1956 mOCEEDINGS
Marine Biological LaboratoryJ
DEC:! il957
WOODS HOLE, MASS.
NATIONAL
SHELLFISHERIES
ASSOCIATION
Volume 47
PROCEEDINGS
of the
NATIONAL SHELLFISHERIES ASSOCIATION
Official Publication of the National
Shellfisheries Association; an Annual
Journal Devoted to Shellfishery Biology
Volume 47
August 1956
Published for the National Shellfisheries Association by the
U. S. Fish and Wildlife Service, Department of the Interior
Washington I957
TABLE OF CONTENTS
SYMPOSIUM: PRODUCTION AND UTILIZATION OF SEED OYSTERS
Introduction L. E. CRONIN. . .
Siirvival and Growth of South Carolina J. D. ANDREWS
Seed Oysters in Virginia Waters and J. L. MCHUGH. . .
Seed Oyster Problems of North Carolina A. F. CHESTNUT...
Production and Utilization of Seed
Oysters in the Gulf Area P. A. BUTLER. . .
Summary T. C. NELSON...
1
2
3
18
19
23
BIOLOGY OF SHELLFISH
G. GUNTER
Determination of How Long Oysters have C. E. DAWSON
been Dead by Studies of their Shells and W. J. DEMORAN. . . . 31
On the Shell of Bivalve Mollusks C. N. SHUSTER.... 34
Siirvival and Growth of Venus mercenaria ,
Venus campechiensis , and their Hybrids
in Suspended Trays and on Natural D. HAVEN
Bottoms and J. D. ANDREWS.... ^3
Growth of Young Venus mercenaria , Venus A. F. CHESTNUT
campechiensis , and Their W. E. FAHY
Hybrids and H. J. PORTER 50
BIOLOGY OF SHELLFISH ENEMIES
Our Present Knowledge of the Oyster
Parasite " Bucephalus " S . H. HOPKINS .... 58
Flatworm Pseudostylochus ostreophagus
Hyman, a Predator of Oysters C. E. WOELKE.... 62
Some Effects of High -Frequency X-Ray W. J. HARGIS
on the Oyster Drill Uro salpinx M. F. ARRIGHI
cinerea R, W. RAMSEY and R. WILLIAMS 68
Copper, a Possible Barrier to Oyster Drills J. B. GLUDE.... 73
Trapping Oyster Drills in Virginia. III. The
Catch per Trap in Relation to Condition of
Bait J. L. MCHUGH. ... 83
ENVIRONMENTAL CONDITIONS
Some Features of the Hurricane Problem G. E. DUNN....104
SHELLFISH FOOD
A Continuous Water Sampler for Estimation P. A. BUTLER
of Daily Changes in Plankton and A. J. WILSON. .. .109
SHELLFISH POISON
Public Health Significance of
Paralytic Shellfish Poison:
A Review of Literature and
Unpublished Research
E. F. MCFARREN
M. L. SCHAFER
J. E. CAMPBELL
K. H. LEWIS
E. T. JENSEN
and E. J. SCHANTZ.
,11J+
SHELLFISH TECHNOLOGY AND PUBLIC HEALTH ASPECTS
Effect of Aureomycin Chlortetra- A. ABBEY
cycline in the Processing and A. R. KOHLER
Storage of Freshly Shucked Oysters and S. D. UPHAM 1^3
Panel Discussion on Freezing and Processing
Southern Oysters
Introduction C. F. LEE.... 1^4
Investigations of the Body Fluid M, FINGERMAN
and "Brown-spotting" of the Oyster and L. FAIRBANKS. .. .146
Research on Handling and Processing A. NOVAK
Southern Oysters and E. A. FIEGER. . . .1^+8
Oyster Research from Florida State B. WATTS
University H. LEWIS and M, SCHWARTZ 151
ASSOCIATION AFFAIRS
Annual Convention, Officers, and Committees I56
Editors ' Notes 158
Information for Contributors 158
Titles of Other Technical Papers Presented at the Convention I6O
Directory of Members of the Association I6I
CONVEM'ION SYMPOSIUM
on
PRODUCTION AMD UTILIZATION OF SEED OYSTERS
The symposium was introduced by Dr. L. Eugene Cronin who also
presided. Five biologists representing different major oyster -producing
areas along the eastern and gulf coasts of the United States presented
the following topics: Mr. Joseph B. Glancy, "The Supply of Seed Oysters
in the New England-New York Area"; Dr. Harold H. Haskin, "The Seed Supply
in Delaware Bay"; Dr. J. D. Andrews and Dr. J. L. McHugh, "A Critique on
the Use of South Carolina Seed Oysters in Virginia Waters"; Dr. A. F.
Chestnut. "Seed Problems in North Carolina"; and Dr. Philip Butler, "The
Production and Utilization of Seed Oysters in the Gulf Area". Dr. Thurlow
C. Nelson summarized the reports, including the papers by Mr. Glancy and
Dr. Haskin which were not available for publication. The papers by Dr.
Andrews and Dr. McHugh, Dr. Chestnut, and Dr. Butler, and the summary by
Dr. Nelson are reproduced in the following section.
-1-
SYMPOSIUM ON THE PRODUCTION AND UTILIZATION OF SEED OYSTERS
L. Eugene Cronin
Chesapeake Biological Laboratory
Maryland Department of Research and Education
Solomons, Maryland
The production and utilization of seed oysters offer greater
problems and greater challenges than any other aspect of oyster biology
and the oyster industry. We have brought together speakers representing
the oyster industry and the oyster biologists so that these problems and
present opinions can be effectively summarized in one session. The
panelists also represent every major oyster -producing area of the Atlantic
and Gulf Coasts.
No aspect of oyster culture offers greater variety than the seed
oyster problem. Some regions are faced with a grave and serious economic
problem because of the shortage of seed oysters. In other regions seed
oysters are so abundant as to interfere with growth and reduce the market
quality of the crops. In between lie areas where seed production and
utilization are more nearly in balance. All of these areas have grave
and important problems which merit our concerted attention.
As a biologist, I am interested in the fundamental problems pre-
sented in the production and utilization of small oysters. We have be-
gun to appreciate the differences between and similarities among seed
produced at different sites and transplanted to new sites. There is an
exciting opportunity for increased yield through improved use of various
kinds of seed in different waters. We must understand the genetic
differences between seed and the effects of various environmental situa-
tions on seed from different sources. This is one of the avenues by
which we might achieve greater production, faster growth, and improved
quality of oysters for specific uses.
The economic problems involved in various coastal areas are also
varied and complex. They range from the relatively simple protection of
natural sets on good growing areas to the possibilities of transplanting
seed for many hundreds of miles along the coast.
Our panel members present reports from different coastal areas
and these will be summarized and commented upon by Thurlow C. Nelson,
Dean of American oyster biologists.
THE SURVIVAL AND GROWTH OF SOUTH CAROLINA SEED OYSTERS
IN VIRGINIA WATERS"""
Jay D. Andrews and J. L. McHugh
Virginia Fisheries Laboratory, Gloucester Point, Virginia
Introduction
Most of the seed oysters planted on private grounds along the
Atlantic Coast of the United States are obtained from public seed beds.
The supply depends largely upon a wild crop over which there is little
control. It is to be expected, perhaps, that the quantity of seed avail-
able at various localities along the coast is in proportion to the dura-
tion of the warm season. It follows that oystermen are usually searching
southward for their supply of seed and the ramifications of this hunt are
complex and ever changing.
Between 1825 and 1880 millions of bushels of Virginia oysters
were shipped north to oyster -growing areas from Delaware to New Hampshire
(Goode 1887) • In 1879^ for example, two million bushels were exported
from Maryland waters alone at a price of seven cents per bushel. Some
200 sail-powered "run boats" were engaged in the transfer of oysters from
Chesapeake Bay to northern waters. The cost at the point of delivery
was 25 to 35 cents a bushel. Most of these Chesapeake oysters were mar-
keted immediately, but some were planted for use the following summer and
fall. Evidently most were of marketable size when shipped north; the
primary purpose of relaying was to hold them for sale in the succeeding
summer and early fall when native oysters were spawning and poor in
quality.
By 1880 northern dealers had established shucking plants in
Norfolk and Baltimore, and thereafter shipments of oysters in the shell
to northern ports declined. The search for southern oysters has never
ceased, but now small seed oysters may be held in northern waters for
several years before marketing, and few are taken north of New Jersey.
Growing southern oysters for several years in northern waters is a far
different task than holding large oysters through one summer season be-
fore marketing, for survival and growth become important as well as the
ability to fatten.
As production of market oysters on private grounds increased in
Virginia, the home market absorbed most of the supply of seed, and as
recently as ten years ago less than 10 per cent of James River seed was
sold out of State. Today the sale of seed oysters from public grounds
of the James River for direct transport out of State is forbidden, and
northern growers have turned to private grounds and the seaside of
Eastern Shore f or their supply.
1
Contributions from the Virginia Fisheries Laboratory No. 73-
-J-
These limitations on the export of seed were necessary under the
present organization of the industry in Virginia, for the amount of groiind
under lease has been increasing, the demand within the State has been
great, and in the last few years the price has steadily increased. Despite
the ban on direct shipments out of State, the annual catch of seed oysters '
from the James River has increased. Potential seed areas on public grounds
in other rivers have not been utilized and seed production on private
grounds has been slow to develop. Prior to 19^7 considerable quantities
of Pamlico Sound seed oysters were used in Chesapeake Bay and particularly
on the seaside of Eastern Shore. This practice ceased when the state of
North Carolina placed on oysters an export tax of 50 cents per bushel
(Chestnut 19^9)- Until recently shipment of seed from South Carolina has
been virtually barred by various laws of that state, but now that regula-
tions have been revised and South Carolina is ready to encoiH'age produc-
tion of seed for northern planters (Wallace 1956).
In South Carolina most oysters are grown in the intertidal zone
and the beds are characterized by heavy sets. Planters are intrigued by
the high count per bushel but they recognize that consequent crowding
may produce inferior shucking stock. It is not clear, moreover, whether
oysters from the high-salinity waters of South Carolina can be trans-
planted successfully to the much less saline waters of upper Chesapeake
Bay. In addition to these problems, scientists have been concerned about
the growth and survival characteristics of southern oysters. Little
attention was paid to quality and fitness of stock in the early days of
extensive transplantation along the coast, and control of pests and
diseases was given no consideration. It might be surmised that whatever
damage could be done by mixing stocks and transplanting pests has already
occurred, but recent troubles with the fungus Dermocystidiimi in Delaware
Bay, and the possibility that the fungus may have been introduced in
Chesapeake Bay some years earlier, suggest that unrestricted transplant-
ing may yet be unwise.
The Chesapeake Biological Laboratory at Solomons, Maryland, be-
gan studying the characteristics of out-of-state seed grown in Chesapeake
Bay a number of years ago (Beaven 19^9) J in 1951^ in cooperation with the
Bears Bluff Laboratory and the Maryland laboratory, studies of South Caro-
lina seed oysters were begun in Virginia. Small numbers of these oysters
have been held in trays for growth and mortality observations and upon
these experiments is based a preliminary estimate of the usefulness of
South Carolina seed in Chesapeake Bay.
We have attempted to compare the growth, survival, and fattening
qualities of native and South Carolina oysters. We have assumed that
the intensity and duration of setting in South Carolina waters will
necessitate the removal of seed oysters at an early age --probably less
than nine months. To hold stock longer in South Carolina produces a
very dense cluster of oysters which can scarcely be separated a year
later. In our experiments South Carolina and native spat of the same
age were placed in trays when one to three months old and grown side by
side. Data were obtained on oysters of three different year-classes
-h-
from the two sources. The history of each group is given in Table 1.
Patterns of Mortality
The pattern of mortality of native Chesapeake Bay oysters has
been described by Hewatt and Andrews (195^). The death rate is high
during warm periods (June to October) and extremely low during the
winter and spring. Sporadic departures from this usual pattern, caused
by mortalities from unknown causes, occur in some areas (Beaven 19^6).
In Figure 1 the pattern for native oysters is depicted over a period of
three years (Trays 11 & 12). Figure 1 and Table 2 reveal also that in
the warm period the mortality of South Carolina oysters (Trays h & 38)
often is little more than half as great as that of natives. Andrews
and Hewatt (1957) have shown that South Carolina oysters are more
resistant to the fungus, Dermocystidium marinum , which is the cause of
most summer deaths in trays. During winter and spring, however, the
death rate in South Carolina oysters is appreciably higher than that of
natives. In the warm winters of 1952-53 and 1953-5^; these losses were
relatively inconspicuous, but when winters were cold, as in 195^-55 and
1955-56, deaths were frequent in February and March and again in May
and June (Fig. l). The causes of these deaths in later winter and again
in -late spring are unknown. When organisms are transplanted to colder
climates, minimal temperatures are often limiting, but oysters grown
intertidally in South Carolina usually are exposed to lower temperatures
and greater extremes than those held subtidally in trays at Gloucester
Point. It appears that susceptibility to winter mortalities involves
other factors in addition to low temperatures --perhaps diseases, favored
by cold waters, to which South Carolina oysters are more susceptible than
natives. The winter survival of South Carolina oysters in their native
waters is imknown.
For convenience in computing biomass, it is best to express
mortality in terms of survivors, as in Figure 2. Mortality and growth
records were not collected in the first year because weights and counts
of spat were difficult to obtain. For convenience, also, survivorship
was computed on the basis of an original stock of 1000 oysters in each
lot. Death rates for each period between observations were applied to
the number of survivors at the beginning of the period. From Figure 2
the number or percentage of survivors at any age in months can be deter-
mined.
South Carolina oysters (closed circles) had less seasonal varia-
tion in death rate, hence the survivorship curve declines rather steadily,
but the curves for native oysters (open circles) show steep declines in
summer and almost no drop in winter. These curves include the unusual
year of 195^ when over half the native oysters, but only one-fourth of
the South Carolina oysters died. The South Carolina oysters had a
distinct advantage in survival during this warm year.
-5-
Table 1. History of Virginia aud South Carolina oysters
grown in trays at Gloucester Point
Year of
Tray
Origin
Date
birth
number
transplanted
1951
h
South Carolina
July 1951
11
James River
Nov. 1951
12
Corrotoraan River
Nov. 1951
1952
28
South Carolina
Nov. 1952
27
York River
Aug. 1952
1953
38
South Carolina
Nov. 1953
39
Chincoteague
Nov. 1953
1+0
■
York River
Aug. 1953
-b-
8
K
I
/9S3
AMJJASO^^DJFMAMJJASONDJfMAMJJASONDUFMAMJ
/9S'¥-
/3£S
/9se
Fig. 1. Patterns of mortality in oysters from Virginia (Trays
11 and 12) and South Carolina (Trays ^4 and 38). Mortality for
each month is expressed as the average number of deaths per 1000
oysters per day.
-7-
Table 2. Mortalities of oysters In trays in the warm and cold seasons
at Gloucester Point, Virginia
Tray
number
Mortality in per cent
Year
Source
(Ji
Warm months
ne to Oct . )
Cold months
(Nov. to May)
Annual
(June to May)
1951
k
South Carolina
9
16
2k
1952
k
11
12
South CEirolina
James River
Corrotoraan River
7
k
3
6
k
13
8
3
1953
k
11
12
South Carolina
James River
Corrotoman River
10
2k
17
6
5
6
15
28
22
195^
k
11
12
South Carolina
James River
Corrotoraan River
2k
57
51
19
1
k
39
57
53
1955
k
11
12
South Carolina
James River
Corrotoman River
22
26
30
31
8
2
kS
32
32
1956
k
11
12
South Carolina
James River
Corrotoman River
25
16
25
:;
••
• •
• •
In years in which average winter and summer temper at ures are
nearly normal, it appears that losses in South Carolina and native
oysters may be about equal. Although summer losses are less in South
Carolina oysters, winter deaths are more serious than in natives. The
designation of "warm" and "cold" winters is difficult, but after 19^8
Virginia had six consecutive warm winters during which the three winter
months rarely had average temperatures below normal. In each of the
past two winters (195^-55 & 1955-56), two of the three winter months
had average temperatures well below normal and these were by far the
coldest winters since 19^8. During this experiment (1952 to I956), two
quite warm and two rather cold winters were experienced. It appears that
warm winters and warm simmers (1952-53 & 1953-5^) favor the survival of
South Carolina oysters, but cold winters (195^-55 & 1955-56) and cool
summers (1956 permit greater survival of natives (Table 2).
Apparently South Carolina oysters are not immune to winter
mortalities at any age, whereas all oysters reach two years of age be-
fore summer losses from Dermocystidium become heavy. In low-salinity
waters, where no deaths occur from the fungus at any age. South Caro-
lina oysters may suffer high winter losses (Beaven 1953)- In the lower
bay, therefore. South Carolina oysters appear to have no advantage over
natives in ability to survive and in the upper bay they may be quite
Inferior.
Growth
The growth of oysters, expressed as weight in the shell after
cleaning, shows small differences between Virginia and South Carolina
oysters of the same year-class but large variations among year-classes
(Fig. 3)' In other words, environmental differences apparently caused
greater variation in growth than genetic differences between native and
South Carolina oysters. The oysters of the 1951 year-class (Trays k,
11, & 12) grew faster than those of the two succeeding year-classes.
At the end of 2h, 36, and k& months of age they were 4o to ^^-5 per cent
heavier than the 1952 year class at the same age (Trays 27 & 28). In
two of the three year-classes. South Carolina oysters were heavier than
natives at the beginning of the experiment, but soon the natives exceeded
them in weight. There is some indication that South Carolina oysters
may never reach a size as large as natives. Marketable oysters of three
to three and one-half inches weigh from 60 to 90 grams.
Yields
In these experiments the yield of oysters is the resultant of
losses from deaths and gains from growth. In the computation, average
weight is multiplied by number of survivors; this is less complex than
the method used by McHugh and Andrews (1955)- To facilitate comparison
of groups, the biomass or total weight has been converted to relative
biomass or yield based upon an initial weight of I9 grams per oyster.
-9-
/ooo
J2 ;^4 /2 :z^ o /z 24- 36
Fig. 2. Numbers of survivors from initial lots of 1000
oysters; calculations were based Upon the death rates of oysters
suspended in trays from the Virginia Fisheries Laboratory pier.
The 1951 year -class is represented by Trays 11 and 12 from Vir-
ginia and Tray k from South Carolina; the 1952 year -class by
Trays 27 (Virginia) and 28 (South Carolina). Tray 39 contained
oysters from the seaside of the Eastern Shore of Virginia.
Native oysters are represented by open circles and South Caro-
lina by closed circles.
-10-
200
/2 JZ^ 3G 4€ €0
/Z O /2
A^e Jn /nonfhs
Fig. 3. Mean growth rate in total weight, including shell,
of oysters from Virginia and South Carolina. The 1951 year-
class is represented by Trays 11 and 12 from Virginia and Tray
4 from South Carolina; the 1952 year-class by Trays 27 (Virgin-
ia) and 28 (South Carolina); and the 1953 year -class by Trays
i+O (Virginia) and 38 (South Carolina). Tray 39 contained
oysters from the seaside of the Eastern Shore of Virginia.
Open and closed circles represent native and South Carolina
oysters respectively.
-11-
<
i 1
•c
c;^'.!
^
=*^
T
^
»~-^.^,^^
1
U 1
•H U t
51
d Sout
from
ys 27
i+0 (V
the se
sented
irginia an
11 and 12
ass by Tra
s by Trays
ters from
are repre
(
r
^
■>JV-
1
1
^
h
^\
from V
Trays
ear-cl
r-clas
ed oys
ysters
cles.
if
7
»«*1I_
---
-^
1
) of oysters
spresented by
a; the 1952 y
the 1953 yea
ay 39 contain
ia. Native o
by closed cir
1
omass
is r
rolin
ina);
. Tr
irgin
lina
N-
^
»===^
/
N*^
ive yield (bi
51 year-class
from South Ca
(South Carol
uth Carolina]
rn Shore of V
nd South Caro
>
r:
^1.
u ^
<
'<
"V
!i^
r
Fig. h. Relat
Carolina. The 19
ginia and Tray k
(Virginia) and 28
ginia) and 38 (So
side of the Easte
by open circles a
^~~~~^
X
s^
^^
=Ste
^e*
r-o
^
;
I I
\ I
i V
ti r
? I
^ !
^ ^
s
P/9/A 9^//e/s^
-12-
This was the approximate size at which each group of spat was separated
from the cultch and weighed. Althoutjli actual weights varied, the month
when each group reached an average weight of 19 grajiis was determined
from the known weight -length relationship (McHugh and Andrews 1955 )•
All points in Figure 2, nowever, are based on actual weights. A value
of 100 was assigned to the initial biomass of 19,000 grams (1,000
oysters at 19 grams each). Yields are expressed as a percentage of the
initial biomass, and at any age they can be read from the graph in any
unit of weight or volume desired.
In all groups relative biomass increased rapidly during the
first two years when growth was rapid and death rates low, and maximum
yield was obtained in 2k to 30 months after setting (Fig. k). In Trays
11 and 12 biomass declined rapidly thereafter for this was the period
of excessive death rate in the surarner and fall of 195^. Although there
were rather wide differences in relative biomass of the two groups of
native oysters of the 1951 year-class, the pattern was very similar.
The decline in biomass was precipitous in the late summer and fall but
tended to rise in spring when few deaths were occurring. If there had
been a measurement at 3^ months (late spring of 195^+)* biomass would
undoubtedly have increased as it did in the spring of 1955 (^1 to h6
months). In the spring of 1956 (53 to 58 months), these oysters were
nearly five years old and growth had declined. The curve for South
Carolina oysters (Tray k) exhibited a distinctive pattern in which the
inflections were less abrupt because the rate of survival was less vari-
able. The sharpest declines in these oysters came in winter and spring
when growth was slow and mortalities fairly high.
In Trays 27 and 28 (Fig. k) the patterns were similar to those
in the 1951 year-class but biomass was maintained near maximum levels
longer because survival in 1955 was comparatively high. These groups
never attained the maximum biomass of the 1951 groups because excessive
mortalities in 195^ depleted the ranks early. It will be noted again
that seasonal fluctuations in biomass are not as drastic in South Caro-
lina oysters (Tray 28) as in natives (Tray 27).
Again, in oysters of the 1953 year-class (Trays 38, 39^ and kO)
biomass did not reach the level achieved by the 1951 groups (Fig. k).
In this latest year-class native oysters (Tray kO) had a distinct advan-
tage over imported oysters; susceptibility to the fungus D. marinum
caused high losses (48 per cent) in Chincoteague oysters Jjlvay 39) in
the summer and fall of 1955 and many deaths occurred in the South Caro-
lina oysters (Tray 38) in the winter and spring of 1956. Figure h
clearly illustrates that these losses altered the biomass curve in
Trays 38 and 39> and these oysters produced much lower yields at market-
able sizes.
