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THE SALMON OF THE YUKON RIVER: : : :: :
eis eee Bos se: By-Charles‘H; Gilbert

From BULLETIN OF THE BUREAU OF FISHERIES, Volume XX XVIII, 1921-22

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Document Gi ORR Ce re en ac bre Sa Sena aae oara ce ROSCOE NOVEMUCK. OT, EQO22

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THE SALMON OF THE YUKON RIVER :
7 3 -¢.% + By’Charles H. Gilbert

From BULLETIN OF THE BUREAU OF ele Volume XXXVITI, 1921-22

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i DOCUMENTS DIVISION

THE SALMON OF THE YUKON RIVER.
os
By Cuaries H. GILBERT,

Professor of Zoology, Stanford University.

&
CONTENTS.

Page.

MVECOCUUICTION)< ¢vs ce 14 Utiswrcrseedlnae tonne suas - ee eee ee 317
The king salmon (Oncorhynchus tschawytscha), eT eee eras ay ae ak wee ato
Rate of travel... ... ets cere : 318
Growth and age at maturity. 320
The chum or dog salmon (Oncorhynchus keta). . 325
Rate Of travel eiivsise seve edicts 326
Wear classes, i056: .55; : 326
Proportions of sexes. .. . 327
Size at maturity.......... y Nau parties fe adau gait a Terre 328
Growth and scale readings. ....... : ee eee ree 320
The sockeye salmon (Oncorhynchus nerka). .. . 330
The coho salmon (Oncorhynchus kisutch). : 331
The humpback salmon (Oncorhynchus gorbuscha)...............-. 332

INTRODUCTION.

The summer of 1920 was spent by the writer, in company with Henry O'Malley, at
that time field assistant of the United States Bureau of lisheries, in investigating the runs
of salmon to the Yukon River. The primary object of the expedition was to ascertain the
advisability of permitting the operation of one or more salmon canneries on the Yukon,
in view of the possibility that they might so curtail the salmon supply that it would fail
to provide natives, and white inhabitants as well, with the stores of fish that they find
essential under the rigorous conditions of the far northern climate. It was to be deter-
mined whether there existed an excess above the needs of the inhabitants that could
safely be used for commercial purposes for export beyond the boundaries of Alaska.

This phase of the situation has been dealt with in a report to the Commissioner of
Fisheries and was published in 1921.'' Some of the details that are given in that report
concerning the movements of the salmon during their run and the rate of travel that they
maintain in their ascent of the river are herein repeated, but the body of the present
paper is concerned with the growth-history of the Yukon salmon and the ages at which
they have reached maturity. ‘The Yukon River is near the northern limit of range for
the Pacific salmon. ‘The effect of the arctic cold on growth and age of maturing is an
interesting problem.

_ Investigation of the Salmon Fisheries of the Yukon River, by Charles H. Gilbert and Henry O'Malley. Bureau of
Fisheries Document No. 909a, pp. 128-154. Washington, ro21.

327

318 BULLETIN OF THE BUREAU OF FISHERIES.

Three of the five species of salmon that occur along the Pacific shores of North
America enter the Yukon Basin in sufficient numbers to constitute distinct runs. These
are the king or chinook salmon, the chum or dog salmon, and the coho or silver salmon.
The names here given are those by which these species are known in other districts of
Alaska and generally along the coast to the southward. Unfortunately, in the Yukon
Basin, there is confusion in this regard. The coho or silver salmon is most frequently
called chinook, while the various grades of the chum or dog salmon are known as “ si/vers,”’
“halj-breeds,’’? and ‘‘dogs.’’ The king salmon alone, of the three species that ascend
the river in numbers, is called by the same name by which it is elsewhere designated.

‘The two remaining species of Pacific coast salmon, the humpback and the sockeye
or red salmon, enter the river each year in small numbers and have no economic impor-
tance. To what extent the individuals of these species may be strays from other streams
that have well-defined runs has not been determined.

The material on which the present paper is based was obtained from June 15 to
July 31, 1920, at the cannery of the Carlisle Packing Co., located in the entrance to
Kwiguk Channel, a branch of the Kwikluak or South Mouth of the Yukon.

THE KING SALMON (Oncorhynchus tschawytscha).

The king salmon is the most highly prized for human consumption of the three
Yukon species. It is also valued for dog feed, especially in the upper course of the river,
for by the time the salmon have fought their way upstream a thousand miles or more even
the richest species contains no more oil than is needed to furnish satisfactory dog feed.
As it enters the mouth of the river, the Yukon king is the richest salmon known to us.
It there drips oil profusely when hung on the racks to dry and is, in fact, too rich for most
successful canning. The canned product, if handled roughly, or if shipped to distant
points, is in danger of breaking down to a substance of mushlike consistency. King
salmon taken at some point higher up the river, where a portion of the oil would have
been expended during the ascent, would in this respect furnish a better commercial

product.
RATE OF TRAVEL.

The run begins at the mouth of the river in the latter part of May or early in June,
almost as soon as the river is clear of ice after the spring break-up; and it lasts as a com-
mercially valuable run for about three weeks. ‘Tradition has it the king salmon appear at
points as high as Tanana and the Ramparts at the same time as the first steamer that
ascends the river from St. Michaels on the opening of navigation. ‘This would indicate
an unprecedentedly high rate of travel in a river with very swift current. Such incom-
plete data as we have concerning the ascent of salmon in other rivers indicate a rate not
to exceed 10 to 20 miles per day. But in the Yukon Basin the distances to be traversed
are great—some of the spawning beds being 2,000 to 3,000 miles from the sea—and the
summer season is much shorter than in any other large salmon river. ‘These two factors
necessitate a high rate of speed in ascending the river, and the fact that this has been de-
veloped in the Yukon salmon is one more instance of close adaptation to the conditions of
their environment on the part of a highly localized race. Rapid ascent of a river means
expenditure of energy out of all proportion to the distance to be traversed. Unusual
stores of potential energy in the form of oil are therefore required by the Yukon salmon.
We have already referred to the unusually rich provision of oil in the case of the king

SALMON OF THE YUKON RIVER. 319

‘salmon, and the same is true of the chum or dog salmon of the Yukon, which excels in
richness and amount of oil the chum salmon from all other rivers in as great a degree as
that which distinguishes the Yukon kings from other king salmon.

As regards the rate at which they ascend the river, we have more reliable and complete
data for the Yukon than have been secured in any other stream. Records were obtained of
their first appearance at a large number of localities. Some of these were ascertained by
means of wireless messages sent during the early days of the run, before the dates of the first
captures should be forgotten. Many others were obtained during our ascent of the river in
early August, when all fishing camps were visited and records were inspected concerning
the run of thesummer. Inanumber of instances complete written records were available,
which gave not only the date on whicl: the first captures were made, but the numbers of
fish taken on each day of the season. While we recognize that the capture of the first
salmon of the season at different points along the river may vary within a few days in
relation to the beginning of the run, we are convinced from an examination of our data
that this source of error is not serious and that reliable conclusions concerning rate of
travel can be drawn from the table (1) presented below. Whenever two or more records
were obtained from different fishermen in the same locality the earliest has been selected.

