depth indicated.
Depth in centimeters. | Computed per cent. Depth in centimeters. Computed per cent.
Observed |_—_—_—_— = Observed
per cent. | Vertical Mean percent. | Vertical | Mean
sun, sun. sun, sun.

Fic. 5.—Work curves for Canandaigua Lake. (See explanation, fig. 3.)

The observations on Canandaigua Lake were also somewhat irregular, not on
account of clouds, but haze. The sky was cloudless, but the hills a few miles up the
lake were nearly invisible in the haze which filled the valley. Under such conditions
the value of the sun’s radiation is much reduced, and it was found to be about 0.95
cal./em.?/min. as compared with 1.30 cal. in the case of the two other lakes. The read-
ings of the sun at the beginning and end of the observations in the lake were in close
agreement. The readings of the first series taken in the water—those taken while
the receiver was going down—were also in close agreement and indicate that 18 to
19 per cent of the radiation in air was present at 100 cm. depth and that each meter
below that depth transmitted about 60 per cent of the radiation received by its upper

232 BULLETIN OF THE BUREAU OF FISHERIES.

surface. At 500 cm., however, the reading rose so that the transmission seemed to
rise to about 74 per cent. The second set of readings—those taken while the receiver
was being raised—again indicated about 60 per cent transmission but showed at all
depths a higher percentage of the radiation at the surface, amounting at 100 cm. to
21 per cent. Comparison with the other lakes shows that the lower value at 100 cm.
is to be chosen, as the transparency of the water is decidedly less than in either Cayuga
or Seneca Lakes. ‘The haze must have become slightly thinner during the later readings
in the water but thickened again before the second reading in the air. The accuracy
of the value at roo cm. must remain somewhat uncertain under the conditions of sky
then prevailing. Since the value of the radiation may alter during haze almost from
minute to minute with no visible indication of change, such as cloud offers, it would
need a very large number of readings to show whether 18 to 19 per cent or a slightly
lower figure should be taken as the value for mean sun at 100 cm. ‘The error is not
likely to exceed 1 per cent in any case, nor is it large enough to affect general relations
of sun to the distribution of heat.

Under these conditions 99 per cent of the sun’s energy would be delivered to the
upper 6.5 m. of water.

We may now put together the general results from the three lakes in which observa-
tions were made.

TABLE 15.—TRANSPARENCY AND TRANSMISSION OF RADIATION—VERTICAL SUN.

|
| Per cent

Trans- | Percent | ae
parency at 100 a a
in centi-

per

meters. | meters. | Santen

ae OO dos Hea gecenetitne TOE sEEOtOOocbEes daca Ud Deb shConruadan Jaapao cod dooude Jag Dare 6.8
Gavia Lake ii os dasctre cietne nee Meimateials Sohbuotiasesa cbSodoqaanen We fcieia Cae elnre wie Dateless 6.2 19.9
GanandaretiaIgalke vo grnine cs crscmavelnie nie eteta cinta enetaielelita ernie aleiviedalwialeleta ais lets jataiels plu isfateiidetetetajerdatalaiate Aa

In these cases there is some parallelism between the percentage of transmission
and the transparency of the lake. ‘This is due to the fact that all these lakes have water
which is only slightly stained and which does not differ greatly in color. In general
there may be little correlation between transparency and rate of transmission.

WORK OF THE SUN IN DISTRIBUTING HEAT.

From the data at hand it is possible to make a general estimate of the part which
the sun plays in distributing the heat gained by Seneca Lake as its summer heat income.
We have as data (a) the amount of heat so gained as the mean of four seasons; (0) the
amount and the distribution of the work necessary to carry this heat through the lake,
assuming that all work is done by the wind; (c) the actual amount of heat delivered
into the water of the lake directly by the sun on one date, and the conclusions drawn
from these observations in the preceding paragraphs. We lack as data (a) the total
amount of heat delivered to the lake during the period when the summer heat income
is gained; (6) the losses of heat during this period from different strata near the surface.

The absence of the data specified and others as well make it impossible to state
the réle of the sun with any approach to exactness. But it is possible to make esti-

FINGER LAKES OF NEW YORK. 233

mates which will show the general situation and in our almost complete ignorance of
the subject, such statements are not without value.

We take, therefore, as the summer heat income of Seneca Lake 34,000 cal./em.?
of surface. Of this sum, 32,400 cal. are found below 1 m.; 28,000 cal. below 5 m.;
and 21,900 cal. below 10 m. ‘These figures are based on the calories found per square
centimeter of the depth in question, and not those per square centimeter of the
surface. In computing the relative work of sun and wind these figures must be .
used, since the sun’s radiation which passes through the shallow water is absorbed by
the bottom of the lake.

The distribution of this heat, attributing all work to the wind, requires about
2,874 g. cm. of work per square centimeter of the lake’s surface. This work is distrib-
uted (fig. 3) at the rate of about 290 g. cm./em.’ of the surface at the surface; 270
g. cm./em.? at 1 m. depth; 202 g. em./em.? at 5 m.; and 125 g.cm./em.? at rom. In
the upper 5 m. there is done about 45 per cent of the total work; about 33 per cent
in the 5 to 10 m. stratum, both of which are within reach of the direct influence of the
sun; about 20 per cent more of the work comes in the 10 to 15 m. stratum.

Applying the experience gained from observations on Lake Mendota, it may fairly
be assumed that Seneca Lake receives about 65,000 cal./em.” of surface during the
period of the summer heat income. The lake loses, therefore, about one-half of the
incident heat.

If we apply the mean sun data of Table 12 to this gross income, the sun delivers
during this period about 13,400 cal. to the depth of 1 m.; 3,000 to 5 m.; and 450 to
10 m. ‘These numbers are, respectively, 41 per cent, 11 per cent, and 1.9 per cent of
the quantity of heat which passes through these levels. (See Table 7 for quantity of
heat.)

The work attributed to the wind at these depths would be diminished by the aid
of the sun in the same ratio that the heat delivered by the sun bears to the total amount
of heat passing through those levels. Computed on this basis, the sun does all of the
work of distributing heat at the surface, 41 per cent at 1 m. depth, 11 per cent at 5 m.,
etc. These quantities may be plotted as on figure 3 (p. 229) and the points connected
by acurve. Then the area ODBO is proportional to the total work done by the sun
under the conditions assumed. This area may be measured with a planimeter. It is
equal to about 16 per cent of the area representing the total work. The part of it
below 1 m. is about 10.9 per cent of the work done below 1 m. of depth.

This represents the maximum possible aid which, under the conditions assumed, -
the sun can give in the distribution of heat, for it assumes that the entire loss of inci-
dent radiation by the lake, amounting to one-half of that received, falls on the wind-
placed heat and that no loss falls on the sun-placed heat. ‘This assumption is evidently
not correct. If, instead, we assume that the sun-placed heat suffers equal losses with
that distributed by the wind, the aid of the sun will be reduced to about 8 per cent
of the total work done and to about 5.5 per cent of the work done below 1 m.

Probably the assumption of equal losses is unfair to the sun. A great part of the
lost heat is in that which is absorbed by the thin stratum at the surface and is used in
evaporation, lost to the air at once or during the following night, etc. Almost all of
the heat in the longer waves of the spectrum is absorbed by a much thinner layer of

234 BULLETIN OF THE BUREAU OF FISHERIES.

water than 1m. Schmidt (1908, p. 240) computes that about 27 per cent of the solar
energy is absorbed by 1 cm. of pure water and about 45 per cent by 1 dm. He uses
Langley’s energy curve for the solar spectrum, which makes his figures somewhat
larger than would be the case in a curve for moderately high sun. In the curve which
we have used as standard (path of rays equals 1.5 atmospheres) about 43 per cent of
the energy would be absorbed by 25 cm. of pure water and 49 percent by 50cm. While
no great accuracy can be claimed for the figures shown by Seneca Lake of about 67 per
cent absorption for 25 cm. and 72 per cent for 50 cm., they are probably not greatly
in error. ‘The differences between them and the data for pure water are much the
same as for greater depths. Thus more than one-half of the sun’s energy is delivered
to the upper centimeters of water from which loss to the air is easy. But much of the
heat so delivered is distributed by the wind from the surface strata to deeper water,
especially in the early part of the warming season when the lake is gaining heat rapidly.
From this source comes the greater part of the heat which the lake gains below 1 m.
in excess of that delivered by the sun. This heat,amounts to 19,000 cal./em.? and much
of it must come from the 40,000 cal./em.’, or more, absorbed by the upper 25 cm. of
the lake. During bright and windy days there must be thus moved down into the
lake by the wind much heat which is lost during cool periods when the whole upper
water of the lake cools down.

It is true that on the whole the heat delivered by the sun to strata below the surface
is more likely to be retained, as the water above a stratum must be cooled to a lower
temperature than the deeper water before any heat can be lost by the latter. But
several times each season there is a general cooling of the upper water, when much
heat is lost, that placed by the sun as well as that placed by wind.

At present, therefore, no accurate estimate can be made of the loss of sun-placed
heat at various depths. The subject must be left here with the general statement
that between 84 and 92 per cent of the work done in distributing heat through the water
of Seneca Lake is performed by the wind, on the assumption that conditions of trans-
parency, etc., on August 1 were average ones. The amount really attributable to the
sun is probably as much as 10 to 12 per cent. More than this can not be said, both in
view of considerations presented above, and also in view of one other consideration
which the study of Lake Mendota has shown. In the early part of the warming period,
when gains of heat are rapid and when the deeper water is securing most of its heat, |
the sun plays a small part in distributing the heat. Later in the summer the sun has
a much larger share of the work, when the epilimnion is forming, when gains of heat
are small (perhaps only 5 to 10 per cent of the incident radiation), and when these
gains are confined to the surface strata.

The foregoing paragraphs have dealt with Seneca Lake alone. The same methods
may be applied to the other lakes with similar results. It is unnecessary to give the
details of the computations; the results are shown in Table 16 (p. 235) and figures 4
and 5 (pp. 230, 231).

FINGER LAKES OF NEW YORK. 235

TABLE 16.—DIVISION OF DISTRIBUTION OF SUMMER HEAT INCOME BETWEEN SUN AND WIND IN THE
LAKES AS A WHOLE AND IN THEIR SEVERAL STRATA. (See figs. 3, 4, 5, and text.)

[Notr.—In this table, as elsewhere in this paper, ‘‘ work"’ means the total work which would be needed to distribute the heat
from the surface of the lake through the adjacent water, computed on the assumption that all heat is put into place by the
wind mixing the warmer surface water with the cooler water below. In the division of the task of distributing heat between
sun and wind it is also assumed that all losses of heat fallon wind-placed heat. This evidently attributes too large a share
is the sun. Probably a fair estimate would be to allow to the sun all that it does below 1 m., i. e., about 10 to 11 per cent
of the total.]

Canandaigua Lake. Cayuga Lake. Seneca Lake.

Sun. | Wind. Sun. Wind. Sun. Wind.

|

Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | Per cent.

Bote LOR lees se ease sree nine wna Sd aa Ste ee tore alctattciatar seta eh 16.9 83.1 15.0 85.0 15.8 84.2
Work, otosm om 31.6 68. 4 aaa 66.9 32.0 68.0
Work, 5 to1om. Ate 2.9 97.1 4.6 | 95-4 6.6 93-4
Mifery Sten devi ts 1 ep aei Reem Oates ier loan Aon omrn Dey AM OUe IDO OoT Cee 62.3 37-7 60, 8 | 39. 2 58.3 51.7
Works Below ese eae CAL eh aren wot catetneceletelsinietniete'= els as 10. 5 | 89. 5 10. 0 | 90. 0 rein wih 88.9
RV Orie lo weer aceon cain or ainnhae Roche eainertel acts we 1.7 98.3 2.4 | 97.6 3.3 | 96.7
PPotaliwork of Slit and witld. 2 ..cckn cena oe Meme ee ees | 1,929 g. cm. | 2,446 g. cm. 2,874 g. cm.
PLANKTON.

The fresh-water organisms which constitute what is known as the plankton may be
separated into two groups, namely, (a) those forms which are large enough to be captured
readily with a regular plankton net whose straining surface is made of bolting cloth,
size No. 20 (new No. 25) and (6) those forms which areso small that they readily pass
through the meshes of this bolting cloth. The former constitutes the net plankton and
the latter may be called the nannoplankton. The latter term has been applied specifi-
cally to those organisms whose maximum diameter does not exceed 25 »; but it is pro-
posed to extend the meaning of this term to include all of the material that passes through
the meshes of the net. ‘The terms “macroplankton’”’ and “ microplankton”’ have been
used to designate these two groups.

METHODS.

The net plankton was obtained by means of a closing net which has been fully
described in a previous paper so that it is not necessary to consider it further here (Juday,
1916). The coefficient of this net is 1.2; that is, about 80 per cent of the column of water
through which it is drawn is strained. The catches from the different strata were
concentrated in the plankton bucket; the material was then transferred to 8-dram_ vials
and preserved in alcohol. In the enumeration the volume of the catch was reduced to
10 cm.’; after shaking thoroughly 2 cm.* were removed with a piston pipette and the
crustacea and rotifers contained therein were counted with a binocular microscope.
The number thus obtained multiplied by the factor five represents the total of such
organisms in the catch. When only a few of the larger crustacea were present, the total
number was ascertained by direct count. ‘The smaller organisms, such as the Protozoa
and alge, were enumerated by placing 1 cm.’ of the material in a Sedgwick-Rafter cell
and ascertaining the number of the various forms in the usual manner by means of a
compound microscope.

Samples of water for a study of the nannoplankton were obtained by means of a
water bottle. The minute organisms were secured from these sarfiples by means of an
electric centrifuge having a speed of 3,600 revolutions per minute when carrying two

236 BULLETIN OF THE BUREAU OF FISHERIES.

15 cm.’ tubes of water. The sedimentation was usually completed in about six minutes.
The material was then transferred to a counting cell with a long pipette and the organ-
isms were enumerated with a compound microscope having a 16 mm. objective and a
No. 8 ocular. Many of these organisms, more especially the minute flagellates, are de-
stroyed by the various preserving agents, so that it is necessary to have the living material
for these enumerations; such counts must be made, therefore, as soon as possible after
the samples of water are obtained.

The results obtained in the various enumerations are shown in Tables 17, 18, and 21.
The figures indicate the number of individuals per cubic meter of water at the different
depths. For purposes of comparison the results obtained for net plankton on Canandai-
gua, Cayuga, and Seneca Lakes in 1910 are shown in Table 18. Observations were made
on the net plankton and nannoplankton of Green Lake, Wis., in 1918, soon after these
were made on the Finger Lakes, and these have been included in Tables 17 and 21 for
comparative purposes also.

NET PLANKTON.

Phytoplankton.—Table 17 shows that the green and blue-green algz were scarce in
the three Finger Lakes at the time of the observations in 1918. Only three forms were
present, namely, Anabaena, Microcystis, and Staurastrum. In Canandaigua Lake a
relatively small number of colonies of Microcystis was found in the upper 10 m. and
Staurastrum was noted in the 10 to 4o m. stratum. In Cayuga Lake Anabaena was
obtained in the upper 5 m. and Microcystis in the upper 10m. In Seneca Lake this group
was represented only by a few colonies of Microcystis in the 10 to 15 m. stratum. A
comparison with Table 18 shows that fewer forms were present in 1918 than in 1910 and
also that the number of individuals was much smaller in the former year. The two
sets of catches on Canandaigua Lake present the most marked difference in this respect.

The net catches from Green Lake, Wis., contained a much larger algal population
than the Finger Lakes, owing to the presence of a large number of filaments of Oscil-
latoria. ‘This form was unusually well represented in the upper 15 m., a maximum of
nearly two million filaments ver cubic meter of water being found in the o to 5 m.
stratum. :

In the Finger Lakes the most abundant diatom, both in 1910 and 1918, was Aster-
ionella, while Fragilaria was second in importance both years. In Canandaigua Lake
the diatom population was substantially the same in these two years, while in Cayuga
Lake the number was much larger in the former year. In Seneca Lake, on the other
hand, the number was larger in 1918 than in 1910.

In Green Lake Asterionella was the only diatom noted, a few individuals of this
form being present in two catches.

Zooplankton.—Uroglena was fairly abundant in the upper 30 m. of Canandaigua
Lake and a few colonies of Epistylis were noted in the 5 to 10 m. stratum. In 1910
Ceratium was the most abundant protozoan in this lake; but it was not found in 1918.

In Cayuga Lake Actinosphaerium and Ceratium were about equally numerous in
1918, both being most abundant in the upper 15 m. ‘The former was not found in 1910.
and the latter was much more abundant in this year than in 1918, the number reaching
more than a million and a half per cubic meter in the o to 5 m. stratum. Dinobryon
was not as abundant in 1918 as in 1910 and Mallomonas was not noted in the former
year.

FINGER LAKES OF NEW YORK. 237

In Seneca Lake Ceratium and Dinobryon constituted the protozoan population.
A relatively small number of the latter was noted in the 5 to 10m. stratum. Ceratium
was distributed through the upper 20 m. but was most abundant in the upper 5 m.

The rotifer population was largest in Cayuga Lake and smallest in Canandaigua
Lake in 1918. In the latter lake rotifers were most numerous in the upper 10 m. while
in Cayuga and Seneca Lakes the largest number was found in the upper 15 m.

The maximum number of individuals in the rotifer group was noted for Synchaeta
in Cayuga Lake, where it reached 44,700 per cubic meter of water in the ro to 15 m.
stratum; the average number in the upper 15 m. was 35,950 individuals. ‘This form
was not found in the other two lakes.

Polyarthra was noted in the catches from each of the three lakes in 1918, but it
was most numerous in Cayuga Lake, reaching a maximum of 21,000 individuals per
cubic meter in the 5 to 10 m. stratum. ‘The maximum number in this lake in 1910
was a little more than ten times as large as this. :

Conochilus was also found in the catches from each of the three lakes, but it, too,
was most abundant in Cayuga Lake, reaching a maximum of 33,750 per cubic meter
in the o to 5 m. stratum.

A few individuals of Anuraea cochlearis were found in the upper water of Canan-
daigua and Seneca Lakes, but this form also was distinctly more numerous in Cayuga
Lake. The catches from Canandaigua Lake contained a few specimens of Notholca
longispina, and the material from Cayuga Lake showed the presence of a few individ-
uals of Asplanchna and Ploesoma in the upper water.

The rotifer population of Canandaigua Lake was substantially the same in 1918
as in 1910. (See Tables 17 and 18.) In Cayuga Lake Polyarthra was not nearly as
abundant in 1918 as in 1910, but the other forms were more numerous, in general, in
the former year. In Seneca Lake not so many forms were represented in 1918 as in
1910, but those that were present were more numerous, so that the total rotifer popu-
lation was somewhat greater in the former year.

In Green Lake the rotifers were more abundant than in Canandaigua Lake, but
they were not as numerous as in Cayuga Lake; the number in the upper 20 m. was
substantially the same as that of this stratum in Seneca Lake.

Copepod nauplii were most abundant in the upper 20 m. or 30 m. of each lake,
but they were present in the lower strata also. A larger number was found in Seneca
Lake than in the other two lakes and the number in Seneca Lake was larger in 1918 than
in 1910. In the other two lakes they were more numerous in the latter than in the
former year. They were more abundant in Green Lake than in any of the Finger Lakes.

Three genera of copepods were represented in the net catches from each of the
three Finger Lakes, namely, Cyclops, Diaptomus, and Limnocalanus; while a fourth,
Epischura, appeared in the 5 to 10 m. stratum of Canandaigua Lake. By far the greater
portion of the copepod population consisted of Cyclops and Diaptomus, the former
being numerically greater than the latter in each of the lakes. Both of these forms
were more abundant in Seneca Lake than in either of the other Finger Lakes. In the
former the maximum number of Cyclops was 25,100 per cubic meter in the o to 5 m.
stratum, with an average number of 21,460 in the upper 15 m. The maximum number
of Diaptomus was 9,810 per cubic meter in the 15 to 20 m. stratum of Seneca Lake.
Limnocalanus was present in the catches from each of the three Finger Lakes, but was
confined to the deeper water.

75412°—22——16

238 BULLETIN OF THE BUREAU OF FISHERIES.

In Canandaigua Lake the Copepoda were more numerous in 1910 than in 1918,
but the reverse was true of the other two lakes.

The number of Diaptomus was larger in the upper strata of Green Lake than in
any of the Finger Lakes, but Cyclops reached a larger number than in Seneca Lake
only in the o to 5 m. stratum.

The Cladocera consisted of representatives of Sida, Diaphanosoma, Daphnia,
Ceriodaphnia, and Bosmina. Bosmina was the most abundant form, and it was present
in the water of Cayuga and Seneca Lakes in much larger numbers than in Canandaigua
Lake. The maximum number obtained was 19,100 per cubic meter of water in the
10 to 15 m. stratum of Seneca Lake. The average number in the upper 15 m. of Cayuga
and Seneca Lakes was 12,770 and 11,200 individuals per cubic meter, respectively.

Ceriodaphnia was found only in the 5 to ro m. stratum of Cayuga Lake and Sida
only in the o to 5 m. stratum of this lake. Diaphanosoma was noted only in the o to 5
m. stratum of Canandaigua Lake.

Daphnia retrocurva was obtained from the upper 30 m. of Canandaigua Lake, and
a few young of this species were present in the 5 to 15 m. stratum of Cayuga Lake and
in the 10 to 15 m. stratum of Seneca Lake.

In Canandaigua and Cayuga Lakes Cladocera were more abundant in 1910 than
in 1918, while the reverse was true of Seneca Lake.