Yields of three, four, or five to one may not seem realistic to
oystermen. It must be remembered that oysters grown in trays are pro-
tected from injury, smothering, drill predation, and other agents of
attrition which operate on natural groionds; these are factors which
-13-
Table 3« The condition index in South Carolina and native oysters
1
held in trays at Gloucester Point, Virginia
Date
Source
Tray
Mean length
Condition
number
mm
index
1 June 1955
York River
27
91
11.0
South Carolina
28
84
12.5
10 Sept. 1955
James River
11
100
9.0
South Carolina
k
106
7.1
h May 1956
York River
27
93
7.8
South Carolina
28
81
6.5
25 June 1956
York River
27
97
11.7
South Carolina
28
96
9.2
These determinations were made by Dexter S. Haven.
■Ik-
cause early losses in planted oysters when tray losses are negligible.
The yield on natural grounds, consequently, never attains the level found
in tray oysters; to achieve high yields, gains from growth must greatly
exceed losses from deaths.
In yields, as in growth and mortality, South Carolina oysters
appear to be at a disadvantage when compared with natives, although
they may retain their peak biomass for a slightly longer time. In years
of low temperatures South Carolina oysters do not attain the biomass of
natives.
Condition
A preliminary attempt has been made to compare the condition
index (Hlggins 1937) or "fatness" of South Carolina and native oysters.
In three of four samples natives had higher indices of condition than
South Carolina oysters (Table 3)' Samples have not been taken in the
fall and winter when most oysters are marketed. Seasonal and annual
fluctuations in condition factor have been so great from river to river
that data must be collected for several years before any firm conclusions
on condition index can be reached.
Discussion of Other Factors
The importance of several other characteristics of South Caro-
lina oysters, when grown in Chesapeake Bay, has not been determined.
These oysters are relatively more elongate than natives and the shell
appears to be thinner. We have encountered more difficulty with break-
age of shells in shucking South Carolina oysters, although it is not
clear whether this is caused by a heavier infection of boring sponge or
by thinner shells. The cupped valves have a deeper cavity in South Caro-
lina oysters than in natives, and they are usually cucullated, that is,
the cavity extends under the hinge. A few measurements indicate that
the capacity of the shell cavity is greater than in natives for a given
weight or size of oyster. The upper valve in South Carolina oysters
lies on the cupped valve like a flat lid whereas in natives it contributes
to the shell cavity.
Siimmary
Most oystermen and biologists recognize that native oysters are
the most satisfactory seed for planting in a given area. Although the
demand for seed in Virginia presently exceeds the supply, there is no.
reason why this situation should continue to exist, for the proper utili-
zation of suitable public grounds such as the Corrotoman and Piankatank
Rivers, and greater attention to the production of seed oysters on private
grounds, should be adequate to supply all planters within the state.
-15-
If these obvious sources of local seed are not exploited, how-
ever, planters will continue to look elsewhere for a supply. The recent
relaxation of laws in South Carolina already has aroused interest among
Chesapeake planters. In comparison with native Chesapeake Bay oysters,
South Carolina seed is definitely superior in resistance to the fungus,
almost equal in growth, but usually inferior in rate of survival during
the cold season. Planters who desire to experiment further with these
seed oysters should consider the interaction of the various biological
factors with the economic and fiscal problems associated with their
import from South Carolina.
Literature Cited
Andrews, J. D. and W. G. Hewatt. 1957« Oyster mortality studies in
Virginia. II. The fungus disease caused by Dermocystidium
marinvim in oysters in Chesapeake Bay. Ecol. Monogr. 27: 1-25.
Beaven, G. F. 19^6. Effect of Susquehanna River stream flow on Chesa-
peake Bay salinities and history of past oyster mortalities on
upper Bay bars. Conv. Addresses Natl. Shellfish. Assoc. 19^6:
38-41.
Beaven, G. F. 19^9' Growth observations of oysters held on trays at
Solomons Island, Maryland. Conv. Addresses Natl. Shellfish.
Assoc. 19^9: ^3-^9.
Beaven, G. F. 1953* A preliminary report on some experiments in the
production and transplanting of South Carolina seed oysters to
certain waters of the Chesapeake area. Part 2. Proc. Gulf
and Carib. Fish. Inst., 5th Ann. Sess: 115-122.
Chestnut, A. F. 19^9. The oyster industry of North Carolina and some
of its problems. Conv. Addresses Natl. Shellfish. Assoc. 19^9:
39-^2.
Goode, G. B. 188?. The fisheries and fishery industries of the United
States, Washington, D. C: 5 sections.
Hewatt, W. G. and J. D. Andrews. 1954. Oyster mortality studies in
Virginia. I. Mortalities of oysters in trays at Gloucester
Point, York River. Texas Jour. Sci. 6: 121-133.
Higgins, E. 1937. Progress in biological inquiries. Bur. Fish. Admin.
Rep. No. 30: 50.
Lunz, G. R. 1953- A preliminary report on some experiments in the
production and transplanting of South Carolina seed oysters to
certain waters of the Chesapeake area. Part 1. Proc. Gulf and
Carib. Fish. Inst., 5th Ann. Sess: 115-122.
-16-
McHugh, J. L. and J. D. Andrews. 1955 • Computation of oyster yields In
Virginia. Proc. Natl. Shellfish. Assoc. ^5 (195^): 217-239.
Also, In Southern Fisherman 15(8), August 1955: 21-39.
Wallace, D. H. 1956. South Carolina legislature passes seed export law.
Bull. Oyster Inst. N. A., 11(9) April 2, I956: 1.
-17-
THE SEED OYSTER PROBLEMS OF NORTH CAROLINA
A. F. Chestnut
Institute of Fisheries Research
University of IVorth Carolina
Morehead City, North Carolina
Abstract
The greatest problem regarding seed oysters in North Carolina is
probably the lack of utilization of available seed. Twenty-five years
ago considerable quantities of seed were exported to the Chesapeake Bay
area. An export tax of 50 cents per bushel on all oysters shipped out
of the state in the shell was imposed in 19^7 and curtailed further ship-
ments.
Small quantities of seed oysters are transplanted from natural
areas to privately-leased beds. The total leased acreage is less than
U,500 acres so the amount of seed oysters utilized is small. D\iring the
past three seasons plantings by the Division of Commercial Fisheries has
increased almost five fold. In recent years the first plantings of any
substantial quantity were made in 195^ when 42,550 bushels of oysters
were transplanted from natural rocks to selected public areas. The total
plantings in 1956 were 205,804 bushels. A program is under consideration
to continue plantings each year.
The seed-oyster areas in the coastal waters are located in two
ecologically different environments. Heavy concentrations of clustered
oysters are found near the inlets growing in waters with salinities
above 30 °/oo and are generally limited to the intertidal zone. Some of
these oysters are transplanted successfully to subtidal grounds in areas
of lower salinity where they grow to marketable size. In the Pamlico
Sound area most seed oysters are located in waters with salinities below
10 o/oo and oysters are growing at various depths up to 20 feet. During
years of excessive rainfall these oysters suffer heavy mortalities.
Oyster sets of high intensity frequently occur in many natural
areas resulting in a high production of seed oysters. In some years
continuous setting occurs from May tlirough September producing large
clusters of oysters in areas which are not worked for commercial harvest-
ing.
-18-
PRODUCTION AND UTILIZATION OF SEED OYSTERS IN THE GULF AREA
Philip A. Butler
U. S. Fish and Wildlife Service Laboratory
Pensacola, Florida
The variety of environmental conditions along the extensive
Gulf Coast imposes a great diversity of techniques in oyster culture,
making it difficult for one person to have available current information
on the entire industry. For this reason, I have called upon marine
biologists in each of the states for assistance in assembling some of
the data essential to our discussion. I should like to acknowledge their
helpfulness and cooperation in providing information; the interpretation
placed upon these data and any errors in statement are my own.
In order to simplify organization of the information, I submitted
a questionnaire to these gentlemen. This material can be covered most
efficiently by itemizing some of the questions and replies. It is
essential that we have a clear understanding of the term "seed oyster."
While most biologists attach a definite meaning to the term, ajnong
oystermen, especially from different geographic areas, you will find
that the concept of a "seed oyster" undergoes considerable change.
The first question, then, was "What does the term 'seed oyster'
mean to oystermen in your state?" The replies were briefly as follows:
no precise meaning, oysters to be replanted, any oyster under legal size,
and any oyster not legally subject to harvest. Perhaps some of these
definitions are broader than what your own local industry understands by
the terra. For the purposes of this discussion I am using the term "seed
oyster" to include any oysters of less than legal size which would be
transplanted primarily for the purpose of growing to a larger size. We
are not concerned here with market -size oysters that frequently are
replanted for conditioning, to await a more favorable market, or to
cleanse them of pollution.
The next question asked was "Does your state provide for restricted
or closed areas for the production of seed oysters?" We learn that in the
approximately 3,500 miles of Gulf coast line there are about 350^000
acres of water bottom set aside for seed culture, all in the state of
Louisiana. This does not imply that all, or even the majority, of this
area is in production at any one time. We asked also if there are any
public reefs or polluted areas where larger oysters are harvested primarily
for transplanting to growing grounds. Two states answered in the affirma-
tive; in the past biennium Florida had a special situation in which oysters
Robert M. Ingle, Assistant Director, Florida State Board of Conservation;
Harold Loesch, Marine Biologist, Alabama Conservation Department; Gordon
Gunter, Director, Gulf Coast Research Laboratory; Lyle St. Amant, Chief
Biologist, Louisiana Wildlife Fisheries Commission; Robert Hofstetter,
Marine Biologist, Texas Game and Fish Commission.
-19-
from a polluted reef were transplanted to a new growing area; and in
Alabama, there was some production from deep-water reefs of older mixed
oysters which were replanted on tonging reefs or on private growing
grounds.
The question must arise in your minds that if this is the extent
of seed oyster culture in the Gulf, is there no demand for additional
seed. In answer to this question, the reply from three of the Gulf
states was they have no significant demand. In Alabama, a few private
planters could utilize additional amounts of seed oysters, and in
Louisiana there is some demand, but it is almost satisfied by the state
seed oyster program. In none of the states is there any import or export
of seed oysters for transplanting purposes and none of the biologists
felt that the oyster industry in his state provides a potential market
for out-of-state seed.
The question must also arise in your mind then, as to just
what the Gulf oyster industry does rely upon for its source of oysters
certainly not exclusively on the natural reef community? The answer
is found in the replies to our question "Has your state planted any
cultch?" I will not give any of the figures, but all of the states do
plant shell; although in Texas it has recently been only on an experi-
mental basis. It is significant that the size of the oyster harvest
in the various states corresponds roughly to the extent of the shell
planting program.
This brief survey of the situation points out fundamental dif-
ferences in the oyster industries of the Gulf and the North Atlantic
states. Although a shell planting program is undertaken in both areas,
transplanted seed oysters are the mainstay of the business in the
northern waters.
Oyster communities in the Gulf of Mexico are still on a more
nearly self -perpetuating basis than those in the depleted areas along
the Atlantic Coast. But this is perhaps merely an illusion and we are
actually witnessing the slow and progressive deterioration of an over-
harvested resource which eventually will require drastic help if it is
to remain productive. It is remarkable that after a hundred or more
years of commercial harvesting, the Gulf oyster community can still be
productive with only the moderate and erratic assistance of additional
cultch.
It is reasonable to predict that in the future man is going to
encroach more and more on the environments suitable for oyster culture.
Depletion will increase and the present bountiful spatfall will be
decimated if remedial measures are not undertaken. Then, the only way
the industry will be able to survive will be by the use of transplanted
seed oysters as in New England now.
This is not intended as a gloomy prediction, it seems to me to
be an obvious conclusion to be derived from the history of the oyster
-20-
industry in other regions both in the United States and abroad. We should
profit by this knowledge of history and prepare now for the establishment
of a permanent and controlled seed oyster program.
Since the need for seed oysters in the Gulf area is negligible
now, we might inquire whether or not this superabundance of natural set
can be of help to the northern industry in its dire need for seed. The
answer is probably no, at least in the immediate future. There are many
contributary reasons for this opinion among which I list the following:
no state harvests at present an exportable surplus and only one state has
an established seed oyster progranr, there is too much evidence that some
oyster parasites are endemic in the Gulf area; the great density of foul-
ing organisms in good setting areas will make production of a clean
exportable product extremely difficult; and finally, we still have no
evidence that Gulf oysters can flourish in any other geographical area
where there is a seed shortage.
We should also inquire whether the oyster industry in the Gulf
area can help itself by stimulating a widespread seed oyster program.
The answer to this is a very definite yes despite the fact that the
demand for seed oysters is still negligible. Much of the uncertainty in
the oyster industry here today stems from the unpredictable fluctuations
in the annual harvest, which are due, in turn, to the failure of the
natural set in particular areas. Too much of the industry is dependent
on a single source for its oysters; individual shucking houses may obtain
almost their entire harvest from a single reef. Creation of a seed
oyster industry and an intensification of programs already started could
do much to stabilize annual production and bolster the economy of the
Industry. Development of seed supplies in different regions would make
it possible to compensate for local failures in the crop. This is
practiced now to some extent in Louisiana.
Uncertainty of the labor supply is a second factor contributing
to the weakness of the oyster industry in some areas. More and more
workers, recognizing the importance of the guaranteed annual wage are
reluctant to enter a business that is both seasonal and erratic.
There are many places where the establishment of a seed oyster
program would not only increase the annual yield, but also would put
many more acres of water bottoms into useful production and create steady
work for the local labor force. Stabilizing production and establishing
year-round cultural techniques would go a long way in solving this
problem of an unpredictable labor force.
In Alabama, for example, there is an opportunity to initiate a
seed oyster program wLicb has manifest possibilities. Old oyster reefs
in the upper part of Mobile Bay are only intermittently productive now
because of the severity of spring freshets. It would be possible to
plant cultch on these bottoms in early summer and harvest a crop of seed
oysters in the late winter months. The heavy spatfall and early rapid
growth in this area could produce a large crop of good-size seed in about
-21-
nine months time, and the oysters could be transplanted before there was
any mortality from fresh water. Such a seed oyster program could utilize
Bubmarginal grounds in many areas along the coast to real advantage.
I should like to conclude this discussion by pointing out the
ever-increasing importance of the state research laboratories to a
flourishing oyster industry. It seems to me that now, before depletion
becomes critical, additional research funds should be made available.
Biologists could be locating the most advantageous setting areas, build-
ing them up, learning their good and bad points. They could be experi-
menting with transplanting seed into different areas along the Gulf
coast to learn what seed survives best and where. They could be finding
out how to improve the stock, and perhaps selecting strains which are
more resistant to the various diseases that may be present here. The
importance of a progressive seed oyster program on the part of both the
laboratory and the industry can not be overemphasized.
-22-
SYMPOSIUM ON THE PRODUCTION AND UTILIZATION OF SEED OYSTERS
SUMMARY
Thurlow C. Nelson, Biologist
New Jersey Division of Shell Fisheries
For the first time in the history of our Association we have In
this symposium a comprehensive view of the state of the oyster industry
from Long Island Sound to the Gulf of Mexico. Much of what we learned is
discouraging, but as in the solution of all problems the essential and
first step is to establish the facts. Once these have been ascertained
it should be possible to bring to bear whatever of our already substantial
knowledge of the oyster may be helpful, and to determine wherein further
investigation is essential. It is ironical that the 67 years since peak
oyster production in I89O, during which we have witnessed its steady
decline to the lowest point in history, also embrace the period in which
we have learned more about the oyster scientifically than in all previous
years. Although the oyster is now scientifically the best known marine
animal in the world, we must agree with Dr. Coker (I956) of the University
of North Carolina who recently concluded: "The oyster still calls for
research."
From the great beds of shells of the fossil oysters, Exogyra and
Gryphaea , the largest and most heavily shelled oysters the world has yet
produced, we learn how nature alone with no exploitation by man some 60
million years ago wiped out these magnificent bivalves. Evidence points
strongly to increasing deposits eroded from the land during rapid uplift
of coastal areas during the Cretaceous period (Nelson 1938). So we can
well appreciate the figures given by Joe Glancy for oyster production
decline in the New England-New York area during the decade 19^5-1955 from
5,0^5,000 to 1,354,000 pounds of meats. Had he chosen the latter half of
this decade the figures would have been even more startling, for they
would have begun with the very destructive hurricane of November 2^, 1950^
during which some seed storage beds in Long Island Sound lost three-
quarters of their stock. Gusts up to 90 miles an hour created at a depth
of 50 feet currents of sufficient magnitude to transport part of the seed
two and one-half miles while burying the remainder. The final punch,
delivered by hurricanes Connie and Dianne in 1955; caused such heavy
losses among market oysters as to cause closing down of one of the oldest
and finest oyster companies of the world, H. C. Rowe and Company of
Connecticut. While deeply lamenting the demise of this outstanding com-
pany, it is heartening news from the climatologists that we have now
passed the peak of hurricane probability in the northeastern area, a
prediction fully substantiated in 1956.
Two other hazards, however, still face the industry of this area
in addition to the ever-present sea stars. Increased industrial activity
in the Bridgeport and New Haven areas is sending a greater load of
-23-
industrial wastes into some of the better seed-producing regions. It is
hoped that increasing interest in recreational use of our coastal waters,
which has grown by leaps and bounds in recent years, will assist in
maintaining the necessary freedom from toxic wastes to permit local seed
production. Recreation and the oyster industry have much in common. Mr.
Glancy held out no hope of supplementing insufficient seed supplies of
this area with oysters from further south even from an area as close as
Delaware Bay. Dr. L. A. Stauber (1950) of Rutgers University showed that
the oyster from Delaware Bay southward is a southern variety which must
have water temperatures of 77° or above to spawn. Transplanted further
north they fail to spawn or to grow after one or two years.
The second hazard, so important with failing spatfalls, is the
oyster drill, Urosalpinx . The big question before the oyster grower is
whether he can afford to add to the already peak price of oysters the
extra expense of keeping drill populations in control through use of the
suction dredge or by other methods. Of equal importance: can he afford
not to fight the drill? We wish the staff of Milford Laboratory and any
others working on the problem full speed ahead and all the luck in the
world in finding a satisfactory method of chemical control. Meanwhile
as full use as possible should be made of such methods of drill eradica-
tion as are available (Carriker 1955 )• Recent reports of success in
burying drills through turning over the bottom are encouraging, although
there are many valuable oyster grounds which have been developed only
through shelling of soft mud incapable of holding oysters where such
methods would destroy the surface. Of equal Importance is the possible
harmful effect of turning over the bottom on the supply of food on the
surface. Fundamental studies by the Danes (Petersen & Jensen 1911 ) led
them to the conclusion that the nutrition of bottom marine animals was
intimately bound up with the brownish film a half inch thick covering
the surface.
Delaware Bay though spared the overwheljuing hurricane losses
visited upon Long Island Sound is now faced with the most serious lack
of seed of all time. Dr. Harold H. Haskin, Biologist in Charge of the
New Jersey Oyster Research Laboratory, traced the history of the natural
seed beds of this area. Fifteen years ago their yield was comparable to
that from the beds of the James River, Virginia, probably the foremost
natural oyster seed producing region of the entire world. At that time
New Jersey beds yielded 1,000 to 2,000 spat per bushel, comparable to
the spatfalls in James River. From 1936 to the late 19^0 's there were
always at least 50 per cent oysters as contrasted with shells on the
Delaware Bay beds. Spatfall in I936 was 5,000 per bushel, while in 19^9
occui'red a maximum set at Beadon's Point bed with 10,000 per bushel.
Since 1950 spatfall has been a failure.
With shift from sail to power in the mid 19^0 's small shallow-
draft boats for the first time were able to dredge the inshore spawning
beds which had for many years served as a great spawning sanctuary. In
an effort to halt the declining production Shell Rock Bed was closed in
1953 for a three year period. In spite of dire predictions of fouling
-2k-
and the necessity for "working the bed", sets there were as good as on
the nearby dredged areas. Evidence was obtained that approximately 50
per cent of each season's set was being killed by spring-dredging
operations. During the three-year closure Shell Rock ratio of oysters
to shell rose from 63 to 89 psi" cent. Also, in spite of tradition against
the heavy sets of the Cape May shore some ^3^000 bushels of this was
moved to Shell Rock where it showed excellent survival, reaching market
size in three years. On the basis of observations, recommendation from
the staff of the Laboratory to the State officials was to restrict
dredging during the 1956 season to 150,000 bushels with Shell Rock opened.
Actually, however, over half a million bushels were removed, and when the
beds were closed after three weeks Shell Rock showed a fall in oysters
from 85 to 18 per cent; Cohansey-Ship John, 33 to 12; Middle, 6h to l4;
and Bennies, formerly the best of all the beds, from 3O to 6 per cent.
The spawning stock present on these beds has been overestimated by at
least four times. To get back to the full production of I5 years ago
beds would have to be closed to dredging for I5 to 20 years with qtuestion
whether the most seriously depleted beds could ever recover.
For the Chesapeake Bay area. Dr. J. D. Andrews presented a report
by Dr. J. L. McHugh and himself on the survival and growth of South Caro-
lina seed oysters in Virginia waters. Tracing the history of transplanta-
tion of southern oysters to northern waters since 1825 it appears that
originally oysters of market size were purchased for relaying and prompt
sale in nearby markets. As demand arose for seed the needs of Virginia
planters for the seed crop of the Janies River resulted in banning its
direct export out of the State. Substantial quantities of James River
natural seed planted first on Virginia grounds, however, have been
purchased by growers in northern waters, notably in Delaware Bay. Since
the annual catch of seed in the James River is not sufficient even to
supply all local needs, Virginia welcomed recent lifting of the ban on
export of seed from South Carolina. Anticipating increased demand for
such seed the Chesapeake Biological Laboratory at Solomons, Maryland,
and the Virginia Fisheries Laboratory in cooperation with the Bears
Bluff Laboratory, South Carolina, have been studying comparative growth
and mortality of South Carolina seed and native stock in Chesapeake Bay.
These studies reveal the great value to the industry of the
Atlantic Seaboard of the discovery by Dr. J. G. Mackin (1951) of Texas
A. & M. College of the marine fungus Dermocyst idium and the extensive
mortality caused by it in waters of the Gulf. No better demonstration
of the importance to the oyster industry of fundamental scientific
research can be found than those brilliant investigations of Dr. Mackin,
of his associates, and others (Ray 195^)- The Virginia Fisheries
Laboratory promptly put these findings to practical use and soon delineated
the areas of infection by this fungus. Within the past two years the
visiting Danish microbiologist, Mrs. Greta Christensen, working at the
New Jersey Oyster Research Laboratory, found foci of infection in nimerous
restricted areas in Delaware Bay. In evei'y instance it was determined
that Chesapeake Bay oysters had been transplanted to these beds.