It will be noted that the lowest rates of travel apparently occur in the lower course of
the river. But the results are here obscured by the known fact that salmon, on entering
the tidal area of a stream, move back and forth with the tides for an undetermined period,
before seriously undertaking the ascent of the river. The influence of this factor, how-
ever, will not alone suffice to explain the constant increase in rate of travel as far up the
river as Tanana, where it had reached an average for the entire river below this point of
62 miles per day over a period of 13 days.

Above Tanana, the rate again decreases, possibly due to the retarding influence of the
Rampart Rapids together with the general increase in current found in the upper portion of
the river, but the rate exhibits an unmistakable tendency again to augment as Dawson is
approached. The first king salmon to reach Dawson in the middle of July, 1920, had
been traveling against a consistently rapid current for 29 days, at the rate of 52 miles per
day, and during this period, as always within the river, had taken no fcod,

TABLE 1.—DaTES OF CAPTURE oF First KING SALMON AT A SERIES OF LOCALITIES ALONG THE YUKON
RIVER DURING SEASON OF 1920.

1 |
| Approxi-. Approxi-
mate Miles / mate Miles
Locality Date. number | traveled Locality. Date. number | traveled
of miles | per day. | | of miles | per day.
| traveled. traveled.
South mouth OLIV Ekicas « sams IME? SV ly scrcoce.s [seems £2 . || Whiskey Creek, above Louden.| June 27 | 622
Run begins south mouth eA NRLERE? Ss | area cent leds Meas ARES «Ol etna. Poa’ t ts RIO 8a «| 659 5S
Pilot Station............ .| June 20 107 2a |) VAnama. <.cccecestisssecseeas) JUMe 28.,| 804 62
Marshall... sass «es tdoias«: 144 29 || Fish Creek, above Rampart |
Russian Mission, ...... 204 4 Rapids dpi ddetons sf Uy 3) ) 8s 47
PARAS vty ve'ciauavse 259 37 || Circle... ..| July om 14227 47
Holy Cross ots 27 35 || Charlic Cree ..| July 32 Tt; 317 49
Halls Rapids, above Anvic...| June 24 346 38 || Eagle .| July 313 1,402
Camp sr miiles below Kaltag...| June 27 440 37 || De Wolf's fish camp...... .| July ry 1,478 1
Kaltag hae 49 SBy cM PW SOIR (acu 9 apescvecd ciara yu asl faheeidOes oe 1,504 5
COV MCTMCN 5 4 sd aie ts bceiiecnire3,s June 29 555 40

The season of 1920 was notably late in Alaska; the break-up occurred in the Yukon
fully a week later than usual, and the salmon were equally delayed in entering. As
shown by the above table, the first king salmon taken in the delta was captured June 13.

320 BULLETIN OF THE BUREAU OF FISHERIES.

The run culminated quickly within a week after that date, then maintained itself at a
fair level for about three weeks, and was practically over by the close of the first week
in July. Stragglers appeared during subsequent weeks in July and August but became
less and less numerous.

GROWTH AND AGE AT MATURITY.

We have no knowledge concerning the feeding grounds of the Yukon salmon and
must leave the question open to what extent, if at all, the young traverse the passes in
the Aleutian Chain and attain their growth in the North Pacific. It is entirely possible
that throughout their life in the ocean, they remain within the confines of the Bering
Sea. None of them have been detected traversing the channels between the Aleutian
Islands, nor have they been recognized elsewhere along lines of their migration routes
in the sea.

Conditions in Bering Sea, it would seem, must be less favorable for rapid growth than
in districts farther south. The northern part of the sea and a strip around the coasts, in-
cluding Bristol Bay, are covered with ice floe during the winter and early spring months.
The temperatures to which the salmon are then exposed must be near the freezing
point. At the time they seek the river mouth in May or June the surface temperature
in Bering Sea approaches 4o° F. Under such adverse conditions growth during the
winter season must be at or near a standstill and in the spring might well not be
resumed before the beginning of the streamward migration. In that event the scales
would exhibit no growth accomplished during the year in which the fish was captured.
A salmon in its fifth year would indicate in its scale structure the completion of four
full years’ growth, and the margin of the scale would be formed by the winter check of
the fourth year. In other districts to the southward the salmon of the spawning run
have already responded to spring conditions and have begun a period of rapid growth
before entering the streams. The scales have participated in this renewed growth,
and the margins exhibit a larger or smaller band of widely spaced rings, which lie out-
side the winter check of the previous year. But in the case of the Yukon king salmon
this is not present. The winter check of the previous year forms the margin, and
usually no trace exists of any growth belonging to the current year. A very few cases
form doubtful exceptions to this generalization, with the outer one to three rings more
widely separated at least in a portion of their course. This feature is shown dis-
tinctly in the accompanying series of photographs of the scales of Yukon king salmon,
ranging from those in their third to those in their seventh year (Figs. 276 to 285).

Another striking peculiarity of the Yukon king salmon is found in their early his-
tory as fry and fingerlings. We did not secure any of the young, although attempts
were made to capture them with minnow seines on their downward migration, near the
mouth of the river. But the central areas of the adult scales contain records of the
early history and show conclusively in every instance that the young remained in
fresh water for a full year’s growth before descending to the sea. In the photographs
that follow, the line ‘‘1” points to the outer margin of the stream growth, which
presents a nucleus of finely crowded lines, beyond which are the widely spaced lines
indicating rapid growth after reaching the sea.

This habit of the Yukon kings is in striking contrast to what is observed in streams
farther south. In the Fraser River, the Columbia, the Klamath, the Sacramento, and

SALMON OF THE YUKON RIVER. 32I

all other streams thus far examined a considerable proportion of the adult salmon are
developed from fry that passed to sea during their first year and completed only a
small portion of their first year’s growth in fresh water. This “sea type’’ develops
at an earlier age than do those that tarry a year in fresh water, and it frequently
constitutes half or more than half the entire run. ‘The absence of the ‘‘sea type” in
the Yukon may well be related to the severity of the fall and winter, the lateness of the
spring, and the shortness of the summer season. It would seem that the hatching of
the eggs, the absorption of the yolk, and the emergence of the fry from the gravels
must be correspondingly retarded.