The Cladocera were more numerous in Green Lake than in Canandaigua Lake, but
they did not reach as large a number as in Cayuga and Seneca Lakes.

The numerical data serve to give a reasonably accurate notion of the plankton popu-
lation of these lakes, but such data alone do not give an adequate idea of the relative
value of the various forms as a source of food for other organisms. When they are
combined with data relating to the weights of the different organisms their value is
very greatly enhanced. By means of small platinum crucibles and a sensitive assayer’s
balance the weights of the more important crustacean constituents of the plankton
were obtained and the results of such determinations are shown in Table 19. Such
data have also been secured for various constituents of the plankton of Wisconsin lakes
and where such results were not obtained for some of the forms from the Finger Lakes,
those from the former lakes have been used in computing the data shown in Table 20.
The dry weight was obtained for all of the material and the wet weight as well for
a few of the forms; after taking the dry weight the material was ignited in an electric
furnace for the purpose of ascertaining the percentages of organic and inorganic matter.

In computing the data for crustacea in Table 20 the number of crustacea per cubic
meter of water in astratum was multiplied by the volume of that stratum and the total
for the lake was ascertained by adding the numbers in the various strata. This total
multiplied by the weight of the particular organism under consideration gave the
amount of such material in the entire lake; this quantity divided by the surface area
of the lake gave the weight per unit area, which is expressed in the table in kilograms
and pounds per square kilometer and acre, respectively.

The amount of material per unit of surface is larger in the deep water than in the
shallow water, but the sides of these lakes have such steep slopes that the results would
not be altered very materially by taking this fact into consideration. Also it must
be borne in mind that these figures are based upon a single set of catches in each lake

FINGER LAKES OF NEW YORK. 239

and that a more extended series of observations might have yielded somewhat different
results. The data in hand, however, are sufficient for a fairly good estimate. No
organisms were weighed in 1910, but for purposes of comparison the data obtained in
1918 have been applied to the numerical results of the former year.

In 1910 Canandaigua Lake possessed the largest amount of crustacean material,
having about 2,579 kg./km.? of surface, while Seneca Lake was second with slightly
more than three-quarters of this amount. Cayuga Lake, however, was less than 10 per
cent below Seneca Lake. The greater portion of the material consisted of copepods
in Canandaigua and Seneca Lakes; in the former they comprised about 67 per cent of
the total amount of crustacean material and in the latter about 79 per cent.

In Cayuga Lake, however, about 72 per cent of the material consisted of the clado-
ceran Bosmina. Of the cladoceran material in Canandaigua Lake in 1910, Daphnia
retrocurva furnished about 30 times as much as Bosmina and about 4 times as much as
Diaphanosoma. Bosmina was the only representative of this group that was obtained
from the other two Finger Lakes in 1910. Among the copepods Diaptomus was the
most important form in this year and Cyclops ranked second.

In 1918 Canandaigua Lake possessed only about a third as much crustacean material
as in 1910 and Cayuga Lake only about four-fifths as much. Seneca Lake, on the other
hand, showed a much larger amount in the former year, the amount exceeding that of
the latter year by about 62 per cent. Thus Seneca Lake in 1918 had almost four times
as much crustacean material as Canandaigua Lake and more than twice as much as
Cayuga Lake. Daphnia retrocurva was again the chief cladoceran element in Canan-
daigua Lake, but it was greatly exceeded by Bosmina in the other two lakes. Diaptomus
furnished the largest amount of crustacean material in Canandaigua and Cayuga Lakes,
but Cyclops was the chief constituent in Seneca Lake.

Green Lake, Wis., possessed a larger amount of crustacean material in 1918 than
was found in the three Finger Lakes either in 1918 or in 1910. It was almost 10 per
cent greater than that of Seneca Lake in 1918, which was the maximum for the three
Finger Lakes. The copepods formed a much larger proportion of the material in Green
Lake than in the Finger Lakes, because the Cladocera constituted a little less than 3
per cent of the total in this lake. Nearly two-thirds of the entire amount of crustacean
material in Green Lake was furnished by Diaptomus.

Table 19 shows that the ash constitutes from 13 to 19 per cent of the dry weight
of the crustacea of the Finger Lakes. In addition, also, it has been found that plankton
crustacea contain from 4 to 9 per cent of chitin, which has no food value. In round
numbers, then, it may be said that about 20 per cent of the dry weight of the plankton
crustacea from the Finger Lakes consists of ash and chitin, while about 80 per cent
may be regarded as actual food material. In the living state from 85 to 90 per cent
of the mass of these organisms consists of water, so that the live weight would be ap-
proximately 1o times as large as the figures given in the dry weight column of Table
20, page 248.

In the crustacea from Green Lake the ash was much smaller, averaging somewhat
less than 6 per cent; adding to this about 6 per cent for chitin leaves about 88 per cent
of food material. The latter figure is higher than that for the Finger Lakes, which
is due to the higher percentage of ash in the material from these lakes.

240 BULLETIN OF THE BUREAU OF FISHERIES.

No determinations of the weight of the rotifers were made for the Finger Lakes,
but such results have been obtained for three species from Wisconsin lakes, namely,
Asplanchna brightwellii, Brachionus pala, and Conochilus volvox. The weight of these
forms has been used as a basis for estimating the weight of the various rotifers in the
plankton catches from the three Finger Lakes, N. Y., and from Green Lake, Wis. ‘The
computations are based on the relative volumes of the different forms, so that they
are to be regarded as estimates and not the results of actual weighings. These estimates
are shown in Table 20.

Cayuga Lake had the largest amount of rotifer material both in 1910 and in 1918,
with 111 kg./km.? (1 pound per acre) in the former year and 145 kg. (1.3 pounds)
in the latter year. It had 4% times as much as Seneca Lake in 1910 and about 3%
times as much in 1918; it had 12 times as much as Canandaigua Lake in 1910 and
about 52 times as much in 1918. Green Lake had just half as much rotifer material
as Cayuga Lake in 1918.

In the rotifers that have been weighed the ash averaged about 7.4 per cent of the
dry weight, ranging from a minimum of a little less than 6 per cent to a maximum
of a little more than 9 per cent. Thus between 90 and 95 per cent of the dry weight
of these rotifers may be regarded as organic matter, but what proportion of this is
indigestible has not been determined. Also it has been found that from go to 94 per
cent of the living rotifer consists of water, so that the weight of the live organisms
would be somewhat more than 10 times as large as the figures given in the table. .

The relative importance of the crustacea and the rotifers as sources of organic
matter which will serve as food for other organisms is shown in Table 20. In Canan-
daigua Lake, which had a very small rotifer population, the ratio of the organic matter
in the rotifers to that in the crustacea was 1:256 in 1910 and 1:292 in 1918. Owing to
the very much larger rotifer population in Cayuga Lake the ratio there was 1:13 in
1910 and about 1:9 in 1918. In Seneca Lake these ratios were about 1:70 each year.
In Green Lake the crustacea contributed about 49 times as much dry organic matter
as the rotifers in 1918.

The dry weight of the crustacea and rotifers combined amounted to 2,588 kg./km.?
(23 pounds per acre) in Canandaigua Lake in 1910; this was the maximum quantity
found in the three Finger Lakes in that year. The minimum amount was noted for
Cayuga Lake, namely, 1,945 kg. (17.3 pounds). (See Table 20, p. 248.)

In 1918 the maximum for these two groups of organisms was found in Seneca Lake
and it amounted to 3,267 kg. of dry matter per square kilometer (29.1 pounds per
acre). Canandaigua Lake possessed the minimum amount for this year, namely, about
852 kg. (7.6 pounds). ‘This was only about one-third as much as this lake yielded
in 1910.

In Green Lake these two groups of plankton animals yielded about 3,458 kg. of
dry matter per square kilometer of surface (31.6 pounds per acre) which was about
10 per cent larger than the amount in Seneca Lake in 1918.

No attempt was made to determine the weight of the alge in the net plankton,
but as the catches appeared under the microscope by far the greater portion of the mate-
rial consisted of rotifers and crustacea, probably three-quarters of it or more. Adding
25 or even 50 per cent to the above figures would still leave a relatively small amount

FINGER LAKES OF NEW YORK. 241

of material per unit of surface. In general, these lakes may be regarded as poor in net
plankton, the usual characteristic of lakes as large and as deep as these. :

The figures given in the various tables represent the amount of material that is
present on a particular date—that is, the standing crop at that time—but they do not
indicate the quantity of such material that is produced annually. Production and
destruction are processes which continue throughout the year, so that it is a very difficult
problem to ascertain just how much net plankton is produced annually by a lake.

NANNOPLANKTON.

The nannoplankton includes the various forms of plants and animals which are so
small that they readily pass through the meshes of the bolting-cloth strainer in the plank-
ton net and are lost. These small organisms are easily obtained with a centrifuge.
The results obtained in these enumerations on the three Finger Lakes of New York
and on Green Lake, Wis., are shown in Table 21.

The Protozoa were represented by rhizopods, flagellates, and ciliates. ‘The rhizo-
pods consisted of Amoeba and some other forms which were not definitely identified.
A minute Monas-like form was the most numerous flagellate found, while Cryptomonas
was present in considerable numbers in Canandaigua and Seneca Lakes. A disk-shaped
flagellate was noted in the upper strata of Cayuga and Green Lakes. Synura was also
present in the surface stratum of Canandaigua Lake.

The only representative of the ciliates was Halteria. It appeared in the upper
strata of Canandaigua and Cayuga Lakes.

The green and blue-green algz consisted of Scenedesmus, Oocystis, and Aphanocapsa.
A colonial form composed of very minute cells, 25 to 100 or more, embedded in a gelat-
inous matrix, has been referred to the genus Aphanocapsa. It appears to be widely
distributed, geographically, since it has been found in all of the Wisconsin lakes from
which nannoplankton has been obtained, and also in the three Finger Lakes. This alga
has usually been fairly evenly distributed throughout the entire depth of the various
lakes. This phytoplankton and the monads constitute the most common elements,
numerically, of the nannoplankton.

The water bacteria belong to this group of plankton organisms, but they were not
taken into consideration in these investigations.

No attempt was made to determine the amount of nannoplankton by weight, but
some results that have been obtained on Lake Mendota, Wis., will serve as a basis for
making a rough estimate for the Finger Lakes. The studies on Lake Mendota covered
a period of more than two years and they consisted of both gravimetric and numerical
determinations. The dry organic matter of the nannoplankton varied from a mini-
mum of approximately 0.8 gr. to a maximum of 3.1 gr. per cubic meter of water. ‘The
numerical determinations which correspond most closely to those of the Finger Lakes
average about 1.0 gr. of dry organic matter per cubic meter of water, so that ikis figure
may be taken as a basis for estimating the amount of nannoplankton material in the
latter. The results of this estimation are shown in Table 22, and also the results for
total plankton. In the latter it has been assumed that the crustacea and rotifers
furnished 75 per cent of the organic matter of the net plankton. Green Lake has not

242 BULLETIN OF THE BUREAU OF FISHERIES.

been included in this table because its net plankton contained a larger percentage of
vegetable material.

These computations seem to indicate that the nannoplankton of Seneca Lake
contained somewhat more than 214 times as much dry organic matter as the net
plankton, while in Canandaigua Lake the former was more than 4 times as great as
the latter. These differences are of the same magnitude as those that have been
obtained on Lake Mendota in midsummer. On an average, also, it may be considered
that this material weighs at least ro times as much in the living state, since most of
these organisms, when alive, are made up of 90 per cent or more of water.

The results shown in this table represent only a single phase of the annual cycle,
and hence they do not give any indication of the yearly production of such material.

. This latter question involves the actual turnover in stock each year and includes the
various relations of the organisms to each other and to their environment; the chief
phases of this question are the rate of reproduction of the various forms at different
seasons of the year, and the relations of the consumers and their foods. The whole
problem is very complex and would require an extended investigation for an adequate
solution.

These quantities of dry organic matter in the total plankton of the Finger Lakes
are very much smaller than those that have been obtained for Lake Mendota, Wis., in
midsummer. In this latter lake the average amount for the month of July in 1915
and in 1916 was 40,630 kg./km.? of surface (362.4 pounds per acre) in that portion of
the lake having a depth of 20 m. or more; the average for August of these same years
was 31,560 kg. (281.5 pounds). The average for Lake Mendota in July is more than
three times the amount shown in this table for Seneca Lake and more than eight times
that for Canandaigua Lake.

Comparisons have been made between the productivity of the land and of the
water, but such comparisons have been based upon the production of beef on the one >
hand and of fish, or oysters, or other edible aquatic forms on the other hand. ‘These
materials are what may be termed the “finished products,’ and statistics relating to
them give no idea of the relative amounts of food required or available for their pro-
duction. ‘This is accounted for by the fact that data concerning the quantity of food
available, either directly or indirectly, for aquatic organisms have been for the most
part wholly lacking and at best only fragmentary in character.

The quantitative results given above for the plankton, however, enable one to
make direct comparisons with the land on material which is not an end product. The
grass produced by a pasture is probably the best land crop for such a comparison, be-
cause it is less subject to artificial conditions resulting from cultivation than the grain
crops. Henry (1898, p. 180) cites an experiment in which a pasture consisting of blue
grass and white clover yielded 165,827 kg. of dry organic matter per square kilometer
(1,477 pounds per acre) between May 1 and October 15. This quantity is just a little
more than four times the average amount of organic matter maintained by the deeper
water of Lake Mendota in July. In other words, a fourfold turnover in the stock of
plankton maintained by Lake Mendota during this month would have yielded as much
organic material annually as the pasture in the above experiment. During the vernal
and autumnal maxima of the plankton the difference is distinctly less than fourfold.
The roots were not included in this yield of grass and, taking them into consideration,

FINGER LAKES OF NEW YORK. 243

we may say that the average difference for the year would be substantially fourfold.
The differences are much greater in the Finger Lakes, ranging from about fourteenfold
in Seneca Lake to almost thirty-fivefold in Canandaigua lake. (See Table 22, p. 250.)

The dry organic matter of the grass was made up of about 25.4 per cent crude
protein, 4.7 per cent ether extract, while the remainder consisted of carbohydrates.
The plankton of Lake Mendota, however, was distinctly richer in nitrogenous material
and in fats; the average for the crude protein was 45.1 per cent of the dry organic
matter and for the ether extract 8 per cent.

Attention should also be called to the fact that the plankton does not represent
all of the food material that is produced by a lake; the bottom fauna and the large
aquatic plants growing in the shallower water make notable contributions to this mate-
rial. The quantity of plankton is not as large per unit of surface in the shallower water
as it is in the deeper water, but the larger bottom population in the former region tends
to counterbalance this deficiency when the question of the total production is con-

sidered.
PLANKTON TABLES.

Tables 17 and 18 show the vertical distribution of the various organisms consti-
tuting the net plankton, giving the number of individuals per cubic meter of water in
the different strata. The members grouped in the different columns are indicated as
follows:

CLADOCERA.—B=Bosmina, C=Ceriodaphnia, D=Daphnia, Di=Diaphanosoma, L—Leptodora,
P=Polyphemus.

Corrropa.—C=Cyclops, D=Diaptomus, E=Epischura, L=Limnocalanus.

NAUPLII.

RotiFERA.—A=Asplanchna, A.a.=Anuraea aculeata, A.c.=Anuraea cochlearis, C=Conochilus,
N=Notholea, P=Polyarthra, Pl=Ploesoma, R=Rattulus, S=Synchaeta, T=Triarthra.

Protozoa.—A=Actinosphaerium, C=Ceratium, D=Dinobryon, E=Epistylis, M=Mallomonas,
U=Uroglena, V=Vorticella.

GREEN AND BLUE-GREEN ALG#.—An=Anabaena, Ap=Aphanocapsa, Coe=Coelosphaerium,
G=Gloeocapsa, L=Lyngbya, M=Microcystis, O=Oscillatoria, S=Staurastrum.

Diatoms.—A=Asterionella, F=Fragilaria, M=Melosira, S=Synedra, T=Tabellaria.

TABLE 17.—ANALYSIS OF NET PLANKTON, 1918.

CANANDAIGUA LAKE, JULY 27, 1918.

| 1. ; Green and
Depth in meters. Cladocera. Copepoda.) Nauplii. Rotifera. | Protozoa. | blue-green | Diatoms.

| alge.

244 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 17.—ANALYSIS OF NET PLANKTON, 1918—Continued.

CAYUGA LAKE, JULY 30, 1918.

Green and
Depth in meters. Cladocera. | Copepoda.| Nauplii. | Rotifera. | Protozoa. | blue-green} Diatoms.

B 14,250
C 130

FINGER LAKES OF NEW YORK.

245
TABLE 17.—ANALYSIS OF NET PLANKTON, 1918—Continued.
GREEN LAKE, WIS., AUG. 20, 1918.
4 Green and
Depth in meters. Cladocera. | Copepoda. | Nauplii. Rotifera. | Protozoa. | blue-green | Diatoms.

alge.

C 5,100
N 3,140
P 5,495
C 4,970

An 27,200

O 1,822,400 |.

TABLE 18.—ANALYSIS OF NET PLANKTON, IgIo.

CANANDAIGUA LAKE, AUG. 20, 1910.

ae : Green and
Depth in meters. Cladocera. | Copepoda. | Nauplii. | Rotifera. | Protozoa. | blue-green | Diatoms.
alge.
B 260 * C4, 500 18, 500 C 130 C 23, 200 | Ap 11, 600 A 34, 800

Hons
OOM
8368

M 61, 900

S 3, 800
AD 11, 600
Coe 3, 800

246 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 18.—ANALYSIS OF NET PLANKTON, 1910—Continued.

CAYUGA LAKE, AUG. 12, 1910.

Green and
Depth in meters. Cladocera. | Copepoda. | Nauplii. Rotifera. | Protozoa. | blue-green | Diatoms.

alge.

A 200 | C1, 648, 600 | A 9, 000 | A 2, 105, 300
A. c. 520 D ts, soo Mr
DS ee 2) BARRA re ana Maree sco oe T 54, 200
S 1, c00 V8) B00} |=). <<sisercinaos
PZOO IN os wicinieteleaine ce |p aesescetiace| psashoosess=
A. c. 650 | C960, c00 A 8, 000 | A 3, 204, c00
| P38, sco D 1s, soo M 7, 700 F 928, 800
: Pl 130 V 650
SHSM cies Satesieihamcs | oto neste ar otetota
I: SIGS |e pares slo neta ctnie osname] Sea ered
A. c. 130] C 665, 600 A 7,700 | A 2, 182, 700
P 12, 600 Dts,500 | M 31,000 F 944, 300
Pl 1.600 RAZ orn Raaaameaare! T 123,800
S350
A140
A. a. 130
.| A. c. 3, 700
N 130
P 6, 000
Pl 910
S250

FINGER LAKES OF NEW YORK. 247
TABLE 18.—ANALYSIS OF NET PLANKTON, 1910—Continued.
SENECA LAKE, AUG. 2, 1910—Continued.
Green and
Depth in meters. Cladocera. | Copepoda.| Nauplii. | Rotifera. | Protozoa. | blue-green| Diatoms.
alge.

TABLE 19.—WEIGHTS OF DIFFERENT FORMS OF CRUSTACEA FROM THREE FINGER
AND FROM GREEN LAKE, WIS.

CANANDAIGUA LAKE.

Lakes, N. Y.,

: Wet weight in Dry weight in
Organism. milligrams. milligrams.
Per cent.| Per cent. Roe Ss
of water.| of ash. .
Name. No. | Total. Each. Total. Each.
0. 0230 22.40 | Adults.
- 0082 13-41 =
+0343 5-45 | Mixed sizes.
I.1100 |. 12. 02 Do.
00296 |. 31-11 | Chiefly adults.
o1or 21.80 | Mixed sizes.
MOE Pare oiak aca) vehaas es See TSO) 1) Os.004% Hloce. sccca 12.70 | Chiefly adults.
Pi ESSE AE] Crean a 12.75 mOSIGH Ua eadassce 3-78 | Large.
532 23-46 0. 0441 2.34 = 0044 90. 00 15-38 | Chiefly adults.
= SENECA LAKE.
Diaptomits= e.poeea dace eiccsevecisieen 200 12.16 0. 0608 6 | 0.0063 89. 64 15-08
Limnocalanus.... = Be 108 37-77 = 3497 5.14 +0476 86. 40 6. 61 > +
Paphriial ees eons es Pea eee eee Resi BRRReHSAaG basen 56 SOOST) Ulunsaaeeees 15-62 | Mixed sizes.
Did RO eee ee ener eee SOO eis csdpracisensrecas |) Sh OOS] CnOO7E, Pac ctc nunca 5-15 | Chiefly adults.
Wimmocalantusss ds eee eee SSO |sscnccceunfsncsasdocc{=* 7 BB] 60325 [lie scecess 3-75

248 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 20.—DryY WEIGHT AND ORGANIC MATTER OF PLANKTON CRUSTACEA AND ROTIFERSIN THREE
FINGER Lakes, N. Y., AND IN GREEN LAKE, WIS.

CANANDAIGUA LAKE.