-25-
The Virginia Fisheries Laboratory kindly offered to cooperate
with the New Jersey authorities and with the laboratory at Bivalve to
the end that only uninfected oysters would be brought in. As the New
Jersey Department of Agriculture now lays down embargoes against importa-
tion of farm crops and animals from areas of dangerous infection, so it
was proposed that shellfish officials take similar moves to limit spread
of this infection in Delaware Bay. Unfortunately, no advantage was taken
of this opportunity hence New Jersey growers especially in unusually warm
summers can expect a new and increasing cause of oyster mortality in
Delaware Bay.
Studies of comparative mortality of local oysters with that of
South Carolina seed carried on from 1951 to 1956 at the Virginia Fisheries
Laboratory showed that the imported seed was relatively resistant to
Dermocystidium with approximately only half as great mortality during hot
summers as in local stock. Growth was almost as good but mortality dur-
ing cold winters was serious. The Virginia scientists in reviewing these
results reintroduce a new concept to our oyster growers: the advisability
of marketing their crops at the time the total weight of meats is at its
maximum. By waiting for growth to reach desired size heavy mortality may
take such heavy toll as to cause serious losses to the grower at the time
of harvest.
Dr. Philip A. Butler (1952), Pensacola, Florida, in a comprehen-
sive report, "Shell growth versus meat yield in the oyster, C. virginica '%
first presented this concept to our Association. In summary: 'The ratio
of total volume to shell volume appears to possess certain advantages in
estimating growth and meat yielding potential of oysters as compared to
the customary dimensional measurements." In simple language: not how
large are my oysters but how much meat have I on my beds? Dr. Caswell
Grave (1912) in one of the most helpful practical reports ever made by
a scientist to assist the oyster industry describes, pages 31^-317> how
any careful oyster grower can easily determine this for himself with no
apparatus other than a dish large enough to hold 20 oysters, a one -liter
and a 100 milliliter graduated cylinder, and a medicine dropper. In
brief, the voliime of the oysters is measured by water displacement in the
dish. The oysters are then shucked, carefully saving all shell liguor.
The meats and shells after draining are then measured separately by water
displacement. The water displaced by the meats plus the shell liquor
give total capacity of the shell cavities. The per cent of the shell
cavities represented by the volume of the meats is a measure of the plump-
ness of the oysters. The per cent of the volume of water displaced by the
unopened oysters represented by volume of the meats gives ratio of meats
to unopened oysters. The ratio of water displaced by the empty shells to
the volume of water displaced by the unopened oysters gives the proportion
of the whole represented by the shells alone.
Dr. A. F. Chestnut reported on oyster seed production in North
Carolina. The highest figure, some two million bushels, was attained many
years ago. In recent years seed production has varied from 200,000 to
600,000 bushels. North Carolina has great potential capacity for producing
-26-
seed; in the Neuse River and south of Roanoke Island lie excellent liimps
with oysters up to three inches long. Shipments have been made to northern
waters, one dealer sending 50*000 bushels to Chesapeake Bay. South of
Morehead City in the intertidal zone along the shores are extensive oyster
bars with large reefs. All oysters below low water are killed by boring
sponge and the oyster drill Urosalpinx . Setting Intensity high, 1,000 or
more spat per shell with peaks of intensity in June, July and September.
Rehabilitation of state beds has been initiated with 80,000 to 200,000
bushels of shells annually with plans calling for half a million bushels
eventually. Seed will be removed from crowded rocks to areas where there
is adequate room. It is recommended that Pamlico Sound be opened to
private leasing. At the present rate of planting it would require 10
years to cover just the mouths of the rivers and coves alone.
North Carolina is an area of great interest to the marine biologist
since Car^e Hatferas like Cape Cod in Massachusetts forms a boundary be-
tween northern and southern forms. It is sincerely hoped that progress
will be made toward leasing at least substantial portions of bottoms, now
barren for lack of cultch, which should produce excellent oysters. An
inspection made in company with Dr. Chestnut revealed new growth on many
of the oysters by the last week in March equal to the best to be expected
in Delaware Bay during the course of an entire season. Also striking
were the clean hard shells devoid of boring sponge attack in oysters
growing in new territory. As yet we know little regarding the mode of
infestation of the shells of living oysters by boring sponges. There is
no doubt, however, that the presence on old beds of large amounts of
heavily infested shells of dead oysters and clams constitutes a reservoir
of infestation so extensive as to guarantee prompt invasion of the shells
of any oysters planted thereon. Since Dr. Chestnut reports the death of
oysters below low water through boring sponge and by the drill Urosalpinx
it appears worth while to explore the results of catching spat upon clean
shells which have been on land long enough to destroy all traces of sponge
within them, and which have been planted on suitable bottom now devoid of
any shells or oysters.
Why not take a lesson from the remarkable success of the Dutch
oyster growers who under orders from Dr. Korringa dredged the cockle shells
infested with shell disease and started anew with clean bottoms? By this
piece of seaboard sanitation he saved the Dutch oyster industry from
destruction. There are few oyster beds of the Atlantic seaboard, in higher
salinities, which now are not literally paved with shells and fragments
heavily infested with the sponge Cliona.
Dr. Philip Butler, F.A.W.S., completed the symposium with a brief
description of the production and utilization of seed oysters in the Gulf
area. With a coastline of ever 3^500 miles only 350,000 acres within, the
entire Gulf area has been set aside for private leasing. While in states
north of the Gulf the size of the annual oyster drop is roughly propor-
tioned to the amount of cultch planted, the Gulf area has been productive
for over 100 years with no real assistance from man. Of chief interest
to the reviewer was Dr. Butler's statement to him several years ago that
-27-
at Pensacola water teniperatures adequate for spawning exist for a month
or longer before discharge of eggs and sperm begins. Only after the
spring plankton bloom occurs do the oysters reproduce. As to the feasi-
bility of supplying northern oyster beds with seed from the Gulf, Dr.
Butler's answer is an unqualified "no", at least in the immediate future.
His reasons are: (l) No Gulf state now has an exportable surplus of seed;
(2) only one Gulf state has an established oyster seed program; (3) Gulf
seed is infected and infested with dangerous parasites and predators;
(k) the great density of fouling organisms renders very difficult produc-
tion of a clean exportable product. In closing Dr. Butler stressed the
ever -increasing importance of state laboratories to a flourishing oyster
industry, with the need for biologists to locate the best setting areas
prior to their critical depletion through removal of parent stock. In
the future much must be accomplished in restitution of depleted areas
while careful records should be kept of the results of transplanting.
Highly commended is Dr. Butler's emphasis on the importance of
state laboratories to a flourishing oyster industry. To which may be
added the further benefits to be secured through close cooperation of
these laboratories with each other. In this, our Association must, and
does, play a vital role in bringing the personnel of these laboratories
together once a year, providing a program through which our problems and
our findings can be presented and discussed.
Also important is Dr. Butler's conclusion that the time has arrived
for the Gulf states to give serious consideration to the production of
seed oysters for their own use. Of equal moment is his firm conviction
that it is not feasible to use these oysters to supply any of the beds in
northern waters.
In closing I wish to restate the following from the last paragraph
of my annual review of the papers presented at this Convention as published
in the Fishing Gazette for December 1956. We greatly missed our usual
associations with Dr. Loosanoff and his associates from the Fish and Wild-
life Service laboratory at Milford, Connecticut. They have much to give
to our Association, but of even more moment is the stimulus received
particularly by younger scientists from papers read and from associations
with other scientists. These young and eager research men have the most
to gain from our meetings. With relatively low salaries and often heavy
financial responsibilities they are the least able to provide the necessary
funds themselves. Let it be stressed with all possible emphasis that the
most important ingredient in every research project is an idea. Far too
often conventions are looked upon as joy rides at the expense of the tax-
payer. Checking with the journalists who cover our meetings will reveal
that in their opinion our Association stands at the very top in the per-
centage of our members who sit through long sessions in spite of lighter
attractions just beyond the hotel doors. It is earnestly hoped therefore
that administrators will make adequate allowance in their budgets for
attendance at our meetings. No finer reward could a young scientist
receive than the recognition from above that his work is worthy of report-
ing to fellow scientists. No surer investment could be made by his
-28-
superiors than to assure the enthusiasm, new ideas, and fresh outlook which
the young researcher would bring back to his laboratory from these meetings.
Literature Cited
Butler, P. A. 1952.
C. virginlca.
Shell growth versus meat yield in the oyster,
Proc. Natl. Shellfish Assoc. 1952: 157-162.
Carriker, M. R. 1955. Critical review of biology and control of oyster
drills Urosalpinx and Eupleura. U. S. Fish & Wildlife Spec.
Fish. Rept. 148, 150 pp.
Coker, R. E. 1956. Role of science in marine fisheries:
and potentialities. Sci. Monthly 82: 176-193.
Grave, C. 1912. A manual of oyster culture in Maryland.
Shellfish Comm. Md. 1912: 279-376.
limitations
Foxorth Rept.
Mackin, J. G. 1951- Histopathology of infection of Crassostrea
vlrglnica Gmelin by Dermocystidium marinum Mackin, Owen, and
Collier. Bull. Mar. Sci. Gulf and Carib. l(l): 72-87-
Nelson, T. C. 1938. The feeding mechanism of the oyster.
1. On the pallium and the branchial chambers of Ostrea vlrginica ,
0. edulis , and 0. angulata with comparisons with other species of
the genus. Jour. Morph. 63: I-6I.
Petersen, C.G.J, and P. B. Jensen. 19II. Valuation of the sea.
1. Animal life of the sea bottom, its food and quantity.
Rept. Danish Biol. Sta. 20: 76.
Ray, S. M. 195^' Biological studies of Dermocystidium marinum , a fungus
parasite of oysters. Rice Institute Painphlet, Spec. Issue, Nov.
1954, llU pp. Houston, Texas.
Stauber, L. A. 1950. The problem of physiological species with special
reference to oysters and oyster drills. Ecology 31: IO9-II8.
-29-
BIOLOGY
of
SHELLFISH
-30-
DETERMINATION OF HOW LONG OYSTERS HAVE BEEN
DEAD BY STUDIES OF THEIR SHELLS
1 2
Gordon Gunter , C. E. Dawson
and Wrn. J. Dernoran-^
Oyster biologists are often called upon in cases of oyster
mortality to determine what caused the damage, usually where there is
conflict of opinion and contingent damage claims are involved. If the
time of the mortality can be set, sometimes even within fairly broad
limits, certain causes or claimed causes of the trouble can be eliminated.
After a mortality has taken place, the remains afford the only clues to
the period of time elapsing since death. Sometimes, if the mortality is
recent, bits of meat are left, but usually only the shells remain. The
age of these shells, as dead shells, is sometimes estimated by the amount
of fouling organisms attached. However, these estimates vary widely and
there are few data upon the matter. The authors attempted to set some
limits upon the ages of dead shells as indicated by the fouling organisms.
The work was carried on at Port Aransas, Texas, and at Ocean
Springs, Mississippi. Oysters ( Crassostrea virginica ) were killed with
an oyster knife and placed overboard in Sea Rac baskets or in bags of
chicken wire. One basket was lowered to the bottom and another was
suspended at the surface at Ocean Springs where the depth was six feet.
At Port Aransas where the water was twelve feet deep a third was suspended
at mid depth. Sets of oysters thus treated were put down at every season
of the year.
Several observations were made: the time of disappearance of all
oyster meats, the time of first fouling, moderate fouling, and heavy foul-
ing. Some of the results are given in Table 1. These are approximate
for comparable objective measurements are difficult to make. The table
relates to oysters on the bottom. Several interesting points are not
amenable to tabular treatment and can only be recounted.
Oyster meats disappeared much more rapidly in bottom baskets
than in suspended bags due to the nonswimming crabs and Thais , which
were especially abundant while the meats lasted. Bits of muscle remained
for several weeks in cool water. Preceding fouling of macroorganisms,
and while putrefaction was still going on, a slime, doubtless caused by
bacteria, formed over all the shells. Fouling by algae, barnacles, and
Crepidula was noticeable before putrefaction was complete and while some
of the meat still remained in the shells. The first visible fouling in
shallow water or upper layers was often a patch of green unicellular
algae. This was followed quickly by small barnacles. In the twelve foot
depths at Port Aransas, few barnacles attached and even after long periods
^' i) Gulf Coast Research Laboratory, Ocean Springs, Mississippi,
2) Bears Bluff Laboratory, Wadmalaw Island, South Carolina
■31-
fouling did not become as abundant. On this bottom the fouling complex
was dominated by bryozoans, Crepidula , and worm tubes, and later small
oysters, rather than by barnacles. In shallow water fouling was heavier
and was dominated by barnacles.
At water temperatures of 10 C oyster meat remains fresh in the
shell for three weeks and more, and fouling is slow. Thus, shells may
remain white and shiny for a month after death or a little more. In con-
trast, d\iring warmer months fouling on shells of recently dead oysters is
noticeable in three to four days, and in a week to ten, days fouling is
extensive.
The rate of fouling is strongly dependent upon temperature.
Therefore, widely separated areas with similar temperatures would be
expected to have similar initial fouling rates. Similarly, the fouling
complex varied more with depth than with locality of the two rather wide-
ly separated areas studied .
There was no erosion of shells or noticeable change or diraunition
of the hinge ligament of shells which had been in the water 73 days.
-32-
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-33-
ON THE SHELL OF BIVALVE MOLLUSKS """
Carl N. Shuster, Jr.
Department of Biological Sciences, University of Delaware
Introduction
The writer has been interested in raollusk shell growth for some
time (Shuster 1951). However, attention was refocused on the subject
this past winter when Robert Livingstone, Jr., Fish & Wildlife Service,
Newark, Delaware, asked the writer to determine the age of surf clams he
had collected. Since then, the problem and the scope of the inquiry
has expanded from the original consideration of age determination to the
comparative anatomy and ecology of bivalves and relation of shell growth
to environmental conditions.
Methods
The methods of preparing shells for this study have not been
elaborate. Generally, the left valve was embedded in gypsum and the
hardened block cut intp one or more sections with a hacksaw or a car-
borundum circular saw. The cut edges of the valve were smoothed by
scouring on a glass plate covered with water and a carborundum powder
and then polished with a cleansing powder. These polished surfaces
were studied for gross structure and sketched. The intact right valve
was then compared with the sections of the left valve.
Some shells were treated with varying dilutions of hydrochloric
or acetic acid to erode shell material. This erosion was controlled in
some cases by coating parts of the valve with paraffin.
The observations are listed under each of the species studied.
The taxonomy of Abbott (195^) has been followed. All of the specimens
were from Delaware waters except where otherwise noted.
Observations
Eastern American Oyster, Crassostrea virginica Gmelin. (Plate l).^
' Contribution No. 5^ University of Delaware Marine Laboratories.
2) Dr. Philip A. Butler, Shellfishery Laboratory, Fish & Wildlife Service,
Pensacola, Florida, has communicated to the writer information on a copper
wheel used to section snail shells for the tourist trade (6 August I956).
This copper saw, manufactured by the Felker Manufacturing Company of
California, has a smooth outer edge with a series of low ridges on its
lateral faces. A slow stream of water is directed over the wheel during
cutting.
^^ The paper by Galtsoff (195^) is excellent for detail of the oyster
shell and chalk deposits. ^<
Plate I. THE EASTERN AMERICAN OYSTER. 1. Outline of left valve,
showing region of sectioning. 2. Silhouette of section. 3- Enlarge-
ment of section, showing gross structure: (CH) chalk lens, (SR) muscle
attachment "line", (CY) prominent lines of conchiolin, and (h) hinge
area. h. Diagram of valve margin, showing "caisson" (CA), mantle (m),
and shell (S). 5« Diagram of shell margin, showing the flaring of
the valves and the "siphonal chamber" (SC).
-35-
Sheets of conchiolin are prominent, especially in the region of
the hinge, where they can be traced from the hinge surface into the
sectioned shell. Most of the shell material has a translucent nature
and is present in varying thickness. The uneveness of shell deposition
is further heightened by the inclusion of "chalk deposit" lenses. The
migratidn path of the adductor muscle is seen as a diagonal, inward and
posteriorly directed, purple -pigmented line through the shell. There is
a tendency for the margins of the valves to flare forming a marginal
chamber (Fig. 5)-
Northern Quahog, Mercenaria mercenaria L. (Plate II ).
The laminated structure of a Venus shell is clearly visible.
The prominent laminae of translucent material in the inner portion of
the shell pass diagonally to the outer shell surface through two regions
of opaque shell of different coloration and texture. The outer opaque
region is cream-colored and is not as hard as the inner one. Purple
pigment, when present in the shell, is prevalent in the translucent
material. Within the outer edge of the translucent shell, conchiolin
and periostracum seemed to be joined. At least, the periostracum is
deeply imbedded in the translucent material.
Disk Dosinia, Dosinia discus Reeve.
The laminated structure of the disk shell is not easy to follow
macroscopically, yet it seems to be essentially the same as that of the
quahog. Although "annual rings" are not as distinct as in other species,
certain Dosinia shell characters related to growth are apparent, especially
the change in shell shape. A tightly adhering periostracum covers the
shell. Surface ornamentation of the shell has an interesting bifurcated
pattern similar to that of circuli on a fish scale. An analysis of the
variation in width and bifurcation of the "concentric" bands of the shell
surface might give information on the growth of this species. This speci-
men came from South Carolina.
Blood Ark, Anadara ovalis Brugiuere.
The ark shell is comprised largely of translucent material which
makes it difficult to see the laminations. Sections cut across the ribs
reveal opaque ovals through which translucent lines traverse.
Surf Clam, Spisula solldissima Dillwyn.
In the bivalve shells studied, the laminated pattern of growth
is most prominent in Spisula . The surface of the chondrophore and sec-
tions of the shell clearly show the continuity of the laminae. The opaque
material, like that of the quahog, is of two colors. Many striations,
fine lines crossing the translucent laminae, can be seen in the opaque
shell.
-36-
Plate II. THE NORTHERN QUAHOG. 6. Outline of left valve, showing
region of sectioning. 7- Silhouette of section. 8. Stereogram of valve
margin, showing gross feature of shell: (OO) outer opaque region, (10)
inner opaque region, (IT) inner translucent region, (GL) prominent growth
lines, (TL) translucent laminae, (OL) opaque laminae, (MS) margin of
shell, (P) periostracum.
-37-
Blue Mussel, Mytilus edulis L.
Except where eroded, the periostracum tightly adheres to the
shell. Large amounts of conchiolin, with a rubbery texture, remain after
treating the shell with acid. The bluish pigment is more or less evenly
distributed throughout, although, depending upon the section, the inner
shell region may be white. Laminar lines can be seen but they are very
faint.
Pismo Clam, Tivela stultorum Mawe.
A left valve of this clam, fron. the western shore of the Gulf
of California, was given to the writer by Robert Livingstone, Jr.
Although the valve broke unevenly during sectioning with a hacksaw, one
piece, from, umbo to shell margin, remained intact. This section revealed
a structure similar to that of Spi sula and Mercenaria . One large frag-
ment -- the posterodorsal quadrat of the valve -- was coated exteriorly
With paraffin and the inner surface of the shell eroded by acid. While
an attempt to "cancle" the whole valve by Weymouth's method (1923 ) had
been unsuccessful, the margins of the "annual rings" on the acid-eroded
piece were revealed by "candling" as translucent shell material.
Discussion
The classical report of Weymouth (I923) on the growth of the
pismo clam delved into the gross structure of a bivalve shell to an
extent not matched by any other paper consulted. It is, therefore, the
departure point for further discussion. On the basis of the present
comparison of Tivela and Spi sula shells, it is believed that if Weymouth
had studied the latter he might well have been stimulated by the clear-
ness of its macroscopic structure to study further this aspect of his
work.
The account in this paragraph is condensed from Weymouth (I923).
There are four layers in the Tivela shell: periostracum, vertical layer,
oblique layer, and nacre. These layers are interrupted by more or less
continuous laminae, which can be traced from the outer shell surface
through the shell and even into the umbo and chondrophore . Microscopic
sections show that the entire shell is composed of extremely thin lamellae,
alternately translucent and relatively opaque. The closer together the
translucent lines, the more apparent are "growth rings" on the shell
surface. Conspicuous groups of translucent lines mark what once was the
inner shell surface j and the "growth lines" on the surface, the corre-
sponding margins of the shell. These prominent translucent lines were
interpreted as annual rings and the fine lamellae as probably represent-
ing a short time rhythm of about the magnitude of individual days or
tides, or some physicochemical periodicity. The thickness of the shell
was related to the activity of the entire mantle. Variations in the
level of the concentric rings on the outer shell surface were ascribed
to slight variations in the extension of the mantle.
■38-
In their brief paper, Owen, Truernan, and Yonge (1953)^ describe
three layers of the shell: a superficial periostracum and underlying
outer and inner calcareous layers. The periostracum is secreted as a
thin sheet within a groove between the outer and middle lobes of the
mantle edge. Outer calcareous layers are produced by the general surface
of the mantle. Thus, the periostracum and outer calcareous layers grow
by increments from the periphery of the mantle, while the inner calcareous
layers normally continue to increase in thickness throughout life. They
reported that additional calcareous layers occur in some genera between
the outer and inner layers of the valves, as in Tivela stultorum (Wey-
mouth 1923) and Tellina tenuis (Truernan 19^2). These additional layers
are produced by the less active portion of the mantle edge between the
extreme edge where growth is most active and the inner calcareous layer
of the valves.
The present interpretation of gross bivalve shell structure
differs somewhat from that of Weymouth (I923) on Tivela , and Trueman
(19^2) on Tellina . Agreement, and disagreement, is based chiefly upon
the concept of shell growth as exemplified by the terms "laminae" and
"lamellae," and "layers." These terms do not have the same connotation.
The first two refer to increments of shell growth, the latter to parts
of these increments.
Shell deposition from umbo to shell margin, if not simultaneous,
appears to be at least regular enough to produce a marked degree of
continuity. This continuity of deposition, from umbo to shell margin,
forms laminae which appear to be the basic macroscopic unit of shell
structure. These laminae are alternately opaque and translucent shell
material. Prominent translucent laminae are sometimes referred to as
"growth lines." Shell "layers," more pronounced in the opaque portion
of the shell, are merely regions along the laminae which are deposited
by the same representative portion of the mantle. Each "layer" grows,
therefore, through the accumulation of related regions of the laminae
(see Fig. 8).
Differences in the kind and amount of shell material deposited
could be related to environmental conditions affecting the rate of shell
deposition: the opaque shell being deposited under the more optimum growth
conditions; translucent shell during periods of slow growth, when, it is
possible, the carbon dioxide level in the mantle tissues might be higher
than during rapid growth. Perhaps the laminated structure of bivalve
shells is comparable to growth rings in trees; opaque shell material to
spring wood, and translucent material to summer wood.