A third peculiarity of the Yukon king salmon consists in the retardation of the
age at which they attain maturity. In the Columbia River, where, owing to the use of
beach seines, wheels, and traps, the smaller salmon are captured in due proportion
with those of larger size, the youngest chinooks of stream type that are captured in the
spawning run are in their second year. ‘These are all male fish, as are those of the next
larger size, which are in their third year. Temale chinooks of stream type do not mature
in the Columbia until their fourth year, when they are not far inferior in numbers to
males of equal age. ‘The commercially valuable portion of the Columbia River run con-
sists of 4 and 5 year fish. Comparatively few individuals reach their sixth year, and
none has to my knowledge been reported in its seventh year. The condition in the
Yukon is far different. No 2-year fish were secured, and but one 3-year fish, which
was a male, 16 inches long, the scale of which is represented in Figure 276.

In spite of the fact that fishing was prosecuted exclusively by gill nets, which
during the king salmon run were of large mesh (84 or 8} inches), fish of diminutive
size were frequently entangled in the web and captured. Special attention was paid
to these, with the object of ascertaining the earliest age at which maturity would be
attained in the Yukon race. In addition to the 16-inch individual in its third year,
above noted, we examined 44 specimens ranging from 17 to 27 inches, all of them males,
in their fourth year. From this it is apparent that no female king salmon mature on
the Yukon until after their fourth year. They are therefore retarded at least one
year in reaching maturity, as compared with king salmon in the more southern part
of the range of the species. (See Figs. 277 and 278.)

Continuing the examination of larger sizes we encountered the first 5-year male
at 25 inches, the males of this age ranging from 25 to 40 inches. In the fifth year, for
the first time, we encountered female salmon, but these were very few in number.
Among the 131 individuals in their fifth year that we have examined, selected wholly
by size without reference to sex, there are 119 males and only 12 females. ‘This indi-
cates a still further retardation in age of maturing of females. Not only are there no
4-year mature females (so abundant in more temperate latitudes), but comparatively
few females develop maturity even at the age of 5. The 12 of which we have record
lie in size within the range of the 5-year males, the smallest being 30 and the largest 37
inches long. (See Figs. 279 and 280.)

The male 6-year fish are numerous, the 79 individuals represented in our series
ranging widely from 29 to 48 inches. ‘There is thus a wide overlap in size between the
5 and the 6 year fish, as is always the case, although, as will be noted, the 4 and the 5
year males show but little overlap. Among the 6-year fish, for the first time, females

322 BULLETIN OF THE BUREAU OF FISHERIES.

are really abundant, exceeding in number the males of equal age. Of the 185 6-year
individuals, selected without reference to sex, 79 are males and 106 females. (See Figs.
281 to 283.)

Another evidence of retarded development is found in the class of 7-year fish. In
streams thus far studied from the Sacramento to the Fraser it is very rare for a king
salmon to attain the age of 7 years. Only two such specimens have been observed to
my knowledge. In the Yukon, however, members of this class are not uncommon.
Although not specially sought for, 42 are included in our series, 10 of these being males
and 32 females. Here, again, the late development of females compared with males
is made evident. (See Figs. 284 and 285.)

Table 2 gives the distribution by sex, age, and length of all the king salmon of our
Yukon series of the run of 1920. For comparison similar data from a series taken from
the run of 1919 by C. F. Townsend, fisheries inspector for the Bureau of Fisheries, are
included in this table. It should be noted that the relative size of these various classes
in our series does not represent their relative abundance in the run. While no selec-
tion was made by sex, frequent selection was made by size at critical points. Thus,
special attention was paid to the smaller sizes, and these appear in our series in
more than their normal proportions. The same is true of individuals approximating
30 inches in length. It was at this size that females first were found, and individuals
of this length were specially selected for examination.

TABLE 2.—KING SALMON FROM MoutTH YUKON RIVER, 1920 AND 1919, DISTRIBUTED BY AGE AND BY

LENGTH.
Number of specimens, 1920. Number of specimens, ror9.
ee ot ; oe noe eats
Lent: 5 years. | 6 years. 7 years. 5 years. | 6 years. 7 years.
4 eee = —| 4 a =
Males.! Fe- | F | we. [Males F | x r
ales. : Te- aye fe .<| ie. |Males.* e- £c TC.
(Males. rales Males.| pinion | Afales. pir) | Males. marine Males males: Males. males:
= = “i | | | | Se | ee -
THINCHESM awe. hecacwas I ye i | ea | | me | . _ Utes
19 inches. 2 | Per eas ol eeeoron | eee athe | |: | eee Ns
20 inches. 4 | i Lear | jibe I.
21 inches. 3 | Ak
22inches. 3
23 inches. 6 r}.. |
24 inches 10 5 | Iscwcerea's | eran Se wlargretertet| aeeeneanga | eee ecey eres
25iNches. . 8 1 5 | j I
26 inches 3 2 | Ir |
27inches..... ; 4] Sik ee lee ro | I he |
AM UCHES Eo acisiacincine ae tinemte cs ral ; ere he an eae 6|.. peter r
zo inches... 20 1 z 2 |
30 inches... . 18 I 1 el ataratare | Beaqua eta ae al eatin | bs | |
yr inmehes.... 12 | I I | cis Re ek leaner r|
g2inches...... 11 3 | 4 i | I ual bad 2 | :
Bi TAL CHES « asacars scavnta ure nina ap sieterae? 5 cy 8 1 I 2 r | I
34 Inches Siverae H 10 2 5 3 3 a. I |
35 inches. a eras | 9 | 9 To 2 1 1 Ti) 10 I
aa | 3 10 2 z 1 z | 4 P| I
xj 9 | 8 I 2 2] 5 | T
7 | 14 |. | 4 | 5} I
7 | 7 | 1 | 3 | 2
5 13 4] 6 f. 2) 3 i T
3 | 13 | 2 2 2 | 1
rf 7 8 | + all Z I 1 | 1
‘| 6 7 Fa 2 | 2 |
i | 4 2 | | 2 aa 2].
45 inches, ..| 3 | zfs | Tilia |
40 inches | °a| I | I | :
47inch ae 2 len | | ;
48 inches. . ee | I | | ;
Potala, «2.2530 : 44 | 119 12 _ 79 | rob ro | 32 | ao | 16 | 5 | 20 | 8
Average length in | | | | | | |
PEEHCS ricieleiye.eleikecdss 23-4 31-3 | 33°5 38-7 38-5 41.8 | gor | 26.3 | 3m | 35-6) 37-5 | 36 417 37-7

SALMON OF THE YUKON RIVER. 323

The following table (3) gives the average sizes attained by the different year classes
in the two years 1919 and 1920, the males and females being stated separately. In
comparing these with similar averages obtained in other districts, we must bear in mind
that our Yukon material shows no growth belonging to the season in which the fish were
captured. Our 4-year individuals had completed three years of growth, but no more,
and similarly with each of the other year groups. However, no strict comparison is
possible between Yukon 4-year fish and the 3-year fish from other localities, for although
the latter had produced a certain amount of new growth in their third year, they had
not completed the growth of the third year when they ceased feeding and were cap-
In like manner no exact correspondence can be expected between 5-year
In com-

tured.
Yukon individuals and 4-year material from the Columbia or the Fraser.
paring growth rates from these different localities, the most satisfactory basis will be
found in completed lengths of the different year classes, computed from the scales.
By length is meant the distance, measured over the curve of the body, from tip of snout
to distal end of middle caudal rays.