1910 1918
Dry weight. Organic matter. Dry weight. Organic matter.
Organism.
Kilograms Kilograms Kilograms Kilograms
per square | Pounds |} per square} Pounds | persquare| Pounds | per square} Pounds
kilometer | per acre. | kilometer | per acre. | kilometer | per acre. | kilometer | per acre.
of surface. of surface. of surface. of surface.
Plankton crusta
OSMIINA «o/s ssc cles seen crels 22.95 ©. 20 15. 80 0.14 27.70 ©. 25 19. 10 0.17
3 667. 10 5.94 517. 70 4.61 94. 70 ~ 84 73-50 65
165. 00 I. 47 154. 70 1. 38 16. 30 -14 15.30 -13
209. 22 1. 86 182. 60 1.62 38. 50 +34 33- 60 .30
Diaptomus.... I, 263. 60 II. 25 1,094.15 9. 74 385. 10 3- 43 333- 5° 3-00
Limnocalanus. sete 168. 00 I. 50 158. 80 I. 42 271. 20 2. 41 256. 40 2.28
Ire tcsttte Seana. SOArnR Steer acaso-ahopo t eUnareTcl bEceA ce Conen Sokoanodog 10, 10 -09 9. 50 .08
Natiplitig: siechiccuthe rl ge 83. 00 -74 72. 21 - 64 5.30 -05 4. 60 +04
IRC RA ran Samm ad SERA AOE 2, 578. 87 22.96 2, 195. 96 19. 55 848. 90 7-55 745. 50 6. 65
Rotilers sock cere sse sce sees c/eraele 9. 25 08 8.56 074 2.76 024 2.55 022
CAYUGA LAKE.
Plankton crustacea
EROS UIN TAS perctotere sere eistelsteieiaisiotsisteiete I, 320. 25 II. 75 909. 52 8. 10 459. 43 4.09 316. 57 2. 82
Daphnia A poceereenbed beortoudoel BapssscsAcar Je seeeeeeee 14. 38 -13 II. 20 .10
Cyclops Res reate 155-41 1.38 135.67 I. 20 374- 61 3-33 327-00 2.90
Diaptomus.... = 255-42 2.27 221.16 1.97 519. 00 4. 60 449. 40 4.00
Limnocalanus. A RES B Dee ocroa N6 IA4ge0d Fon soon aogeho soe 36. 13 +32 34.70 - 28
Gf) UNA ERR AGES Sat onaeeanse 103. 06 -92 89. 66 . 80 68. 00 . 60 59. 20 -52
Total... s:5.0ehs ae Se 1, 834. 14 16, 32 I, 356. or 12.07 I, 471.55 13.07 I, 198. 07 Io. 62
Rotilersiic.ciaciee ona centiaderace ee II0. 91 I. 00 102. 78 .92 145. 24 I. 30 134. 50 1.20
SENECA LAKE.
Plankton crustacea
pianist al Smaooannanasoeconpanood 418. 57 3-72 288. 40 2. 56 421.00 3-75 290. 00 2. 60
dD eae eRe Ree RaS POR AMen aa batt Aceaol Padodtoscd Prano-secaedhengoenaad 16. 70 14 I3. 00 Io
Cyclops Sachi 631. 28 5. 62 534-19 475 I, 491. 60 13-30 I, 262. 00 II. 30
Diaptomus.... 693. 22 6.17 580. 24 5: 24 I, 192. 00 10. 60 I, O13. 20 9. 00
Limnocalanus. A 33-72 +30 31. 50 - 28 69. 00 61 64. 40 57
INavphS Seer roe cetee een mee 218. 25 I. 91 182. 47 1. 62 35.70 SK 30. 30 27
PLOtAl certs Pare cctivceinne cero I, 992. 04 17.72 I, 625. 80 14. 45 3, 226. 00 28. 72 2,672.90 23.84
OUR tater stesso heey nce ornas 24. 58 -22 22.78 ~20 41. 28 | -37 | 38. 22 | +34

FINGER LAKES OF NEW YORK.

249

Table 21 shows the vertical distribution of the organisms in the nannoplankton,
indicating the number of individuals per cubic meter of water at the different depths.
The forms are as follows:

PRotozoa—A=Amoeba, C=Cryptomonas, F=unidentified asymmetrical flagellate, H—Halteria,
M=monads, R=unidentified rhizopods, S=Synura,
GREEN AND BLUE-GREEN ALGa&—Ap=Aphanocapsa, Oo=Oocystis, Se=Scenedesmus
Dratoms—N=Navicula, S=Stephanodiscus, Sy=Synedra.

TABLE 21.—ANALYSIS OF NANNOPLANKTON.

CANANDAIGUA LAKE, JULY 238, 1918.

Depth in Green and blue : Depth in Green and blue- =
areterSs Protozoa. green alge. Diatoms. paeters! Protozoa. green alge. Diatoms.
| | |
aan) C 31, 242,000 | Ap 135,382,000 S 15,621,000 | { C 5,207,000 | AP 98,933,000 N 10, 414,000
Dckaisiter sates ninh dae Ee ee AOI ee aren rae: ||) Seas a Ria 4xH) O00! | Lysis st mooie Wo 8a 200 Sa
Sy 2OO, OOO NUNS goa antale o eieieierstete| siabdielu's # a Fiplem o)eleim I0, 414,000
| C 10, 414,000 | "Ap 182, 245,000 S 36, 449, 000 Seated oa M 31,242,000 | Ap 130,175,000 { S 88, 520, 000
Seseet ane ED { Sy200y odo \|\ehtet ceeds ks. Sy 10,414, 000 C 15,621,000 | Ap 135,382,000 N 5, 207,000
Mises G20, OOO! ran yoccnieceia cisicrsve © sil oe orainie\chatelereteimauaie pst aN oS WWD ee bap eee)! SRR EEA Sb edntoar S 10, 414,000
C 5,207,000 | Ap 187,452,000 S 31, 242,000 6 C 5,207,000 | Ap 130,175,000 $S 26,035,000
TOS eonacas Ie BOO; OO) Ey jciaieaegescieie' Sy 5,207,000 SAV VN 2 MOA TA NOOO || cate aeisictels tetera cintel te sisieesiereititire = thar
Mito S28; ooo aye 05... is:cpe ees SEoe cael clefts ome OS seleT reyes Lea laters o bunlaeheye AD 229, 108, 000 S$ 10, 414,000
C 20,828,000 | Ap 156,210,000 N 10, 414,000
ES raepyoae | H 5, 200,000 Sc 20, 828, coo S 57,277; 000
Ie Weta) ys seie pot Ua oneanud Osaanocccodneoes
CAYUGA LAKE, JULY 30, 1918.
]
EG 3%y/249y OOO) | Saisie es fatb «eis sera |ossenceee rere res M 20,828,000 | Ap 62,484,000 S 5,207,000
| H_ 5,207,000 AP 93, 726,000 N 5,207,000 M 26,035,000 | Ap 67,691,000 S 5, 207,c00
Cosndonaned \) M 26,035,000 Sc 20,828, 000 S 5,207,000 || M 26,035,000 AD 52,070,000 S 5,207,000
net eC ET hes) Pa eee asnradl bn cesarean cenear M 15,621,000 | Ap 62,484,000 |.........-..-.4-
F 26,035,000 Ap 62,484,000 M 10, 414,000 Ap 67,691,000 S 5,207,000
SSopospsscts | M 20,828,000 Sc 20, 828, 000 LG ver yess) | lhankancenoocodsod)stinse neces AAS
| FRE 2).070; 0000. wee cee es
C 5, 207, 000 Ap 78, 105,000 |.
Toe taatasstehs M 36,449,000 Se 10,414,000
LSE CHEETOS | Haine eae saanaada PE ceroaracer cet
SENECA LAKE, AUG. :, ro18.
3 C 41,656,000 AD 72,898,000 S 15,621,000 || C 5,207,000 Ap 36; 449,000) oan coe eclee
mee bose M 145, 800, 000 Qo 5,207,000 Sy 5,207,000 || M 36, 449, 000 Oo 10, 414,000 S 10, 414,000
C 15,621,000 | Ap 161,417,000 S 15,621,000 1 Oey ere pat oonet oun sesor. Peesenransse ce >
ECR M 119, 761,000 GTO; 4145 COOH Poesicttte se cntcnine <a M 20, 828, 000 AD 62, 484,000 S 5,207,000
se C 5, 207,000 Ap 62, 484,000 S 15,621,000 M 5, 207,000 AD 72,898, 000 S 10, 414,000
Seed aie Se M 20,828,000 Warns; 6271000, |e eae mance M 15,621,000 AD 67, 691, 000 S 10, 414,000
ae { C 5,207,000 | Ap 67,691,000 S 15,621,000 M 10, 414,000 AP 46, 863, 000 S 5, 207, 000
Spee M 10, 414,000 OOE265,055 5 COON ears chee ie eieis vic nichers M 5,207,000 Ap 67, 691, 000 S 5,207,000
a5) { C 5,207,000 AD 36, 449,000 S 10,414,000
Teese SS M 10, 414, 000 WOOF ATA OOO cents oisicicials ainiei=
GREEN LAKE, WIS., AUG. 20, 1918.
| |
Baie 207, 0004 baci); seis clot 2 S 5,207,000 > \f M 20,828, 000 AP 72,900,000 S 5,207,000
Ovieaien/e seis M 10,414,000 | Ap 145,800,000 Sy 20, 828, 000 || JEG Syke = 2) | ayegiad ounec cients baubeecnosedgoarn
ao erhicee: | acs J9CHene OnDS Serpaatonbodoorc M 5, 207,000 AD 46, 800, 000 S 5, 207,000
F 10,414,000 | Ap 145,800, 000 S 5,207, A 5,207,000 | Ap 57,200,000 S 5,207,000
Dar ssi WWX0, 4RAVODON era seec.k woes oe Sy 15,621,000 Rae 2G 7 OOOu lee claire tak sjalewisiai = Sy 5,207,000
‘3 F 15,621,000 | Ap 130, 200,000 S 5,207,000 M 5, 207, 000 Ap 67, 700, 000 S 10, 414,000
BOs nice IMia6;035, 000) bs oSseG eee eet sss Sy 15,621,000 M 5,207,000 | Ap 62,500,000 S 5,207,000
Gsasnasos M 10,414,000 | Ap 52,070,000 S 5,207,000 Sy 5,207,000

250 BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 22.—ESTIMATES FOR QUANTITY OF NANNOPLANKTON AND TOTAL PLANKTON IN THREE FINGER
LAKES IN ‘1918.

[Nore.—Total plankton equals net plankton plus nannoplankton. Quantities are shown in kilograms of dry organic material
per square kilometer of surface and pounds per acre. Living material would weigh about 10 times as much as is indicated

in the table.]
Nannoplankton. Total plankton.
Lake. . ;

Kilograms | poyngs | Kilograms| pon, af

per square | per acre, | Per Sauare | por acre.

kilometer. * | kilometer.
(eta rts hy eee BRA: crea aaeanec Jo Saco oanre Jace rcsur same cordednats stick 3, 877-3 34.5 4, 809. 2 42.8
Caer aaa aac ara ane tei otevotur etre tales o's ictopevaltalatetutevel atetatiatelalalurcrs ajeteteretate) lorenatars 5,450.0 48.5 6,947.5 61.6
a en Gone ea aC eonOn aE Garo sou arco Sauricert Gob oUBsoAb ome idyeawieubedacchacscno ste 8, 859. 4 78.8 12, 200. 5 108. 6

BOTTOM FAUNA.

Samples of the bottom at different depths were obtained in the three Finger Lakes
and also in Green Lake by means of an Ekman dredge. This mud was sifted through
a fine meshed net and the organisms found therein were enumerated. The dry weight
and the ash of four of these bottom forms were ascertained. The results of these dredge
hauls are shown in Table 23. The observations were far too few in number to give
anything more than a fragmentary idea of the density of the bottom fauna, since only
two hauls each were made in Canandaigua and Cayuga Lakes and but four in Seneca
Lake; in addition to this they were taken only in the deeper water. Hundreds, or
better still, thousands of observations, covering the bottom of each lake in various places
from the shore line to the greatest depths and extending through the different seasons
of the year, would be necessary to give an adequate idea of the character and abun-
dance of their bottom fauna.

Only four forms have been included in the table because they constituted by far the
greater portion of the material obtained. A few nematodes and an occasional ostracod
and bivalve mollusk were noted in the shallower depths, but they were not present in
sufficient numbers to obtain their weights.

A few larvee of Protenthes were obtained in the 32 m. haul in Seneca Lake and in
the 45 m. haul in Green Lake, but these were the only instances in which this larva

was noted.
Chironomid larve were found in all of the hauls except the one made at 32 m. in

Seneca Lake. They were most abundant in Cayuga Lake, where they constituted by
far the most numerous form at a depth of 113 m. In the other three lakes, however,
they formed only a minor element of the bottom population, both in numbers and
in bulk. Earlier in the season they were probably more numerous, because many had
undoubtedly transformed to the adult stage by the time these observations were made.

In Canandaigua and Seneca Lakes the relict amphipod Pontoporeia was second in
importance, while it was third in Cayuga Lake and first in Green Lake. It was most
abundant at a depth of 45 m. in Green Lake, where it furnished the largest amount of
dry organic material that was found in any of the hauls, namely, about 8,214 kg./km.?,
or nearly 75 pounds per acre.

Oligochzta were found in all except one haul; that is, the one at 34 m. in Cayuga
Lake. In half of the hauls they furnished the greater portion of the organic material.

FINGER LAKES OF NEW YORK 251

The largest amount was obtained at 32 m. in Seneca Lake, where it reached 1,693 kg.
of dry material per square kilometer, or a little more ‘than 15 pounds per acre.

The deepest haul in Cayuga Lake yielded a larger amount of organic matter than
the deepest haul in any of the other lakes, while the one at 34 m. was the poorest of all,
due most probably to the fact that it was made on a very steep slope. Green Lake
showed the second largest amount of material in its deepest water and Canandaigua
Lake was third. In Seneca Lake the amount at 110 m. was only about three-quarters
as great as at 172 m. In general, it appears that the bottom fauna in the deeper water
of Green Lake yields a larger amount of dry organic matter per unit area than these
three Finger Lakes.

TABLE 23.—NUMBER OF INDIVIDUALS AND WEIGHT OF Bottom FAUNA OBTAINED AT DIFFERENT
DEPTHS IN THREE FINGER Lakes, N. Y., ANDIN GREEN LAKE, WIS., IN 1918.

CANANDAIGUA LAKE, JULY 238, 1918.

Nae Dry weight. Organic matter.
Depth in n per
setae e Organism. moter Kilograms | Pounds | Kilograms | Pounds

bottom. | Pet square per per square per

* | kilometer. | acre. kilometer. acre.
(CUT Os ge ndaerc ogenderigudodopoceade dooce ssoadeen B00 219.2 1-95 155-0 1.38
DO sor sisisl= = anitopore teresa ciaeieloseisiviers isintoterys ciate Stole teiate aatelo-she stefan 977 469-0 4-17 352-0 3-13
ligochinetalnrecce cite cce lac ciae lente castes seta aieiianare afelateye eters 1,420 522-9 4-65 459-1 4.08
(GRA GHGS. odes ocogaonsdosgncssaononmdscnsaccandsacchs 45 12.0 +I 8.5 +07
A eeisiaeieieiets Lethe hig = bro aap OOnE DOC IE EST Ob TeEoneme SE GaRC menane 844 405-1 3-60 303-8 2-70
Olipockisetas ere nae. ocean vise neisieeeis serait ie ele ooteisicieieteieiars 890 326.8 2-91 286.9 2.55

CAYUGA LAKE, JULY 30, ror18.
(CUTEST Che Sr oan OPInAR SE CaRDEOOB ACE CORE RSS DEE ROC AcGeee 133 36.4 +33 25-7 23
S35 a5i/sia'9 IPOntoporeuial erin emscsowis news naeuisaiceiasie sh aes cw'ciceeletes 178 85.4 -76 64.0 57
Girronioiitissee merece tonto citroen eeniat cincty aicaae cieetece | 3, 863 1,058.5 9-42 784-4 6.66
TIZ.---000e TENG) ER ee anddoosooeeeanee oad siren aonegarodeacaodte | 710 340.8 3-03 255-6 2-24
LO) TOT a nis ere oe onaco poneeoc cue Jou be .on concn dunoacdosos deccs 1,288 474-0 4-22 416.2 3-70
SENECA LAKE, AUG. 1, 1918.

ieee eR ca CHOC CRE REE ENB CGO ERODE CRORE poe cnde 89 31-2 +28 28.8 26
Abeta Pontoporeia 532-8 4:74 399-6 3-55
Oli poctibet as dee cen lwemneeecl ie teins ae coe inomae oh oe ee y 1,928.0 17-16 1,692.8 15-07
7 eee en IE Chironomus. 158.0 I. 40 III.7 -99
Pontoporeia 405-1 3-60 303-8 2.70
MN ipockinetae men ee eo esa s aalainieles cision se cicainee cis cielo melererarnice 489-4 4:35 429. 7 3-8a
ironomus. . 120.6 I-07 85.3 - 76
SOS Pontoporeia.. 170-4 1.52 127.8 I-14
Oligochaeta. . 147-2 1.31 129.2 1.15
Chironomus. . 12.0 II 8.5 +07
IGA. opincsare Pontoporeia. . 63-8 “57 47-8 +43
Olivachnetamecerena ccna soncienccker sn craesteee stant cee tee 473-2 4-21 415-5 3-70

252 BULLETIN OF THE BUREAU OF FISHERIES.
LITERATURE CITED.

BircE, Epwarp A.
1915. The heat budgets of American and European Lakes. Transactions, Wisconsin Academy

of Sciences, Arts, and Letters, Vol. XVIII, pp. 1-47. Madison.
1916. The work of the wind in warming a lake. Ibid., pp. 341-391.
tg2t. Limmnological apparatus. Ibid., Vol. XX (now in press).

BircE, Epwarp A., and CHANCEY JUDAY.
1914. A limnological study of the Finger Lakes of New York. Bulletin, U. S. Bureau of Fish-
eries, 1912, Vol.X XXII, pp. 525-609. Washington.
HAMBERG, AXEL.
1911. Dichteunterschiede und Temperaturverteilung hauptsachlich der Binnenseen. Peter-
manns geographische Mitteilungen, Bd. 57, pp. 306-312. Gotha.
HEnry, W. A.
1898. Feeds and feeding. 657 pp. Published by the author, Madison, Wis.
HuItTFELD-Kass, H.
1905. Temperaturmessungen in dem See Mjésen und in drei anderen tiefen Norwegischen Seen.
Archiv for Mathematik og Naturvidenskab, Bd. XXVII, No. 2, pp. 1-6. Kristiania.
Jupay, CHANCEY.
1916. Limmological apparatus. Transactions, Wisconsin Academy of Sciences, Arts, and Letters,
Vol. XVIII, p. 566-592. Madison.

ScHMIpDT, WILH.
1908. Uber die Absorption der Sonnenstrahlung im Wasser. Sitzungsberichte der kaiserlichen

Akademie der Wissenschaften, Bd. CXVII, pp. 237-253. Wien.

DISTRIBUTION AND FOOD OF THE FISHES OF GREEN
LAKE, WIS., IN SUMMER

&
By A. S. Pearse

University of Wisconsin

75412°—22——_17 253

IMVTNIIVOD

J)niel 2uoaspees

om
oo:
om
5

eetet=tsl

*DOUIdSILNOUd

Kapmp soahy

auv1 N33IYD
30
dVW dDIHdVUDOUGAH

DISTRIBUTION AND FOOD OF THE FISHES OF GREEN
LAKE, WIS., IN SUMMER.

a

By A. S. PEARSE, University of Wisconsin.

&
CONTENTS.
Page.
IbTapere lite aloe Se odoaapagee Gods HSS do ae GaN eGaToeene 4 cHis (er aaee Bo eeuo De OOOO oor bee orton aia 255
Distr DitelOneOl the fISHES ay. ts eye oases ole panna cle ayes aha ste nce svaucl Mea syaceersis| ania raVeterersiqerisle:sinis Wusima gies le # 256
IreOalOr WASTES, «665 pon moc bconco se ch OG ode ips (BU aSaecedgeE secooumosssoncguEedoogoot GuC 262
(Genieraltremarks or),foods 3.7). 25 -ioeie 42 si ieien-lo- = = serail are clafaniepipita tke vivlonratpais acetals 266
Discussion and conclusions...... HES MR APNE Gals SaON Ane ston char DOGS ore Cot DESC AOE 270
LH Mers INGA Bon .botke on opoondsaaato pod neHooe4 pede cboooDddboE cod SUC COORD OBO AAOr OE 272
INTRODUCTION.

Green Lake is of particular interest on account of its depth (237 feet). It measures
11.9 km. in length, 3.22 km. in width, has a maximum depth of 72.2 m., and a mean
depth of 33.1 m. Its area at a depth of 7om.is 2.1 km.? The water is very clear and
the plankton content rather poor. The shores are for the most part sandy or stony,
and the slope of the beaches is usually deep. “a

During the summer of 1919 the writer camped at the western end of the lake from
August 11 to September 5. In front of the camp was a considerable stretch of sandy
beach (frontispiece) ; the deepest parts of the lake and Spring Lake Creek (at the south-
west corner of the lake) were readily accessible by rowboat. Temperatures were
taken once each week and are recorded in Table 1.

TABLE 1.—TEMPERATURES OF GREEN LAKE IN DEGREES CENTIGRADE, 1919.!

Depth, in meters.

Date. ] ]
I 5 10 | 12-5 15 25 35 ASM aoe 55 65
22.2 22.2 16-4 9-5 8.1 6.4 5-7 502 5-0 43
21.6 21.7 19.8 13-2 9-5 6.6 5-8 5.5 5-0 4-9
21.2 20.7 * 20.6 12.6 9.1 6.0 6.0 5-8 5-0 49
20.2 19-7 19-5 16.6 9-9 7-1 6.15 Co 5-0 4.8

1 The deep-sea thermometer used in taking the temperatures was loaned by C. Juday, of the Wisconsin Geological and
Natural History Survey.
255

256 BULLETIN OF THE BUREAU OF FISHERIES.

Fishing was carried on at various depths in the open lake and in Spring Lake Creek
with gill nets measuring 75 by 4 feet. A 30 by 4 foot minnow seine was used in shallow
water along the shores. ‘Trot-lines baited with earthworms were set a few times,
particularly to catch bullheads. Two hundred and three fishes, belonging to 17 species,
were examined, special attention being given to the ciscoes, which were plentiful in
deep water.