Korringa (1952 ) stated that "shell growth occurs periodically"
in the oyster. He does "not believe in alternation of prolonged periods
of tissue growth with periods of shell growth in the oyster, but"
supposes "that both may occur simultaneously, and under favorable
nutritional conditions, continually." Brief observations suggest that
shell growth and tissue growth do indeed proceed at different rates.
Just what the different growth rates may be is not known although it
-39-
has been shown that Ca ^ in seawater is Incorporated into inorganic shell
material within a 2k-hour experimental period (Bevelander 1952). In
Delaware Bay bivalves the fastest shell growth does not occur during the
periods of gonad ripening, gamete discharge, and fattening of the body.
While development of gametes and glycogen stores may not be "growth" in
the strictest sense, obvious changes in the meat weight of bivalves
occur during the period of less rapid shell growth. Growth of bivalves
may occur in a step-wise fashion, with shell growth followed by tissue
growth. The great extensibility of the mollusk mantle makes it possible
for shell deposition to occur without an accompanying and simultaneous
addition to the mantle tissue.
The juxtaposition of the mantle and the inner surface of the
shell suggest that the mantle, shell, and periostracum function as a
"caisson" within which the deposition of shell material occurs un-
hindered by the direct action of the environmental seawater (see Fig. h).
In comparing the oyster with those bivalves possessing siphons,
it seems possible that the chamber formed by the flaring of the margin
of the oyster shell may serve a distinct function. Within the confining
"siphonal chamber," the mantle edge could function in a manner analogous
to the sleeve-like siphons of clams (see Fig. 5).
A significant contribution from the field of paleobiochemistry
helps to form a concept of the comparative anatomy of bivalve shells.
Abelson (1955^ 1956) has found a remarkable identify of amino acids be-
tween the quahog, Mercenaria mercenaria , and its fossil forebears of
millions of years ago. This retention of the basic chemical nature of
the organic matrix of the quahog shell is an indication of the "conserva-
tive" nature of the evolution of shell structure. Although it can be
predicted that they also would have the laminar pattern of growth, it
would be of interest to section fossilized bivalves.
The biochemistry of bivalve shell pigments and conchlolin is
also of interest. According to Comfort (1950) the shell pigments of
bivalves are intimately associated with the conchiolin of the shell
and resist extraction. These appear to be chromoproteins, possibly
with prosthetic groups related to the melanins, for which no successful
technique of extraction has yet been devised. The dark pigment of
Mytilus was determined to be a melanin. Observations in the present
study on the distribution of shell pigments indicate that the colors
are more prominent in the region of the translucent laminae. This could
be due to the greater amounts of conchioloin in the translucent shell.
Beedham's (195^) histochemical tests and chromatographic analyses on
parts of the shell and ligament of several bivalves indicated a difference
between the composition of the amino acid content of the conchiolin of
the inner layers of the valve and ligament and that in the rest of the
shell. Despite these differences in the amino acid content, the studies
of Abelson (1955^ 1956) indicate that the fundamental organic complex
has remained essentially unchanged for millions of years.
-i+0-
Summary
In summation tentative statements on certain comparative aspects
of bivalve raollusk shell growth can be listed.
1. The well-known laminar construction of bivalve shells is being examined
to see if internal and external "landmarks' can be correlated with shell,
growth.
2. The laminar pattern of shell growth was common to all the species
studies. Sections through the shells of Mercenaria mercenaria , Spisula
solidlsimraa, Tivela stultorum , and Doslnia discus are remarkably similajr.
Laminations in the shell of Crassostrea virglnica are most clearly evident
in the hinge area.
3- The observed similarity in the "architecture" of bivalve shells in-
dicates that comparative studies may enable biologists to reach a better
understanding of the correlations between shell structure and the natural
history of the mollusks. It is believed that information on the relation-
ship of growth patterns to environmental factors will give additional in-
sight into the lives of these mollusks, and thus, may be of practical
value in the management of shellfish crops.
h. In this preliminary study, an attempt to relate the width of the
laminae to environmental factors has not been made, although it is evident
that the more prominent groups of translucent lajninae have been interpreted
as annual rings by other workers.
5. It appears that the translucent laminae are deposited during periods
of slow shell growth; opaque layers, during rapid growth.
6. It may be that the perlostracura in conjunction with the mantle and
shell forms a "caisson" within which shell deposition can proceed un-
hindered by direct action of the environmental water.
7. The slight concave flaring of the inner surface of the majrginal area
of the oyster shell, may, by "shaping" the mantle edges, provide the
mechanical advantage derived from the siphon in other bivalves.
Literature Cited
Abbott, R. T. 195^. American Seashells. Van Nostrand.
Abelson, P. H. 1955. Paleobiochemistry. Carnegie Inst. Wash. Yearbook
No. 5^: 107-109.
Abelson, P. H. 1956. Paleobiochemistry. Sci. Amer. 195: 83-92.
Beedham, G. E. 195^. Properties of the non-calcareous material in the
shell of Anodonta cygnea. Nature 17^: 75O.
-kl-
Bevelander, G. 1952. Calcification in mollusks. III. Intake and
deposition of Ca^5 and p32 in relation to shell formation.
Biol. Bull. 102: 9-15.
Comfort, A. 1951- Pigmentation of molluscan shells. Biol. Rev. 26:
285-301.
Galtsoff, P. S. 195^. Recent advances in the studies of the structure
and formation of the shell of Crassostrea virginica . Proc. Natl.
Shellfish. Assoc. 45: 116-135-
Korringa, P. 1952. Recent advances in oyster biology. Quart.
Rev. Biol. 27: 366-308; 339-365.
Owen, G., E. R. Trueman, and C. M. Yonge. 1953- The ligament in the
Lamellibranchia. Nature 171: 73-75-
Shuster, C. N. Jr. 1951- On the formation of mid-season checks in the
shell of Mj^a. Anat. Rec. Ill: 127.
Trueman, E. R. 19^+2. The structure and deposition of the shell of
Telllna tenuis . Joiir. Roy. Micros. Soc. 62: 69-92.
Weymouth, F. W. 1923. The life history and growth of the Pisrao clam
(Tivela stultorum Mawe). Calif. Fish & Game Coram., Fish Bull.
No. 7: 1-120.
-1+2.
SURVIVAL AND GROWTH OF VENUS MERCENARIA ,
VENUS CAMPECHIENSIS ^ AND THEIR HYBRIDS IN SUSPENDED TRAYS
AND ON NATURAL BOTTOMS"""
Dexter Haven and Jay D. Andrews
Virginia Fisheries Laboratory, Gloucester Point, Virginia
Introduction
In the course of laboratory experiments on spawning of mollusks
and propagation of larvae and young, Loosanoff and Davis (1950) of the
Milford La'ooratory of the U. S. Fish and Wildlife Service crossed the
southern hard-shell clam, Venus campechiensis Gmelin, with the northern
species Venus mercenaria Linne (Loosanoff, personal communication). To
determine the ecological adaptations of the hybrids, groups of the parent
species and their reciprocal hybrids were sent for testing to six labora-
tories from Maine to Florida. The northern quahog or hard-shell clam
inhabits the shores of the Western Atlantic from the Gulf of St. Lawrence
to Florida and the Gulf of Mexico; the southern quahog has been recorded
from Chesapeake Bay to Florida (Abbott 195^) although it is doubtful
that it occurs naturally in Chesapeake Bay for we have not encountered
it. Since the two species cross easily in the laboratory, questions
arise about the validity of the species and the amount of natural
hybridization which occurs in areas south of Chesapeake Bay where the
ranges overlap. The characters used by conchologists to distinguish
Venus campechiensis are obesity, great width of lunule, thickness of
shell, persistence of growth ridges, and absence of purple color
internally.
The first series of clajns, received in Virginia in May 195^^
was planted in screen-covered boxes dug into the bottom at Gloucester
Point near the Virginia Fisheries Laboratory. This experiment was a
joint project with James B. Engle of the U. S. Fish and Wildlife Service.
Although all four groups of clams were of the same age, the hybrids
were distinctly larger when received from Milford. In the fall of 195^
when the boxes were first examined, mortality had been high, particularly
in the groups containing the smaller clams; some predation was evident.
Later in the fall hurricane Hazel dislodged some of the boxes and serious-
ly curtailed the experiment.
After this experience, we conceived the idea of growing clams
in boxes in trays suspended in the water; by this method oysters have
been carried successfully through several hurricanes at Gloucester Point.
Later it was discovered that Belding (1912 ) had used a similar method
some 50 years earlier. The primary purpose of the tests was to compare
-L Contributions from the Virginia Fisheries Laboratory, No. 7^«
-h3-
growth and mortality of the two species and their hybrids under identical
environmental conditions. With all four groups in one tray, the habitat
was essentially similar, and predation, type of substratum (Pratt 1953)^
and accessibility were easily controlled.
Methods and Procedure
In November 195^ j Dr. Loosanoff shipped a second series of clams
selected arbitrarily for uniformity of size from lots of the same age.
The clams were grown in wooden boxes filled with sandy mud, suspended
about one foot off the bottom in "Sea-Rac" trays. The wooden boxes,
37 X 16 X U inches and subdivided into four 9 x 16 inch compartments,
were covered with a lid of one-fourth inch mesh hardware cloth. With
lids on, the boxes were submerged in water and refilled; this removed
mud snails, coarse shells, and rocks from the muddy-sand bottom. The
substratum in the boxes was seldom eroded, but a layer of soft mud one-
quaxter to one inch thick accumulated between examinations. Examinations
were made once a month dviring the growing season, but less frequently
during the winter. The clams were washed from the boxes over a screen.
Individual clams were measiured but weights and volumes were obtained by
groups. Length is defined as the greatest dimension of clams from the
anterior to the posterior margin.
Mortality of Clams
Upon arrival in Virginia, each group of clams, containing from
125 to 1^5 individuals, was placed in one of the four compartments. In
November 195^^ therefore, the density was about 125 clams per square
foot, and the mean length was approximately 11 mm in each group. In
July 1955 "the clams were rearranged in two boxes, which increased the
space available and decreased the density by half. In late October
1955^ the clams had reached such a size that crowding was again suspected
and differential mortality had changed the density in the various com-
partments. At this time numbers were marked on all clams; 25 of each
group were placed in boxes and the rest planted on natural bottom. The
density of clams in the boxes was reduced to about 10 per square foot,
and average lengths of the groups were from 25 to 33 n™-
Two years of observations revealed that the death rate of the
native species, V. mercenaria, was low during all seasons (Table l).
At these early ages and small sizes, neither disease nor environmental
factors caused much death among clams of the northern species, although
they were bred artificially from brood stock obtained in Long Island
Sound. During the warm seasons, all groups had low mortalities, and it
may be surmised that in Virginia sximmer conditions are probably not
limiting to the species or the hybrids. In winter, however, the southern
species had heavy losses and the two hybrids had important losses
(Table l).
■kk-
After 25 of each group had been placed in trays, the remainder
of the numbered clams was placed on natural bottom. In June 1956
about two-thirds of these clams were recovered by diving. In all groups,
boxes (empty shells) and dying clajcs comprised less than three per cent
of the total recovered except in V. campechiensls which had a death
rate of 7^ per cent. As the warm season progressed, all groups of clams
were rapidly decimated. Shell fragments began to appear in June, in-
creased in abundance in July, and a large quantity was recovered in
August. Positive identification of predators was impossible, but the
size and nature of shell fragments, higher losses in the groups of
smaller clams, and the long period of predation cause us to suspect the
blue crab (Callinectes sapidus ) .
Growth
Growth of c
ber each year. V.
growth rates (Fig.
0.5 to nearly 11 gm
in the 1956 season,
survived the second
half as fast as the
of six gm the first
season.
lams began in April or early May and ceased in Novem-
campechiensis and the two hybrids had very similar
1). In trays these groups increased in weight from
in the 1955 growing season and from 11 to 29 gm
However, none of the clams of the southern species
winter. The northern quahogs grew little more than
others; they reached a length of 26 mm and a weight
season and 38 mm and 17 gm at the end of the second
During the growing season of 1956, clams retained in the suspend-
ed trays outgrew their counterparts in natural bottom (Table 2) although
relatively few of this last group survived. This supports our belief
that boxes of muddy sand suspended off the bottom in trays provide a
suitable habitat for growth and survival of clams.
Yield
The potentiality of these clams as seed for Virginia waters
depends ultimately upon the yield to the clammer. The amount of crop
obtained and rapidity of harvest after seeding or setting depend upon
rates of growth and survival of clams before a marketable size is reached,
All the southern clams died before reaching a marketable size. During
the two years of the experiment, the hybrid clams usually have had a
greater biomass or yield than the northern clams (Fig. 2). Relative yield
or biomass has been discussed by Andrews and McHugh (1957)' None of the
clams has reached marketable size yet, however, and the slow growth of
the northern clams is almost compensated by the high rate of survival.
Discussion
The causes of clam mortalities in Virginia waters are unknown,
yet it is significant that when predation was prevented losses were very
-1+5-
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ol 5
V.CAMPECHIENSIS $x V. MERC ENARIA (f
V.MERC EN ARIA $ x V CAMPEQHIENSIS cf
O — o V.MERC ENARIA
© — © V.CAMPECHIENSIS
N J F
1954
J A S
1956
Fig. 1. Mean weight, including shell, of clams grown in
boxes suspended in trays at Gloucester Point, Virginia.
-kl-
o
-I
Ui
V. CAMPECHIENSIS 9 x V. MERCENARIA 6
V. MERCENARIA 9 x V. CAMPECHIENSIS rf
V. MERCENARIA
V. CAMPECHIENSIS
NDJFMAM JJASONDJ FMAMJJASO
1954 1955 1956
Fig. 2. Relative yield (biomaBs) of clams grown in boxes
suspended in trays at Gloucester Point, Virginia.
-h7a-
Table 2. Mean Lengths and weights of clams in trays and in natural bottom,
September ik, 195 6''"
Length (mm)
Weight (gm)
Group
Tray
Natural
Tray
Natural
bottom
bottom
V. mercenaria
37
33
15
13
V. mercenaria x V.
campechiensis
kk
ko
26
19
V. campechiensis x
V. mercenaria
h3
39
26
22
All clams were grown in trays until October 1955 when part of each
group was planted on natural bottom. Subsequently, there were heavy
losses in the bottom-living clams from predation.
-48-
low in the northern species at all seasons. Methods for reducing winter
mortalities of northern quahogs in Maine have been discussed by Dow and
Wallace (1951). The deaths of the southern clams and some hybrids in
late winter suggest inability to withstand low temperatures. The experi-
ments imply that V. campechiensis may be unable to persist in Chesapeake
Bay long- enough to breed and establish a population. The test in trays
was fairly rigorous in respect to temperatures, for the water was shal-
low, and the winters of 195^-55 and 1955-56 were the coldest in a decade.
The southern clams living in natural bottom also died at a high rate in
the winter of 1955-56.
Growth of the hybrids was clearly superior to that of the northern
clams. It appears that this desirable characteristic may be traced as
much to inheritance from the southern quahog as to hybrid vigor, for V.
campechiensis equalled the hybrids in growth in Virginia waters. It
must be remembered that the progeny of V. mercenaria were obtained from
brood stock native to the cold waters of Long Island Sound. Clajns
native to Chesapeake Bay may grow faster.
The relative yield of the hybrids and the northern clams at
marketable size is undetermined. If growth becomes slower with age, and
winter losses continue, then the hybrids may yet be exceeded in yield by
the northern quahog.
Literature Cited
Abbott, R. T. 195^ • American seashells. D. Van Nostrand Co., Inc.,
New York, 5^1 PP-
Andrews, J. D. and J. L. McHugh. 1957- The survival and growth of
South Carolina seed oysters in Virginia waters. Proc. Natl.
Shellfish. Assoc. ^7(1956): 3-17-
Belding, D. L. I912. A report upon the quahaug and oyster fisheries
of Massachusetts, including the life history, growth and
cultivation of the quahog ( Venus mercenaria) , and observations
on the set of oyster spat in Wellfleet Bay. Commonwealth of
Mass., Boston: 13^ ppj 69 pi.
Dow, R. and D. E. Wallace. 1951- A method of reducing winter mortalities
of Venus mercenaria in Maine waters. Convention Addresses Natl.
Shellfish. Assoc. 1951: 15-21.
Loosanoff, V. L. and H. C. Davis. 1950. Conditioning V. mercenaria
for spawning in winter and breeding its larvae in the laboratory.
Biol. Bull. 98: 60-65.
Pratt, D. M. 1953* Abundance and growth of Venus mercenaria and
Callocardia morrhuana in relation to the character of the bottom
sediments. Jour. Mar. Res. 12: 60-7^.
-k9-
GROWTH OF YOUNG VENUS MERCENARIA ^ VENUS CAMPECHIENSIS ;
AND THEIR HYBRIDS.
A. F. Chestnut, W. E. Fahy, and
H. J. Porter
Institute of Fisheries Research University of North Ceirolina
Morehead City, North Carolina
Growth studies of the hard clam, Venus mercenaria , have been
centered primarily on the large size groups. Studies in the northern
peirt of the range of the species have shown that shell growth occurred
during the months of April through November (Kellogg 1903^ Belding 1912,
Haskin 19^+9, Pratt 1953, Gustafson 195^, Pratt and Campbell 1956).
Belding (1912) foiond in Massachusetts 51«7 per cent of the total growth
for a year was attained during August and September. Gustafson (195^)
showed the peak of growth in Maine to be between mid-July and mid-Septem-
ber; Pratt and Campbell (1956) reported that most of the growth in a
year took place before mid -July in Rhode Island. In North Carolina
Chestnut (1952) showed that greatest growth occurred in April and May
and least in September.
The following studies were made with clams under 30 nim spawned
from known parents and grown under laboratory conditions by Dr. Victor
L. Loosanoff and his associates at Milford, Connecticut. Rate of growth
was studied for 18 months in Bogue Sound, North Carolina, at the Insti-
tute of Fisheries Research. Grateful acknowledgement is made to Dr.
Loosanoff for supplying the clams.
Methods
Two groups of hybrid clams, V. mercenaria + x V. campechlensis
and the reciprocal cross, were received from Milford in May 195^ • A
second shipment received in September 195^^ contained four groups of
clams, V. mercenaria , V. campechiensis , and their hybrids.
The clams were kept in wooden frames about four inches deep and
18 inches square with plastic screen on the top and bottom. Beach sand
was sifted over the clams until each box was half filled. The boxes
were partially buried and kept in the intertidal zone where they were
exposed each low tide. Measurements of the greatest length and total
weight were made a monthly intervals.
In previous studies where small clajns under 15 mm in length were
used mortalities frequently resulted among clams left undisturbed for
longer than a month. Complete filling of the boxes with sand and heavy
fouling of the screens prohibited the circulation of water. It was
necessary to remove small predators, such as drills and crabs, which
■ 50-
passed through the mesh and were trapped inside the boxes. When sets of
native clams occurred in the boxes, they could be distinguished from
experimental clams by their smaller size; they were removed to prevent
any masking effects.
Comparison of Growth of Hybrids
The first shipment of hybrid clams, V. mercenaria + x V.
campechlensis '^and the reciprocal cross, was planted on May 10, 195^«
The average length of both groups at the beginning of the studies was
7.1 ram (range k.O -,11.0 mm). Data are found in Table 1. After seven
months mercenaria x campechlensis + averaged 23.9 nim in length and the
other cross averaged 24.5 mm' This difference is not considered signifi-
cant.
Approximately 80 per cent of the total increase in length
occurred in May, June, and July with the greatest growth during June,
The studies were discontinued in January 1955- A sudden freeze while
the clams were left exposed following measurements resulted in a mortality
of 81 per cent in one group and 42 per cent in the other.
Comparison of Growth of Five Groups of Clams
A second series of experiments begun on September I5, 195^^ was
concluded in January 1956. The hybrids ranged in length from 3 '5 to
27.0 ram. Two size groups were established; all clams under 10 mm were
separated from those 10 mm or larger. The five groups in this series
were comprised of mercenaria , two groups of mercenaria ^ x campechlensis
^ and two groups of campechlensis 9 x mercenaria <^ . Because of the
large number of individuals in each group, random samples were measured
and weighed from September through January 1955- All the clams in each
group were measured in successive months beginning in February 1955. No
data are included for campechlensis which suffered heavy mortalities by
February 1955- A summary of the average length and weight at 6 month
intervals of the five groups is shown in Table 2.
The greatest increase in length occurred in the smaller hybrids,
which averaged 3^-9 and 35.6 mm at the end of 15 months (see Fig. l).
During the first six months within the smaller size group fluctuations
occurred in average length as shown in Figure 1. These merely reflect
the normal variation in random samples. The two larger groups of hybrids
averaged kO.k and 4l.2 mm, respectively. Venus mercenaria showed the
slowest growth rate and averaged 26.2 mm. The total increase for both
crosses in the smaller hybrid group was 29-2 mm, but mercenaria + x
campechiensis '^was l.k g heavier than the reciprocal cross. In the
larger series of hybrids campechiensis ? x mercenaria '^"showed a greater
increase in total length and total weight. These differences in rate of
growth as measured by total length or weight between the hybrid clams
were not great enough to be considered important.
-51-
Table 1. Growth and survival of two groups of hybrid clams.
V. campechiensiB
^ X V. mercenaria °
Average
No. of live
Date
Length mm.
Range ram.
clams
195if
May 10
7.1
U. 0-11.0
199
June 10
11.0
7.5-16.0
190
July 9
16.8
12.5-23.0
171
Aug. 10
20.1+
15.0-27.5
170
Sept. 10
21.9
16.0-29.0
170
Oct. 11
22.9
16.0-30.0
169
Nov. 11
23.8
16.5-30.5
1^
Dec. 9
23.9
16.5-31.0
169
1955
Jan. 10
25.1
17.0-31.0
32
V. merceneiria + x
V. campechiensis
195^
May 10
7.1
4.0-11.0
170
June 10
10.7
5.5-15.5
1^
July 9
17.0
8.5-22.0
169
Aug. 10
20.8
13.0-26.0
168
Sept. 10
23.1
15.0-29.0
168
Oct. 11
23.7
15.0-29.0
168
Nov. 11
2i+.2
15.0-30.0
162
Dec. 9
24.5
15.5-30.5
15U
1955
Jan. 10
2U.7
17.0-30.0
90
Feb. 10
2i+.9
17.5-29.5
a
-52-
Table 2. Average increase in length and weight of five groups of clams.
Sept.
March
Sept.
Dec.