TABLE 3.—AVERAGE LENGTHS, FOR CERTAIN YEAR GRovPS OF YUKON KING SALMON, 1920 AND 1010.

3-year group. 4-year group. s-year group. 6-year group. 7-year group
Sex and year. | : =a : 7 . rar | :
Average | | Average Average | .; Average Average
er. umber. y Number. by er.
Number. fength. | umber. lect Number. length, umbe length. Number. lensth
| 7 ae
Males: Inches. Inches. Inches. Inches. Inches.
TOMVaiesc yeaa R TA 5 16 44 23-4 119 31-3 79 38-7 10 41.8
Se). eee i liad pred 4o 26.3 16 Br 20 37-5 7 4-7
Females: |
TORN: dsceiasyy sient ° | ve] o! ‘ 12 $3.5 106 38.5 32 4o. I
Troe Petes eee ° o | 5 35-0 | 35 36 8 37-7
| | |

For comparison with other regions we have calculated the growth for each year of
their lives of 77 fish belonging to the fourth, filth, sixth, and seventh year classes and
present the results in Table4. We have followed Fraser’s latest paper® in taking 1.5 inches
(40 mm.) as the average length of the fry when the first scale ring was formed. Several
differences are encountered in comparing our results with Fraser’s. His material was
largely taken in the Gulf of Georgia and included a mixture of fish that would mature
during the then current season with others that would delay maturing for one or more
years; also, doubtless, a mixture of races, bound for different river basins and unlike in
certain of their characteristics. His measurements are throughout smaller than by our
method, inasmuch as they do not include the length of the middle caudal rays.

Table 4, which follows, shows with regard to each year class that the growth during
the year that precedes maturity is greater than during the corresponding year of classes
that reachagreaterage. Thus the third year’s growth of fish that mature in their fourth
year is greater than the third year’s growth in fish that would not mature until their fifth,
sixth, or seventh years. Furthermore, it is greater in 5 than in 6 year fish and greater
in individuals that mature in their sixth than in those that mature in their seventh year.
The third-year growths form a regularly ascending series from 7.3 inches in the oldest
year class to 12.4 inches in the youngest, and the lengths of the fish at the end of their
third year form a similar advancing series. According to this table we should find
that the largest series of 3-year fish in the sea at any time is composed of those indi-
viduals that will earliest mature. The same is true of the growth of the fourth year

2? Further Studies on the Growth Rate in Pacific Salmon, by C. M. Fraser. Contributions to Canadian Biology, 1918-
1920, pp. 7-27. Ottawa, rozr.

32 BULLETIN OF THE BUREAU OF FISHERIES.

and of the fifth. Slow growth and smaller size mean deferred maturity in all years
except the first and the second.

The failure of similar results to appear in Doctor Fraser’s article, above referred to,
may be due to the mixed nature of his material. His second, third, and fourth year
classes are not composed of fish maturing in their second, third, or fourth years, but are
accidental assemblages of fish that were in their second, third, and fourth years at the
time they came into his hands. His second-year class doubtless contained individuals
that would eventually mature variously in their second, third, fourth, and fifth years;
and his third-year class, fish that would mature in their third, fourth, and fifth years.
Under such conditions differential methods of growth of year classes could not be dis-
covered, even if they should exist. In Doctor Fraser’s 1915 material it was indicated
that the 4-year fish that were preparing to spawn were larger than those of equal age
that would remain in the sea for another year. That result was in harmony with
our present findings but was not verified by him in the material of 1916.

TABLE 4.—CALCULATED GrRowTH OF YUKON KING SALMON.

|
} ? Inches of growth at end of— Inches of growth during—
Num
| ber of |__ =
Year class. | speci- | | ; | lik: | : | |
mens. | First |Second) Third | Fourth| Fifth | Sixth | First |Second| Third | Fourth] Fifth | Sixth
| | | |
year. | year, | year. | year. | year. | year. | year. | year. | year. | year. | year. | year.
| |
| | | |
Fourth 7 26')) - Sarsisi by 623-0) 2.6 8.9 12.4 | OP fl geaart
eau ie : | 33 2.7 | 2.6 | 22 33-7 2.7 | 29 9.4 | 11.7 | Chau [serene se
Dake - 22 3 | 11.6 | 19. 2 27.8 38 - 3 8.6 7 6 8.6 10. 2 | ° z
Seventh fi} ster5 25] 117] 19 27 34] 407| 25] 92 7-3 8 w| 6.7
| Ve _ a =i
AVWETHEO: Saaliikw ees 2.7, 11.9 21 20.5 36 | 40. 7 | 2.7 9.2 9. 2 9.4 5.6 6.7
| |
I

In the following table (5) is given the average weight for all specimens of a given
length, the males and females being stated separately. The weights were taken with
an ordinary spring-balance scales reading to pounds and half pounds. No high degree
of accuracy can be claimed for this method, but the results present interesting terms
of comparison with the king salmon races of other rivers. The number of records
available for each length is insufficient for a wholly reliable average, a fact that will
explain irregularities in progression in the table. It will be noted that females of equal
length with males average slightly heavier than the latter. There was no noticeable
elongation of the jaws in the males at the time this material was examined.

TABLE 5.—AVERAGE WEIGHTS BY UNITs of LENGTH, YUKON KING SALMON, 1920.

Females.

Males. Females. Males.