In making examinations the skin, fins, mouth, and gills first received attention.
The fish was then slit open from vent to chin, and a careful inspection of the visceral
organs was made. The contents of the intestine was stripped out on a glass plate and
teased apart with needles under a binocular microscope, this being supplemented with
a compound microscope when necessary. The intestine was then slit open and
examined for food and parasites.

The data relating to parasites are reserved for a general publication dealing with
several Wisconsin lakes; those concerning distribution and food are presented in this
paper.

FISHES CAUGHT IN GREEN LAKE.

Ambloplites rupestris (Rafinesque): Rock bass.

Ameiurus natalis (Le Sueur): Yellow bullhead.

Ameiurus nebulosus (Le Sueur): Speckled bull-
head.

Amiacalva Linnaeus: Dogfish.

Boleosoma nigrum (Rafinesque): Johnny darter.
Catostomus commersonit (Lacépéde): Common
sucker.

Cyprinus carpio Linnaeus: German carp.

Esox lucius Linnaeus: Northern pike, pickerel.

Eupomotis gibbosus (Linnaeus): Pumpkinseed.

Fundulus diaphanus menona (Jordan and Cope-
land): Top-minnow.

Other species doubtless occur in the lake.
living on the shore of the lake, says that gars are often seen.

in the lake several years ago.

Lepomis incisor (Cuvier and Valenciennes): Blue-

gill.
Leucichthys birget Wagner: Cisco.

Micropterus dolomieu Lacépéde: Smallmouth
black bass.

Micropterus salmoides (Lacépéde): Largemouth
black bass.

Notropis atherinoides Rafinesque: Shiner.

Perca flavescens (Mitchill): Yellow perch.

Pimephales notatus (Rafinesque): Blunt-nosed min-
now.

Joe Norton, an experienced fisherman
A sheepshead was caught

DISTRIBUTION OF THE FISHES.

In order to determine the distribution of the fishes in Green Lake four methods
were used. Gill nets were set at various depths; a minnow seine was used alongshore;
trot-lines were set; and some trolling was done with a spoon hook.

The five gill nets used were always set tied together in a “ sea all being of the

same size (4 by 75 feet), but differing in the mesh (bar measure: 34, 1, 1%, 2, 3 inches).
Nets were set in the morning and pulled the following day. Table 2 gives a complete
list of the catches in the string of gill nets.

FISHES OF GREEN LAKE, WIS. 257

TABLE 2.—GiL-NET CaTCHES IN GREEN LAKE, 19109.!

re ; 2 ‘ :
Size of | Depth | Time Size of | Depth | Time
Date. ety ee ee Catch. Date. rem, ||O eee Tp Catch.
Inches. |Meters. | Hours. Inches. |Meters. | Hours.
Aug. 13... % 41-5 22.5 | 3 ciscoes. Aug. 26... H% 6 23-5 | rperch. —
4-5 22.5 | 14 ciscoes. I 6 23-5 | x centharcid.
1} 41-5 22.5 | 6 ciscoes. 1% 6 23-5] 1 pickerel, I rock bass.
a AIS 22.5 | Nothing. 2 6 23-5 | 1 bluegill, 2 pickerel.
41-5 22.5 | 2 ciscoes. 3 6 23-5 | Nothing.
Aug. 14... 8 71-5 23-6 | Nothing. Aug. 27...| (?) 3 23.7 | Nothing.
I 71-5 23.6 | 8 ciscoes. I 3 23-7 | 1 pickerel.
Aug.1s...| (8) 20 23-3 | Nothing. 1% 3 23.7 | 3 bluegills, : perch.
Aug. 164.. 4% Sa.5 23-7 | Nothing. 1% 3 23.7 | 1 rock bass.
I 68 23-5 | 1 rock bass. 2 3 23-7 | x pickerel.
I 8 23.5 | 1 crayfish. Aug. 28... % 1.8 23-5 | 5 perch.
1%4 Bion 23-5 | 1 crayfish. I 1.8 23-5 | 2 pickerel.
2 LB ey 23-5 | 2 pee 1% 1.8 23-5 | 4 pickerel.
3 §t5 23 2 su 2 1.8 23-5 | 1 rock bass.
15 23 I ae ath black bass. 3 1.8 23-5 | Nothing.
Aug. 18... 8 5 2a Nothing. Sept.17... % I 7-6 | rpickerel,1pumpkinseed.
1% 5 23 1 pickerel. I I 7-7 | 4 perch, 9 pickerel.
1% 5 a2 a rock bass. I I 7-7 | « pumpkinseed.
Aug. 19... A 70.3 24-2 | 2 ciscoes. 1% I 7-2 | x bluegill, 3 perch.
I 70.3 24.2 | 68 ciscoes. 1% I 7-2 | 12 pickerel.
1% 70.3 a4-2 | 27 ciscoes. 2 I 7-2 | 3 bluegills, 1 largemouth
a 70.3 24.2 | 3 small ciscoes. black bass.
3 70.3 24.2 | x small cisco. 2 I 7-2 | 6 pumpkinseeds.
Aug. 20...! (?) 50 23.5 | Nothing. 3 I 6.8] Nothing. _
¥ 5° 23-5 | 1 cisco. Sept.2.... % 4 23-5 | 3 perch, x pickerel.
2 5° 23-5 | 1 Cisco. I 4 23-5 | 1 pickerel.
Aug. 2r...| (3) [37-44 23-3 | Nothing. 14 4 23-5 | 1 pickerel, 1 carp.
Aug. 22...| (3) ar 22.7 | Nothing. 2 4 23-5 | Nothing.
Aug. 23...] (#) 8-10. 5 23-5 | Nothing. 3 4 23-5 | Nothing.
2 8-10. 5 23-5 | 1 pickerel. Sept.4.... % |r. 5-3 24.5 | 1 pickerel, x rock bass.
3 8-10. 5 23-5 | 1 smallmouth black bass. reo |r. s=3 24.5 | 1 rock bass.
Aug. 25.../ (?) a- 3.6 22.5 | Nothing. 14 |1.5-3 24-5 | 1 pickerel, 1 rock bass.
4 | a- 3.6 22.5 | 5 perch. 14 |1-5-3 24-5 | rclam(Lampsilisluteola),
14 | 2- 3-6 22-5 | x bluegill. 2 |r.5-3 24-5 | Nothing.
1% | 2- 3-6 22.5 | 1 pickerel. 3. |i-5-3 24-5 | Nothing.
134 | 2- 3-6 22-5 | 1 rock bass.
a 2- 3.6 22.5 | 3 bluegills.
2 a- 3-6 22.5 | rx sucker.

1 All nets were 4 by 7s feet.

2 Indicates that nets of the other meshes than those listed for catches on this date were set at the depth given, but nothing
was caught.

3 Indicates that five nets having 34, 1, 134, 2, and 3 inch meshes were set, but nothing was caught.

4 Set string of nets on steep slope.

5 Bare bottom.

6 Among plants.

7 Spring Lake Creek, half mile above mouth; set nets alternately from either bank, away from mouth, in following order:
3, 14, %, 1, and 2 inch mesh.

Table 3 gives a summary of all the gill-net catches (except that of Sept. 1 in Spring
Lake Creek) arranged according to depth.

This summary shows that ciscoes are confined to depths below 40 m. and the
“catch per hour’’ figures indicate that ciscoes are the most abundant larger fishes in
the lake. Young ciscoes probably spend a year or more in shallow water, for schools
of from 100 to 200 fingerlings were observed three times, swimming in the middle of
the lake at the surface in bright sunlight. The pickerel ranges deeper than other
shallow-water species.

There is a zone above the ciscoes (20 to 40 m.) where there are few or no fishes.
Footing up the “catch per hour’ for all species at all depths we have the following
figures: Total hours all nets were set—419.4; catch per hour—bluegills, 0.094; carp,
0.01; cisco, 1.447; largemouth black bass, 0; rock bass, 0.1; perch, 0.13; pickerel,
0.207; pumpkinseed, 0; smallmouth black bass, 0.03; sucker, 0.053.

If the abundance of fishes large enough to be caught in gill nets is judged by the
“catch per hour,” the species occur in the following ratios in Green Lake during the
summer: Cisco, 48; pickerel, 7; perch, 4; rock bass, 3; bluegill, 3; sucker, 2; small-

258 . BULLETIN OF THE BUREAU OF FISHERIES.

mouth black bass, 1; carp, + ; large mouth black bass,1+ ; pumpkinseed,*+. These fig-
ures probably are almost correct with two exceptions: There are doubtless schools of carp
too large to be caught in the nets used; and the pickerel, because it is fairly abundant
and probably moves about more in search of food, is captured more often than the
other fishes considered. ‘There seems to be no question that the cisco is far more
abundant than any other species.

TABLE 3.—SUMMARY OF GILL-NET CATCHES IN GREEN LAKE, 1919, GiviNG DEPTH AND CATCH PER

Hour.
Sach ime : | ee see Small- |
Depth in meters. hia a ai hee Perch. Bic Carp. | Sucker. moa Cisco.
inches ; bass.

10 to 20.

20 to 40.

40 to 72

It is interesting in this connection to compare the results for Lake Mendota during
the summer of 1919. Lake Mendota has a maximum depth of 25.6 m. It differs from
Green Lake ecologically in that its lower water stagnates (Birge and Juday, 1911).
This means that the deeper parts (below 8 to 15 m.) are without oxygen during August,
September, and October. The important ecological feature in this lake as a habitat
for fishes is the fact that the water above the thermocline is well aerated and warm,
while that below is without oxygen and comparatively cool. The temperatures of the
water in Lake Mendota during the period work was being done in Green Lake are avail-
able through the courtesy of President E. A. Birge, of the University of Wisconsin.

While the writer was working in Green Lake, Leslie Tasche was setting a string of
five nets (precisely like those used in Green Lake) in Lake Mendota. The summary of
some of his catches will serve as a basis for comparison between the two lakes. The
nets were set in Lake Mendota on the steep slope off the end of Picnic Point, where gen-
eral conditions are much like those in Green Lake.

1 This species is included because young or adults were caught in the lake by other methods of fishing than gill nets; +
indicates an amount less than o. 1 per cent. throughout this paper.

FISHES OF GREEN LAKE, WIS. 259
TABLE 4.—TEMPERATURES OF LAKE MENDOTA IN DEGREES CENTIGRADE, IgIQ.
Depth in meters.
Date.
|
if ° See, ae 9 Io Ir 12 13 T5031 y Oi | 20 23
| |
| | il

24.1 24-I | 24.0 18.1 14-0 12.5 Il.5 II-3 10.4 | I0.r 9-8 9-4
23-3 22.6 | 22-4 22-3 16.3 12.7 11-6 I0.9 10.4 Io. I 9-8 9-7
21.3 21-3 21.3 2I.2 16.9 13-1 12.2 11.6 II-5 To. 4 | 9-5 9-7
20-3 20-3} 20.2 20.2 18.5 15-7 12.8 12.2 io. 8 10.2 | 10.0 10.90

FIsHES CAUGHT IN GILL NETS IN LAKE MENDOTA.

Ambloplites rupestris (Rafinesque): Rock bass.

Catostomus commersonii (Lacépéde): Common
sucker.

Cyprinus carpio Linneus: German carp.

Esox luctus Linneus: Northern pike, pickerel.

Lepisosteus osseus (Linnzeus): Gar.

Lepomis incisor (Cuvier and Valenciennes): Blue-

Leucichthys sp.?: Cisco.

Micropterus salmoides
black bass.

Perca flavescens (Mitchill): Yellow perch.

Pomoxis sparoides (Lacépéde): Crappie.

Roccus chrysops (Rafinesque): White bass.

Stizostedion vitreum (Mitchill): Wall-eyed pike.

(Lacépéde): Largemouth

gill.
TABLE 5.—GILL-NET CATCHES IN LAKE MENDOTA, 1919.!
,
Size | Depth! Time Size | Depth | Time
Date | mesh. set. set. Catch: a mesh. set. set. Catch.
Inches. | Meters.| Hours. Inches. | Meters.| Hours.
June 24 4 23 25 6 perch. Aug. 22... % 3| 22.5 | 5 perch.
I 23 25 55 perch. I 3 22.5 | 2 perch, r rock bass.
4% 23 25 I cisco. 4% 3 22.5 | x bluegill, r sucker.
2 23 25 Nothing. 2 3 22.5 | 1 white bass.
June 25.. £3 21 23 Nothing. 3 3 22.5 | 1 carp.
June 26.. 4) 22 27-5 | Nothing. Aug. 23... % Ir 24.5 | 18 perch.
I 22 27-5 | 1 perch. I 7 24-5 | 111 perch.
July 28.. 3 23 22.5 | Nothing. 4% 5 24-5 | Nothing.
July 30.. ( 22 22 Nothing. 2 4 24.5 | 1 wall-eyed pike.
Aug. r.... % 19 24 Nothing. 3 3 24-5 | Nothing.
I 18 24 10 perch. Aug. 26...| (?) 22 24 Nothing.
4 16 24 I Cisco. Aug. 27 8 24-5 | 3 perch.
2 15 24 Nothing. I 6 24. 1 largemouth black bass,
3 14 24 Nothing. 16 perch.
Aug. 2.... % 3 24 2 perch. | 14" 5 | 24-5 | Nothing.
P 7 24 I gar, 14 perch, 1 rock 2 5 24-5 | I carp.
< bass. 3 4 24-5 | 3 Carp.
4 6 24 1 rock bass. Aug. 28 % 16 22.5 | Nothing.
2 9 24 Nothing. I 10 22.5 | 75 perch.
14 24 Nothing. 4 6 22. 5 | 1 rock bass, 1 white bass.
Aug. 7.... } seas 24 Nothing. 2 4 22.5 | Nothing.
I 22 24 I perch. 3 4 22.5 | 1 carp.
Aug. 8.... % 13 23-5 | 9 perch. Aug. 29... % 14 23-5 | Nothing.
I 8 23-5 | 98 perch, I 13 23-5 | 8 perch.
4% 7 23.5 | 3 rock bass. 1% 14 23-5 | Nothing.
2 5 23-5 | Nothing. 2 12 23-5 | Nothing.
3 4 23.5 | Nothing. 3 Io 23-5 | 2 carp, x largemouth
Aug. 9.... % 13 25 19 perch. black bass.
I II 25 254 perch. Sept. 2.... (?) 22 23-5 | Nothing.
4 9 25 3 rock bass. Sept. 3.... % 7 23 9 perch.
2 7 25 1 largemouth black bass. I 8 23 52 perch, 1 crayfish.
5 25 1 carp. 1% 10 23 x cisco, 1 sucker.
Aug. 12 3 23 24 Nothing. 2 1 23 I cisco.
Aug. 13 @ 19-10 | 24 | Nothing. 3 14| 23 | Nothing.
Aug. 14 KK 3 23.5 | Nothing. Sept. 4 % 19 24 | Nothing.
I 4 23.5 | 22 perch. I 18 24 | x perch.
4 6 23.5 | x pickerel. 1% 15 24 | Nothing.
2 8 23.5 | 1 carp. 2 12 24 1 carp.
II 23-5 | x carp. 3 9 24 Nothing.
Aug. 19... re) 22 24 Nothing. Sept. 5.... % 6 23-5 | 6 perch.
Aug. 20... % 17 24 Nothing. I 7 23-5 | 1 crappie, 28 perch.
I 14 24 12 perch. 14 7 23.5 | 1 crappie.
14 12 24 1 cisco. 2 8 23-5 | Nothing.
2 12 24 I cisco. 3 8 23-5 |i carp, 1 largemouth
3 12 24 Nothing. black bass.
Aug. 21...| (8) 2-4 24 Nothing. s
I 2-4 24 I crappie.

1 All nets were 4 by 7s feet.
2 Indicates that five nets, having 34,1, 134, 2, and 3 inch
meshes, were set, but nothing was caught.

3 Indicates that nets of the other meshes than those listed
for catches on this date were set at the depth given, but noth-
ing was caught.

260 BULLETIN OF THE BUREAU OF FISHERIES.

The data summarized in Table 5 cover a somewhat longer period of time than that
including the catches in Green Lake. It might have been longer, for fishing in Lake
Mendota was carried on from March 29 to September 29, 1919; but the general results
do not differ markedly from those already published for this lake (Pearse and Achten-
berg, 1920), and therefore only the period necessary to make adequate comparisons
with Green Lake is listed. The summary shows clearly that perch were abundant in
deep water in June and that they gradually migrated to higher levels as that region of
the lake lost its oxygen. This migration offers a striking contrast to the conditions in
Green Lake, where there is oxygen at all depths during the summer and where the
common deep-water fishes (ciscoes) remain in the depths of the lake.

Table 6 gives a summary of catches in Lake Mendota from August 13 to September
4, grouped to show the total catches at different depths.

TABLE 6.—SUMMARY oF GiLL-NET CATCHES IN LAKE MENDOTA, 1919, GIVING DEPTH AND CATCH

PER Hour.
Size . Large-
: Time Wall- . :
Depth, in | mesh, . P Crap- | Rock | Blue- 1 White c mouth | ;:; Pick- | Cray-
meters. in sees h. pie. bass. gill Sucker.| eyed | bass. TD: | black Cisco. erel. | fish.
inches. hours pike. bass.

Tht0.23 50.8

Total.

Footing the total catch per hour for all species caught in Lake Mendota the results
are: Perch, 4.71; carp, 0.14; white bass, 0.05; cisco, 0.04; largemouth black bass, 0.03;
rock bass, 0.02; sucker, 0.02; bluegill, 0.01; crappie, 0.01; pickerel, 0.01; wall-eyed pike,
0.01; gar, +; crayfish, 0.05. Most of the fishes were not caught below 10 m., the only
exceptions being the carp, cisco, and perch.

The perch is by far the most abundant fish large enough to be caught in gill nets at
all depths in Lake Mendota. The comparative number of fishes for the two lakes
judged by catches per hour in gill nets, is shown in Table 7.

FISHES OF GREEN LAKE, WIS. 261

TaBLE 7.—CoMPARISON SHOWING RELATIVE NUMBERS OF FISHES IN GREEN LAKE AND LAKE
MENDOTA, AS JUDGED BY CATCHES IN Gil NETS.

Lake | Lake Lake
G Green Green
Men- | Men- : Men:
Lake. | dota. || Lake. | dota Lake. | dota
= \|
| 12 a7x \l|\Sucker:44scSaccch be tan 6 a
21 x || Wall-eyed pike.........]........ I
4 + + || White bass............. fpneese: 5
aeecasa se I bass. 9 2) |
+ + | Smallmouth black bass 3 - Totals s:.. <jelsgeles | 186 506
Largemouth black bass 35 3 |

This table shows that Green Lake does not have as many fishes large enough to be
caught in gill nets as Lake Mendota. This is certainly true of the smaller fishes also, as
judged by catches with minnow seines alongshore. The bearing of this fact will be
discussed later. Table 7 also shows that there is an interesting compensatory relation
between the fishes of the two lakes. The deep-water, bottom-feeding fishes—the perch
in Mendota and the cisco in Green Lake—are much more abundant in both lakes than
all the shallow water species together. ‘The perch is absent from the deeper waters
of Green Lake but in Mendota largely replaces the ciscoes in deep water and is
more abundant than the pickerel, which exceeds it in Green Lake. The carp, crappie,
largemouth black bass, wall-eyed pike, and white bass are more abundant in Lake
Mendota. The bluegill, cisco, pickerel, rock bass, smallmouth black bass, and sucker
are more abundant in Green Lake. It is interesting to note that the two fishes which
probably are most similar in habits (the smallmouth and largemouth black bass)
together have the same ratio of abundance in the two lakes. However, the smallmouth
was the only one caught in gill nets in Green Lake and the largemouth the only one
caught in Lake Mendota. These facts indicate that the two basses compete with each
other and that peculiarities in the two lakes make each best fitted to one of them. In
other words, there is room for a certain number of bass, and in Green Lake conditions
are best suited for the smallmouth, in Lake Mendota for the largemouth.

The hauls for four days with the minnow seine are given in detail. These were
made on a sandy beach bearing a scanty growth of aquatic plants at the west end of
Green Lake from the shore line to a depth of 114 m.

August 16.—Eighteen blunt-nosed minnows, 2 perch, 6 smallmouth black bass.

August 18.—Two largemouth black bass, 3 perch, 4 smallmouth black bass, 2 top minnows.

August 20.—Three Johnny darters, 2 largemouth black bass, 3 perch, 4 pickerel, ro shiners, ro
smallmouth black bass, 3 top minnows.

August 29.—Four bluegills, 25 Johnny darters, 19 largemouth black bass, 17 perch, 1 pickerel,
1 shiner, 51 smallmouth black bass, 10 top minnows.

Summary.—Four bluegills, 18 blunt-nosed minnows, 28 Johnny darters, 23 largemouth black bass,
25 perch, 5 pickerel, rz shiners, 71 smallmouth black bass, 15 top minnows.

Arranged in the order of their abundance, as judged by the catches in minnow
seines, the small shore fishes rank as follows: Smallmouth black bass, 18; Johnny darter,

7; perch, 6.2; largemouth black bass, 5.8; blunt- “see minnow, 4.5; top: minnow, 3.7;
tier Be pice 1.2; bluegill, 1.