Total
195^
1955
1955
1955
Increment
V.
mercenaria
av. length
6.7
9.9
2U.5
26.2
19.5 mm
av. weight
0.09
0.3
5.0
6.9
6.8 g
V.
camp. ? X V.
mere.
o-
av. length
5.7
10. i+
32. U
3^.9
29.2
av. weight
0.05
0.6
10.5
13.6
13.5
V.
o
mere. + x V.
camp.
c/
av. length
e.k
9.9
l>h.l
35.6
29.2
av. weight
0.07
0.2
12.8
15.0
1I+.9
V.
mere. + x V.
camp.
c/
av. length
17.2
19.5
38. U
1+0.4
23.2
av. weight
1.5
2.2
19.3
22.9
21.1+
V.
camp. + X V.
mere.
c/
av. length
16.2
18.6
39.3
1+1.2
25.0
av. weight
1.2
1.9
21.7
2i+.l
22.9
■53-
Fig. 1. Increase In average length of Venus mercenarla and
hybrids at monthly intervals.
40'
30'
20-
-*=^»
10'
j( — x merc^ X camp-
• — • comp. J X mere, d*
* — * mercenario
19 5 4
t »
19 55
A
.51+-
Greatest increase in length occurred dxiring the five month period
April through August (75 to 8^ per cent). Growth rate decreased in
September, but showed a slight increase in October and November. The in-
crement in total weight within each group followed the some pattern as
that for total length.
Notes on Survival
Heavy mortalities were noted during the months of January and
September. Some mortalities during the cold months were due to exposure
of the clEims following measurement before they were returned to the
bottom. Heavy mortality during September 1955 may be attributed in part
to a sharp reduction in salinity. Average rainfall per month from May
195^ through July 1955 varied from 0.6 to 6.2 inches. Salinity was
rather stable during this period ranging from 31 to 37 o/oo. In August
and September 1955 three hurricanes passed through the area accompanied
by heavy rains. Salinities dropped to 15 o/oo when a total rainfall of
i+3'8 inches was recorded for the two months. Salinities increased in
November 1955 to range between 27 and 32 o/oo and by December were above
30 o/oo.
A peculiarity was noted in the behavior of the siphons of the
hybrid clams. During low tide the siphons frequently were observed lying
extended on the bottom. This condition was never noticed in mercenarla ^
and such behavior might render the hybrids vulnerable to predators.
Discussion
Hybrid clams produced by crossing mercenaria and campechiensis
grew more rapidly than the species mercenaria . Unfortunately, the
species campechiensis did not survive for further comparison. Failure
of campechiensis to survive the cold weather suggests a possible lack
of resistance to cold. Native campechiensis are found in North Carolina
growing in the intertidal zone, however, the clams used in this study
were progeny of clams from Florida. Further studies to compare the
survival of native campechiensis would be of interest.
The pattern of monthly growth rates as measured by increase in
total length was similar for the small and large size groups of hybrids.
These results are similar to the previous findings in the same area
described by Chestnut (1952) for adult mercenaria .
A comparison of the growth of mercenaria with results of Gustafson
(195^) for similar size clams in Maine show that growth occurred over a
much longer period in North Carolina.
Fiirther studies should be made in subtidal areas of this locality
to determine the effect on growth rate and mortalities.
■55-
Literature Cited
Belding, D. L. 1912. A report upon the quahaug and oyster fisheries
of Massachusetts. Wright and Potter Printing Company, Boston,
13h pp.
Chestnut, A. F. 1952. Growth rates and movement of hard clams, Venus
mercenarla. Proc. Gulf & Carib. Fish. Inst. Uth Ann. Session:
T+9^59^
Gustafson, A. H. 195^- Growth studies in the quahog, Venus mercenaria.
Proc. Natl. Shellfish. Assoc, h^: lifO-150.
Haskin, H. H. 19^9- Growth studies on the quahaug, Venus mercenaria .
Natl. Shellfish. Assoc. Conv. Add.: 67-75.
Kellogg, J. F. 1903 • Feeding habits and growth of Venus mercenaria .
N. y. Sta. Mus. 10 (71): 3-28.
Pratt, D. M. 1953- Abundance and growth of Venus mercenaria and
Callocardia morrhuana in relation to the character of the bottom
sediments. Jour. Mar. Res. 12 (l): 60-7^1.
Pratt, D. M., and D. A. Campbell. 1956. Environmental factors affect-
ing growth in Venus mercenaria . Limnol. ajid Oceanogr. 1 (l):
2-17.
-56-
BIOLOGY
of
SHELLFISH ENEMIES
■57-
OUR PRESENT KNOWLEDGE OF THE OYSTER PARASITE " BUCEPHALUS "
Sewell H. Hopkins
A. & M. College of Texas, College Station, Texas
The purpose of this report is to put on record, for oyster
biologists, what parasitologists now know about the oyster-castrating
flatworm " Bucephalus ".
In 1827 the German zoologist von Baer discovered a larval tre-
matode (cercaria) which developed from branching tubular parasites in
the gonads of European fresh-water "clams". This cercaria had a tail
with a bladder-like stem and two long flexible lateral branches. In
its characteristic swimming position, hanging in the water, head down,
with tail branches stretching to each side, it resembled the head of
a steer, so von Baer named it Bucephalus, meaning "ox head".
This type of cercaria is now known to be the characteristic
larval form of an entire family of trematodes or flukes, the Bucephalidae,
whose numerous adult forms live in the intestines of marine and fresh-
water fishes. The second cercaria of the Bucephalus type, Bucephalus
haimeanus , was foimd by Lacaze-Duthiers (185^) in European oysters and
cockles of the Mediterranean Sea. The third one, Bucephalus cuculus
McCrady (187^) was found at Charleston, South Carolina, in American
oysters, Crassostrea virginica. Both Lacaze-Duthiers and McCrady
noted that the gonads of parasitized oysters were destroyed, so that
these oysters were completely sterile. "Parasitic castration" of the
hosts is caused by all the bucephalid larvae known to date, whether in
oysters, cockles, clams, scallops, pearl oysters, mussels, or fresh-
water clams.
Textbooks give the following account of the life history of the
oyster Bucephalus : Cercariae emerge from sporocysts (the branching tubes
in the gonad of the oyster) and swim around until they happen to run in-
to a silverside minnow ( Menidia ). The cercaria then penetrates the skin
of the silverside, encysts in its flesh, and grows but does not become
sexually mature. When the infected silverside is eaten by a billfish
or needle gar ( Strongyliora ), the bucephalid comes out of its cyst and
develops into an adult in the intestine of this third and final host.
There is good evidence now that this textbook account is not
quite right. It is based partly on guesses by European parasitologists,
who have never done any experimental work on Bucephalus to this day,
and partly on a pioneer study by Tennent (I90i|, I905, I9O6, I9O9) of
Johns Hopkins University fifty years ago. Tennent was handicapped not
only by being a pioneer, but also by a prejudice against "splitting
species" which let him to believe that all bucephalids must be physio-
logical varieties of one species. In consequence, he combined stages
of at least two and probably three different species into one composite
-58-
life cycle, the one given in the textbooks. Temient never proved that
the immature bucephalids in silversides, or the adults in needle gars^
had any connection with the larval forms in oysters. The only thing he
did prove is that oysters could be infected (100 per cent, in his experi-
ment) by injecting feces of bucephalid -harboring gars ( Lepisosteus ) into
the mantle cavities of oysters. It is unfortunate that two different
fishes called "gars" were involved in Tennent's account, for of course
there is no kinship between the marine needle gar, Strongylura , and the
true gar, Lepisosteus , of lakes, rivers, and estuaries. Unfortunately,
Tennent paid no attention to the characteristics of the adult bucephalids
of the gars ( Lepisosteus ) which he used in his oyster-infecting experi-
ments, because he assumed that all bucephalids were the sajne species.
Now, the only bucephalid known from true gars is very different from
any of the several species in needle gars and silversides, and has its
immature encysted stage not in silversides but always in mullets ( Mugll
cephalus and M. curaema ) . Our present knowledge of the life history of
the oyster bucephalid rests here, with the probability but not yet the
certainty that the cereariae from oysters penetrate the fins of mullets
and encyst inside the fin rays. If this is true, then the adult forms
develop in the intestines of gars ( Lepisosteus ) which eat the infected
mullets. Oysters presumably become infected by contact with the feces
of infected gars (Hopkins, 195^).
I have seen statements in the literature to the effect that
Bucephalus cannot be an important oyster parasite because' it is so un-
common. True enough, in most places hundreds of oysters may be examined
without finding a single Bucephalus infection. But in some places a
high percentage of the market-size oysters contain this parasite, and
therefore contain no gonads and produce no eggs or sperm. In Tennent's
time, fifty years ago, some oyster beds in Pamlico Sound and in Newport
River above Beaufort, North Carolina, had Bucephalus infections in as
high as 33 per cent of the oysters. Even higher percentages of infection
in local areas have been reported to me by colleagues in recent years,
and not all in the South; one such report concerns a small river in New
Jersey. I have known bayous in Louisiana which could be counted on to
show Bucephalus in 10 to 25 per cent of all oysters over one year old.
The oyster beds with a high incidence of Bucephalus , whether North or
South, seem to be found mostly in low salinity estuaries or in small
marshland waterways . Bucephalus seems to be rare or absent in broad
open bays or sounds where the salinity is higher and the oysters are
surrounded by a much larger volume of water. This agrees with what would
be expected if oysters are Infected only by contact with fecal material
from gars.
The effects of Bucephalus on oysters are no better known now than
at the time of my last rejoort (Menzel and Hopkins, 1955j 1955a). Except
in the very early stages of the infection, bucephalid sporocysts always
destroy the gonad completely; usually not a single egg or sperm cell can
be seen in an oyster which contains mature sporocysts. There is some
slight evidence that in the fairly early stages of infection, while
sporocysts are still confined to the gonad region, Bucephalus may
■59-
stimulate growth of the oyster, as similar gonad parasites of snails
have definitely been proved to do. There is much better evidence that
older Bucephalus infections damage tissue other than the gonad and inter-
fere with growth. Presumably the parasite would eventually kill the
host, if the oyster did not die of old age or something else first, but
this has not yet been proved. Gastronomically, Bucephalus may be con-
sidered a beneficial parasite in southern waters, not only because it
gives the oysters some badly needed birth control, but because the
sporocysts remain in the oyster the year around while the reproductive
elements are mostly lost in the long spawning season (half the year, on
the Gulf Coast). Bucephalus -infected oysters have an excellent taste
and are fat -looking and full of glycogen when uninfected oysters are
spawned out, thin, and tasteless. On several occasions, I have rather
facetiously suggested that it might be a good idea to produce Bucephalus
infections in a whole bed of oysters, and thus supply caponized oysters
for a premium market. Even if that idea is not entirely practical, I
still think that Bucephalus is a very interesting parasite and deserves
further study.
Literature Cited
Baer, K. E. von. 1827. Beitraege zur Kenntnis der niedern Thiere.
Nova Acta Acad. Nat. Curios. 13: 523-762.
Hopkins, S. H. 195^- The American species of trematode confused with
Bucephalus ( Bucephalopsis ) hairaeanus. Parasit. hk: 353-370*
Lacaze-Duthiers, F.J.H. de. 185^. Memolre sur le bucephale Haime
(Bucephalus haimeanus ) helminthe parasite des huitres et des
bucardes. Ann. Sci. Nat., Paris, Zool., Ser. k, 1: 29^1-302.
McCrady, J. 187^. Observations on the food and the reproductive organs
of Ostrea virginiana , with some account of Bucephalus cuculus
nov. sp. Proc. Boston Soc. Nat, Hist. l6: I7O-I92.
Menzel, R. W. and S. H. Hopkins, 1955- Effects of two parasites on the
growth of oysters, Proc. Natl. Shellf. Assoc, k^: 184-186.
Menzel, R. W, and S. H. Hopkins. 1955a. The growth of oysters
parasitized by the fungus Dermocystidium marinum and by the
trematode Bucephalus cuculus . Jour, Parasit. 41: 333-342.
Tennent, D, H, 190i+. A study of the life history of Bucephalus
hameanus , a parasite of the oyster. Dissertation, Johns Hopkins
Univ., Bait.
Tennent, D. H, 1905- Feeding experiments for determining the life
history of an oyster parasite. Biol. Bull, 8: 233-235.
.60-
Tennent, D. H. 1906. A study of the life-history of Bucephalus haimeeinus t
A parasite of the oyster. Quart. Jour. Micr. Sci., N.S.
k9: 635-690, pis. 9-42.
Tennent, D. H. 1909' An account of experiments for determining the com-
plete life history of Gasterostomum gracilescens . Science, n. b.
29: h32-k33-
■ 61-
THE FIATWORM PSEUDOSTYLOCHUS OSTREOPHAGUS HYMAN,
A PREDATOR OF OYSTERS
Charles E. Woe Ike
State of Washington, Department of Fisheries
Shellfish Laboratory, Quilcene, Washington
General Biology
In the spring of 1953 the Department of Fisheries of the State
of Washington received a request from the Olympia Oyster Growers Associa-
tion to investigate unusually heavy losses of spat of Ostrea lurida
during the first year following setting. Investigation of these losses
led to the discovery that the flatworra is a predator (Woelke, 195^)*
Experimental lots of cultch were placed in water at staggered in-
tervals through the setting season and removed for examination after
periods ranging from two weeks to nine months. These experiments, to-
gether with observations on commercial cultch, were designed to ascertain
the time and magniturde of losses. In late September 1953 heavy spat
losses were noted on both experimental and commercial cultch. Over 70 per
cent of the dead spat had very small holes of an unusual oval shape in
the right valve ranging from 106 x 113 to 180 x 260 microns with an
average of 1^7.4 x 189-9 microns (Plate l).
Observations and laboratory experiments proved the causative or-
ganism was a flatworm of the Polycladida (Plate 2). The discovery that
a flatworm possesses the ability to penetrate an oyster shell was new
and was greeted with some skepticism by both oyster growers and scientists.
Specimens were sent to Dr. Libbie Hyman for identification. She reported
them to be an undescribed species of the genus Pseudostylochus . In 1955
Dr. Hyman published a description of this new species and gave it the
specific name ostreophagus .
From September 1953 to September 195^+ the number of spat per
square inch on one commercial planting of cemented egg-divider cultch
declined from 28.3 to 3«^ spat. From samples collected at least once a
month it was found that over 90 per cent of the dead were victims of the
flatworm. Population density of the worm in this particular area was in
excess of 600,000 per acre. It has been found that flatworms will destroy
spat from setting size to U mm at a rate of 85 per month and spat from
4 to 12 mm at a rate of hi per month. In laboratory experiments the
worm successfully attacked the spat of the Olympia oyster ( Ostrea lurida),
the Pacific and Kumamoto oysters ( Crassostrea gigas ), and the Virginia
oyster ( Crassostrea vlrginica ) as well as Olympia oysters up to two
years of age.
Destruction of the oyster by the flatworm is accomplished by
penetrating the shell and in some manner separating the adductor muscle
-62-
I— EQUALS i4 INCH
Plate 1. Typical oval hole found in upper valve of
dead oyster spat .
■63-
from the right valve. The worm then crawls between gaping valves and
ingests the entire live oyster. Physical irritation has caused worms to
regurgitate whole live oysters. The actual manner in which penetration
of the shell is accomplished is not too well understood. However,
repeated observation of worms attacking oysters, and the presence of
gelatinous mucoid droplets on the incomplete shell perforations of attack-
ing worms, suggest that penetration is accomplished chemically. There
is some evidence that once the shell has been penetrated the worm extrudes
the edge of its pharyngeal folds through the small hole into the shell
cavity. The adductor muscle is then severed and the oyster gapes, be-
coming easy prey to not only the flatworm, but also other scavengers in
the immediate vicinity. Experiments by Smith (1955) to determine whether
flatworm homogenates would dissolve oyster shell gave negative results.
His experiments showed also that Pseudostylochus ostreophagus was primarily
a predator and not a scavenger.
Distribution of the worm on any given bed or in any general area
is extremely variable. They are essentially subtidal and as such are very
common in the Olympia oyster dikes. Diked areas located highest in the
intertidal zone contained greater numbers than lower ones. The worm is
present on nearly all oyster beds in Puget Sound.
Specimens of the most common flatworm found in the Pacific seed
oyster producing areas in Japan were collected by the author and sent to
Dr. Libble Hyman. These were found to be the same species attacking the
Olympia oyster. Samples of dead spat of Crassostrea gigas in Japan in-
dicated that the flatworm caused losses as high as k'^.l per cent in some
areas. The presence of live flatworms in the shipments of Pacific oyster
seed arriving at Washington ports from Japan fairly definitely establishes
that it is another exotic introduced to our waters with this oyster.
Life History
Life history studies conducted in 195^ and 1955 revealed that in
Washington egg laying extends from March through October. Freshly laid
eggs average 1^7 microns in diameter. Estimates of fecundity based on
egg density and size and number of egg masses deposited by individual
worms in one season gave a range of 3>373 to 84,332 eggs, an average of
31,472 per worm. Incubation time at 15-17° C ranges from 3O to 3^ days
before hatching. The typically polyclad larvae measure about l4l x 208
microns at hatching. Part or all of the larvae are free swimming for an
unJoiown period of time. Worms as large as ll40 x 6k0 microns have been
taken in plankton samples and worms up to 0.5 cm in length have shown
swimming tendencies in the laboratory. There is some question as to
whether a definite "settling size" actually can be found. Food of the
larval worm is not known. A maximum of I6 larvae per 20-gallon plankton
sample has been found.
In the laboratory worms grew from an "apparent settling size" of
ll40 microns to O.5O cm in 21 days and from O.5O cm to 1.4-9 cm in 66 dayB.
-64-
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-65-
From November through July random samples of large numbers of worms show
virtually all sizes up to the maximum found (3 -20 cm) at any given time.
The disappearance of adult worms in the field and loss of all laboratory
stock in midsummer for ttoee successive years probably indicates a life
span of one year or less.
In laboratory experiments the worms definitely avoided strong
light. Temperatiires in excess of 35 C are fatal after a one hour
exposure. Salinities below 10.2 °/oo are fatal after seven days, 7-9
°/oo at three days, 5-^ °/oo in 2k hours andfresh water after one hoiir.
Relative abundance of a yeair class and salinity may be related since
salinities of less than 28 °/oo prevailed with low populations and over
29" 5 °/oo were accompanied by strong year classes.
Control
Fresh water treatment of oyster seed is the most obvious method
of control and has been successful experimentally. Commercial scale
dipping of seed oysters in a salt brine has been very successful.
Japanese seed oyster growers have used chlorinated lime baths at a con-
centration of about ij-50 °/oo with moderate success. In one commercial
operation the worms were forced off the cultch by placing sesd oysters
high in the intertidal zone for three weeks. Another grower claims to
have had success driving the worms from his beds by burying perforated
containers of creosylic acid in diked areas. Presumably the acid very
slowly diffuses from the jar and stimulates the worms to move. Alternating
electrical current at a density of about 0.95 milliamps per cubic cm
caused an actual tissue breakdown and death of worms.
Summary and Conclusions
A newi oyster predator Pseudostylochus ostreophagus Hyman intro-
duced to Pacific Coast oyster beds from Japan has caused extremely heavy
losses of Ostrea lurida spat. Life history studies indicate it follows
a typical polyclad type of development. A life cycle of a year or less
is indicated. Reproductive success or failure may be dependent on
salinity. A number of promising control measures have been discovered
which probably will result in the development of practical control
measures .
Literature Cited
Hyman, L. H. 1955- The polyclad flatworms of the Pacific Coast of
North America: Additions and corrections. Amer. Mus. Novitates
170J+:i+-7.
Smith, L. S. 1955- Observations on the polyclad flatworm Pseudostylochus
ostreophagus . Master of Science thesis. University of Washington.
-66-
Woelke, C. E. 195^- A newly identified oyster predator. Wash. Dept.
Fish. Res. Papers 1 (2): 1-2.
.67-
SOME EFFECTS OF HIGH-FREQUENCY X-RAYS ON THE OYSTER DRILL
UROSALPINX CINEREA"''
William J. Hargis, Jr.
Virginia Fisheries Laboratory, Gloucester Point
Mary F. Arrighi, Robert W. Ramsey, and R. Williams
Medical College of Virginia
Scientists of the Department of Agriculture (Bushland et al.
1955) recently announced the successful eradication of the screw -worm,
Callitroga hominivorax , from the Dutch Island of Curacao. This was
accomplished by releasing x-ray sterilized males, which competed success-
fully with normal indigenous males for the females. After such matings
the monogamous females deposited only sterile egg masses. Although
several releases were necessary, eventually no fertile eggs were detected
at any of the numerous observation points. Subsequent checks failed to
reveal any live flies.
Because existing information concerning ecology and reproduction
of drills appeared favorable, our group was encouraged to investigate
this technique as a possible control method for oyster drills. The present
paper is a report of a series of experiments which were designed to
determine the lethal dose.
Specimens collected from the York River, Virginia, were transported
to Richmond wrapped in moist cheesecloth, and held in perforated plastic
dishes in a covered, aerated, thirty-gallon aquarium of seawater which was
constantly filtered. Locations of dishes in the all -wood rack were
randomized in order to eliminate possible position effects. The animals
were fed for several hours once a week by placing pieces of oyster meat
in the dishes. During the irradiation period both control and experimental
animals were transfered to small plastic boxes and handled in the same
manner except for the actual x-ray exposure of the latter. Moist blotting
paper was placed in each box to prevent desiccation. Following the last
dose the blotting paper was removed and both controls and irradiated
drills were returned to their regular containers in the tank.
The x-ray source was a beryllium window 1000 KVP machine located
at the Medical College of Virginia. The snails were placed around the
periphery of a circular wooden platform which was rotated at approximately
two revolutions per minute. Dose rate measurements were made under the
same conditions, with a thimble chamber substituted for one of the plastic
This reserach was conducted under a contract with the U. S. Fish and
Wildlife Service, No. 14-19-008-2372, Study of Oyster Drills in Chesapeake
Bay. Contributions from the Virginia Fisheries Laboratory No. 75.
-68-
boxes. Two millimeters of aluminum filtration were added to remove the
very soft components of the beam. The half -value layer in lead is I.3
millimeters under these operating conditions. At a dose rate of 576
roentgens per minute the minimum dosage of 3>000 r required an exposure
of 5 minutes and 12 seconds. Larger doses were secured by increasing,
doubling, tripling, etc., the exposure time. For convenience higher
levels were obtained by successive increments of 3*000 r each.
Series I
On February 3> 1956, six groups of drills not segregated by sex
were irradiated at dose levels from 3*000 r to 18,000 r. Subsequent
daily observations made over an 8l-day period yielded the cumulative
mortality data illustrated in figure 1. Mortalities exceeded kO per
cent only in the 6,000 r group. The others were near or below the level
of the controls. Although there is this single exception to the general
mortality curve pattern it seems evident that, under the conditions of
the experiment, dose levels up to and including 18,000 r do not have a
marked lethal effect on U. cinerea.
Series II
The cumulative mortalities of foiir groups of males and six
groups of females irradiated in April were greater than those of the
controls (Fig. 2). Of the dose range administered, from 21,000 r to
48,000 r, we are able to conclude that the lethal dose for this group
of drills is from 2^,000 r to 27,000 r. Although there are some slight
discrepancies between these curves (£•£• the 48,000 r ?+ experienced
lower mortalities than lower dose groups) we may assume that, given a
longer observational period, all the drills receiving doses higher than
27,000 r would have died.