16 inches. . 1] Ten FE 34 inches. . ; 15 18. 2 18.3 4
17 inches I 2 \| 35 inches.. 18 20.3 20. 4 12
2oinches..... 4] 4 |. 36inches.. 7 21.7 22 14
21inches, . 3 al. : 37inches. . 9 22.4 23:9 rr
22 inches... 3 5 | 38inches.. Io 25.2 26-3 19
23 inches. . 6) 5:8 |. 39inches. 10 26.8 28 | 13
24inches. . ro | 6-2"): soinches.... 12 29.8 30.5 19
25 inches. | II Fed | 4tinches.. 4 | 34:3 32-9 1s
25 inches. . 5 er Ble 42inches.. Om 36. 2 a0 16
27 inches... ea 9-6 ].. : || 43inches.. are 7 35-9 38.3 9
28 inches... aC 7 10.1 Nesas . eal 44tnches... 5 41-2 4r8 4
29inches... 5 21 | 1704. 431nches. . 3 | 43-7 42 I
3oinches.. 19 2.6 ur x || 4g6inches.. I 40 4025 2
3rinches.. 3 14 | 14 x || 47imches... 2 49:5 as teen.
32inches. . 15 14-8 17 | 3 || 48inches, . 1 48
Bg NCheS si onacied 5 | 16.4 | 17.7 Ir

SALMON OF THE YUKON RIVER. 325

‘The nuclear area of the scales of Yukon king salmon is of extremely small size and
contains correspondingly few rings. Undoubtedly this indicates comparatively very
small size for the fingerlings at the time of their downward migration. Our table
indicates an average size for migrating fingerlings of 234 inches. This is based on the
assumption that the fry are 114 inches long when the first scale ring is formed. If, as
seems more probable, they are slightly longer than this, our computed lengths of
migrating fingerlings would be correspondingly increased but could not much exceed
3 inches. The greatest length indicated on any scale examined by us is 4% inches.
The number of nuclear rings for each year class is as follows:

TABLE 6.—NUMBER OF NUCLEAR RINGS, YUKON KING SALMON, 1920.

| Individuals having nuclear rings to the number of—

| Average
Year class. a > | pum ber
5 | 6 a 5 ) | 10 1r 1 13 14 | ol rings
} | |
| | |
Fourth. 1 I 18 7 9 areal ee 8.
Fifth. .. 1 4 ir 9 34 18 | 3 I I 91
Sixth. . 1 10 26 39 | 290 | 11 I 9
Seventh..:.... 8 | 7 9 | 5 | I 7-9

THE CHUM OR DOG SALMON (Oncorhynchus keta).

The chum or dog salmon of the Yukon does not differ from other races of chums that
frequent streams in the more southern portion of its range either in external appearance
or in any of the structural peculiarities that distinguish this species. As is the case else-
where, individuals captured in the sea or those that euter streams well in advance of the
spawning period are symmetrical silvery fish, easily mistaken at a glance for the sockeye
salmon. The discoloration of the skin and the elongation of the jaws, which are later
provided with greatly enlarged teeth, are of universal occurrence in this species (as,
indeed, in all of the species of Pacific salmon) when sexual maturity is approached. In
shorter streams that are colonized by chum salmon, the fish delay entrance until nearly
ripe and when first seen have already lost their silvery livery. But in the Yukon, this
species penetrates to spawning gravels in the far upper reaches of the river, and it pop-
ulates as well practically all the tributaries in the middle and the lower course of the
stream. We find, accordingly, among the chums entering the mouth of the river a
mixture of colonies, some of which are bound for the headwaters, in reaching which they
will spend six weeks or more, and others that have not far to go. It is undoubtedly for
this reason that the entering fish vary so widely in different portions of the run in the
extent of development of those striking characteristics that accompany maturity.

During the season of 1920 all the early chums were of bright silvery color and had
abundant oil and a pinkish flesh that turned a deeper red on drying. But in a short
time changes appeared, even at the mouth of the river. At first occasional individuals,
usually males, appeared in a more advanced stage, with brightly colored bars on the sides
of the body and with long hooked jaws. When these were first observed they stood out
conspicuously from their fellows, which were still in the “silver” stage. By the last of
June these seasonal changes had become obvious in the great mass of chums then
running. It was the rule for the males to exhibit elongated jaws, provided with canine
teeth, and to show the beginnings of the bright cross-bars that characterize the spawning
males of this species. It might be thought that this development would continue un-

326 BULLETIN OF THE BUREAU OF FISHERIES.

checked until the end of the season, but, strangely, during the second week in July a
fresh run of chums that was no further advanced than were the chums of early June
made its appearance. These also were of bright silvery color and had symmetrical
jaws and abundant oil. Although entering relatively late, it seems safe to assume that
this run was far from its spawning period and had far to go. Along all the lower and
middle portions of the river fishermen who prepare dried salmon for winter use dis-
tinguish between the silvery chums and the others. ‘The “silvers” have flesh of brighter
color, rich in oil, and of more substance when dried. The others are known as ‘dog
salmon,” with intermediate stages called ‘half-breeds,”’ and are far inferior in value for
human consumption or as dog feed. ;

The Yukon chums in their prime are doubtless of far higher quality than chums
from any other river. ‘The differences between them and other races of chums are of
similar nature to those that distinguish the Fraser River sockeyes from the same species
known as red salmon in the average Alaska streams and to those that distinguish the chinook
salmon of the Columbia from the same species (‘‘king salmon”’) in the shorter streams of
the north. ‘The differences in all these cases are not only of similar nature, they are due
to the same cause. The fine quality of Yukon chums, Fraser sockeyes, and Columbia
chinooks is due to the great length of stream which they must traverse, while fasting, on
the way to their spawning grounds and to the large store of oil that they must lay up
for use at this time. In no other respects are the chum salmon of the Yukon different
from the same species found elsewhere. The Yukon king salmon, as we have previously
noted, are characterized by the same excessive provision of oil. They also exhibit in the
different portions of the run equally striking differences between bright individuals,
relatively green as to eggs aud milt, and the sexually advanced forms, with hooked
jaws and discolored skin. It would be no less logical to recognize two or three kinds of
king salmon than it is to distinguish, as is popularly done on the Yukon, two or three
kinds of chums, according to the degree of their advancement toward spawning.

RATE OF TRAVEL.

The chum salmon is generally known as a species that spawns exclusively in the
lower courses of streams, often scarcely above the reach of the tides and never far from
salt water. It is a remarkable reversal of habit in the Yukon chums that colonies of
them should penetrate more than 2,000 miles to the upper tributaries of that great river;
and it testifies to the flexibility of organization in salmon that a species that is in general
not adapted to long journeys while fasting, can, under spur of necessity, make such journeys
without food and exhibit great speed and endurance. From records of the first appear-
ance of chums at a large number of stations during the season cf 1920, it was apparent
that their rate of travel was not far below that of the powerful king salmon. They
entered the river about a week jater than the kings, at Tanana they were not more than
10 days behind the latter, and at Dawson they were some 14 days behind the kings.
The lower 800 miles of the river, as far as Tanana, were traversed at the rate of 50 miles
per day, and the next 700 miles, between Tanana and Dawson, were covered at the rate
of 35 miles per day. The lower 1,500 miles were ascended at the rate of 42 miles per
day.

YEAR CLASSES.

We have already noted that the king salmon of the Yukon are retarded in their
development and mature on the average more than one year later than the king salmon

SALMON OF THE YUKON RIVER. 327

from southern waters. A similar retardation is observed in chum salmon, which aver-
age distinctly older in the Yukon than in any other region of which we have record.