These results again show the dominance of the smallmouth over the largemouth

black bass in Green Lake, and (although the writer has not kept statistical records of

262 BULLETIN OF THE BUREAU OF FISHERIES.

hundreds of hauls) there is no doubt that the opposite is true in Lake Mendota. The
Johnny darters are characteristic shallow-water fishes on sandy shores everywhere in
Wisconsin. Some lakes, however, have other species of darters more abundant along-
shore. For example, the Iowa darter (Etheostoma iowe, Jordan and Meek) is the abun-
dant one in Oconomowoc Lake. ‘The minnows are characteristic more or less of all
shallow-water habitats. The perch ranges through all bottom habitats and is probably
the most versatile of our lake fishes. The pickerel, bass, and bluegill belong with the
shore vegetation, and, as vegetation is not very plentiful in Green Lake, these fishes are
not numerous.

On the evening (6.30 p. m.) of September 2, a trot-line 20 feet in length, bearing
49 No. 1 Limerick hooks baited with earthworms, was set outside a rush-grown bar
extending from the bay behind Blackbird Point (front.) westward; depth, 1.2 to 2 m.
Next morning (6.30 a. m.) the catch was 1 bluegill, 5 perch, 1 dogfish. At 6.50 p. m.
on September 3, 50 hooks were set inside the same bar (1 to 1.5 m.) on 200 feet of line.
The catch at 6.50 a. m. on September 4 was 7 bluegills, 4 perch, 1 rock bass, 1 mussel,
Lampsilis luteola (Lamarck).

If these trot-line catches mean anything, they indicate that there are more blue-
gills inside the bar and that perch occur in equal numbers on either side. Perch, as
has been suggested heretofore, are versatile fishes which invade practically all available
habitats. Bluegills, though fitted to live among aquatic vegetation, are remarkably
quick to take advantage of any new sources of abundant food. An instance of this
was observed in Green Lake on the evening of August 22. The lake was very calm
and on its surface were numerous ants, of some species that had been making its nuptial
flight during that day. The whole surface of the west end of the lake was at intervals
marked by little ripples caused by fishes feeding on the ants. All fishes observed from
a rowboat before darkness fell were bluegills, though other species were doubtless
taking advantage of this unusual supply of food.

FOOD OF THE FISHES.

The foods eaten by the fishes of Green Lake in 1919 are given in the following lists.
The figures used in connection with foods all mean per cent by volume as estimated by
the writer at the time of examination; + indicates an amount Jess than o.1 per cent.
Lengths of fishes are given in millimeters and do not include the caudal fin. Fishes are
arranged in alphabetical order according to scientific names. Summaries for all species
are given in Table 8. Unless otherwise mentioned all catches are off the sandy shore
at the east end of the lake (frontispiece).

Ambloplites rupestris (Rafinesque). Rock bass.

August 16.—Depth, 8 m.; number examined, 1; length, 108. Food: Chironomid pupe, 2; cray-
fish, 98.

August 22.—Number examined, 1; length, 30. Food: Chironomus larve, 25; mayfly larvae, 50;
Hyalella, 20; Eurycercus, 5.

August 23.—Number examined, 1; length, 47. Food: Chironomus larve, 5; large blue water
mite, 30; ostracods, 2; cyclops, 12; Eurycercus, 3; Ceriodaphnia, 18; sand, 30.

August 26.—Number examined, 2; lengths, 192, 57. Food: Chironomus larve, 2.5; C. pup,
2.5; crayfish, 50; Ceriodaphnia, 45.5.

August 27, 28.—Number examined, 2; lengths, 190, 208. Food: Crayfish, roo.

FISHES OF GREEN LAKE, WIS. 263

September 4.—Number examined, 3; lengths, 213, 171, 111, average, 165. Food: Crayfish, 66.7;
Cambarus virilis, 33-3.

Summary.—Number examined, 12 (2 empty); lengths, 30 to 213, average, 134. Food: Insect larve,
11.8; insect pup@, 0.6; crayfishes, 64; mites, 4.2; ostracods, 0.2; amphipods, 2.9; entomostracans, 12;
sand, 4.2.

Two-thirds of the food of this species consisted of crayfish.

Ameiurus natalis (Le Sueur). Yellow bullhead.

August 29.—Mouth of Spring Lake Creek; number examined, 2; lengths, 290, 270. Food: Fish,
32-5; mayfly nymphs, ro; insects, 17.5; Gelastocoris, 6.5; crayfish, 10; Hyalella, 12.5; Ceriodaphnia, 1;
plants, ro.

Summary of food.—Fish, 32.5; insects and nymphs, 34; crayfishes, 10; amphipods, 12.5; entomos-
tracans, 0.1; plants, ro.

A third of the food of this species was fish and a third insects.

Ameiurus nebulosus (Le Sueur). Speckled bullhead.

August 29, 1919.—Mouth of Spring Lake Creek; number examined, 9; lengths, 265 to 320, average,
302. Food: Mayfly nymphs, 2.8; dragonfly nymphs, 1; crayfish, 25.6; cladoceran, 0.1; amphipods,
0.8; Hyalella, 2.1; Spheriide, 0.6; Planorbis, +-; Physa heterostropha, 31.4; oligochetes, 3; Herbobdella
punctulata, 4.2; seeds, 8.9; plants, 10.1; Myriophyllum, 3; filamentous alge, 0.8; unknown débris, 5.6.

Summary of food.—Insect nymphs, 3.8; mites, 0.5; crayfishes, 25.6; amphipods, 2.6; cladoceran,
0.1; Spheriide, 0.6; snails, 31.4; annelids, 7.2; plants, 22; alge, 0.8; unknown, 5.6.

The favorite foods of this bullhead were snails, plants, and crayfishes.

Boleosoma nigrum (Rafinesque). Johnny darter.

August 20.—Number examined, 5; lengths, 32 to 46, average, 40.2. Food: Chironomus larve,
66; Hyalella, 10; ostracods, 0.2; sand, 23.8.

August 22.—Number examined, 1; length, 34. Food: Chironomus larve, 95; sand, 5.

August 24.—Number examined, 1; length, 38. Food: Chironomus larve, 75; sand, 25.

August 26.—Number examined, 4; lengths, 37 to 47, average, 41. Food: Chironomus larve, 92.5;
sand, 7.5.

Summary.—Number examined, 11; average length, 38.3. Food: Chironomus larve, 82.1; amphi-
pods, 2.5; ostracods, 0.1; sand, 15.3.

Catostomus commersonii (Lacépéde). Common sucker.

August 16.—Depth, 14.5 m.; number examined, 2; lengths, 542, 510. Food: Chironomid larve,
23.5; Sialis nymph, 2.5; insects, 0.5; ostracods, 1; amphipods, 60; Eurycercus, +; oligochetes, 0.5;
Spheriide, 6.5; mud, 1; sedimentary débris, 4.5.

August 25.—Depth, 4 m.; number examined, 1; length, 364. Food: Chironomid larve, 4; Lepto-
cella larva, 1; Hyalella, 2; Spheriide, 76.8; Amnicola, 1; Valvata tricarinata, 0.2; sand, 15.

Summary.—Number examined, 3; lengths, 364 to 542, average, 445. Food: Insect and larve, 19.3;
amphipods, 40.7; entomostracans, 0.7; clams, 29.9; snails, 0.4; oligochetes, 0.3; sedimentary débris, 3;
mud and sand, 5.7.

The sucker partakes of a considerable variety of foods, the most important being amphipods, little
clams, and insects.

Cyprinus carpio Linnaeus. German carp.

September 2.—Number examined, 1; length, 133. Food: Chironomid larve, 2; Hyalella, 25; ostra-

cods, 33; Eurycercus, 1; Ceriodaphnia, 10; Spheriide, 15; plant remains, 3; fine débris, 10; sand, 2.

Esox lucius Linnaeus. Pickerel.

August 16.—Depth, 11.5 m.; number examined, 2; lengths, 553, 576. Food: Shiners, roo.

August 18.—Depth, 5 m.; number examined, 2; lengths, 466, 410. Food: Minnows, 50; fish
remains, 50.

August 20.—Number examined, 1; length, 402. Food: Fish remains, 70; ostracods, 10; Chara, 20.

August 22.—Number examined, 1; length 100. Food: Shiners, roo.

264 BULLETIN OF THE BUREAU OF FISHERIES.

August 23.—Depths, 4.6, 11.5 m.; number examined, 2; lengths, 550, 495. Food: Perch, 25;
shiners, 15; fish remains, 60.

August 26.—Number examined, 3; lengths, 570, 635, 665. Food: Fish remains, 100 (2 empty).

August 27.—Number examined, 2; lengths, 307, 565.. Food: Fish remains, 100 (1 empty).

August 28.—Number examined, 5; lengths, 300 to 475, average, 393. Food: Minnows, 100 (3

empty).
September 2.—Number examined, 2; lengths, 485, 600. Food: Fish remains, roo (1 empty).

September 3.—Number examined, 3; lengths, 211, 490, 540, average, 414. Food, Fish remains,
Ioo (1 empty).

Summary.—Number examined, 24; lengths, 100 to 665, average, 445. Food: Perch, 2.5; shiner,
21.5; minnow, 15; fish remains, 58; ostracods, 1; plants, 2

Eupomotis gibbosus (Linnaeus). Pumpkinseed.

September 1.—Mouth of Spring Lake Creek; number examined, 4; lengths, 163 to 168, average, 165.
Food: Chironomid larve, 2; dragonfly nymphs, 25; Planorbis, 33.3; Physa, 17.7; Valvata, 2; Sphe-
riide, 5; Herbobdella punctulata, 15.

September 2.—Near mouth of Spring Lake Creek; number examined, 1; length, 73. Food: Chi-
ronomid larve, 92; Spheriide, 8.

Summary.—Number examined, 5; average length, 146. Food: Insect larve and nymphs, 59.5;
snail;, 26.5; small clams, 6.5; leeches, 7.5.

Fundulus diaphanus menona (Jordan and Copeland). Top minnow.

August 15.—Number examined, 1; length, 52. Food: Hyalella, 100.

August 18.—Number examined, 1; length, 52. Food: Chironomid larve, 60; chironomid pupe, 19;
gordiacean in chironomid pupe, 1; sand, 20. -

August 20.—Number examined, 2; lengths, 46, 59. Food, Chironomid larve, 10; chironomid pupe,
15; Hyalella, 25; Ceriodaphnia, 25; Pleuroxus, 1.5; Bosmina, 10; Acroperus, 15; ostracods, 2.5; sand, ro.

August 21.—Number examined, 4; lengths, 50 to 53. Food: Chironomid larve, 11.3; chironomid
pupe, 23.8; Hyalella, 44.3; Ceriodaphnia, 14.3; Bosmina, 0.5; Chydorus, 1.5; ostracods, 0.5; sand, 4.

August 22.—Number examined, 1; length, 55; Food: Caddisfly larve, 45; Hyalella, 50; ostracods, 5.

August 23—Number examined, 3; lengths, 18 to 53, average, 38. Food: Chironomid larve, 30;
chironomid pup2, 6.7; Hyalella, 20.2; Ceriodaphnia, 8.3; Chydorus, 6.7; ostracods, 23.3; sand, 5.

Summary.—Number examined, 12; lengths, 18 to 55, average, 44. Food: Chironomid larve, 17.9;
caddisfly larve, 3.8; chironomid pupe, 13.7; Hyalella, 31.8; cladocerans, 16.6; ostracods, 6.4; gordiacean,

o.1; sand, 5.9.
Lepomis incisor (Cuvier and Valenciennes). Bluegill.

August 25.—Number examined, 4; lengths, 164 to 186; average, 177. Food: Chironomid larve, 1.3;
dragonfly nymphs, 0.3; Leptocerus dilutus larve and cases, 13.3; collembolan, +; ants, 8.8; mite, +;
Hyalella, 66.7; Eurycercus, +; Amnicola, 0.3; Ancylus, +; plants, 1.5; alge, 0.3; sand, 7.8.

August 26.—Number examined, 1; length, 176. Food: Chironomid pupe, o.2; Chara, 99.6; plants,
0.2.

August 27—Number examined, 3; lengths, 143 to 170, average, 160. Food: Leptocerus dilutus
larve and cases, 58.3; crayfish, 33.3; plants, 6.6; sand, 1.7.

August 29.—Spring Lake Creek; number examined, 1; length, 173. Food: Dragonfly nymphs, 15;
insects, 40; seeds, 5; plants, 20; fine débris, 20.

August 30.—Number examined, 2; lengths, 43, 157. Food: Chironomid larve, 25; chironomid
pup2, 15; collembolan, 50; fine débris, ro. f

September 1.—Spring Lake Creek; number examined, 1; length, 175. Food: Sponge, 10; Myrio-
phyllum, 80; wild rice seeds, ro. Z

September 3—Number examined, 1; length, 172. Food: Melanoplus femur-rubrum, 35; crayfish, 65.

September 4.—Number examined, 5; lengths, 164 to 188, average, 176. Food: Leptocerus dilutus
larve and cases, 64.8; Physa, 1; Planorbis, 0.2; Potamogeton, 7; plants, 17.6; alge, 6

pi tae ieee examined, 18; lengths, 43 to 188, average, 165. Food: Insect larve, 33;
insect pupz, 1.7; adult insects, 12.9; mite, ++; crayfishes, 9.2; amphiods, 14.8; Revecsy wer: +; snails,
0.5; sponge, 0.5; siestS 21.3; alge, 1.7; fine débris, 2.2; sand, 2.2.

FISHES OF GREEN LAKE, WIS. 265

Leucichthys birgei Wagner. Cisco.

August 13.—Depth, 41.5 m.; number examined, 10; lengths, 148 to 288, average, 199. Food:
Chironomid larve, 0.3; Mysis, 5; Pontoporeia, 76.6; copepods, 1.6; ostracods, 5; Spheride, 11.1; Amni-
cola, 0.6; Planorbis, 0.2; brown, spindle-shaped seeds, 0.8; plants, 0.5; bottom ooze, 1.6; calcium car-
bonate crystals, o.1; unknown, 1.1.

August 4.—Depth, 71.5 m.; number examined, 8; lengths, 207 to 246, average, 225. Food: Chirono-
mid larve, 3.3; Mysis, 13.3; Pontoporeia, 24.2; Canthocamptus, 3.3; ostracods, 12.5; oligochetes, 21.7;
Spheriide, 0.8; brown seeds, 0.2; dandelion seed, 0.2; bottom ooze, 12.6.

August 19.—Depth, 70.5 m.; number examined, 12; lengths, 154 to 296, average, 228. Food:
Chironomid larve, 0.2; Silais nymph, 0.4; Pontoporeia, 73; oligochetes, +; Spheriide, 14.8; Valvata,
0.1; Linnea, 0.2; Amnicola, 0.3; Planorbis, 0.6; brown seeds, o.1; plants, 0.4; bottom ooze, 9.8.

Summary.—Number examined, 30; lengths, 148 to 296, average, 218. Food: Insect larve, 1.1;
Mysis, 4.7; amphipodis, 61.2; copepods, 1.3; ostracods, 3; Spheriidz, 9.9; snails, 0.8; seeds, 0.4; plants,
0.3; bottom ooze, 8.2; calcium carbonate crystals, +; unknown, o.3.

The cisco feeds largely on crustaceans and molluscs in summer. Eighty-eight per cent of its food
is made of bottom ooze and the organisms associated with the bottom. Perhaps the ciscoes turn more to
plankton at other seasons. If so, their feeding habits differ markedly from the perch, which is the deep-
water fish in Lake Mendota, for it feeds largely from the bottom at all seasons (Pearse & Achtenberg,
1920).

Micropterus dolomieu Lacépéde. Smallmouth black bass.

August 15.—Number examined, 6; lengths, 46 to 57, average, 51.5. Food: Chironomid larve, 6;
Orthocladius, 30.1; mayfly nymphs, 0.6; chironomid pup, 4; insects, 0.8; Acroperus, +. Eurycercus,
0.1; Ceriodaphnia, 57.8; plant remains, ‘o.3; filamentous alge, +; sand, 0.3. .

August 16.—Depth, 14.5 m.; number examined, 1; length, 392. Food: Perch, 50; grasshopper, 50.

August 18.—Number examined, 2; lengths, 52, 56. Food: Chironomid larvae, 35; mayfly nymphs,
7.5; beetle larve, 5; chironomid pupz, 30; Hyalella, 225.

August 21.—Number examined, 1; length, 55. Food: Chironomid larve, 35; Eurycercus, 1;
Ceriodaphnia, 64.

August 23.—Depth, 10 m.; number examined, 1; length, 395. Food: Fish remains, roo.

Summary.—Number examined, 11; lengths, 46 to 395, average, 114. Food: Fish, 13.6; insect larve,
31.8; insect pup, 7.6; insect adults, 5; amphipods, 4.1; cladocerans, 37.6; plants, 0.2; sand, 2.

Micropterus salmoides (Lacépéde). Largemouth black bass.

August 18.—Number examined, 3; lengths, 49, 58, 61. Food: Fish, 5; chironomid larve, 3.3;
damselfly nymphs, 13.3; mayfly nymphs, 6.7; chironomid pupz, 15.7; Corixa, 8.4; Chydorus, 0.3; amphi-
pod, 2.7; Hyalella, 4; ostracods, 0.3; Eurycercus, 0.3; Ceriodaphnia, 39; sand, r.

August 19.—Number examined, 1; length, 52. Food: Chironomid larve, 15; chironomid pupe,
40; Eurycercus, 10; Ceriodaphnia, 30; sand, 5.

August 20.—Number examined, 1; length, 63. Food: Chironomid larve, 25; chironomid pupz, 75.

August 21.—Number examined, 3; lengths, 63; 63, 64. Food: Chironomid larve, 6.7; mayfly
nymphs, 5; chironomid pup, 9.3; fly, 3.3; Hyalella, 13.3; Ceriodaphnia, 61.3; sand, r.

August 22.—Number examined, 8; lengths, 55 to 283, average, 97. Food: Chironomid larve, 9;
mayfly nymphs, 6.3; chironomid pupe, 13.5; midges, 14; fly, 0.3; crayfish, 8.1; Hyalella, 28.5; ostracods,
0.1; Chydorus, 0.1; Eurycercus, 0.8; Ceriodaphnia, 7.2; plants, 10.6; sand, r.5.

Summary.—Number examined, 16; lengths, 49 to 283, average, 78. Food: Fish, 1; insect larve,
16.1; insect pupe, 18.6; adult insects, 8; crayfish, 4; amphipods, 18; cladocerans, 24.8; ostracods, o.1;
plants, 5.2; sand, 1.4.

Only one of the fishes examined was over 88 mm. in length. This one had eaten chironomid pupe,
15, and plants, 85. The most important foods for all bass examined are insects and their immature
stages (42.7), cladocerans, and amphipods.

266 BULLETIN OF THE BUREAU OF FISHERIES.

Notropis atherinoides Rafinesque. Shiner.

Only one shiner was examined for food and it was empty. It was supposed that shiners would be
easy to catch alongshore and they were therefore neglected until the period for study was nearly com-
pleted—then none was to be found.

Perca flavescens (Mitchill). Yellow Perch.

August 15—Number examined, 2; lengths, 68, 73. Food: Chironomus larve, 10; Orthocaldius
larve, 15; mayfly nymphs, 2.5; caddisfly larve, 5; Hyalella, 15; ostracods, 0.5; Ceriodaphnia, 52.

August 18.—Number examined, 5; lengths, 70 to 113, average, 81. Food: Chironomid larve, 25;
mayfly nymphs, 3; chironomid pupe, 34; Hyalella, 12.4; Chydorus sphericus, 0.2; Eurycercus, 1.2;
Ceriodaphnia, 23.2; sand, 1.

August 22.—Number examined, 2; lengths, 93, 97. Food: Chironomid pupe, 37.5; Hyalella,
59-5; Ceriodaphnia, 0.5; plants, 2.5.

August 23—Number examined, 1; length, 74. Food: Chironomid larve, 22; caddisfly larve, 2;
chironomid pupe, 15; Hyalella, 32.8; Eurycercus, 23; Ceriodaphnia, 5; sand, o.2.

August 25.—Number examined, 5; lengths, 115 to 127, average, 122. Food: Chironomid larve, 5;
mayfly nymphs, 4; chironomid pupe, 1; mite, 4; crayfish, 16.2; Hyalella, 19; ostracods, +; Physa,
39-6; Amnicola, 5; plants, 2.6; Arcellalike seeds, 1.4; alge, 0.2; unknown, 2.

August 26.—Number examined, 1; length, 121. Food: Sialis nymphs, 85; sand, 5; unknown, ro.

August 28.—Number examined, 4; lengths, 118 to 132, average, 126. Food: Chironomid larve,
19.3; mayfly nymphs, 12.5; caddisfly larve, 2; chironomid pupz, 2.5; Hyalella, 53.5; Physa, 6.2;
plants, 1.2; sand, 0.5; bottom débris, 2; unknown, 0.3.

August 30.—Number examined, 8; lengths, 72 to 83, average, 77. Food: Chironomid larve, 9;
mayfly nymphs, 14.3; chironomid pupe, 4.4; Hyalella, 49.8; Chydorus, +; Eurycercus, 2.1; Cerio-
daphnia, 18.1; plants, 0.6; Arcellalike seeds, 0.6; sand, I.1.

September r.—Spring Lake Creek; number examined, 7; lengths, 183 to 268, average, 216. ood:
Fish, 2.9; chironomid larve, 0.1; caddisfly larve, 3.6; dragonfly nymphs, 85.5; Hyalella, x; Physa, 3.3;
Spheriide, 1.4; Herbobdella, 1.1; plants, 2 :

September 2.—Number examined, 1; length, 130. Food: Leptocerus larve, 5; plants, 95.