These data suggest that there may be a sexual difference in
susceptibility to x-ray injury. All three of the high dose levels
administered to males produced total mortality by the sixty-fourth day
after irradiation. In comparison, only one group of females had been
eliminated by the same time. None of the female groups which received
doses in excess of 33*000 r was eliminated by the sixty-ninth day when
the experiment was terminated. The experiments were not designed to
test this point, however, and the data are not amenable to statistical
analysis.
This phase of the experiment was terminated when the remaining
irradiated drills and some of the controls were sacrificed for gonad
smears. Although these smears appeared to indicate some adverse effects
produced by radiation, the small number of subjects involved and the
uncertainties of the interpretation render further conclusions unwise.
.69-
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Fig. 2. Series II. Percentage mortality occurring in ten groups of
oyster drills, Urocalpinx cinerea , which were subjected to varying dosages
of high-frequency x-rays. The numbers in parentheses are the individuals
in each group. Isolated points on graph indicate points of two or more
curves which are identical.
-71-
We have shown that Uro salpinx clnerea from the York River,
Virginia, can tolerate high dose levels of high-frequency x-rays. Like
many invertebrates, drills survive irradiation for longer periods of
time than mammals usually do. It is interesting that Bonham and Palumbo
(1951) found that the gastropods Radix and Thais withstood large doses of
high-frequency x-rays.
Even if irradiation is applicable as a control tool, the costs of
handling and treating with an x-ray machine would be prohibitive. How-
ever, more economical sources, such as Cobalt -60, could probably be made
available for commercial dosages.
Literature Cited
Bonham, K., and R. F. Palumbo. 1951« Effects of x-rays on snails,
Crustacea and algae. Growth 15: 155-188.
Bushland, R. C, A. W. Lindquist, and E. F. Knipling. 1955. Eradica-
tion of screw -worms through release of sterilized males. Science
122 (3163): 287-288.
-72-
COPPER, A POSSIBLE BARRIER TO OYSTER DRILLS
John B. Glude
U. S. Fish and Wildlife Service
Annapolis, Maryland
The oyster drill ( Urosalpinx cinerea ), a small carnivorous
gastropod with a healthy appetite for young oysters, has long been
recognized as a limiting factor in oyster production in the saltier
waters of the Eastern Coast of the United States (Carriker 1955 )•
Many investigators have searched for methods of controlling
this predator, but few have considered seriously the possibility of
fencing subtidal oyster beds to exclude drills. The recent development
of the aqualung makes it possible to install low fences on oyster beds
which occur at depths of 5 to 50 feet.
A project to design a fence which would stop oyster drills was
begun at the U. S. Fishery Laboratory at Boothbay Harbor, Maine, in the
autumn of 1955 with the assistance of Gareth W. Coffin and George W.
Griffith. Drills from York River, Virginia; Chincoteague Bay, Maryland;
and Milford, Connecticut, were shipped to Boothbay Harbor and kept in
tanks of warm sea water so they would crawl actively.
Laboratory Experiments
The first approach was to determine if drills would cross all
metals. Zinc and iron were tried first but the drills readily crawled
across strips of these metals. Next, 10 drills were placed in a wooden
tank of sea water and surrounded by a horizontal three -inch strip of
22-gauge (.02^" thick) copper sheet. The drills did not cross the
copper; in fact, each one retracted its foot and remained motionless as
long as the copper plate was in position.
The experiment was repeated by placing 25 Urosalpinx inside a
2i|-inch square enclosure of eight-gauge (.128" diameter ) copper wire
on the bottom of a wooden tank and oyster spat just outside of the wire
to serve as bait. During the first seven hours, while the water was
gradually warmed from 5 to 25 C, nine drills crawled to the wire,
touched it with a tentacle or foot, and turned back. Most moved only
a short distance away from the wire, then retracted their foot and re-
mained motionless for the duration of the experiment. After 2k hours
the drills became inactive. Since there was no flow of water through
the tank, it is likely that the copper concentration gradually increased
until the drills were immobilized.
In a later experiment 25 drills were placed inside a 2V-inch
square enclosure made by laying a 10-gauge (.102" diameter) iron wire
-73-
on the bottom of a vooden tank, containing clean warm sea water. Three
of the drills immediately crossed the wire which proved that wire was
not a mechanical barrier.
The iron wire was replaced with lU-gauge (.O65" diameter) copper
wire and 30 Urosalpinx were placed within a 15 -inch square enclosure in
a wooden tank without running water. Oyster spat were placed outside
of the enclosure to attract the drills. No drill crossed the copper wire
and at the end of 10 days all were dead. The increase in copper concen-
tration resulting from ionization of five feet of 1^-gauge copper wire
in k'^ gallons of sea water at I9.5 to 22.5° C proved lethal to oyster
drills. A control lot of drills held in a similar tank without any
copper had a mortality of less than 5 per cent during this period.
Two experiments showed that the oyster drill, Urosalpinx , and
the mud snail, Massa obsoleta, must touch the copper or brass or
approach it very closely to be repelled. Both species failed to cross
a 1/8-inch diameter copper wire placed on the bottom of a tank, but
both succeeded when the wire was covered with a l/8-inch of clean sand.
In another experiment the l/8-inch copper wire was bent upward to provide
5/8-inch to 3/^-inch clearance between it and the bottom of the tank and
several Nassa crawled under the wire. Apparently the concentration of
toxic ions is great enough to repel the snails only in the immediate
vicinity of the copper.
Several experiments demonstrated that copper or brass effectively
repels Nassa in running water. The water was too cold (2 to 5 C) to
try similar experiments with Urosalpinx which is not very active below
10 C. Since Nassa was repelled by copper to about the same extent as
Urosalpinx at higher temperatures, it was substituted in these experi-
ments. In one experiment a clean eight-gauge copper wire was placed
across the bottom and up the sides of a wooden tank which was 12 inches
across the ends and 3^+ inches along the sides. Running sea water at a
flow of 230 milliliters per minute entered at one end of the tank and
left through a standpipe at the other which maintained a water depth of
three inches. Twenty Nassa were placed at the downstream end of the
tank and two cracked soft -shell clams, Mya , were placed upstream of the
wire to serve as bait. After 18 hours the flow was increased to 1200
milliliters per minute, and three hours later to 3^ 5^0 milliliters per
minute. Since no Nassa had crossed the wire, the flow was later in-
creased to if, 800 milliliters per minute. Even at this flow a single
copper wire effectively stopped Nassa . Wlien the wire was removed the
snails spread throughout the tank.
In a similar experiment a one-inch brass screen fence was
placed across the width of a tank 12-inches wide and 3^-inches long and
a flow of 9>^80 milliliters of sea water per minute was introduced at
one end. None of the 25 Nassa placed downstream of the fence succeeded
in crossing this barrier to reach the cracked claiLS which had been placed
there as bait .
-7U-
The effectiveness of copper and brass screen fences at greater
current velocities was tested in a long trough eight inches wide by-
seven inches deep. Sea water at 3 to 4° C was introduced at one end of
the trough through a two-inch diameter pipe, and the depth was maintained
at k^ inches which produced a surface velocity of 11 centimeters per
second. Nassa obsoleta and Littorina littorea were placed inside two-
inch high rectangular enclosures of brass and copper and their movements
recorded. The snails were encouraged to escape by their tendency to
move upstream and by the cracked clams which had been placed upstream
as bait. Later the current velocity was increased to 23 centimeters
per second (0.^5 knots) at the surface and l6 centimeters per second
(0.31 knots) at the bottom by reducing the depth of the water to three
inches. None of the snails crossed the barriers at these current
velocities which are similar to those fo\md on subtidal oyster beds.
The possibility of reducing the cost of a drill barrier by
using a narrow strip of brass screen at the top of a plastic screen
fence was explored. An l8-inch square enclosure l|- inches high was made
of wooden lath and lined with Saran plastic screen. The plastic was
fastened to the wood with iron wire staples and the fence was nailed to
the bottom of a wooden tank filled with sea water warmed to 20° C.
Three of the 33 Urosalpinx placed inside of this enclosure crawled
over the fence during the first 9O minutes which proved that the plastic
itself is not an effective barrier for oyster drills. A l/4-inch strip
of brass screen was then fastened to the upper part of the fence with
copper tacks; however, the brass was in contact with the iron staples
which held the plastic in place. During the next 2-| hours three drills
crawled up the plastic, over the brass, and down the outside of the
fence.
All of the iron staples were then removed from the fence and the
33 drills were again placed inside the enclosure. During the next 2k
houcs we saw seven drills which crawled up the plastic to the brass and
then crawled or fell to the bottom. None crossed the barrier.
For a fiirther verification of these results iron staples were
driven through the brass screen and into the wood lath at two-inch
intervals, and 66 Urosalpinx placed inside the enclosure. In 2k hours
seven crawled over the fence. This demonstrated that the iron, being
more active, had ionized instead of the copper when the two metals were
in contact. This had destroyed the effectiveness of the fence since the
drills are not repelled by iron ions as they are by copper. It was
found later that this effect had been reported in 1824 by Sir Humphry
Davy in relation to preservation of copper sheathing on ships, Davy
also showed that when metallic copper is coupled to iron or zinc it
fails to prevent fouling.
Laboratory experiments similar to those with oyster drills
described above were conducted using the snails Nassa obsoleta ,
Littorina littorea, Littorina obtusata, and Thais lapillus. The snails
-75-
Nassa and Th ais were repelled by copper ions to about the same extent
as Urosalpinx. The two species of Littorina proved to be more resistant
to copper ions . The eight-gauge copper wire stopped Urosalpinx , Nassa ,
Thais; whereas a few Littorina of both species crossed it. A one-inch
or two-inch brass screen fence of 10 to 20 meshes per inch contained all
of these species in laboratory experiments even at a water velocity of
16 centimeters per second.
Field Tests of Copper Barriers During 1956
The first field trials of copper barriers were conducted at Mill
Cove, West Bath, Maine during May and June, using the mud snail, Nassa
obsoleta. This snail is extremely abundant in the intertidal zone and
is easily attracted to any bait such as a cracked soft -shell clara or
hard-shell clam. Since we had observed that Nassa was repelled by
copper to about the same extent as Urosalpinx in laboratory experiments
which had been conducted during the winter, this species seemed to pre-
sent a suitable substitute for Urosalpinx for preliminary field trials.
The first experiment which was set up in Mill Cove consisted of
a brass screen fence four inches high and five feet square. The brass
mesh was pushed down into the soft mud flats so that it extended above
the surface 2-g- inches. The mud snails were removed from the inside of
this enclosure and placed around the outside along with several hundred
other Nassa which were collected from the adjacent flats. A number of
cracked soft-shell and hard-shell clams were placed inside of the
enclosure to act as bait. The area was inspected daily or every other
day during the period from May k to June k, 1956. Only 20 Nassa were
found inside the enclosure after the first three days, during which
occasional Nassa were found that had been missed when the area was
cleaned .
A control plot consisting of a four-inch high galvanized iron
hardware cloth fence surrounding a baited enclosure was maintained during
part of this time. The mean number of Nassa entering the control plot
per day was 7>71 as compared to 0.7^ for the test plot.
The second experiment consisted of two identical 15-inch square
enclosures made of four-inch brass screen of four-mesh per inch. These
fences projected above the flats approximately 2^ inches. Cracked
clams were placed inside of the "offshore" experimental area and large
numbers of Nassa were collected and placed aro\md the outside of the
fence periodically. The "inshore" experiment was exactly the opposite
in that the bait was placed around the outside of the enclosure and 100
Nassa were placed inside of the enclosure. Each plot was observed daily
or every other day from May 6 to May 25, 1956. Diiring this time, no
snail was found inside of the "offshore" experiment. None of the 100
snails escaped from the "inshore" enclosure from May 6 to May 18, even
though the experimental animals were replaced with newly collected
Nassa twice during this period. On May 18 four pieces of iron wire were
-76-
laced into the brass screen, and by the following day only I3 Nassa
remained within the enclosure. On May 22, 100 new Nassa were placed in-
side of the enclosure with the pieces of iron wire still in place. By
the next day only 27 remained inside of the enclosure, and by June h all
of these had escaped. The results of this experiment substantiated
laboratory observations that a copper barrier is rendered ineffective if
a piece of iron is in contact with the fence. In this case the copper
is protected from ionization by the more active iron; and the iron ions
are not toxic to these gastropods.
The third field experiment using Nassa consisted of a 36-inch
square enclosure eight inches high constructed of 12 mesh per inch Saran
plastic screen fastened to a wooden lath frame and inserted three inches
into the sediment . A one inch wide strip of new 8 mesh per inch brass
screen was fastened to the outside of the top lath on this fence. Bait
was placed inside of the enclosure upon each observation, and Nassa
which had been collected from the adjacent flats were placed around the
outside of the test area. No Nassa crossed this barrier during this
experiment which ran from May 8 to May 25-
The fourth copper barrier experiment was set up in the inter-
tidal zone immediately in front of the Boothbay Harbor Laboratory,
using the snail Littorina littorea . The test plot consisted of a 15-
inch square enclosure formed by inserting a four inch high, six mesh
per inch brass screen into the flats 1-| inches. The control fence was
the same size but was made of four mesh per inch galvanized iron hard-
ware cloth. The two experimental areas were approximately four feet
apart and were at about the same tidal level and in the smae sandy bottom.
One hundred medium-to -large -size Littorina were placed Inside each
enclosure on May 1^. After three days only h^ Littorina remained within
the control area while the original 100 remained within the test area.
The experiment was repeated by placing 50 Littorina in each enclosure
on May 21. Eight days later only two Littorina remained within the con-
trol area, whereas the original 50 remained within the test area.
The fifth experiment which was conducted at Mill Cove, West Bath,
Maine, using the mud snail Nassa , consisted of a control plot surrounded
by a four inch barrier of galvanized iron hardware cloth and four experi-
mental areas . One experimental area used the same plastic screen fence
which had been described under Experiment 3* except that a brass mesh
strip at the top was replaced with a strip of copper, 3 A inch wide.
The second experimental plot utilized the same 15-inch square brass
enclosure which was described above under Experiment 2, "offshore",
except that the mesh was inverted so that the shiny part of the brass
which had previously been below the surface of the flats was now exposed.
The third experimental area utilized an identical brass mesh enclosure
which had previously been used in the Experiment 2, "inshore", and this
fence was again used in its original position. The fourth experimental
area was enclosed by a four inch high plastic screen fence with a one
inch wide strip of used brass screen around the outside of the top lath.
Each area was baited with cracked clams upon each observation, and the
niimber of Nassa which had entered the enclosure was recorded.
-77-
During the 28 days of this experiment 69I Nassa entered the
control area, or an average of 24.7 per day. Only eight Nassa entered
the plastic-fenced enclosure with the copper strip around the top, or
an average of 0.35 Nassa per day. Only one Nassa surmounted the
second experimental plot which consisted of the four inch brass fence
which had been inverted before use.
During the first four days, 1"08 Nassa (27 per day) crossed the
second experimental brass fence which had not been inverted, and it
seemed likely that the brass had become corroded enough that too few
copper ions were being released to repel Nassa . This fence was then
inverted to expose uncorroded brass, and the mean number crossing it
each day dropped to 0.9'+- After about two weeks, however, this fence
became less effective once again.
The fourth experimental plot which was enclosed by a plastic
fence, topped with a one inch wide strip of used brass, was nearly
ineffective since the mean number of Nassa crossing it each day was
16.6 as compared to 2^.7 in the control. It has been reported by
Edmonson and Ingram (1939) that copper alloys release less copper ions
after they have been dried in air following an immersion in sea water.
Since the brass screen used in this experiment was treated in this way,
it seems likely that this may explain the poor results.
The first field experiments using Uro salpinx are now being con-
ducted at Chincoteague Bay on the oyster grounds of Mr. Richard Kelly.
Since these beds are exposed at low tide and have a tremendous popula-
tion of large drills, they provide an ideal location for copper barrier
experiments. The present experiment consists of three plots: a con-
trol three feet by six feet in area surrounded by a four inch high strip
of galvanized iron hardware cloth; a similar plot fenced with a four
inch high brass screen; and a third plot fenced with an eight inch high
12 mesh per inch plastic screen with a 3/^ inch wide copper strip around
the outside of the fence near the top. Each area was baited with about
a half bushel of small oyster spat, and large numbers of Urosalpinx
were gathered and placed around the outside of each enclosure to supple-
ment the natural population. During the period from June lU to July 23 >
593 Urosalpinx entered the control area, or an average of ik.^ per day.
Only 14 Urosalpinx were found inside of the enclosure fenced by a brass
screen, and two of these were believed to have crawled under the fence
through a hole dug by crabs. Excluding these two, the average number
entering this plot was 0.3 per day.
The other experimental area surrounded by the plastic and copper
fence has been extremely successful. Only two Urosalpinx have been found
inside of this plot, and both of these are believed to have crawled under
the fence when one corner was washed clear of the bottom by wave action.
The effectiveness of this fence after kO days is very encouraging.
■78-
Discussion
The toxicity of copper to aquatic plants and animals has been
reported by many authors. Harvey (1955) states that the concentration
of cupric ions which is poisonous to marine plants and animals varies
around 1,000 milligram per cubic meter. Monier -Williams (1950) quotes
Atkin's (1932) statement that most marine mollusks will not tolerate
more than 0.1 to 0.2 ppm of copper, but that estuarine species tolerate
copper more readily. Marks (1938) lists copper tolerance of some gastro-
pods and shows that O.O5 to 0.15 Ppm of copper added to sea water was
lethal to some species. Hale 19^8) states that fresh water snails were
destroyed in most cases within U8 hours by use of copper sulfate in
doses of 0.5 to 2.0 ppm. The value of copper in the prevention of marine
fouling is well documented by Woods Hole Oceanographic Institution (1952)
in its publication describing research conducted for the U. S. Navy.
Chow & Thompson (1952) describe an improved method for determining the
concentration of copper in sea water. None of these authors mention
Urosalpinx or its close relatives.
Several American investigators, including Engle, Newcombe,
Lindsay and McMillin, have found that copper sulfate kills the pre-
hatching stages of oyster drills in the egg cases (Carriker 1955)-
None of these authors considered it an effective control for adult
drills.
Only three references to the use of physical or chemical barriers
for control of drills have been found. Ota (19^6) states that is is
possible to protect oysters grown by the "umbrella" type of oyster culture
against the attacks of Rapana , a Japanese oyster drill. Ota recommends
a special guard of metal consisting of a tin plate six inches in diameter
with the edges turned downward and inward fastened to the supporting
pole. In this application the metal serves as a mechanical barrier to
these large drills. Suehiro (19^8) quoted by Korringa (1952) described
how Rapana with its soft foot is unable to climb over a spiny object
like a chestnut bur clasped over ropes and poles. Carriker (1955)
describes Glancy's method of preventing Urosalpinx from crawling up a
vertical pipe by interposing an inverted cylinder in which foul gases
are supposed to collect .
No published report has been found which describes the repelling
effect to Urosalpinx or other oyster drills of ions released from metallic
copper in sea water which were observed in the experiments described
above .
Application
Further research is necessary before copper can be recommended
for protection of commercial oyster beds from drills. Laboratory results
must be checked by additional field tests to determine the length of
time a copper barrier will remain effective. Fouling by organisms and
-79-
silting must be controlled and the effect of copper ions on oysters and
other marine species adjacent to the fence must be determined. An
economical and practicable fence must be designed, and better methods
for releasing copper ions must be explored.
Nevertheless, the discovery that ions from metallic copper repel
the oyster drill Urosalpinx may point the way toward effective control
of this predator in many areas. A vertical mesh fence a few inches
high seems to be the most promising design to decrease silting, and the
use of plastic screen may help to reduce the cost. The fence might be
installed aroimd a seed oyster bed by divers using aqualungs after all
drills have been removed. The fence might be left in place until the
oysters were large enough to resist the drills, or possibly until they
were ready for transplanting, or for harvesting.
The eastern oyster drill, Urosalpinx , and the Japanese drill,
Tritonalia ( Ocenebra ) japonica , are both serious predators of the native
oyster, Ostrea lurida, in the Pacific Northwest. Since this small
oyster is grown in diked pools in the intertidal zone, a simple fence
which released copper ions might be installed on top of the concrete
dikes to exclude Urosalpinx . If Tritonalia is also found to be repelled
by copper ions, and if the oysters are not harmed by the copper, this
method may solve the drill problem for this valuable industry.
Additional experiments are planned to test the effect of copper
ions on the other oyster predators, Eupleura, Thais, and Busycon.
Summary
1. Laboratory tests showed that the oyster drill Urosalpinx would not
crawl across clean copper or brass although it would cross iron,
zinc, and Saran plastic.
2. A clean copper wire as small as 1^ gauge repelled Urosalpinx in
still-water laboratory experiments.
3. In slow currents an eight-gauge copper wire repelled Nassa obsoleta
which was substituted for Urosalpinx because it is more active at
low temperatures and repelled by copper to about the same extent.
4. Brass and copper screen fences two inches high were not crossed in
the laboratory by Nassa obsoleta , Thais lapillus , Littorina littorea
or Littorina ob tusata at current velocities of O.3I to 0.45 knots.
Urosalpinx could not be tested under these conditions because of
low water temperatures which rendered them inactive.
5. The copper or brass fence loses its effectiveness if it is in con-
tact with a more active metal such as iron. Under these conditions
iron ions which do not repel drills are released instead of copper
ions.
-80-
6. The results of the field tests of copper barriers in Maine, using
Nassa, have corroborated the laboratory observations. The great
difference in the number of Nassa entering the control areas and
those entering the experimental areas demonstrated that these gastro-
pods are definitely repelled by copper ions.
7. The decrease in effectiveness of brass fences after three to four
weeks in the intertidal zone suggests that better methods of releasing
copper ions over a longer period of time should be sought. The
possibility that brass or copper fences would remain effective for
a longer period in subtidal areas is being explored through additional
experiments which are now being conducted in Chincoteague Bay.
8. Practical applications might include installation of low fences
which release copper ions around subtidal seed oyster beds by
divers using aqualungs, but cannot be recommended until problems
of biofouling, silting, economy, and effect of copper on oysters
and other marine species are solved.
Literature Cited
Atkins, W. R. G. 1932. The copper content of sea water. Jour Mar.
Biol. Assoc. U.K. 18: 193-197-
Cajrriker, M. R. 1955* Critical review of biology and control of oyster
drills Uro salpinx and Eupleura . U. S. F.W.S. Spec. Sci . Rept . :
Fish. Ikd: 159 pp.
Chow, T. J. and T. G. Thompson. 1952. The determination and distribu-
tion of copper in sea water. Part I. The spectrophotometric
determination of copper in sea water. Jour. Mar. Res. 11 (2):
124-138.