The earliest report on the ages attained by this species and on the relative propor-
tions of the year classes was based on a small collection taken at Bellingham, Wash.,
early in August, 1910.5. The number investigated was too small (58 in all) to give
reliable averages, but the percentages indicated do not differ materially from those
obtained in 1916 by Dr. C. M. Fraser from collections of adequate size taken at Nanaimo
and Qualicum, in the Gulf of Georgia. In both cases the majority of the chums were
found maturing at the age of 3 and 4 years, with very few individuals at 5 years and an
occasional rare specimen in its second year. Table 7 gives the results derived from
both sources and also, for comparison, includes a similar grouping of Yukon chums.

TABLE 7.—YEAR-CLASS DistripuTiION, SOUTHERN AND YUKON CuuMm SALMon,

Southern chums: | Per cent. | Per cent. | Per cent. | Per cent. | Number.
SQUIRT pan s6.eis Vv dais f resettle 4 Op ein'esatsia gp Vastly oem s ia : eaee ° 53-5 44.8 1.7 58
Sefer etter 2 eV pg ia een oh Pea nas ont = SES — | ° 34.5 64.3 1.2 1, 309
UMMERTIG dative geen dae tia ria as Aig eit nc ae 5 F Ot 46.6 52.4 .9 700
Average of southern chumis...... seins ts va) ere | o1 44.8 | 53.8 fa 2,058
Yukon chums. .............. ae ds erry Jo EA | ° 33 638, 1 28.6 448

The Yukon chums mature in their third, fourth, and fifth years, as is the case in more
southern waters, but the number of 3-year-olds is diminished from nearly half to one-
thirtieth of the total number, and the 5-year fish show a corresponding increase from 1
to nearly 30 per cent. The retardation in the maturing of the northern race is thus
evident.

PROPORTIONS OF SEXES.

It has commonly been reported that dog-salmon males are greatly in excess of the
females, but no thoroughly satisfactory investigation of this subject has been made. ‘To
accomplish this, an examination would have to be made of the ratio of males to females
at frequent intervals throughout an entire run. It might well be expected that the
proportions of the sexes would differ widely during consecutive portions of the run,
with the result that any deficiency in the number of females observed at the beginning of
the run would be compensated for by an excess of females later on. Such an occur-
rence has been repeatedly observed in certain sockeye colonies. Four-year male sock-
eyes entering Rivers Inlet, British Columbia, in 1917, varied from 100 per cent of the
4-year class in early July to 52 per cent on July 31; and the 5-year males varied from 59
per cent of the 5-year group on July 10 to 23 per cent on July 31. It is clear, therefore,
that a series of observations on fish bound for one river only will be necessary to enable
us to determine this point.

Doctor Fraser's results, from fish taken partly near the mouth of the Little Qualicum
River and partly from the vicinity of Nanaimo, agree in showing from both dis-
tricts an increased percentage of males in the older year classes. ‘The percentages of
males in the third, fourth, and fifth year classes in the Nanaimo lot, range 42.6, 62.1, and
100; in the Qualicum lot, 51, 63.8, and 86.4. If these represented the average percentages

5 Age at Maturity of the Pacific Coast Salmon of the Genus Oncorhynchus, by Charies H. Gilbert. Bulletin, U. S. Bureau
of Fisheries, Vol. XXXII, rg12 (1914), p. 18 Washington, r913.

328 BULLETIN OF THE BUREAU OF FISHERIES.

during the entire season we should have a considerable preponderance of males over
females on the spawning beds and we should also have indicated a relatively earlier
maturing of females than of males. Both of these results would be unexpected. While
no determination has been made of the ratio of the sexes in dog-salmon fry, analogy with
other species of salmon would make it appear probable that males and females are in
approximately equal numbers at the time of hatching. If this be true, a final excess of
males in the spawning run could only be brought about by selective mortality directed
against the females. It does not seem probable that this exists. As regards an earlier
maturing of the females than of the males, producing a heavier percentage of females in
the younger groups, we can only note that this would be the reverse of what occurs in
king salmon, sockeyes, and cchos.

In the Bellingham material, previously referred to, we found 67 percent males and 33
per cent females, the proportion of males and females being approximately the same in
the third and the fourth year groups. In Doctor Fraser’s material, the totals showed
59 per cent males and 41 per cent females.

The Yukon specimens, 448 in number, contained 57.6 per cent males and 42.4 per cent
females. The 3-year fish had 53.3 per cent males; the 4-year fish, 53.8 per cent; and the
5-year fish 67 per cent.

SIZE AT MATURITY.

The length azd weight frequencies are given in Tables 8 and 9, which follow. ‘These
indicate unmistakably that the northern race is retarded in its growth and reaches a
smaller size in each year class than is attained in Puget Sound and the Gulf of Georgia
by fish of equal age. To compare with the average lengths of Yukon chums, we repeat
below those given by Doctor Fraser based on Qualicum and Nanaimo material, As
measurements of the latter were taken only to the base of the middle caudal rays and
our measurements include the length of the middle rays themselves, we have added
714 per cent to Doctor Fraser’s measurements to make them comparable.

TABLE $.—YuKON CHUM SALMON, 1920, GRouPED By AGE, SEX, AND LENGTH.

Number of individuals in— Number of individuals in—
eter Third year. | Fourth year. | Fifth year. Length, | Third year. | Fourth year. | Fifth year.
: Fe- Fe- Fe- la Fe- ? Fe- Fe-
Males, matles,| Males. Pearl Males. Sanit | Males. tntes! Males. ES Males, limaaless,
— 2 —— es =
ax inches........ | REA Real Cceree lapeeees 2ginches.........)....005 tage ns 2 Sitadelic
22 inches Cictell Ren cate eae lS seeene Pol Renn nA || 29.5 inches sisvace 2 i oes
22.sinches,......|....... BZ lieceee 7 P| bea eter goinches.........]...cse0feeenee I Panera
23 inches.. 2 sinters i II . |} 30.5 inches Et
23.5 inches a | I I 16 . || 3z inches Pe eer
24 inches. . oa Re | 3 31 I 3 || 31.5 inches Bites > sis< >
24.5 inche 4 | | 9 $I 6
25 inches.. | 10 14 I 8 Total) s<s | 8 7 164 141 86 | 42
25.5 inches | as) Is 9 || Average length | |
26 inches. . | 24 12 3 4 injinches’.;..... 24 23: | 26.4] 24-4] 282) 25.7
26.5 inches 26 4 4 4 | Gulf of Georgia, |
27 inches.. ites 25 |oseeees 10 5 | average length |
27.5 inches alleys 24 F7 10 I in inches |
28inches........ ail een erate 16 I (Fraser)..-... 28 9659) | <BOn% || BQ. |i eneselly shades
28.5 inches... | | Ween: 15 1 |
| |