September 3.—Trot-line near bar; number examined, 6; lengths, 122 to 143, average, 134. Food:
Sialis nymphs, 8; dragonfly nymphs, 10; chironomid pupe, 4; crayfish, 10; RES LLS 44; Ceriodaphnia,
4; oligochztes, 10; plants, 4; sand, 4; bottom débris, 2.

Summary.—Number examined, 43; lengths, 73 to 268, average, 112. Food: Fish, o.5; insect larve,
34.1, insect pupe, 8; mite, 0.5; crayfishes, 3.2; amphipods, 28.2; ostracods, +; cladocerans, 10.7;
snails, 6.6; clams, 0.2; leeches, 0.2; oligochetes, 1.2; plants, 3.8; sand,1; bottomdébris, 0.4; unknown,
0.5.

The chief foods of the perch are insect larve, amphipods, and other crustaceans. It is worthy of
note that the large perch caught on September x in Spring Lake Creek had eaten 85.5 per cent dragonfly
nymphs. The perch’s food in all habitats is largely from the bottom and from the aquatic vegetation.

Pimephales notatus (Rafinesque). Blunt-nosed minnow.

Three of these little minnows were examined, but only one contained food. This one was caught
August 30, measured 52 mm. in length, and had eaten chironomid larve, 50, and chironomid pup, 50.

GENERAL REMARKS ON FOODS.

Arranged according to their use by all of the 15 species studied in Green Lake,
the foods come in the following order: Insect larve (21.7), amphiphods (16.5),
fish (9.6), crayfishes (7.8), cladocerans (7.6), insect pupe (6.7), plants (4.5), snails (4.4),
clams (4.1), insects (3.3), ostracods (3.3), sand (2.5), mud (2), oligochzetes (0.6), leeches
(0.5), unknown (0.4), mites (0.4), Mysis (0.3), algae (0.2), copepods (0.1).

Sixty-seven and seven-tenths per cent of the food of the fishes of Green Lake is
arthropods; 31.7 per cent, insects in all stages; and 35.6 per cent, crustaceans. About

FISHES OF GREEN LAKE, WIS. 267

85 per cent of the food comes from the bottom (65) and the water plants (20), leaving
only one large item—the cladocerans—unassigned, and probably a portion of this
item should be placed with the bottom and water plants. It is of course impossible to
give exact figures in assigning animals used as food to particular habitats, but there is
no doubt that the fishes get the greater part of their food from the bottom and from the
shore vegetation. The open-water plankton (which to be sure is poor in this lake)
is of little importance, except perhaps as food for the young of ciscoes and other fishes.
According to the ratios of particular foods consumed (during the period when
observations were made), the fishes of Green Lake may be arranged as follows:

Fish.—Pickerel (97), yellow bullhead (32.5), smallmouth black bass (13.6), largemouth black
bass (0.9), perch (0.5).

Insect larve.—Johnny darter (82.1), pumpkinseed (59.5), blunt-nosed minnow (50), perch (34),
bluegill (33), smallmouth black bass (31.9), top-minnow (21.7), sucker (1g), largemouth black bass
(16.7), rock bass (11.8), yellow bullhead (10), speckled bullhead (3.8), carp (2), cisco (1.1).

Insect pupe.—Blunt-nosed minnow (50), largemouth black bass (18.6), top-minnow (13.7), perch
(8), smallmouth black bass (7.8), bluegill (1.7), rock bass (0.6),

Adult insects —Yellow bullhead (24), bluegill (12.9), largemouth black bass (9.3), smallmouth
black bass (5), sucker (0.3).

Mites.—Rock bass (4.2), speckled bullhead (0.5), blunt-nosed minnow (0.5), bluegill, +.

Crayfishes.—Rock bass (64), speckled bullhead (25.6), yellow bullhead (10), bluegill (9.2), large-
mouth black bass (4.1), perch (3.2).

Mysis.—Cisco (4.7).

Amphipods.—Cisco (61.2), sucker (40.7), top-minnow (35.2), perch (28.6), carp (25), largemouth
black bass (18), bluegill (14.8), yellow bullhead (12.5), smallmouth black bass (4.1), rock bass (2.9),
» speckled bullhead (2.6), Johnny darter (2.5).

Cladocerans.—Smallmouth black bass (37.6), largemouth black bass (25.4), top-minnows (16.6),
rock bass (12), carp (11), perch (10.7), yellow bullhead (1), speckled bullhead (0.1), bluegill (+).

Co pepods.—Cisco (1.3).

,Ostracods.—Carp (33), top-minnow (6.4), cisco (3), pickerel (1), sucker (0.7), rock bass (0.2), Johnny
darter (0.1), largemouth black bass (0.1), perch (++).

Clams (all Spheriidz).—Sucker (29.9), carp (15), cisco (9.9), pumpkinseed (6.5), speckled bull-
head (0.6), perch (0.2).

Snails.—Speckled bullhead (31.4), pumpkinseed (26.5), perch (6.6), cisco (0.8), bluegill (0.5),
sucker (0.4).

Leeches—Pumpkinseed (7.5), perch (0.2).

Oligochetes.—Speckled bullhead (7.2), perch (1.2).

Nematodes (Gordiacean).—Top-minnow (0.1).

Sponges.—Bluegill (0.5), sucker (0.3).

Plants.—Speckled bullhead (22), bluegill (21.3), yellow bullhead (10), largemouth black bass (5.2),
pereh (3.8), carp (3), pickerel (2), cisco (0.7), smallmouth black bass (0.2).

Alge.—Bluegill (1.7), speckled bullhead (0.8).

Bottom ooze.—Carp (10), cisco (8.2), sucker (3), bluegill (2.2), perch (0.5).

Sand.—Johnny darter (15.3), top-minnow (5.9), sucker (5.7), rock bass (4.2), bluegill (2.2), carp
(2), perch (1), smallmouth black bass (0.2), largemouth black bass (0.1).

Unknown.—Speckled bullhead (5.6), perch (0.4).

268

BULLETIN OF THE BUREAU OF FISHERIES.

TABLE 8.—Foop oF FisHES OF GREEN LAKE, AUG. 12 TO SEPT. 4, I9I9.

Aver-
Mbee |aeceH I I ae Cr Am | Clado-| Cope- | Os
wes er en . nsect | Insect . ay: : * ‘O- pe- tra-
Common and scientific name. eran iaee: Fish. Rees || Sr a Mites. ees Mysis.| phi- eapariel aie
ined. | lime- pods.
ters.
Bluegill, Lepomis incisor... ... 18 TOSI) ciateleiciele 33 1.7 | 12-9 + Qe ||entecevar 14-8 Beesoe cl osacec
Bullhead, speckled, Ameiurus
MeMMlOsus seri hemes 9 302 I Sicianents Carl Rorece| dorane eo PACA Raabe 2.6 Cy 4) Beier sce soc
Bullhead, yellow, Ameiurus
MAC ALIS HE teers ercietaelerascfeieletare 2 280) sau okGl, yl iaclaee Ey te eee TOM bree cee 12-5 Sed see elle aoe é
Carp, Cyprinus carpio. I 133 \paece ons FY) Ui bocopor acacorc| Hocse sdf Saobnn beoscee 25 en ees oe 33
Cisco, Leucichthys birgei...... 30 2IShl.. feats reap dl Sarre Soo er act A een Anv7i\ i OXea? | nfo I-3 3
Johnny darter, Boleosoma
itigherlk pa eooaensbeemonecs «| Ir S31 bereeer ys Nonarcod lobadod tapedat||soctad laocoone Eel bagdecd lrosoncds -I
Largemouth black bass, Mi-
cropterus salmoides......... 16 78 “9 16.7 18.6 CHER Aerie AniSiA ls ei sia 18 City. Gl Pees er <x
Minnow, blunt-nosed, Pime-
phales notatus.............- I
Perch, Perca flavescens. . 43
Pickerel, Esox lucius | 24
bps raat a Eupomotis gib- |
Si SS gaa Aumeooeencccownedn } 5
Rock bass, Ambloplites rupes- |
ELIS a ieteht a leroleteiactnicts tain xtale 12 bey agate) 11.8 | s1O1| crete recite 4-2 (<n ene 2:9 TQ Wasanens +2
Smallmouth black bass, Mi- |
cropterus dolomieu..........| It 114 13-6| 31-9] 7-8 Bal secre ere lS cisrereie ereteisies Oe 1 PS ACD) nericae Mneae inc
Sucker, Catostomus commer- |
SEMIN ary cinae Wau ies ite trae | 3 UV AH Ie aye ae Re 4B )\| sacha Baal tables ele notes Boag |e casea leases A
Top minnow, Fundulus dia- | f
phanus menona.,........... 12 ZU Gs ase | 20-7 | 13-7 |cceeseleeeeves|eeweres[eseeses 35-2 656i eae 6.4
PAST OTAGC oes as ji wie nie sete 1198 177 9-6) 21-7 6.7 3:3 ais 7.8 -3| 16:5] 7-6 an 3
Common and scientific name. | Clams. | Snails a poay NEC Ps aS a Pees Plants. | Alge. ac Sand. ee
|
Bluegill, Lepomis incisor.........|........ Cat? |onesrey saeco isioooscc 4 0.5 21-3 1-7 2.2 2. 2ieee sean
Bullhead, speckled, Ameiurus
ICD IOSiiSaey atone aiatcietiiateereisinlata 0.6 Poe W lore orroar Pala erwvatelsini als arerotat te 22 ON Meas cere cicemmnes 5-6
Barbee yellow, Ameiurus nat-
Pec Cyprinus carpio.. /.
Cisco, Leucichthys birgei-. e
Jakaay: darter, Boleosoma nig-

Tarpeninith black bass, Microp-
terus salmoides
Minnow, blunt-nosed, Pimepha-
les notatus
Perch, Perca flavescens. .
Pickerel, Esox lucius

Pipe insced, Eupomotis gibbo- r
Gatetarernicieterstaiciocteistal aint reeset eee 6.5 26.5 bt Sogo Hae siociad Mdsnoacr HARE SASS as Asda) asosend yao Ancdaiireossrcs
Rock ‘bass; AmbJoplites rispestras oo o:o/5s, cel Soa caine ul alaccieie nieve | Stele myesetaso | stot otek beret] Cfepreteteare el ate ten et cree] es creamer pe mien rige Aravye een aew <
Smallmouth black bass, Microp-
agit) Wirt TR Ge aso ord Measeneel pitas cc Gono aesd Bonddcrry oobi cecl|-adeuein Sa itor iet sc (oe coarse OW sac cenic
Sucker, Catostomus commersonii 29-9 SY binecd a SPER Ged op oot-e =GAln's > Bralepal teehee 3 Soi Pa ee ets ara
Top minnow, Fundulus diapha-
SUIS TCM cieie aivis vie’! aievaieroiotersin | seivicmst=totd] dete uraveiet | a tetera siete le metaie svete rome Paes) Be B Sree] bo a6 Yd rinse! 5. Oi Fee aoe
PASTETA SEA. shelaiticiwtafeiate tel stvisl> 41 44 oe -6 + + 45 <2 2 25 | “4
1 Total.

Table 9 gives the foods eaten by the fishes caught in Lake Mendota during the time

covered by the observations in Green Lake.

It will be noted that a greater variety of

fishes was caught in Lake Mendota (22:15), and that foods differ somewhat in the two

lakes.

Fishes in Green Lake eat an excess of: Amphipods (13.6), larval insects (11.4),
oligochzetes (5.6), clams (4.1), insect pupz (0.4), mites (0.4), and Mysis (0.3).

Those

in Lake Mendota excel in: Adult insects (13.8), fish (7.2), algae (5), plants (3.7), copepods
(1.5), cladocerans (1.4), ostracods (0.7), bottom ooze (0.7), sand (0.3).

FISHES OF GREEN LAKE, WIS.

TABLE 9.—Foop oF FisHES oF Lake MENpOTA, AUG. 10 TO SEPT. 15, 1919.

Common and scientific name. ber

ined.

Num-

exam-

Aver-
age
length
in
milli-
meters.

Fish.

Insect |Insect
larve.| pupe.

Cray-

; Mites. fishes.

Clado-
cerans.

Cope-
pods.

Bluegill, Lepomis incisor......... ;
Bream, Notemigonus crysoleucas ....
Bullhead, speckled, Ameiurus ne bu-
OSUS. . cee ncn cree emer reese rtennceee
Bullhead, yellow, Ameiurus natalis. .
Carp, Cyprinus CALDIG demi ptis/-jneetae
Cisco, Leucichthys sp.?..... ors
Crappie, Pomoxis sparoides. AA
Gar, Lepisosteus osseus.........+-..+
Johnny darter, Boleosoma nigrum... .
Largemouth black bass, Micropterus
BalmOIdes nr sacri. read
Minnow, Notropis heterodo:
Perch, Perca flavescens!. .
Pickerel, Esox lucius
Pike, wall- eyed, Stizostedion vitreum.
Pumpkinseed, Eupomotis gibbosus. .
Rock bass, Ambloplites rupestris..... | I
Shiner, Pimephales notatus ey
Silversides, Labidesthes sicculus......
Smallmouth black bass, Micropterus
olomilette nena etek seteirertentyieiniors
Sucker, Catostomus commersonii.....
Top minnow, Fundulus diaphanus

oh

Ov QnaBuH

w

a
ssp DO RUNO OW

ub

Common and scientific name.

Clams.

tozoa.

Bluegill, Lepomis incisor..............+.+
Bream, Notemigonus crysoleucas........ -
Bullhead, speckled, Ameiurus nebulosus. .
Bullhead, yellow, Ameiurus natalis. .
coe: Cyprinus CATION cali tas ccm
Cisco, Leucichthys sp.?....
Crappie, Pomoxis sparoides.
Gar, Lepisosteus osseus.
Johnny darter, Boleosoma
Largemouth black bass, Micropterus sa’
ANIMES SAP oma cne eee ane dherscetiels)= a
Minnow, Notropis heterodon.
Perch, Perca flavescens!....
Pickerel, Esox lucius...........++.++-
Pike, wall-eyed, Stizostedion vitreum
Pumpkinseed, Eupomotis gibbosus. .
Rock bass, Ambloplites rupestris. ..
Shiner, Pimephales notatys......
Silversides, Labidesthes sicculus.........
Smallmouth black bass, Micropterus dolo-

Sucker, Catostomus comm: rsonii
Top minnow, Fundulus diaphanus me

1 No perch were examined in 1919.

These are figures for 1915 during the same season of the year.

2 Total.

TABLE 10.—COMPARISON OF Foops EATEN BY FISHES OF GREEN LAKE AND LAKE MENDOTA, 1919.

Green Take

Take: dota.
(isha ).ch ct sh emcee 9-6 16.8
Insect Jarve... ae 21-7 10.3
Insect pupe... 6.7 6.1
Adult insects. . 3-3 17-1
Matesem antics “4 ae
Crayfishes. 7-8 6.8
Mysis...... +3 =
Amphipods 16.5 2-9

Green oes Green

Lake. dota Lake
9 | SPONGES) eo Sa deans: a
1.6 || Protozoa. =

3-7 || Plants. . “5

+ Alger. :), 3:1: 2
5 Bottom ooze 2

-6 || Sand...... 2-5

Ped] | PRI MARMIOVIEL. ate, ctcte <icitloietee +4

75412°—22——18

270 BULLETIN OF THE BUREAU OF FISHERIES.

: It will be noted (Tables 8, 9, and 10) that the foods eaten in excess in Green Lake
are largely those associated with the bottom; those most eaten in Lake Mendota are
found for the most part in shallow water with plants, or in the open water. These
differences are in part accounted for by the stagnation of the deeper water and in part
by the greater abundance of food resources in the latter lake. In Lake Mendota there
is an abundance of food in the deeper parts, but such supplies are not easily accessible
to fishes in summer because there is no oxygen below 8 to 12 m. Birge and Juday
have recently made observations with mud dredges which, with the earlier work of
Birge (1897) and Marsh (1903), indicate clearly that there is actually less food in Green
Lake, as regards both bottom fauna and plankton, than in Lake Mendota. There are
some common fishes in Lake Mendota (silversides, crappie, gar, white bass) which are
rare or absent in Green Lake. ‘These ‘‘extra”’ fishes feed to a considerable degree on
plankton, insects (in or on the surface of the water), and fishes. There is apparently
no chance for them to be abundant in Green Lake.

DISCUSSION AND CONCLUSIONS.

Green Lake is a fine clear body of water, with sandy and pebbly shores, and great
depth. Seventeen species of fishes were caught in it during the summer. The lake
stratifies in summer, but the lower water always contains oxygen, and of course remains
cool (5° C.).

Lake Mendota has nearly twice the area of Green Lake but is only a third as deep.
It stagnates during the summer in its depths and a large part of its water is without
oxygen for about three months. Notwithstanding this handicap, Lake Mendota has
more than twice as many fishes (as judged by the catch per hour in gill nets) in a unit
area.

During the summer the distribution of the fishes in Green Lake shows definite strat-
ification. From the surface down to a depth of 10 m. all species of fishes caught in the
lake, except adult ciscoes, were found; from 10 to 20 m. only large pickerel, small-
mouth black bass, and suckers occurred; from 20 to 40 m. no fishes were caught; from
40 to 70 m. ciscoes were the only fishes caught, and were abundant. Reighard’s (1915,
p- 246) idea that ciscoes inhabit the intermediate water and are not caught in gill nets
set on the bottom is no longer tenable in the light of results presented in this paper.
A. R. Cahn has also caught many ciscoes in gill nets set on the bottom in Oconomowoc
Lake.

While gill nets were being set in Green Lake, 22 species of fishes were caught in
Lake Mendota by the same methods. ‘There are, then, not only more individuals, but
a greater number of species in Lake Mendota. ‘There were no fishes caught in gill nets
in this lake in the lower, stagnant water, except an occasional perch. Most fishes stay
above the thermocline, where oxygen is plentiful but the water warm. The perch
apparently congregate just above the thermocline and make short excursions into the
stagnated region to take advantage of the food offered by the rich bottom fauna.

The most abundant species in each lake is one which feeds very largely from the
bottom in deep water. In Green Lake this species is the cisco; in Lake Mendota, it is
the perch. Both species are present in both lakes, but a single and different species is
dominant in each lake. The cool water in the depths of Green Lake abounds with
ciscoes; the perch is not abundant and, in fact, was never caught in deep water. Al-

FISHES OF GREEN LAKE, WIS. 271

though ciscoes are present in Lake Mendota they are few in number and the perch is the
abundant fish in deep water, except when stagnation forces it out during the summer
(Pearse and Achtenberg, 1920). The perch appears to be about equally abundant in
both lakes in shallow water.

There are perhaps two reasons why ciscoes are not abundant in Lake Mendota
and why perch are comparatively scarce in Green Lake. ‘These are concerned with tem-
perature and food. ‘The perch may live in shallow water at rather high temperatures,
but because the summer stagnation has made Mendota unsuitable for ciscoes, it has
also been able to dominate the deep water. To flourish, the cisco appears to require
cold water in summer and finds ideal conditions in the depths of Green Lake. There
appears to be no good reason why the perch should not occur in the deeper parts of
Green Lake. Perhaps it has never crossed the ‘‘barren zone” between the depths of
20 and 40 m. Perhaps the ‘‘attractive’’ food which takes it to the bottom of Lake
Mendota is lacking. The characteristic animals in the bottom of Lake Mendota are
enormous numbers of midge larve (Corethra, Chironomus, Protenthes, etc.). Little
clams, oligocheetes, crustaceans, and protozoans are also present. On the bottom of
Green Lake the fauna is much the same, except that the crustaceans (particularly am-
phipods) are very abundant and midge larve are few.

The relatives of the cisco are usually found in the depths of lakes and in the cooler
parts of the ocean. The relatives of the perch are mostly found in shallow regions of
fresh water. ‘The ciscoes apparently invaded fresh water from the ocean as the glaciers
receded and have remained in the cooler parts. ‘The perch has probably migrated into
the depths of lakes from adjacent shallow waters to take advantage of the abundant
stores of food there. Reighard (1915, p. 242) even classifies the perch in his “ Vegeta-
tion Community,” though he also found it in deeper water in Douglas Lake.

Not only are the fishes which feed on the bottom most abundant in both lakes,
but the animals found in or on the bottom are most used for food by all the fishes in the
lakes; that is by all species of fishes considered together. In Lake Mendota, however,
more plankton is consumed by the fishes than in Green Lake, and this probably for two
reasons: (1) There is actually more plankton in the lake, and (2) a large portion of the
bottom is not readily accessible on account of stagnation.

The shallow waters in the two lakes under consideration are quite different. Green
Lake has sandy and stony shores, with comparatively little vegetation; Lake Mendota
has varied shores and large numbers of aquatic plants. These differences are
reflected in the two basses, the smallmouth being the common one in Green Lake and
the largemouth in Lake Mendota. The smallmouth in Green Lake feeds largely on
shallow water cladocerans, insect larve, and fishes. The most important foods of the
largemouth in Lake Mendota during the summer are fishes, adult insects, crayfishes,
amphipods, and alge. In this lake the smallmouth partakes largely of adult insects.
The largemouth apparently becomes the dominant bass because it feeds more during
the summer, which is its chief growing period, on food which is found in the shore vege-
tation rather than on the bottom.