Davy, Sir Humphry. I82U. On the corrosion of copper sheathing by sea
water, and on methods of preventing this effect; and on their
application to ships of war and other ships. Phil. Trans. Roy.
Soc. London 11^+: 151-158.
Davy, Sir Humphry. I82U. Additional experiments and observations on
the application of electrical combinations to the preservation
of the copper sheathing of ships, and to other purposes. Phil.
Trans. Roy. Soc. London 11^+: 2^2-246.
Edmondson, C. H. and W. H. Ingram. 1939- Fouling organisms in Hawaii.
Bernice P. Bishop Museum, Occas. Papers Ik: 25I-3OO.
Hale, F. E. 19^8. The use of copper sulphate in control of microscopic
organisms. Phelps Dodge Refining Corp., N.Y. hk pp.
Harvey, H. W. 1955- The chemistry and fertility of sea waters.
Cambridge' Univ. Press., Cambridge, 224 pp.
-81-
Korringa, P. 1952. Recent advances in oyster biology. Quart. Rev.
Biol. 27: 266-3O8 and 339-365.
Marks, G. W. 1938. The copper content and copper tolerance of some
species of raollusks of the Southern California Coast. Biol.
Bull. 75 (2): 22i+-237.
Monier-Williams, G. W. 1950. Trace elements in food. John Wiley &
Sons, Inc., N.Y. 511 pp.
Ota, F. 1946. Kasagata-shiki yoreiho ni tesuita (Oyster culture by
the umbrella method). Kumamoto Fisheries Assoc, (mimeogr.
pamphlet ) .
Suehiro, Y. 19^8. A method to exterminate Rapana, the natural enemy
of the oyster. Contr. Cent. Fish. St a. Japan, I9U6: 98-100.
Woods Hole Oceanographic Institution. 1952. Marine Fouling and its
prevention. U. S. Naval Inst., Annapolis, Md.: 388 pp.
(Also W. H. 0. I. Contr. 58O.)
-82-
TRAPPING OYSTER DRILLS IN VIRGINIA
III. The Catch per Trap in Relation to Condition of Bait
J. L. McHugh
Virginia Fisheries Laboratory, Gloucester Point, Virginia
INTRODUCTION
In the covirse of trapping experiments previously described
(Andrews 1955> McHugh 1955 )> a question arose concerning deterioration
of bait with time. It is fairly obvious to those who fish the traps
that the condition of the bait changes. The smallest oysters die first,
through predation by drills, crabs, and other enemies, and through
smothering in the muddy bottom. Barnacles and other organisms on the
shells also die from various causes. The valves of the dead oysters
soon separate, and some are lost through meshes of the trap, so that
the volume of bait also decreases. Stauber (19^3) found that efficiency
of traps decreased as the interval between lifts increased. He found
also that the catch increased significantly after rebaitlng.
A series of 20 traps was fished from the Virginia Fisheries
Laboratory pier from July 1953 to December 1955- Although the traps
were not rebaited until early October 195^> the catch per trap was
greater during the second summer. If bait does deteriorate, as Stauber
(19^3) 3'ii'i others have concluded, this increased catch must reflect
an increase in abundance or availability of Urosalpinx in 195^ • But by
October 195^> the bait consisted mainly of isolated valves, and the
few surviving oysters were thick-shelled and blunt. It was decided to
conduct a controlled experiment with these traps to test the effect of
rebaiting. This experiment began in October 195^ and continued through
the summer of 1955-
The rebaiting experiment seemed to show that both Urosalpinx
cinerea and Eupleura caudata preferred fresh bait to old oysters and
shell as Stauber (19^3) already has contended. It was realized, however,
that the amount of bait in the traps might also influence catch, and
that the quantity had not been well controlled in previous experiments.
If the catch of drills should be a function of amount of bait rather than
kind of bait in traps, then the results of the previous experiment would
be open to question. Consequently, in 1955 a more extensive experiment
was conducted, in an area offshore from the Laboratory pier, in which
both kind and amount of bait were controlled.
Contributions from the Virginia Fisheries Laboratory No. 76.
-83-
REBAITING EXPERIMENTS
Methods
The traps fished from the Laboratory pier were arranged in two
series of ten each, one on each side of the pier, as Illustrated by
McHugh (1955). Five traps from each series were selected (using a
table of random numbers), and these were rebaited with fresh seed oysters
from the James River. Bait in the remaining ten control traps was
augmented where necessary with old bait discarded from the randomly-
selected experimental series, so that volumes of bait in each trap were
approximately the same.
Catch in Experimental and Control Traps Prior to Rebaiting
These traps were fished continuously, at intervals of one day
to one month, beginning July 9^ 1953' On July 29, 195^; the arrangement
was altered by moving traps 1 and 2, at the offshore end of each series,
to the inshore end of the pier, and renumbering them as 11 and 12.
Only catches made after this date were used in estimating performance
of the experimental and control traps before rebaiting.
Control traps caught 78O Urosalpinx and 21 Eupleura ; those
selected later for rebaiting caught 6^0 Urosalpinx and 28 Eupleura .
The ratio of the two Urosalpinx catches differed significantly from 1:1
(X = 13.80, P much less than O.Ol), therefore this difference was con-
sidered in analysing the results of the rebaiting experiment. The ratio
of the two Eupleura catches did not differ significantly from 1:1
(X^ = 1.00, P about 0.6).
Catch in Experimental and Control Traps After Rebaiting
By the end of the second week, rebaited traps had caught U70
Urosalpinx and 32 Eupleura , whereas the controls had taken only 315 and
2 respectively. Within three weeks, however, the initial advantage had
been lost. In experimental and control traps, from November 195^ to
April 1955 inclusive, catches of both species maintained approximately
the ratios observed before the experiment began. In May 1955j however,
both species were caught in larger numbers in rebaited traps, and this
superiority was maintained, with occasional deviations, until the experi-
ment was terminated early in December 1955 • From May to December, 572
Urosalpinx and 5^+ Eupleura were caught in rebaited traps, but only 440
and 17 respectively in controls. By this time bait in all traps was in
poor condition.
From October 12, I95U, to December 2, 1955, experimental traps
caught about I.3 Urosalpinx for each Urosalpinx caught in controls.
This catch differed significantly from the expected catch (X^ = 105.^+,
P very much less than 0.001). During the same period experimental traps
-81+-
caught about k.k Eupleura for each Eupleura caught in the controls. This
differs significantly from the expected ratio of 1:1 (X^ = ^7.2, P very
much less than O.Ol).
Sizes of Drills Caught on Old and New Bait
Ab mentioned previously, new bait caught more drills than old.
It would be of value to know whether the sizes of drills caught on the
two kinds of bait differed, and the data suggest that new bait caught
relatively more small drills (Table l). Indeed, in the period from
October 18 to December 1, 195^^ the total catch of Urosalpinx ik milli-
meters in length and over apparently did not differ in the two kinds of
bait (X^ = 3'25> P greater than 0.05 ), and the excess catch in the re-
baited traps was made up of drills 13 mm and smaller (x = 22.08, P much
less than O.OOl). The arbitrary division between 13 and ik mm was chosen
because it gave the best separation between yearling and older drills.
From April to November 1955 the total catch on new bait exceeded
the catch on old (x^ = 13.05, P less than O.OOl). This excess catch in
rebaited traps was distributed evenly over all sizes, and frequency
distributions of shell height of drills from the two kinds of bait were
almost identical.
To determine whether placement of rebaited traps was random with
respect to shell height of drills available to them, the frequency dis-
tributions of shell height of Urosalpinx on the two sets of traps were
compared for the period August 12 to October 11, 195^^ prior to rebaiting.
As shown in Table 1, traps that were later rebaited had been catching
fewer large drills than those that were not changed, and this difference
was statistically significant (x = 15.72, P less than 0.001, for
Urosalpinx ik- mm in shell height and larger). There was no great differ-
ence in frequency distributions of shell height of drills 13 mm and
under (x^ = 0.40, P greater than 0.5).
The excess catch of small drills in rebaited traps therefore
probably has no biological significance. The same traps caught a higher
ratio of small to large Urosalpinx before rebaiting, and new bait simply
increased the frequency of capture of all sizes.
CONCLUSIONS FROM REBAITING EXPERIMENT
It has been demonstrated that the catch of oyster drills by traps
in the York River, Virginia, can be increased substantially by rebaiting
traps. New bait apparently maintains its superiority over old for at.
least a year after rebaiting^ and therefore it probably follows that
seed oysters are superior to older oysters, and older oysters are superior
to shell, for attracting drills. This is not unexpected, in view of the
findings of Stauber (I9U3), Haskin (I95O), and others.
-85-
Table 1. Frequency distributions of shell height in
Urosalpinx cinerea caught in experimental
and control traps before and after rebaiting
Experimental
(rebaited)
Control
(not rebaited)
13 mm
and less
l4 mm
and over
13 mm
and less
ik mm
and over
"Before rebaiting
12 Aug - 11 Oct 5^
202
427
215
551
After rebaiting
18 Oct - 1 Dec 5I+
161
379
87
331
April - Nov 55
179
523
130
kk3
-86-
Eupleura seems to respond to new bait more vigorously than
Uro salpinx. This could be interpreted in at least two ways, either
Eupleura is more destructive of young oysters than its fellow -predator,
or it deserts oysters more readily for other food when young oysters are
not available. It has been observed repeatedly at Gloucester Point that
although Eupleura is not uncommon in eel-grass beds near shore, it does
not climb pilings of piers as Uro salpinx does. This may help to explain
the relative scarcity of Eupleura in traps, and the large increase in
catch when desirable bait is introduced.
For both species the similarity in catches in experimental and
control traps in winter and early spring may be primarily a temperature-
controlled phenomenon. In other words, although both drills may move
about when water temperatures are relatively low, their sensitivity to
differences in bait may be repressed. The observations of Janowitz
(1957)^ that rapidity of shell growth rather than age of oysters is the
significant factor in attracting drills, are suggestive, for the growth
of oysters in Virginia practically ceases in the period December to
March.
EXPERIMENTS WITH VARIOUS KINDS AND AMOUNTS OF BAIT
Methods
On July ik, 1955^ an experiment was set up to test the relative
merits of seed oysters, adult oysters, and oyster shell, each in three
different quantities by volvune, as bait in chicken-wire traps. Seed
oysters were obtained from the James River, adult oysters were taken
with tongs in shallow water near the Virginia Fisheries Laboratory pier,
where they had been placed at various times during the past two years,
shell likewise was tonged from the bottom near the pier.
Volumes of bait were selected to correspond with 6, 12, and 18
adult oysters, which measured about one, two and three quarts respectively.
Seed oysters and loose valves of dead adults were measured in these
volumes.
Thirty-six traps of galvanized chicken wire, of the usual dimen-
sions, were baited in equal numbers with different combinations of kinds
and amounts of bait. Three kinds and three amounts gave nine combina-
tions, thus each combination was given four replications.
Four long stakes were driven in the river bottom to form a right-
angled cross around a central stake. Each arm of the cross extended 100
feet on each side of the central stake, and the arms were roughly parallel
with and at right angles to the river bank. The center of the cross was
about 400 feet from shore and water depth ranged from about five to seven
feet at mean low water .
-87-
Tarred hemp line, one-quaxter inch in diameter, was cut in 100-
foot lengths and attached to Isjrge wrought -iron rings which were free
to move up and down each stake. Traps were attached to these main lines
at 10-foot intervals with snoods of three-eights inch tarred hemp line
10 feet long. On each main line the trap nearest the center was attached
five feet from the center stake. Placement of various combinations of
bait was chosen using a table of random numbers.
Analysis of the Catch
Urosalpinx cinerea . The 36 traps were fished at weekly intervals
until September 15 > 1955 inclusive. On the next fishing date, September
22, because lines were beginning to rot, one trap was lost. The experi-
ment continued until October 28, inclusive but for the original purpose
of the experiment the results were progressively less satisfactory, be-
cause bait, particularly seed oysters, deteriorated with time, various
traps were lost and replaced, or lost and recovered at a later date,
and the catch was declining, probably because water temperatures were
dropping.
For these reasons, the experimental observations were separated
into three periods for analysis. The results are summarized in Table 2,
in which catches have been grouped so that each number represents total
catch in four replicate traps over a period of several weeks. The last
period includes all observations in which one or more traps were missing.
The durations of the first two were chosen to include approximately the
same total catch in each.
In the first period, bait was fresh, and it would be expected
that differences in attractive power of baits, with respect to kinds and
amounts, would be at a maximum. In the second and third periods, dif-
ferences might decrease or disappear.
The frequency distribution of individual catches was skewed
strongly to the right, and more than half the catches contained no drills.
A transformation therefore was necessary before the analysis of variance
could be applied. The square -root transformation was chosen, but first
each individual catch was increased by adding 3/8.
The transformed data for the first period were treated by
analysis of variance (Table 3). None of the interactions between
factors was significant, and the variance ratios computed for different
quantities of bait and successive weeks of fishing were no greater than
would be expected by chance. The catches in different kinds of bait,
however, differed by amounts greater than usually would be expected by
chance (F = 5-52, F o.Ol = ^.7^)- Under the conditions of this experi-
ment, it appears that seed oysters are superior to adult oysters, and
adult oysters superior to shell, as bait for Urosalpinx cinerea.
-88-
Table 2. Catch of Urosalpinx per trap in the period July 21 to
October 28, 1955 inclusive, on three kinds and three
quantities of bait. The four replicate treatments have
been grouped, and catches have been grouped by periods
according to the condition of the bait. Traps were
fished weekly.
Inclusive
Number of
weeks
Amounts of
bait
Kinds of bait
dates
Seed
Adults Shell
Totals
21 July
to
18 Aug.
5
1
2
3
10
29
38
12 13
8 5
22 8
35
k2
68
Totals
77
h2 26
ii+5
27 Aug.
to
15 Sept.
k
1
2
3
18
18
22
19 19
12 7
21 16
56
37
59
Totals
58
52 k2
152
22 Sept.
to
28 Oct.
6
1
2
3
8
20
32
20 28
16 5
18 2i+
56
1+1
7h
Totals
60
5^ 57
171
-89-
Table 3. Summary of analysis of variance of the
transformed catch of Urosalpinx per trap
in the period July 21 to August 18, 1955,
inclusive.
Natiire of
effect
Source of
variation
Sum of
squares
Degrees of
freedom
Variance
estimate
Main factors
Weeks (w)
Amounts (A)
Kinds (K)
0.98
1.11
2.77
1+
2
2
0.24
0.56
1.38
First order
interactions
K X W
A X W
K X A
0.60
2.05
1.93
8
8
h
0.08
0.26
0.1+8
Second order
interaction
K X A X W
2.73
16
0.17
Residual
Replication
35.^5
135
0.26
Total
U7.62
179
-90.
The data for the second period showed evidence of heterogeneity
only with respect to the catches of successive weeks (Table k). The
relatively large catches of August 27 following Hurricane Hazel were
primarily responsible for this result. Catches in traps commonly in-
crease substantially after storms. There was no evidence that catches
on different kinds of bait, or on different quantities of bait, differed
significantly in the second period.
Catches on missing traps in the last period were each assumed to
be zero for purposes of analysis. Most of the lost traps were recovered
at a later date by careful searching with a hooked pole, ajid catches on
recovery were never inconsistent with the assumption that catches in
missing weeks were zero. Records of the catch show that during the
period in question about half the catches contained no drills, 32 per
cent contained one, and about 18 per cent contained two or more. There
was no significant difference in distribution of catches on seed oysters,
adults, or shell, nor on the three quantities of bait. Therefore, the
assumption that all missing catches were zero has an even chance of
being correct, and there is no evidence that any other distribution of
estimated catches would fit the facts better. As illustrated in Table
5, there was no good evidence of heterogeneity in catches recorded for
the third period.
Eupleura caudata. Only 15 Eupleura were caught during the entire
experiment. Catches were too small to justify an analysis of variance,
but it is interesting that the largest total catch (9) was made In traps
baited with seed oysters, and the smallest (2) on shell. Catches on
different quantities of bait were similarly Inconclusive.
Deterioration of Bait
If it be assumed that the characteristics of shell as bait did
not change during the experiment, catches on shell can be used to test
rates of deterioration of seed and adult oysters. The total catches of
Urosalpinx per week on shell in the three periods were 5*2, 10.5 and 9»5
respectively. The Increase from the first to the second period was
caused by an increase in abvmdance of drills by recruitment of young
born in the summer of 1955* The increased availability persisted through
September and early October, but catches declined again, probably in-
fluenced by falling temperatures, toward the end of the third period.
In the first period, both seed (jc = 100.0, P very much less
than O.Ol) and adult oysters (xr = 9«85> P much less than O.Ol) were
superior to shell- In tiae second period, seed oysters probably were
still superior {yc = 6.10, P less than 0.02) but catches on adult oysters
could not with any great confidence be said to exceed catches on shell
(x^ = 2.38, P about 0.2). In the third period catches on seed, adults,
and shell did not differ significantly (x^ = O.16, P about O.7).
-91-
Table h. Summary of analysis of variance of the
transformed catch of Uro salpinx per
trap in the period August 27 to September
15> 1955; inclusive.
Nature of
effect
Source of
variation
Svrni of
squares
Degrees of
freedom
Variance
estimate
Main factors
Weeks (W)
Amounts (a)
Kinds (k)
7.38
0.66
0.44
3
2
2
2.46
0.33
0.22
First order
interactions
K X W
A X W
K X A
0.52
2.84
0.39
6
6
4
0.09
0.47
0.10
Second order
interaction
K X A X W
2.61
12
0.22
Residual
Replication
25.22
108
0.23
Total
40.06
143
-92-
Table 5. Summary of analysis of variance of the
transformed catch of Urosalplnx per
trap in the period September 22 to Octo-
ber 28, 1955, inclusive.
Nature of
effect
Source of
variation
Sum of
squares
Degrees of
freedom
Variance
estimate
Main factors
Weeks (W)
Amounts (a)
Kinds (k)
3.63
1.09
0.00
5
2
2
0.73
0.5^
0.00
First order
interactions
K X W
A X W
K X A
1.58
0.80
2.91
10
10
k
0.16
0.08
0.73
Second order
interaction
K X A X W
5.71
20
0.28
Residual
Replication
28.23
162
0.17
Total
^3.95
215
-93-
Deterioration of bait with time is illustrated in Figure 1.
Formulae for the two lines, computed by the method of least squares, were
as follows: for seed oysters log Y = 0.662 - 0.00812X, for adult oysters
log Y = 0.236 - O.OO287X. Both lines intersect the axis Y = 1 in the
vicinity of 82 days after the experiment began. This signifies that on
October k, under the conditions of this experiment, seed oysters and adult
oysters were no longer superior to shell as bait for Uro salpinx . For
practical purposes, of course, bait becomes inefficient long before \t
loses its potency completely. Consequently, it might be worth while to
compute the period in which bait loses half its attractive power. For
seed oysters the half -life was about 27 days, and for adults about 36
days.
It is interesting also to compare these results with results of
the rebaiting experiment at the Laboratory pier. Control in the pier
experiment was established by retaining old bait in half the traps. For
purposes of comparison, this old bait can be considered as adult oysters.
The lower regression line in Figure 2 was fitted by the method of least
squares to points representing the ratio of total weekly catch on new
bait to total weekly catch on old. The upper regression line represents
the ratio of catches on seed and adult oysters, computed from data
illustrated in Figure 1. The lower level, and greater slope of the
line representing the pier experiment probably reflects the relatively
greater numbers of drills near the pier, and decreasing water temperature.
New bait no longer exhibited a significant advantage over old bait after
about 40 days, and the half -life under these conditions was about I9 days.
Variation in Catches of Individual Traps
Some traps consistently caught more drills than others with
similar bait. For example, trap number I7 took U7 drills during the
experiment, and the weekly catches of this trap included the three largest
catches of all traps. Trap number 7> on the other hand, contained the
same amount and kind of bait, but caught only seven drills altogether.
Because kind of bait influences the catch, comparisons of individ-
ual catches are legitimate only within replications. Testing against ex-
pected catches based on average catch in each of the replications of four,
the pooled chi-square values summarized in Table 6 were computed. Although
tests at the lowest level did not always produce evidence that the varia-
tion was greater than would be expected b;y chance, the summed chi -squares
for the three kinds of bait all showed evidence of heterogeneity at the
one per cent probability level or better, two of the tliree amovints of bait
produced equally conclusive results, and one gave less than one chance in
twenty that a larger value of chi-square could result by chance. The. sum
of all chi-square values also strongly favored the view that chance was
not the only factor influencing the catch in replicate traps.
Such undue variation could come about through uncontrolled
variations in the attractability of the traps themselves, but it would
-9U-
M^ 2t 28 4- Ji /3 25 /
Ju/y Aug
a /£ 22 29 G li 20 27
Sep/ Ocf
Fig. 1. The ratio of the catch on seed and adult
oysters to the catch on shell in the offshore experi-
ment of 1955. Open circles: seed-shell ratio; black
circles: adults-shell ratio.
-95-
O /O 20 30 40 SO 60 70 30 SO /OO
//amber o/^ c/^ys
Fig. 2. The ratio of the catch on seed oysters to the
catch on adult oysters at the Virginia Fisheries Laboratory
pier in 195^ and in the offshore experiment of 1955. Open
circles: offshore experiment j black circles: Laboratory
pier.
-96-
seem logical to search first for evidence of non-randora distribution of
drills over the trapped area. The two lines of traps were oriented
parallel to shore and at right -angles to it, and depth of water and
chELracter of bottom fluctuated. As shown in Figure 3 catches tend
strongly to decrease in an offshore direction. In constructing Figure
3, allowance was made for differences in catch by the three kinds of
bait by adjusting catches by appropriate factors.
Parallel to shore, smallest catches seemed to occur at the two
ends of the line, highest near the center. The two ends respectively
were not far from the Laboratory pier and a pier on adjacent residential
property downriver. The proximity of these piers, the pilings of which
harbored a rich community of fouling organisms, may have constituted a
disturbing element. The trend was quite irregular, and perhaps not bio-
logicaJ.ly significant.
Sizes of Urosalpinx Caught on Different Kinds of Bait
In view of the previous conclusion that no differences of bio-
logical significance appear to exist in the frequency distribution of
shell height of drills caught on new and old bait, it is worthwhile to
examine the shell height distribution of Urosalpinx caught on the three
kinds of bait used in these experiments (Table 7)' It is interesting
that the difference in total catch on the three kinds of bait is con-
fined entirely to adult drills (x^ = 26. 70, P much less than O.OOl).
Total catches of Urosalpinx 13 mm in height or smaller (58, 58, and 59
drills respectively) were essentially identical.