SALMON OF THE YUKON RIVER. 329

TABLE 9.—YUKON CHUM SALMON, 1920, GROUPED BY AGE, SEX, AND WEIGIIT.

| Number of individuals in— Number of individuals in—
|
Weight. Third year. | Fourth year. Fifth year. Weight. | Third year. | Fourth year. | Fifth year.
| ae
Fe- Fe- | Fe- .| Fe- Fe- Fe-
Males. males. Males. males, Males. males... Males. males. Males, males. Males. males.
oe - 2 = | a | =
MDOUMOS. gai ei ce [ssa 1h ere © leveasselii . || 12 pounds....... F 13
EF DOMMIOSs a as s00s I Base steerer Oe ii ck sd bias +) 83 OGG. 45 hes lsd Bliss
6 pounds. 3 t 7 si ee 3 || 14 pounds......../. 4
7 pounds 3 I 28 52 j 3 17: || 17 pounds.....2.. I
8 pounds... B) | «ion 3 52 | ° 18 s |
QPOUMAS: cai 854 )s0sedes lessees 47 2] 20 6 || Total... P 86 42
ro pounds........ ori lbica ¢f3 22 Jrscecee 18 3 || Average weight
Sb DOUDASI ness lids one]: ene ro i Pe a eee ; im pounds..... 10.5 q
| |

The length-weight relationship, indicated in Table 10, is given without reference
toage. The average weight of all males and, separately, of all females that have the same
length is stated. According to this table, females average slightly lighter than males of
equal length, those from 23 to 28 inches in length averaging 97 per cent of the correspond-
ing males. The reverse of this might have seemed reasonable because of the slightly
lengthened jaws in the males.

TABLE ro.—AVERAGE WEIGHTS, BY UNITS oF LENGTH, YUKON CHUMS, 1920.

Males. Females. | Males. Females.
| | — @ a
Length. | . | Length.
Speci- | Average | Average Speci- || Speci- | Average | Average = Speci
mens. weight. weight. | mens. | mens. weight. | weight. mens,

2zinches............ ° a 4 1 || 27 inches 69
92 INCHES... ca siens ns ° 4 5.1 9 || 28inches.. Aft: 43
BS ADCHES 5:0 cs esses s 3 5.7 | 5-7 28 || 29 inches 21
24inches..... 19 6.7 6.4 73 || 30 inches 5
25 inches..... why 36 7-3 23 40 | 31 inches : 6
BO ICES 0.5550 ce ess 56 8.2 7.9 24

GROWTH AND SCALE READINGS.

In Figures 290 to 298 are presented photographs of a series of scales of Yukon chum
salmon that include representatives of all the year classes found in our collection. All
of these agree in belonging to the sea type—that is, the scales were wholly formed in
the sea, the fry having passed out of the river at a very early age, before even the nuclear
plate and the first scale ring had been formed.

The Yukon chunis agree in this respect with their southern relatives. All leave their
native streams as soon as the yolk is absorbed and they are free swimming. In more
southern districts this seaward migration is easily accomplished. The eggs are laid
in gravels not far removed from the tides, and the young, when free, easily drop down
with the current to the shore line. The case is less simple with the Yukon fish, many
of which have 2,000 miles or more to cover at a period when they average only 114 inches
long. No information is available concerning the dates on which this migration is
effected. Observations farther south indicate a very early descent to the sea in the
spring of the year. It is not known, however, to what extent hatching of the eggs and
development of the young on the Yukon are retarded by the very low temperatures to

330 BULLETIN OF THE BUREAU OF FISHERIES.

which they are exposed. Growth during the seaward migration can not be considerable,
for none of the material that we have examined indicates the formation of the scale
nucleus while still in the stream.

Growth of this species in the sea seems to proceed with remarkable regularity, with
the result that the scales are diagrammatic in their simplicity and seldom afford any
difficulty in determination of age. In the case of the Yukon race, such uncertainty as
may be experienced is concerned with the interpretation of the peripheral region of the
scale and is based on the fact that the scale margins differ widely in condition among
individuals captured on the same date. It is generally recognized that individuals of a
given race will vary materially in the date on which they begin the rapid growth of the
spring after the winter pause. Among the fish captured in May or early June in more
southerly waters an occasional individual may indicate no growth of the current season,
while others will vary in the number of peripheral wide rings by which the amount of
spring growth may be computed. In the Yukon dog salmon, however, this variation
at the time they leave their feeding grounds and enter on their spawning run is extreme.
An occasional fish, as shown by Figure 296, had begun no new growth of the year, the
margin of the scale being formed by the close-ringed check of the previous winter.
Others, as represented in Figure 294, had barely inaugurated the new growth, which is
indicated by two or three wide rings outside the winter check. There then follow fairly
complete series with ever-increasing growth of the season, as shown in Figures 297,
290, 291, and 292, the last named having finished an average season’s growth for the
third year, with the exception of the winter check.

When it is recalled that these dog salmon enter the Yukon in company with the
king salmon and that the king salmon have not in any case made unmistakable growth
for the current season, the habit of the dog salmon in this regard seems most peculiar.
In the early and middle parts of the run, to which alone we had access, none of the
individuals examined had begun a winter check at the margin of the scales for the cur-
rent year. Where a marginal winter check existed, it had been formed the previous
winter and presented no real difficulty in determining age. If the latter part of the
run should be found to contain a group of individuals in which a check was forming
at the scale margin and also another group with scales like Figure 293, in which the
marginal check belonged to the previous winter and no further growth had been regis-
tered, a real difficulty might arise in determining the age of such individuals. The
two groups would show essentially similar scale structure, but one would be one year
older than the other. It is not probable, however, that representatives of these two
classes would be found together in any portion of the run. As the season advanced we
should expect to find extremely few, if any, that had failed to produce some new
growth of the year.

THE SCCKEYE SALMON (Oncorhynchus nerka).

A few scattering sockeyes (Alaska red salmon) enter the Yukon River during
July and early August. In 1919 the Carlisle Packing Co. put up 22 cases of talls and
6 cases of flats of this species and handled a total of about 300 fish. The sockeyes
appeared even less numerous in the following year, when only 5 cases, containing about
60 fish, were packed.

If a permanent colony of red salmon exists in the Yukon, it must ascend to the
lakes near the source of the river, but we have no knowledge that such spawning grounds
for this species exist. That individuals ascend the river for long distances is certain,

SALMON OF THE YUKON RIVER. 331

for we learned of their occasional occurrence up the river from men who were acquainted
with the different species of salmon, and we observed one, a male, decidedly pink in
color, at Ruby on August 14, 1920, some 650 miles above the mouth of the river.