Why is it that Lake Mendota has a greater number and variety of fishes than
Green Lake in spite of the fact that (1) it has half the volume and (2) that a consid-
erable portion of its bottom with much food is cut off by stagnation for three months
during each year? The writer has thought over the whole question with care and

272 BULLETIN OF THE BUREAU OF FISHERIES.

can see no answer except—mud. The thick layer of soft mud on the bottom of Lake
Mendota is rich in organic materials and contains a very abundant fauna of detritus
feeders. The mud and its animals form an enormous store of organic material. This
makes aquatic plants and plankton abundant; this in turn gives opportunity for fishes
(silversides, etc.) which feed on pelagic organisms to flourish and makes those which
feed on plants and small fishes more abundant. Green Lake is a fine, healthful habitat
for fishes in somewhat the same way that a desert on land is healthful. Its possibilities
are limited because it lacks mud. Rich ‘‘soil” is just as important for raising animals
from aquatic pastures as it is for those on land. Petersen (1918) has recently made a
similar generalization in regard to the ocean.’

BIBLIOGRAPHY.
BirGE, Epwarp A.

1897. Plankton studies on Lake Mendota. II. The Crustacea of the plankton from July, 1894,
to December, 1916. Transactions, Wisconsin Academy of Sciences, Arts, and Letters,
Vol. XI, 1896-97, pp. 274-448. Madison.

BirGE, Epwarp A., and CHANCEY JUDAY.

1g1t. The inland lakes of Wisconsin. The dissolved gases of the water and their biological sig-
nificance. Wisconsin Geological and Natural History Survey, Bulletin No. XXII,
Scientific Series No. 7, xx-+259 pp. Madison.

Jupay, CHANCEY.

ro14. The inland lakes of Wisconsin. The hydrography and morphometry of the lakes. Wis-
consin Geological and Natural History Survey, Bulletin No. XXVII, Scientific Series
No. 9, xv-+137 pp. Madison. 6

Marsu, C. DwicHrT.

1903. The plankton of Lake Winnebago and Green Lake. Wisconsin Geological and Natural

History Survey, Bulletin No. XII, Scientific Series No. 3, vit-94 pp. Madison.
Pearse, A. 5S.

1918. The food of the shore fishes of certain Wisconsin lakes. Bulletin, U. S. Bureau of Fisheries,

Vol. XXXV, 1915-16, pp. 247-292. Washington.
PEARSE, A. S., and HENRIETTA ACHTENBERG.

1920. Habitsof yellow perch in Wisconsin lakes. Bulletin, U.S. Bureau of Fisheries, Vol. XXXVI,

1917-18, pp. 293-366. Washington.
PETERSEN, C. G. JOH. ;

1914. Valuation of the sea. II. The animal communities of the sea bottom and their importance
for marine zoogeography. Report, Danish Biological Station, Vol. XXI, 1913, 42+68
pp. Copenhagen. :

1918. The sea bottom and its production of fish food. A survey of the work done in connection
with valuation of the Danish waters from 1883-1917. Ibid., Vol. XXV, 1918, 82 pp.

PETERSEN, C. G. Jou., and P. BoySEN JENSEN.

rg11t. Valuation of the sea. I. Animal life of the sea bottom, its food and quantity. Report,

Danish Biological Station, Vol. XX, 1911, 81 pp. Copenhagen.
REIGHARD, J.

rg15. An ecological reconnoissance of the fishes of Douglas Lake, Cheboygan County, Michigan, in
midsummer. Bulletin, U. S. Bureau of Fisheries, Vol. XXXIII, 1913, pp. 215-249.
Washington.

WAGNER, GEORGE.

1911. The cisco of Green Lake, Wisconsin. Bulletin, Wisconsin Natural History Society, Vol. IX,

pp. 73-77. Milwaukee.

1 Birge and Juday have found as many as 30,000 Corethra lary per square meter in the mud on the bottom of Lake Mendota.

2 Dr. R. E. Coker, after reading the manuscript for this paragraph, suggests that the richness of food stores in a lake may
perhaps be connected with the fertility of the soil in the surrounding drainage area, Dr. R. H. Whitbeck, professor of geography
in the University of Wisconsin, assures the writer that the drainage basin of Green Lake is less fertile than that of Leke Mendota.

GENERAL INDEX.

Page.

Ambloplites rupestris, distribution and food............ 256,
259, 262, 268, 269

Ameiurus natalis, distribution and food....... 256, 263, 268, 269
BESTEST o sn stoned seoenboosemondaacodads 256, 263, 268, 269
Amia calva, distribution 256

Andalusia Chute, Mississippi River, mussels. . 97,104, 109, 119
Auglaize Riversmusselssi\o. Nopscmcnticces snseelclest ene 92,93

Birge, Edward A., and Chancey Juday: Further limno-
logical observations on the Finger Lakes of New York 209-252
bluegill, distribution and food............ 256, 259, 264, 268, 269
Boleosoma nigrum, distribution and food. .... 256, 263, 268, 269
bream, distribution and food 269
bullhead, speckled, distribution and food . 256,263, 268, 269

Wrellowieaacec ici mecinccrettac ele Cotneileriare cts 256, 263, 268, 269
Caddo Lake, La. and Tex., mussels...............0..05 98, 109
Calumet Deep River, mussels...............00eeceeeeeee 95
Canandaigua Lake, N. Y., limnological observations (see

Manger Takes IN. W..) = 5 main s-ciore he stetalelejsieintolaiste eisictatonin 209-252
CALCITE O WLC CE «are feselciata ree cid felata wateinie epeieiaaielajee een inonttet c 191
carp, German, distribution and food...... 256, 259, 263, 268, 269
Catostomus commersonii, distribution and food......... 256,

259, 263, 268, 269
Cayuga Lake, N. Y., limnological observations (see Fin-

gexplsaicesstNepw/-))axtvialcibio taleleisalaleafere nisisiny anielesemsis a ese 209-252
Center Tale inid (ni 1sselsii.t5 af sisseisisisieivisie nis ejnieisin’s evsinipie’s 102
GhicagosRivercmmusselsie. cr crctaleca:nitisie sieleleis'sivie lee eieidiafoete 96
Chillicothe: sm11Ssels oc: jn)ef0)s)«:orefsj aia ae! sfoiatarelateiwieio dt vleteiworelle 109
chinook salmon, early history and seaward migration in

Columbia and Sacramento Rivers.................0.. 1-74

AlevinSHOLAN Langa pier tisiciee siemisisennia tris isieieieisiejaisisieleiee 69

CAPVEHE ANd Ce cae retate eletale eiatsiaieie aimiale/aielaleisieleieta/a sjelelalat siete otto 69

Bibliography ratceitee ante aresley se siete ei 71

California coastal streams, collections. . sac 42

COCCIGTITR 7S Se OBES OORE COUR AEAICMBE Nat «-. 68,69

coastal streams, California and Oregon, collections. . 42

Columbia River collections. ............seceeeeeeees 7

PEM gtr ee SCOCE DOES ORAONE 5

females and males, relative sizes..... 66

Ery Cave ole erence sere esc ecce tees 68, 69

lengthieemenscsce ceric ce 9 7°
liberation from hatcheries...... «++ 69,71
plantingeer cass is ieee se Son 68
growth, rapid periods of. . 51
Tate Ob Ficmuadereiniew 45,70
investigation, history of. 3
ROE OLS ee eaters eiteoale we eeale ie siaicte\cls tino wrelale 6
Problemisn jen cecneravectee tase teen ween es 5
length, estimated at beginning of intermediate
BLOW CI ce are oes eetatniee Seles oun ozardosig nae 14,48
ERY sire eee OR eI aarteuretnatid 70
yearlings........ Asda ogbaboucaaGOBUCoCOUee Bb aa 70

liberation of fry from hatcheries..................-.- 69, 71

males, precociously mature..... : « 69,71

males and females, relative sizes. . . it 66

migration 47, 48, 49; 53, 57) 60, 62, 70

miscellaneous collections. ... 42

Oncorhynchus tschawytscha................0.0ce0ee 3

Bad

chinook salmon, etc.—Continued. Page.
Oregon coastal streams, collections.................. 42
lating eee e. cin nce cae meuees S elaorateiard 68,69
plates, explanationjofis, i cin/ascietieciecins sues bigard asian 72
Practical suggestions.............0.eee0+ Sooocnonntes 68
problems, statement of............sssse05 dondignadne 5
TALCOLELOWEINS se Sten ee chic cee recess aieis's eialslevstetaicicle 45,70
Sacramento River collections............ soos peibacc 32
scales—
analysis........... elaierelsietstdaidioe cee sinaisiaiisestcta cee 6
UI ee seh evs cs dosacademmunene tee Seoocencacos 6
bands.c.2c6 55 kaise tdees 6, 25, 26) 49; 53) 54) 57 58; 60, 70
check migratory: ss sce aus civla'sicie sissiese demas Sates 18
check} primary: joie sce ccssdotoeteetors 18,54, 59,70
CRE CHD ats aia ataeio caine njarate acl sia sres sete ee 6
Columbia River data... .........cecceceeceeeeees 52
developmentiols ctr a..cdecaeecdeeeneecct ee ne 5I
PetleralizationS rents sac senee ccs cciss Gaacscehaeece 53
growth, intermediate............ 13,14) 25, 29) 53) 57,60
prOWwth New. 2 =f saeSephiesscecaeeebeeene 25, 26, 53,59, 60
hatchery specimens... .5..0.ccceccccsceevcevees 953
intermediate band...............-+ 26, 53) 54,57) 58,70
intermediate growth............. 13) 14) 25) 29) 53,57) 60

migratory check

MIC WE ROW EMG otats cletclatajete’ercrelelcratateteresiaictareteta
DHOtOpTAaphs | ssa eee cise c cise leiceloidee tecetestre nee 6
Primary CHECK. jaciace se acieaceseeetsice heist: « 18, 54,59, 70
Vingsiss ce. laieic ce ces acces 6, 12, 25) 53) 54) 58, 59, 60, 70
‘Sacramento River datas. oes... os'dacececwecbies 59
GPTERITIST) AMCs ele rale o vie\etsie’viulatatehaletarera'aiaiele wie ayarerciera 6,54, 60
Winter bandon veces cus elcwsinaweviclele’s tie 6, 25,49, 54, 60, 70
sex, proportions 65

variations.... 65
springruns.... 5
summary... St 7°
VEAL PS LENE Moly eicivicisieielsie'elotelsv eicieteecicie seeiveieseee Jo

cisco, distribution and food... « 256,259, 265, 268, 269

Clark, H. W., observations on food of mussels........... 9

Clark, H. W., et al.: Natural history and propagation of

reste wAberstet1sSels sycintalsisieisicinsiclisieie nists sivioisin es eieiaersictcle

Clinch River, Tenn., mussels.........

Cobitis, genital orgams.......... ee XOX
barbatula.......... Pee XOX
eno REC tI GD ROOD oOCODOSAGADSCOOO CMe DOETAG 189, 191

Coker, R.E., et al.: Natural history and propagation of

fresh-watermmursselss.chiosu-nicemr eee rect eeniceee a eeee

Columbia River, seaward migration of chinook salmon in.

Coregonidz, peritoneal membranes, ovaries, and ovi-

197,200

Coregonus, peritoneal membranes, ovaries, and ovi-

. 189,197

crappie, distribution and food...... + 259, 269

Cumberland River, mussels............ ++ 97,109

Cyprinus carpio, distribution andfood............... 256, 259,

263, 268, 269

273

75-182
1-74

274

Page
Des Moines River, mussels. ......--.2++eeeceeeeceeeeeees 114
Detroit River, mussels 99
Distribution and food of fishes of Green Lake, Wis. ,in
SUTERITIET Se, of osn cin nicole so asnseluisis|e elaleiuisinlalslejsjalaluleinia)e\eiv.sie/e 253-272
bibliography. .........0.-ce2scccereseescrserecensrs= 272
dogfish, distribution. ...........--.+..+- 5 256
Early history and seaward migration of chinook salmon
in Columbia and Sacramento Rivers.............-+.++ 1-74
eeligenital organs. 25. .2)....s nope tee meet enmcteeaivisectaee 189, 19t
elasmobranchs, relationship to salmonoids.............. 200
Esox lucius, distribution and food........ 256.259, 263, 268, 269
Eupomotis gibbosus, distribution and food. .. 256, 264, 268, 269

Fairport (Iowa) Fisheries Biological Station, mussels... 80,

84, 92,9394, 100, 109. 114, 121, 125,126, 127,

137) 138, 140) 143) 150, 155) 159, 160, 163, 165

Feeder Canal, Fort Wayne, Ind., mussels........... 84,92, Io1
Finger Lakes, N. Y. (Canandaigua, Cayuga, Seneca),

limnological observations..... 209-252

absorption of sun’s energy .. . 223
bottom fauna...... aeertiress aA cite
distribution of heat. . 218, 223, 233) 234) 235
(SoA TEC Ren apanrssndoonorepaannsoceandec7c: ec 213
Green Lake, Wis., bottom fauna comparison. 251
plankton comparison .. 6). eccie sie asecnencenees 236,
237) 238, 239) 240; 241, 245, 247; 248, 249
heat budgets...............-+0% 211
heat distribution 218, 223, 233
Green (059 ome IS ODED Ace SO cSUD DATS Wap 219
distributed work 221
heat and work as measured at depth............ 222
SED ELACELON CURVES yore) e ateininia ainlateyaiatalniaiolelsbyelvye iota ptsl= 221
work of sun and wind..................-.. 218, 234, 235
hy poliminion yaa ic sti antec ss tabi eer a alatetebass/e 213
Lake Mendota, Wis., plankton comparison. ...... 241,242
iterate cited. cc. lese.o/eis.nis.<iers-ce1ini=ia) ates) ete bai che atetta at 252
Ma Crop laMictorn ye aicccleciedsis cistaisictasnicl stern (alsitale eee 235
methods of plankton collection...................... 235
micraplanktomaietaadhve tes sasktesteas dele oe seater. 235
PATIMOPLAMItOMM «fo erccias afeleresee titan tee ees Sat Oarete 235) 241, 249
MICE ATIC COMM oa eiciirroteinicis(asiviccteieliniacetiere bie eta es 235) 236, 243
Phatop lar econ octets oni cielsiancciaccsiasictaeitole ae vastarinte r= 236
plankton eos dsijgascerenss cae cecieeiaee eats tare 235,250
Collectior,mLeEHOdSS «5515 <:5.21< 10:s/areinie)-Isieinie efelsle= ial» 235
fabless. ss sactvaicclarhcatentelcarsialeieia cinta sim aestaat etait 243
radiation, transmission and transparency of......... 232
Stamimerhegt income sy, onesie 3 cjsie wie eine telolD ni 215,222,223
sun, work in distribution of heat......+....... 218, 234) 235
sun’s energy, absorption of.............00..20.0ce eee 223
transmission of, by waters of the various lakes.. 224,
228, 230, 231
thermal re girs os rejo1- = xsels,<1+ aeleiniolsiatpte aes isiale a cielo intarela 213
lite Gre fr GhneweaGonepoobeobncacconoaderonpeectcdsicc 213
transmission, of radiation...... 232
of sun’s energy by waters of the various lakes;.. 224,
Sor 230, 231
tratisparency, of radis tern eo ope cco 1o(0:ni0(n ofnisin stains sls sala 232
wind, work in distribution of heat. . 218, 234, 235
ZOOPIAMNELOM isd oryierel- «is ee le ere aietoiwluyo hae lolol eiste <iefaleeiae 236
alsoultuve jaan anoid Satin ar staini-feicisasmieiamian sereeaesietm cas 203
fishes, general:
GCOTISCLV ELIOT oy: ocics cia brace cielaisiaiejaiepinelelcininaiainie wleles slelaia 155
etiital OL GANS a0 ore As) aare we cieearars Beaty be sale erausiels Mites ie 188
hosts of mussels... . 120,137,148, 151,155,162
rescued from ection iran Sal banoehosoe seonasce 162

GENERAL INDEX.

Page.
fishes of Green Lake, Wis., in summer, distribution and
LOO sete ncicis Hhete sarin! stolete state cimiateralofalaicveraterstatatatstararels orataiets 253-272
Dibliograp la ypc ete ssiaatalelsnyojesieeseieienl-ieiee eoesnpeecieleanine 272
comparison with fishes of Lake Mendota. . 261, 269, 270, 271
GIStr a MGOM sfercere siete ere scais e blateeisictelet eteieeia tetelers 256,270
fOOd 5. Aaa els matinee risk ane ace ener os 262, 266, 269, 271
gill-net catches, 1919... ........0-2eeeeeee 257, 258, 261, 270
SDECICS CAM OBE iclacierste ats oteisie sieiese steele iets’ aieialaisieeiai ae 256
SET atria tyondeioior<.c).eloic winieiajeleeelejete © stele ere elots yale eters aes 270

fishes of Lake Mendota, Wis., in summer, distribution
and food:

comparison with fishes of Green Lake..... 261, 269, 270, 27%
£OOD ceva eeisionisielanereiciacinaleiainelatarestelaleh sins ania eae 269,271
gill-net catches, 1919... =. .....2.0---008 259, 260, 261, 269, 270
Species \Catl SAG eon sree crete (se sete ualeialelele seins 259

food, and distribution, of fishes of Green Lake, Wis., in

SUTIN OT erie cs alaewieiei ota nie -lepp pie alesis ates ee eee 253-272
Fundulus diaphanus menona, distribution and food.... 256,
264, 268, 269

Further limnological observations on the Finger Lakes of
ING WAWOTKG ST . = 0:10: .:tcteiels ctorcerals arate sol akie’s Castner eae eee
literature cited

Galaxides: genital! organi i). c7o.0.0% 07 wire octesiae els neice ainiortic 190
ganoids, relationship to salmonoids....................- 200
parvdistribution and food me. iiem os cack eect et eens 259, 269
Grand River, Mich., mussels........ 84,95, 102, 104, 109, 110, 118
GreatiLakesjunussels 15; So 0b Sess os ae wale cette 99
Great Lakes drainage, mussels. . 80, 82,167
Green Lake, Wis.:
bottom fauna. . . 251,271
description)...5 1) 22th Binder oteoens 255,270
fishes (see fishes of Green Lake, Wis.,in summer)... 253-272
hydrographiomap re .so. ei seieeet welche see eee 254
Plankton : ooscsscc sees owihe datotnaa cheddar deter 235
shallow waters compared with those of Lake Men-
Gata te 24 iaosssmsn oindiasdindae dénaie eee eee ee Ree 271
tem peratires; SUIMIMET ZOIO mie te.-1-)-teleiviel= eleleto eb wale tele 255
Gulf of Mexico drainage, mussels.............0.00e0seeee 82
Holston River, Tenn., mussels...............20-c0eeeeee 109
Homer; Minn, mussels’ scjccsie.c<aicieseteiissiehinerciaieiets 89, 102, 125
Howard, A. D., et al.: Natural history and propagation
of fresh-water mussels.5... closes cqiniccatyektiaii aca ae 75-182
Ilinois River, mussels 1-10.<.cenassceennsosoneteeeee 109,124
Tndiana/lakesmiasselSex ta reciv selec ticles cis wert iele vietelefonte 99, 102
industrial wastes, harmful effects... ............0.000005 124
James River, N. Dak. and S. Dak., mussels............. 96
Johnny darter, distribution and food......... 256,263,268, 269

Juday, Chancey, and Edward A. Birge: Further limno-
logical observations on the Finger Lakes of New York 209-252

KankakeeRiver; mussels: J... a csssac cease cna: 104
Kendall, William Converse: Peritoneal membranes,
ovaries, and oviducts of salmonoid fishes and their sig-
nificance in fish-cultural practices................... 183-208
Lake Amelia, Minn., mussels. ............0+seeeeseeeees 92
Take Brie mussgels..b;;., cassie vine = ee sis ieleonieimalat- tees 99; 100
Lake Maxinkuckee, Ind., mussels......... 83, 85,92, 98, 109, 122
Lake Mendota, Wis.:
bottoms ie cnn ae paalaiciorsletsatere s neee sti (ite 271
description
fishes (see fishes of Lake Mendota, Wis.,insummer).. 259,
260, 261, 269, 270,271
pee COTA Leas Sorin oUneeOLedeaUnice Sasecenees 98, 103, 108

GENERAL INDEX.

Lake Mendota, Wis.—Continued. Page.
Manttoplaniktortls) 1 cic scic\sevicis fees aii Enpatoncsag 241, 242
shallow waters compared with those of Lake Green.. 271

, temperatures, summer 1919.........- Sieista ae leteicietiete = = 259

Lake Michigan, mussels..............- 108

Lake Michigan, Traverse Bay region, mitscelos aeeleniniefees 99

Lake Pepin, Minn., mussels........ Ryaneters eataatcte diaeklciose 88,

89, 93,97, 98, 103, 108, 109, 118, 141, 159, 164

Lake Pokegama, Minn., mussels.............00ss000se8 91,118

Lake St. Clair, Mich., mussels....... abadoaooneonde SHAMS 99

Lakes of Middle Western States, mussels.............. 6 98

Lakes of Upper Central States, mussels... pyc 99

jamprey, genital and visceral organs . 188, 189

largemouth black bass, distribution and food. . 256,

2595 ane 268, 269

Lepidosteus, genital and visceral organs.............. 188, 201

Lepisosteus osseus, distribution and food.............. 259, 269

Lepomis incisor, distribution and food.... 256, 259, 264, 268, 269

Leucichthys:
birgei, distribution and food.................. 256, 265, 268
peritoneal membranes, ovaries, and oviducts 197
sp., distribution and food............. 02... cece 259, 269

limnological observations on the Finger Lakes of New

Vork (see Finger Lakes, N. V.).........2-00e-eeeees 209-252

Mom CHO WAL ieee tet tetate mescle fs ohalalafe ae elesnla[ololquulnsetn ainialolaidisisieie’s IgI

Lost Lake, Ind., mussels RAC Kiadcubeneoee adeebboe Bebaanded 92

Peyonis Se MICH = SoITMUISSE1S oye fleets efele) «le /e)s\aye nae) aiiolsieinla(cleiisja ai « IIo

WMarlisort, pA Tks ti 1SSO1S 2 ayy mis ciateleye + i0iz)jeieje/eiclaleleratercieiels sto 109, 128

Mallotus, oviduct................ SORE E cue Anat ese rc 191

Maumee River, mussels ; . 92,111

Micropterus dolomieu, distribution arid roodae sty 265, 268, 269
BAN OL ESo sraraeraMoa lercihas Sever ale nerettree ee 256, 259, 265, 268, 269

migration, seaward, of chinook salmon in Columbia and

SaciarientomRiVers sas tetas sews seiciotretiere nieleterottee orn 1-74
Minnesota streams, mussels............ 00000000 eue 108, I10, 118
minnow, distribution and food............... 0.0. e eee 269

blunt-nosed.......... ... 256, 266, 268
Mississippi River, mussels....................5 80, 84, 89, 92,93,

96,97, 98, 100, 102, 104, 109, 110, 112, 114,
IIs, 118, 119, 120, 125,127,137, 163,167

Missouri River, mussels..................06- 96,99, 102, 114-123
Murenide, genital organs.......... ahoobadadadnaas 188, 190, I9r
mussels, fresh-water, natural history and propagation.. 75-182
BUNA ASSOCIALES ler etoiststtaie n eisicisieialnisielsitiei eee siete eicsete 119
Ipreedin gin teceecise cs - Sere 85
age begun........ yatot cen cs7
brood pouches 138
deposition of eggs, seasoms.............0.60.000005 140
RESTUIZAON een ee eet sis ie)sjaieieisralels kite npaista se 138
incubation of eggs, seasons 140
marsupia 138
ovulation 138
byssus, species known to have. ..............0...0-. 158
Chillicothe stata fo ae sevnacre ronrd ee eee Seles I09
(COMMMEN SALISI se tenet tai fei-lite) fete eile tel snare rete ele 119,120
commercial species................- 98, 101, 107, 141,152,154
Comipetition 1oOntood ere reset acacs rch ete teks « 120
conditions of existence.
conservation.

culture...
aquaria
CRATES Th iccjciiteresieicvalsinnr cette eemta cts 84, 109, 127,137,159, 164
PeuSee see poet OO SCAG OD HOTU OARS SO SOE 164
porldsteee cece IOI, 125,126, 127, 137) 159, 163, 164
tanks or troughs 84,92,93, 125,126, 165
density of population. .................... sigAeOG aoe 84

mussels, fresh-water, etc.—Continued. Page.
digestive gland cont so sleetsacietereteicteis ifelasor otelsi saciaeerie 173
distribution (see also habitat)—
banks ofistreams, effects... .js:csie <0 sisrsjeisepctein cisis/e = 97
barriers in streams, effects. . . z 96
horizontal ese ojos maysisjsteisisjste sisieaise ses anise ante ate 97
esi Atticl itialers ysis aistetalolaisiaisinrels's sitio sivalvieie steko 95
diversity in form of(shell......< ces + oc ese cm eelsmnins 170
enemies. . eee e eee a weer esac tenner eseesrens 122
iene (eA habitat) raraardvaiatcha eiatare/a isis cjacteyarnjatafelacd 94
external features OfSHELN 5 1.o)0 0011 «elem +(e sisieisniaiiuei 168
Fairport (Iowa) Fisheries Biological Station, ponds,
ENS 6 Ago poanars ota Ironousodaeeaaber 80, 84,92,93,
94, 100, 109, 114, 121, 125,126, 127,137,
138, 140, 143, 150, 155, 159, 160, 163, 165
Feeder Canal, Fort Wayne, Ind...:............. 84,92, 101
feeding habits. oc os ssaes:sacale teas og ate sites vie act Beers = 86,114
FOO oie ch cwig = asarerern te soretsvaie min en apo Teaaple os CISA amin = 79,87
UT 255 She eaacdReAGOUROCREOOON BOSCO eD
Ce WTS Spa arinedoncer ineaneredt: ddcr <anpe
Clark, H. Walton, observations. ..
Competition for coc: <= cistacosapier sia garmateesareiesis ois
GlESni Gh eiarconer see cepporommarddescccr sume aes
LEECH: sy. <iotaraiere(oiaasaiefoeictoleiere pani siete ae elarcacie cs 88,90
GUI Cpa Somanceornandanos yar aeroo7as. pret
discrimination under normal conditions as
feeding) habits... cape -wnaapeers se ccremaeba dejentatee =
fishmedty ogee asedaciate eas ccs ees le ae eee
Mapellates sa vere seta c iter cistssisiststlncnmiceicieieneieestalet
meh egal bate YS ec) paganocec Manos anaceesaeorncesn
peal ee eeiaoebe OO
observations 88, 90, 91,93
organic matter, os0ce- haces sams Se . 88,114
Palmellales tira ststststileiniata\erattslotaietabtele-olaiaValcterelahet tof 90
Pyekcerel ys lOO say, ei<in 5 is/alotnistal apts) afainialsia alersietsieislsieis 90
Plankton crane ccd se smie.« <i teba (abstain Taina 88,92, 114
Schrader, Franz, observations.................- 88
Shira, A. F., observations 93
significance of problem.................20se0000- 87°
tadpole tailsiicscoc csoaistakistiesioasiciats Mais easy tas 90
utilization of food materials...............+..+++ 89
wevetable marten: ocissicis\cleinlnlslelsio'eslvie(sleaieleisteleiaiatc 89,90
water content... 88,114,120
form ofishell) diversity, in) a).cn:. aietereiatefeteteicls lalate are bie 170
173
173
143
148
144
hooklessiora proms EVEL eee icte vicina lnt=!= «ivi ccer sei eteiels 144
mature, months found.................00s0005 141,142
Gulfiof, Mexico drainage 22 5 2)... «<0 mene tastes a 82
Habitat sc ceeerscicectsteicissete metetee letane ree eiasahers ete re arse a7 94
bod yiokswaters cc cccs oc cielo salts « a icte%e, srt ete stand 94
bottom.. .. Ior
Ge a aooncocnsb i aaboo dadveden sneer on soaat.c 100
current III
GUS 019 Aanced sgede conccanonpoobococOonmendagbcardasin 107
issokved (AGEs me cerita eietelaiateletelasererera ste sel= See ey)
lakes....... 97, 101, 102, 103, 108, 111, 115, 117, 118, 124,125
110
100
minerals in solution... .0.. ives. ceils tire ck lecicc. = 114
ponds..... 100, IOI, 103, 109, 115, 121, 124, 125, 126, 159, 165
QGr a Cn go nowendorsoueccnL EE, BAIS ORE I00, 103

streams. ... 94, 101, 102, 105, 109, 111, 116, 117, 118, 123, 125

276 GENERAL INDEX.
mussels, fresh-water, etc.—Continued. mussels, fresh-water, etc.—Continued.

habitat—Continued. Page. tivers—Continued. Page.
SWAMPS soo eaelese soso aaetaidowiats aisle se raleia ine ave ero 100 Holston River, Lent... ic icicscccevevcescvesvere | XOD
typical..... 119 Uiltiois iver. 225: ei cece eeee 109, 124
vegetation... 118 James River, N. Dak. and S. Dak. . 96
water content. . 113 Kankakee River... «- 104

habits ee ccesiscteie + 79,82 Maumee River... . e+ 92) XIE

To erage boouobicrembobocanghorosnpnbsg2asnapolabata6 172 Minnesota streams. . 108, 110, 118

omens Marana eae atatetaleietsieliaiatettatefelaiera cteriatel ieee 89, 102,125 MMISSISSIppi RAVE: aciac ie stele tiscclons cisfemisiccinie 80, 84, 89,

hosts ie se 120, 137,148, 151, 162 92, 93,96, 97,98, 100, 102,104, 109, 110, II2,

infection..... - 120,137,151 114, 115, 118, 119, 120, 125, 127, 137, 163, 167
optimum........ Seam aE ace Rasen dostoboensnes 162 MissouriRiver.s-.scsseee ee eee nee 96,99, 102, 114, 123

internal features of shell. . .... +. 169 Musselshell River, Mont. ............2.sceeeeeee 96

internal structure of soft body..............-.-+...55 173 Red'Riverse descent eee 82,96, 99, 114, 123

juvenile stage. . ++ 84,93, 118, 123,137,157 Rock Castle River tccnesceweeeetecserse cement 109

labial palpi. . 1.0.0.0... ese ee ee eeec sence eeee se eenes 173 Shell(Rivers Mints. cence vescsocsacneesccereseae IIo

lakes— St.Francis River; /Ark....s.00csu-ssaceesheneene 128
Caddo Lake; avand\\Texs-n-m:-a02eee eee sees 98, 109 ESSE 9a cad obeeastecahindoodbedooueen 92
Center Lake, Ind. +. 102 SUibfaryiRiver sos ceo care eee te eee eee 92
Great Lakes. 2.02.0 -0c2ese-sc2steceseeerswccerns 99 Vellow, River, Itids.csc.cssuccessceasecn sheers 9t
Great Lakes drainage................-..+5-- 80, 82, 167 D7 | WaseeeRneetmerioe tion mon SnmOnntmasoactondnokntatcs 168
Indiana lakes: SOS a ee eee 99, 102 abnormalities in growth..................-00000- 133
Lake Amelia, Minn......................00.005- 92 CAlCATCONS JAVETe ae teleiais nisiniele Aalclera a nia siereiaitiors ets 129
1 or Coe rbe ce Sb Coe bccoracddrigudesacrcacocood 99; 100 diversity IMLOMMl ests ee cee pete cere eee 170
Lake Maxinkuckee, Ind.......... 83,85,92,98, 109, 122 external features.......... Pecbencrpeb pce neGGee 168
Gake'Mendota,Wis:s sa.civciccscnceeeeens 98, 103, 108 Fairport (Iowa) station. . 125,126,127
Byake Muichipati’ cera cree see ree cena atatels 108 formation 125,129
Lake Michigan, Traverse Bay region............ 99 growth. ..... 125
Lake Pepin, Minn.... 88, 89,93,97,98, 103, 108, 109, 118, growth rings. . 129

I4I, 159,164 hypostracum.... seat

Lake Pokegama, Minn..................2ss000 91,118 internal features. ........ arathX69)
Lake St. Clair, Mich........ Saadwis doa pads sees 99 measurements of growth. 125
Lakes of Middle Western States................ 98 Mississippi River........ 125,127
Lakes of Upper Central States.................. 99 mother-of-pearl layer. . 130
Dosti@akesinds cel ncsco tages eee oe 92 nacreous layer. ...... 130
Oneida\Take; Ni Wid ogee cscs 103, 108, I10, 119 periostracum. .. 129
PikeTake; Isdiis 2 joss hse ee oe oe 102 prismatic layer. 5 129
Rice Rake, Wiss ees Oats hic oa ie 98 FINES oe oeieaiee seine alaslelsta Pere 129,132
Winona Lake, Ind..................... 86, 102, 108, 109 Significance Of rimgs........0+e-seeeecescecererss 132

lifethistoryaees leew cea nese emetic temeelans 79, 135-182 . 128

Lipfolds'.4 35s thens cco nua dcoesnke CO ee ae 173 soft body............eeeeee oo | (X7E

Rae PIRP Atte EI SU ana! an aera tannin ayeee 173 stomach........ Oma A

LOeGIMOLION SEs. 2.55222 55 dois.n dye ode see ee 79,82, 118, 123 structure....... 167

yous) Mich ip. .c sais see nin neoaaenee Meeetees 110 internal 173

Madison, Ark.............- . 109,128 symbiosis....... weteeeeee II9,120

mantle, form and functions. . 171,173 unfavorable conditions for .

metamorphosis without parasitism - 137,156

MLOUC ts Ha as hasan soe Tee steers Sree eX73'

natural history. . 81-134

organ of Bojanus. : 173

PALASICES Raatyeinise selene sale cathe eae aah o's, dase teers 121

parasitism..... . I19,120,137,148
PEUTIC Ys 2 -) 70) vin vie din epee ee eee oes aie eee 155
metamorphosis without. . o” 56 sewage discharge........... Sow dee wantan tee Maa 124

PYOV AIG ss sale siete cS awelniniew oe cists aizndls blatewhe atelsealenterere 119 shifting bottom... 123

propagation... .. 80, 135-182 stream barriers . 96

protections s s:fi.ris ok delcise siaise aisles Mela aiaatet ecsicteeen brass 80 turbidity....... 114,123

PO CHIN fois aio enh odin ulelom wen nue sek ee ae ee 173 WA PG ATNS horus, feccelssiaisicine wins eRe sislelals pagans 124

rivers— Winter Habits 2-075 ois hsralays olaislarwlsinuaieisicin’y winlenieee lanl 85
Andalusia Chute, Mississippi River..... 97,104, 109, 119 Musselshell River, Mont., mussels... ..........020ceeeeee 96
Auglaize Riversss7. 22+ 209- nse ce-an 4 +aeeanee- 97,93 | Natural history and propagation of fresh-water mussels. 75-182
Calumet Deep River : 95 bibliography. sv. een ean nisceenceenee sees 177
Chicago River...... : 96 | Neoceratodus, ventral mesentery... ..........-se00-e00s 188
Clinch River, Tenn. - 84,109 | New York, limnological observations on Finger Lakes. 209-252
Cumberland River.. - 97,109 | Notemigonus crysoleucas, distribution and food........ 269
Des Moines River... .. 114 | Notopteride, genital orgams................+
MetroitMRivers pats senda wea Mewar sass wswaeieee 99 | Notropis atherinoides, distribution and food
Grand River, Mich... . 84,95, 102, 104, 109, 110, 118 WeterOd OMe sivas c wae csieieate elobleleieminia ace etree eaeets

GENERAL INDEX. 277

Page.
Oncorhyncus, genital and visceral organs and mem-

POL ATICS ie aictn/elolaleruslainialaisinlelciei=(eieilslal<im 188
Porbuscha ls. caleseee <eenen == -. 188
Rasnitobieycejiare sslawientecicittsest 188, 194
pi tag 3A GoouancoDDpESconto C 188
TSCHAW.U ESCHER oreo cteteiciatsrasisieteinieisicjeitiele! sietelaistelai= iat =ia!elele 188

Oncorhynchus tschawytscha, early history and seaward

TTS ACG So anne DAR GSH OLONODSOod IUOCUa UD OMOATIoon nanos 3

PET ta OLE uuls rn prteteretsieteecicineteniesjsorenwialsielacissieicieefe 188
Oneida Lake, N. Y., mussels................. 103, 108, 110, 119
Osmeride, genital and visceral organs and membranes.. 200
Osmenus, genital orgams.............s.eeeeeeeeeeee IQI, 200, 201

Ged CT son scant son cbonagesspnpeosaccoussccoEeas 189

ERLE Ree tieet alec = <isl/ala afeiniclelslelsielnieinicie\cialw'slstete'sininia 197
Pearse, A. S.; Distribution and food of the fishes of

Green Lake, Wis., in summier...................000- 253-272

Perca flavescens, distribution and food.... 256,259, 266, 268, 269
Peritoneal membranes, ovaries, and oviducts of salmon-
oid fishes and their significance in fish-cultural prac-
PA COS ere ete ate ise eicic sk iciainieiaisteraie a fate sislaversiaieianisiaieiacters 183-208
= UVORICS COUISIIICER yy) oie ercinia.c ele eieiare sya) 6'e siaie\sicle > se 200
pickerel or Northern pike, distribution and food........ 256,
259, 263, 268, 269
pike, wall-eyed, distribution and food................ 259, 269
Pike Lake, Ind., mussels................ 5 ees, aso)
Pimephales notatus, distribution and food.... 256, 266, 268, 269
Pomoxis sparoides, distribution and food. . 259,269
Protopterus, ventral mesentery..........-..200s00e0e00s 188
pumpkinseed, distribution and food.......... 256, 264, 268, 269
ce Tate. Was. StUISSEIS 0) siare's c cjain(oin\nia'eolaic/=)siein(wrelalass/<.0 98
Rich, Willis H.: Early history and seaward migration of
chinook salmon in the Columbia and Sacramento
ISS Bade soacepr anuncasodcddd duoaocsdaaurvacsc socacte 1-74
Red iver MUSSELS Sach afecctainiais sioisla(s cial eleieiein's 82,96, 99, 114, 123
Roccus chrysops, distribution and food............... 259, 269
rock bass, distribution and food........... 256, 259, 262, 268, 269
Rock Castle River, mussels. .:.........00ceeeceeeeseees 109
Sacramento River, seaward migration of chinook salmon

To SSR Ec ode bine SC make, comn Suibe TLC GUE CU UG SaE CHCOS DCH 1-74
Salmo, genital and visceral organs and membranes 188

SOD Obie ctocata at inteetd ata eiclarsieferivinid icin ialetete ste leeietaeiatmeieia)atete 188
AGS SA pas aseodoogoncosnannecdccn Sodearooausascnene 188
PERT RE op oe ee goba se aad soo MON USNE Td SB OMS Anse osopesad 188
salmon, chinook (see chinook salmon).................+- 1-74
Salmonidz, genital and visceral organs and membranes. 187,

188, 189, 190, 191, 194, 200
salmonoid fishes, peritoneal membranes, ovaries, and
oviducts and their significance in fish-cultural prac

PICES ee igs lcie eee State ristetniciate wok elec vemicist=[cieteieie aie le 183-208
aod omiinta liwsscerane pyar viaisin as wisiate sisisanis pce ceicicicio acs 185
supporting membranes... .............0.2000eeee 187

Bin lad detaepremetseet tein ctemates ade clas ec ex'cjercinteWintses ove 187
Alister FAnonteACeetedtserisieeisiecis c diveeaikicitseies cicimic'e'sl< 187
anatomical facts, relation to fish culture............ 203
@oreOne as nee ae eiaike oe Ualsssiacid ces bes claeegate sins 189
Coreponiidne semaine hie sates cis «vie a oldiniailsne cies te oe 197, 200

salmonoid fishes, etc.—Continued. Page.
Careporntise ony eecicencia catia cteeieleranieiaieinmisicle <feiwietatesisiate 197
elasmobranchs, relationship... . : 200
fish-cultural practices, relation of eratnicd facts to. 203
ganoids, relationship’. |<. --o--2-crccsscercreercrsners 200
genital organs, structure and development.......... 188
gonads. .
kidneys......
Leucichthys
liver ene
mesentery .
ayes = aap has agcUs so némseaee Hos soadquecetnae 188
ventral. . 188
mesorchium. .. . 188
mesovarium . 188
Grane naece, siete OBS aac aetna se cisisteiaisicwraic 188,194
OVAaNian Mem PLANES eee a. ='a5/c)-!a\01e\s'a'e n's\s}e-cjeie ein 188, 189, 191
OVARIES seacaeieesivciees ... 189,190, 191,197
oviducts. .. 189, 190, 194, 197, 200
a4 187
peritoneal membranes...............+-+--0-2------- 197
peritoneum and supporting membranes of viscera... 187
Salma Species Olat cece ne ceciacccacecieislcisisninics as 188, 191, 196
Salmonide2. . . 187,188, 189, 190, 191, 194, 200, 201
Salvelinus, species “Wie ence uotCnaonco Beso OAS 188
viscera, supporting membranes. ..............0.000 187
works consulted 5 206
Salvelinus, genital and visceral organs and GSS. 188
PIMC CO IIS aerate a aete a ae iolalelare see =ele[etsine cia loietn\aw miciere 5) 188
fontinalis. . 188
kundsha... 188
malma... 188
marstoni. 188
oquassa...... ei 188
Stapnaliss cp pcccmctast decanter ate sleiawlsivicte aleistere 5 188
Schrader, Franz, observations on food of mussels....... . 88
Seneca Lake, N. Y., limnological observations (see Finger
Tales INA Wia)s neat nc ticninaecin citich Gicw tice sine Niaislelaisionisc 209-252
sewage discharge, harmful effects. . . 124
Shell Riven, Marin’, sttsselsmecs -1-tatarisiolelole'e fete sini eteitstaiareie ein 110
Shiner, distribution and food............. 256, 266, 2
Shira, A. F., observations on food of ectecels Senta tata 93
Shira, A. F., et al.: Natural history and propagation of
fresh-water WNSSelsi-.o. eae eneetemccieieiniaetelelno nese 75-182
smallmouth black bass, distribution andfood.. 256, 265, 268, 269
smelts, genital and visceral organs and membranes..... 189,

190, I9I, 194, 197, 198, 200, 201, 202

St. Francis River, Ark., mussels. ........5....-se0eeeees 128
St. Joseph River, mussels. . 2 92
St. Mary River, mussels................... A 92
Stizostedion vitreum, distribution and food. . 259, 269
SHUT PeOE OVICMCELESS em ee ee eame er aniecieminaeiaian cele eiciela 189
sucker, common, distribution and food.... 256,259, 263, 268, 269
top minnow, distribution and food............ 256, 264, 268, 269
trout, brown, genital organs...............-eseeeee-ee ee I9t
fresh—wa teri ac eeeseeeeniaeemneninclariimemionesiasteisicci¢ 189
white bass, distribution and food. ...................- 259, 269
whitefishes, oviduct..........
Winona Lake, Ind., mussels
yellow perch, distribution and food....... 256, 259, 266, 268, 269
Vellow River, bnd), mittssdlseyocjsecceetcissee oe oleae or

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