We examined 23 specimens in 1920 on July 5, 7, 8, 9, and 13. Thirteen of these
were in their fifth year (see Figs. 299 and 300), having spent their first year (perhaps 15
months) in fresh water and having descended to the sea in their second year. ‘The
scales exhibit a vigorous fresh-water growth, followed by three complete year records
at sea. A few of these scales, as in Figure 300, have a marginal check, which was
formed during the preceding winter; but a majority have at the margin from one to
four wide rings denoting new growth of the year.

In addition to the individuals in their fifth year, one year of which was spent in
fresh water, we have eight that had remained in fresh water an additional year and were
maturing in their sixth year. A scale of one of the latter class is represented in Figure
301, the division between first and second year’s growth in fresh water being clearly
indicated. Here, again, the growth of the new year is faintly but unmistakably shown
along the anterior left-hand margin of the scale.

A third class of individuals is represented by Figure 302, these itaving descended
to the sea soon after hatching and prior to the growth of the scale. ‘The two salmon
we examined belonging to the sea type, one a male 27/4 inches long, the other a female
23% inches long, had matured in their fourth year, one year earlier than any of those
that had lingered in fresh water.

Whether the Yukon red salmon are strays from some colony to the southward
or form an unflourishing local race can not be determined at present. ‘There is no
reason to believe that more than one race is represented in our meager material.

THE COHO SALMON (Oncorhynchus kisutch).

The coho or silver salmon develops a regular run in the Yukon River, appearing
sparingly at the mouth of the river in the latter part of July, but the run does not show
any real development until in August. The Carlisle Packing Co., in 1919, packed 7
cases of cohos on July 14 and 3 on August 2. From August 3 to 9, 59 cases were put
up and in the following week 985 cases. The total pack to August 30 was 3,181 cases.

In 1920 this species was entering the mouth of the river in very limited numbers
during the last week in July and does not appear in the cannery pack of that year, as
canning operations were discontinued before the run had developed. During the early
half of August, between the mouth of the river and Tanana, we found at all fishing
camps that occasional individuals were being taken. But we were unable to learn of
its occurrence in the main river above Tanana. It is well attested that the species
enters the Tanana and spawns in one or more tributaries of the Kantishna. How
generally it is distributed over the basin we were unable to ascertain.

When the coho enters the river it is a perfectly symmetrical fish, with brilliant
silvery color, but in traversing the lower portion of the river it takes on a red livery,
and the males assume at the same time the characteristic snub-nosed appearance of
the breeding fish, the upper jaw becoming bluntly hooked over the lower in a manner
characteristic of this species.

Scales of Yukon cohos are represented in Figures 286 to 289. As in all other coho

colonies that we have examined, those from the Yukon are always in their second year
6447°—22_9

332 BULLETIN OF THE BUREAU OF FISHERIES.

of sea growth when captured. Outside the narrow-ringed central area, which records
the life in fresh water, we invariably find in this species a vigorous summer growth,
succeeded by a well-marked winter check, and this in turn followed by an extensive
marginal growth of widely-spaced rings, which measure the growth of the current
season of capture.

In the southern part of its range, where the coho uniformly spends one season in
fresh water before migrating seawards, the spawning run (aside from a few male grilse in
their second year) consists exclusively of 3-year fish. As we proceed northward, how-
ever, we encounter individuals that have tarried two years in the streams and are
maturing in their fourth year. These are more abundant in the Yukon than in any
other stream we have examined. Our small collection of 31 individuals comprises 12
that have spent one year in a stream and are 3 years old (see Figs. 286 and 287) and 18
that remained two years in fresh water and are in their fourth year (Fig. 288). If the
customary proportions are shown in this collection, some 60 per cent of the young
spend two years in fresh water. One individual of our collection (Fig. 289) had appar-
ently spent three years in the river and was maturing in its fifth year. The number
of individuals at our disposal is too small in the various classes to give reliable averages.
Six 3-year males average 23.8 inches in length (middle caudal rays included, as in all
our measurements); four 3-year females, 24.6 inches. Eleven 4-year males (two years
in fresh water) average 24.5 inches; six 4-year females, 25.3 inches. As males are
consistently larger than females among Pacific salmon, we have additional reason for
distrusting the adequacy of the above figures. The 5-year male (three years in stream)
is 23 inches long.

THE HUMPBACK SALMON (Oncorhynchus gorbuscha).

Scattering humpbacks enter the river in July and August and are then so near
their spawning time that they would be unable to ascend the stream for any considerable
distance. We observed one ripe male at Andreafski on August 3 and were unable to
learn of the occurrence of the species beyond that point.

The individuals observed were all small and without value, having often liquid
milt and partly free eggs. Four specimens measured from 20 to 22 inches in length
and weighed from 4 to 5 pounds. As in the case of all other humpbacks that have
been examined for age, these were in their second year and had proceeded to sea as soon
as free swimming, their scales registering none but sea growth. The small size was
doubtless due in part to the fact that they were maturing so early in the season, thus
greatly limiting the growth of the second year. The scales all indicated this history,
for the area representing growth of the second year was narrow and contained a partial
check at the margin.

4 We do not here include the few male grilse, which in more southern districts mature during the first year at sea.

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Butt. U. $. B. F., 1921-22. (Doc. 928.)

I'iG. 290.—Scale of chum salmon taken trom mouth Yukon River July 2, 1920. Female. 23!2 inches long, weight
5 pounds; in its third year.

(Doc. 928.)

[O2 1-22;

UW. SB. Fs

BULL.

weight

inches long,

Male, 23

7, 1920

1 Yukon River Ju

cale of chum salmon taken from mout!

292.5)

Fic

6 pounds; in its third year.

(Doc. y28.)

veight 9

n from mouth Yukon River July 31, 1920 2 inches lon

of chum salmon take

scale

ar,

3; in its fourth ye

ound

inches long, weight

Female, 23

ium salmon taken from mouth Yukon River July 7, 19

of ch

Seale

Fic. 2

5 pounds; in its fourth year

Bury. Us .S. B:

Female, 26 inches long, weight

20.

2, 19

Fic. 296.—Scale of chum salmon taken from mouth Yukon River July

7 pounds; in its fifth year.

Buty. U. S. B. F., ro21-22. (Doc. 928.)

Tic. 297.—Seale of chum salmon taken from mouth Yukon River July 7, 1920. Vemale, 24!2 inches long, weight
7 pounds; in its filth year,

ies)

Buyt. U. S. B. F., 1921-22. (Doc. 928.)

Fic. 208.—Sceale of chum salmon taken from mouth Yukon River July 7

ro pounds; in its filth year

1920.

Male,

$ inches

long,

weight

22. (Doc. 928.)

1921-2

BULLE. Uso: 3B:

“2
Se

almon taken

inches long,

Male, 27

6 pounds; in its fifth year.

Female, 23 in

fifth year

weieht 9 pounds; i its

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