This experiment suggests that although adult Urosalpinx are
sensitive to differences between seed oysters, adult oysters, and shell,
young drills are not. This may indicate a difference in food preference
between young and adult drills. Or, as Dr. Thurlow Nelson has suggested,
young drills are inveterate climbers, and this favors their wide distri-
bution on materials that are moved across the bottom by currents. This
could account for their relatively greater abundance on shells and adult
oysters.
SUMMARY AND CONCLUSIONS
Ten traps, of a series of 20 that had been fished for about a
year without replacing or augmenting bait, were selected at random and
rebaited with seed oysters in October 195^- The catch of Urosalpinx and
Eupleura increased significantly immediately, but the superiority of new
bait over old declined steadily on successive fishing dates. Nevertheless,
rebaited traps remained more attractive to drills for more than a year,
except for a six-month period in winter and early spring, when the catch
of Urosalpinx was about equal in new and old bait. There is no evidence
that drills caught on the two kinds of bait differ in size. Eupleura
responded more vigorously to new bait than did Urosalpinx.
-97-
Table 6. Tests of variations in the catch of individual traps,
represented by summation of chi-square values at the
various levels. Figures in parentheses represent the
numbers of degrees of freedom.
Amount
of
Kind of bait
Pooled
bait
Seed
Adults
Shell
1
1.10
(3)
7.26
(3)
11.48**
(3)
19.84*
(9)
2
25.85**
(3)
Ik . 00**
(3)
2.53
(3)
42.38**
(9)
3
37.91**
(3)
2.55
(3)
9.16*
(3)
49 . 62**-
(9)
Pooled
64.86**
(9)
23.81**
(9)
23.17**
(9)
111.84**
(27)
* Probability of a larger value of chi-square O.O5 or less.
** Probability of a larger value of chi-square 0.01 or less.
-98-
Z ^ G 8 JO JZ /4 /G /8
Trsp /camber
Offshore Jnshore
Fig. 3. The total catch of Uro salpinx in a series
of traps arranged in a line at right angles to the
shoreline in the York River at Gloucester Point. Black
circles: seed oysters; divided circles: adult oysters;
open circles: shell. The catches on adults and shell
were weighted by appropriate factors so that the
average catch per unit of effort was equal to that on
seed oysters.
■99-
Table 7- Numbers of small and large Uro salpinx
cinerea caught on seed, adult oysters,
and shell in 1955-
Shell height
Kinds of bait
Seed
Adults
Shell
13 mm and less
ik mm and over
58
137
58
90
59
66
Grand totals
195
..„
ikQ
125
-100-
Thirty-six traps were set out in July 1955 to test the relative
catching power of seed and adult oysters and oyster shell, and to measure
the relative merits of different amounts of bait. In the first five
weeks the greatest catch of Urosalpimc was made on seed oysters, and the
smallest on shell, and odds were less than one in 100 that these differ-
ences could occur by chance. For the next ten weeks also, the greatest
catch was made on seed and the least on shell, but these differences
were not significant statistically. There was no evidence, at any time
during the experiment, that quantity of b^it affected the catch. Only
a few Eupleura were taken, and catches on the different kinds of bait did
not differ significantly, but total Eupleura catch followed the sequence
demonstrated for Urosalpinx greatest on seed and least on shell.
The rate of deterioration of bait can be expressed as the time
in days during which it loses half its power of attraction. In the experi-
ments described here this was determined in relation to catch on shell,
and gave values ranging from 19 days at the Laboratory pier to 36 days
for adult oysters in the offshore experiment. Undoubtedly rate of
deterioration is a function of the abundance of drills, kind of bait,
water temperature and salinity, and many other things. Ignoring environ-
mental effects for the moment, the results here obtained apparently fit
a logical pattern, for the relatively short half -life of new bait at the
pier is linked with a greater abundance of drills, and the greater half-
life of adult oysters as compared with seed oysters in the offshore experi-
ment matches the greater attraction of seed for drills. On the other
hand, it must be noted that both experiments, but especially that con-
ducted at the pier, covered periods in which water temperatures declined
appreciably from the late summer maximum, and declining catches probably
were hastened by falling temperatures. This is confirmed by increased
catches on new bait at the Laboratory pier in the siimraer of 1955*
Available evidence suggests very strongly that catches of in-
dividual traps in the offshore experiment varied to a degree much greater
than chance alone would allow. Apparently distribution of drills over
the trapped area was non-random, and the pattern of catches suggests that
abundance decreased rather regularly from the inshore to the offshore
part of the experimental area. This is consistent with previous observa-
tions that beds of eelgrass near shore harbor a large natural population
of drills.
With respect to shell height of Urosalpinx caught on seed,
adults, and shell, the results of the offshore experiment are at variance
with those of the experiment at the pier. Catches of drills 13 mm or
less in height were identical on the three kinds of bait, but larger
drills were most strongly attracted to seed, and least strongly to shell.
This suggests seasonal or local differences in habits of young and adult
Urosalpinx, possibly related to food or depth preferences, and reactions
to gravity.
-101-
Literature Cited
Andrews, J. D. 1956. Trapping oyster drills in Vriginia. I. The effect
of migration and other factors on the catch. Proc. Natl. Shell-
fish. Assoc. k6: l40-15^.
Carriker, M. R. 1955- Critical review of biology and control of oyster
drills Urosalpinx and Eu pleura . U. S. Fish and Wildlife Service,
Spec. Sci. Rep. Fisheries l^lS: vi + I50 pp.
Raskin, H. H. 1950. The selection of food by the common oyster drill,
Urosalpinx cinerea Say. Proc. Natl. Shellfish. Assoc. kO: 62-68.
Janowitz, E. 1957« Further studies in the attraction of Urosalpinx
by oysters. Natl. Shellfish. Assoc. Convention paper
(unpublished).
McHugh, J. L. 1956. Trapping oyster drills in Virginia. II. The
time factor in relation to the catch per trap. Proc. Natl.
Shellfish. Assoc. 46: 155-168.
Stauber, L. A. 19^3. Ecological studies on the oyster drill, Urosalpinx
cinerea , in Delaware Bay, with notes on the associated drill,
Eupleura caudata , and with practical considerations of control
methods. Unpublished manuscript. Oyster Research Laboratory,
New Jersey.
-102-
ENVIRONMENTAL CONDITIONS
SHELLFISH FOOD
SHELLFISH POISON
■103-
SOME FEATURES OF THE HURRICANE PROBLEM
Gordon E. Dunn
Weather Bureau Office
Miami, Fla.
How is a Hurricane Formed?
In the past there have heen two principal theories of hurricane
formation: (l) the convection theory, and (2) the frontal theory.
Advocates of the convection theory believed that calm moist air of the
doldrums was favorable for convection either because of surface heating
or high moisture content of the air or both. Heated air began to rise
and resulted in numerous cumulo-nimbus clouds and widespread showers
and thunderstorms. Then pressure mysteriously began to fall, cumulo-
nimbus clouds gradually coalesced, and if the area was sufficiently far
from the equator for rotation of the earth to be effective, a cyclonic
circulation was initiated. Development of the circulation continued
until full intensity was reached through release of heat by condensation.
While it is true that small hurricanes appear to be one huge convective
cloud and there is no doubt that the hurricane is essentially a con-
vective mechanism, the convective theory of formation left too many
questions unanswered, among them: What is the starting mechanism, what
causes theinitial fall in pressxure, and why are there so few hurricanes?
One of the notable advances in meteorology was the introduction
of air mass analysis and the frontal theory of storm formation by the
Norwegian meteorologists after World War I. In the early 1930's, some
meteorologists attempted to apply these theories to hurricane formation,
that is, they formed along a front or boundary between the southeast
trades of the southern hemisphere and the northeast trades of the northern
hemisphere, in the same manner as in the temperate zone. Unfortunately
there is no density discontinuity here and the large majority of tropical
storms in the Atlantic, at least, do not form along the so-called tropical
front or intertropical convergence zone but rather in the trade wind
zone. The frontal theory of hurricane formation is no longer in vogue.
We do not yet have a complete explanation of the formation of
hurricanes but we do know the following:
(1) Hurricanes will develop only over comparatively warm water with tem-
perature 80-81 F and higher. The energy for increasing kinetic energy
must come from the warm ocean.
(2) Hurricanes form only in pre-existing disturbances, the most common
of which in the Atlantic is the easterly wave. A deep easterly current
is usually present over the developing tropical storm.
(3) There must be high-level divergence to remove accumulated air from
the system and to. permit pressur-e to fall at the surface.
-lOU-
Now these three conditions are present almost every day some-
where over the tropical Atlantic Ocean although not necessarily in the
proper jiixtaposition. Since there have been several years when only
two tropical storms were noted over the whole Atlantic Ocean, it is
obvious that some rather unique combination of weather conditions is
required for hurricane formation. The exact starting mechanism has
eluded us so far.
What Moves a Hurricane?
Once a tropical storm has formed and has been detected, the
principal forecast problem is one of movement — both rate and direction.
Accuracy of our warnings from the standpoint of timeliness and geography
will depend upon our ability to handle this problem. Many of the techni-
ques in use in the temperate zone are ineffective here. Hurricanes are,
to a large extent, steered by the basic current in which they are im-
bedded; that is, the stream of air surrounding the storm from the sur-
face up to 60,000 feet or so. Since these storms are located out over
the oceans, evaluation of this steering current poses a difficult prob-
lem to the forecaster. Our only source of information is that provided
by observations from land stations which are often too far from the
hurricane to be useful and from the Air Force and Navy hurricane
reconnaissance planes. Our present procedures entail 'boxing' of the
hurricane at approximately 20,000 feet; that is, sending planes around
the storm outside the hurricane circulation itself to measure, if possible,
this steering current. We are making an assumption here that the 20,000
foot level is representative of the steering current from sea level up
to 50 or 60,000 feet and we know that this assumption is often incorrect.
There have been some good results with this technique but at the same
time, it is ineffective when the regional circulation of the atmosphere
is changing rapidly with time. Also there is probably a significant in-
ternal contribution to the storm's movement from the storm itself which
cannot at the present time be calculated.
Some meteorologists have advanced the theory that the course of
the hurricane might be changed slightly by seeding a certain quadrant of
it with dry ice or silver iodide. They reason that the hurricane, at
least to some extent, will move in the direction of the greatest con-
centration of energy which could be induced in some desired quadrant by
seeding there. In this way the hurricane could be detoured for a few
hours, long enough perhaps for it to miss some concentration of popula-
tion. It is believed that the majority of meteorologists are very pessi-
mistic of the practicality of the theory.
What was the Steering Pattern in 195^ and 1955?
In both 195^ and 1955 all major circulation features were dis-
placed north of normal. This included the jet stream, temperate zone
westerlies and sub-tropical and tropical easterlies. The principal warm
-105-
season weather control for the Atlantic and eastern U. S. is the Azores-
Bermuda anticyclone, or HIGH. Warm tropical air and tropical storms
form on the underside of this HIGH and move first westward and then
northward around it. During the past two years, and indeed frequently
since the middle 1930's, this HIGH has been displaced north of its
normal position and has been stronger than usual. This forces hurricanes
inland across the Atlantic coast which would normally recurve harmlessly
northeast and out over the open Atlantic. In addition, a trough of low
pressure forms underneath the HIGH which seems to be favorable for above-
normal hurricane freq.uency.
What are the Prospects for 195^?
Several hundred more years of hurricane statistics will be
needed before averages will mean anything. In the Cape Fear area of
North Carolina, there were no more than eight destructive hurricanes
between 17^0 and 1953* or an average of one every 27 years. Hazel
came along in October 195^ and three more in 1955 making four in 11
months. I would be foolish to make any definite prediction how many
hurricanes there will be this year or where they will strike. However,
people living along the North and Middle Atlantic coasts have some basis
for optimism. The circulation this year is just about opposite to that
of last year. This summer, so far, mid-latitude westerlies and sub-
tropical easterlies have remained south of their normal position, which
means westerly winds aloft have been prevailing as far south as Jackson-
veille and, for as long as they continue, will shunt any hurricanes,
which form, away from the coast from the Carolinas northward. Of course
I would emphasize neither I nor any other forecaster can tell now what
the circulation may be by September. Certainly we would expect some
retreat northward to a more normal position.
What are the Causes of the Hurricane Tide?
Mr. David H. Wallace tells me that the 1955 hurricanes alone
caused $10,000,000 damage to the oyster industry in the area of North
Carolina, Chesapeake Bay, and Delaware Bay. Probably wave action and
sub -surface currents are more important in producing oyster damage but
I will take a few minutes to discuss the hurricane -produced tide which
may only indirectly affect the oyster beds.
Of all the destructive agents of the hurricane, sea action is
responsible for the most of the damage and most fatalities. Hurricane
induced floods are second and direct effect of the wind third.
The greatest concentration of destructive power unleashed by
most hurricanes occurs as they move inland from the sea. It is here
that so much of the energy stored in the swells and waves from way out
at sea is expended. The added surface frictional drag begins to ex-
tract energy from the air at a greater rate as the storm crosses the
■106-
coastline. This concentration of destructive energy is reflected in
the record of destruction and death wrought by hurricanes along coastal
areas back through history. Bay far the majority of deaths attributed
to hurricanes occur at the coast where tides rise to abnormal heights.
One storm wave on the shore of the Bay of Bengal in 1881 is reported to
have caused the death of 300jOOO persons.
Storm tides, rising on occasions to 12 or 15 feet or more above
normal, and pounding waves have proved to be most difficult for man on
shore to cope with. A rapid rise of the water suddenly places man in an
unnatural habitat. Pounding waves and lashing winds are too much for
the average structure to withstand.
Rapid change of conditions brought about by a storm tide affects
not only i^an but all living creatures within reach of the flood waters
and the tidal range. At least temporarily, the ocean overruns its usual
bounds and new boundaries are established. Adjustment to new boundaries
involves considerable erosion, cutting new channels, and relocation of
sandbars. All these changes are rapid with the rising tides of a hurri-
cane; adjustments to new surroundings must be rapid. Those who can't
keep the pace in adjusting suffer. Many small creatures whose natural
homes are bioried or washed away must seek locations and build new homes
after these changes in coastal topography. Many others become casualties.
The problem of forecasting the storm tide which a given hurricane
will create is complicated by many factors which are as variable as the
coastlines which the storms affect. The first requirement in forecasting
the tide is to predict very accurately the point where the center of the
storm will move across the coast. Ten or 20 miles displacement of a storm
track to the reight or left of a point on the coast can mean a difference
between severe flooding and tides below normal. On a nearly straight
coast the highest tides occior 20 to 50 miles to the right of the track
of the storm center depending upon the size of the storm. To the left
of the storm center the wind circulation is such that water is blown
away from the shore thus creating tides below normal. Such extremely
low tides should be watched with suspicion because occasionally the wind
is holding the water away from the coast and then, stopping rather abruptly,
allows the water to return with enough momentum to create abnormally high
tides. This is a definite danger in bays and estuaries particularly. If
there is a deficiency of water on one side of an estuary, there is usually
an excess on the other side. Then when the force that holds water out of
gravitational equilibrium is suddenly decreased or removed, the effect may
be likened to tipping a pan of water and starting a natural oscillation.
There have been occasions when this return of water coincided with the
astronomical high tide and resulted in serious flooding.
In hurricane Hazel of 195^ tides up to 18 feet above (MLW) mean
low water, the highest tides of record along the North Carolina coast nor-
mally were reported just to the right of the "eye". A section of the coast
about 60 miles long experienced tides ranging from 6 to 12 feet above
the normal high. The highest water occurred where the "eye" crossed the
-107-
coast and 20 to 30 miles to the right of its track. The configuration
of the coast where Hazel crossed is concave; however, it is not certain
how much if any influence this had in the development of excessive tides.
Some other factors currently believed to he favorable to the generation
of high storm tides and which were present in Hazel were: (l) this was
a severe hurricane, that is, high winds and low barometer; (2) the
trajectory of the storm was only slightly curved and this curvature was
to the right; (3) the angle of incidence to the coast was large, about
60 degrees; (k) the continental shelf here has a very gradual slope to
about 50 fathoms 50 miles off shore; (5) the storm moved forward at about
25 to 30 miles per hour and accelerated as it approached and crossed the
coast; and (6) the storm literally "rode in" on top of the normal high
tide. The portion that each of the enumerated conditions contributed to
the total tide is not known but seldom would chance bring such concerted
conditicps for generation of a high storm tide.
The highest hurricane tide on record at Atlantic City, which is
considered representative of the New Jersey coast, is approximately 5-5
feet above normal and recorded in the hurricane of September ik, 19^^.
This tide would have been some 11 feet above mean low water if it had
occiirred at the time of high spring tide. Flooding begins along the New
Jersey beaches at about 6 feet above mean low water. If an intense
hurricane moved inland over New Jersey on a course perpendicular to the
coastline at time of a high spring tide, water levels 12 to 18 feet
above mean low water would be likely. However, the chances of such an
occurrence would appear to be considerably less than once in a hundred
years .
-108-
A CONTINUOUS WATER SAMPLER FOR
ESTIMATION OF DAILY CHANGES IN PLANKTON
Philip A. Butler and Alfred J. Wilson, Jr.
U. S. Fish and Wildlife Service Laboratory
Pensacola, Florida
The growth rates of oysters held in experimental trays suspended
above the bottom at two stations only 1000 feet apart on either side of
our laboratory island have differed markedly for the past several years
(Butler 1953)' At the east station, the oysters grow faster, mortality
is somewhat lower, and more young oysters attach to test cultch. Although
we have not checked other marine animals as closely, this station appears
to be equally favorable for clams and scallops as well as such sedentary
forms as barnacles, mussels and sea-squirts.
During the past year when we have maintained continuous records,
average monthly salinity levels have differed by less than O.5 °/oo
and temperatiires have differed by less than 1.0° C at the two stations.
In the absence of other data, quantitative or qualitative differences
in food appear to be the most plausible explanation for this situation.
Knowledge of the fundamental causes for such differing growth patterns
under apparently similar conditions would be of great practical importance
to the oyster Industry, and for this reason, we have undertaken an in-
vestigation of the problems involved.
Since shellfish are filter feeders, the logical starting point
in our investigation was to obtain estimates of plankton concentrations
and fluctuations at the two stations over a period of time. An accurate
method for the collection and estimation of plankton was essential.
Enumeration of the plankton was not considered feasible because of the
time involved, but there are several methods for estimating chlorophyll,
which is an indirect measure of phytoplankton abundance. In the past,
chlorophyll concentrations have been reported in terms of the arbitrary
Harvey Unit, but with the advent of the quartz spectrophotometer, it is
possible to measure accurately and quickly the different chlorophylls as
well as other plant and animal pigments. The remaining requirement for
this investigation was, then, a suitable method for collecting valid
plankton samples.
The discontinuous pattern of the plankton biomass in the sea
from day to day and even from hour to hour creates real difficulties
in sampling methods. Spot sampling may produce an entirely erroneous
picture. Samples collected hourly from the waters near our laboratory
may vary tenfold in volume of plankton on the same day. Consequently,
we required some method for collecting continuously a relatively small
amount of water which could be analyzed periodically for its plankton
content .
-109-
Capillary bleeders are described in the literatiore to fulfill
this need, but we found them impractical. They clog easily, are tedious
to calibrate, and their rate of flow varies with changes in water depth.
When this type of collector is submerged, an unknown amount of water
surges into the sample bottle until a pressure equilibrium is reached.
It is almost impossible to evaluate the error introduced in this way.
After much trial and error we have developed the arrangement of
equipment shown in Figure 2, which overcomes the disadvantages of a
capillary bleeder collector and offers some distinctive advantages. We
are using this apparatus routinely in our investigation of plant pigments
at the two stations.
As shown in the diagram, the essential feature of the apparatus
is the connection of both vacuum and pressurelines to the six-liter
collecting flask. The degree of vacuum is controlled by the stopcock.
Pressure can be applied to the system by means of the three-way valve.
Water is admitted to the sajnple bottle through the inlet tube, which has
a seven to eight millimeter bore.
In use, pressure is applied to the system, and the sliding rack
holding the collecting flask is lowered to the desired level under water.
The rack, weighted to counterbalance the buoyancy of the flask, slides
down a galvanized pipe set firmly into the bottom.
Pressure within the collecting flask prevents any initial surge
of water through the inlet tube. When the rack is in position, the
tliree-way valve is turned to close the pressure line. Excess pressure
is relieved by the escape of air out of the inlet tube, and equilibriiom
with the outside water is established almost immediately. The three-way
valve is turned again to apply suction to the system, and water flows
into the flask at the pre-regulated rate. The relatively large bore
and slight current make clogging of the inlet tube unlikely. At the
same time, they may hinder the collection of long chains of phytoplankton
and elongate or highly motile macroscopic zooplankton. At the end of
the collecting period, the rack is vigorously shaken to mix the sample
thoroughly. As the rack is raised and pressure decreases on the system,
there is a surge of water out of the collecting flask. Since this is an
aliquot of the sample, its loss is of no importance.
The rate of collection is dependent on the adjustment of the
stopcock: it may be varied so as to fill the collecting flask within any
desired interval from a few minutes to 96 hours. We adjust the stopcock
by trial and error so that approximately 20 drops of water per minute
flow through the inlet tube. At the end of 24 hours the flask is approxi-
mately 80 per cent full and the sample is representative of the entire
mass of water that has flowed past the station during that period of
time. Since the rate of flow in any one collecting flask stay uniform,
differences in the flow rate and total volume collected at two different
stations are of no significance providing, further, that the collections
are simultaneous and each sample is less than the capacity of the flask.
-110-
U S Fish a Wildlife Service Laboratory
Ptniocolo Flortdo
louNOiNcs iM nn
Fig. 1. Chart of the laboratory island, U. S. Fish and
Wildlife Service, showing the location of the two sampling
stations at the nine and six foot soundings on either side
of the island.
-110a-
VACUUM
PUMP
STOPCOCK
I.Omm y
/i
VALVE
3-way
\
PRESSURE
PUMP
7
SUCTION
LINE
CONTINUOUS
WATER SAMPLER
INLET TUBE
COLLECTING
FLASK l«i
SLI0IN6 RACK
U8FWS
Fig. 2. Diagram of equipment used in collecting water
samples .
With this arrangement of the collecting equipment, there is no necessity
for the tedious calibration ordinarily required when using duplicate
collectors.
The critical point in the entire system is the original adjust-
ment of the stopcock on the vacuum line. This is most easily accomplished
by transferring the suction line temporarily to a trial collecting flask
fitted with an inlet tube. With this flask submerged in a large battery
jar, the stopcock can be adjusted by observing the rate of flow into the
trial collecting flask.
Our analytical procedure for estimating concentrations of plant
pigments depends on a combination of techniques fully described in the
literature. Briefly, plankton is removed from the water samples by
suction filtration using Millipore AA filters, as described by Goetz and
Tsuneishi (195I). Such filters retain particles having a diameter of
0.8 micron or greater as well as many smaller ones. Depending on the
concentration of plankton, samples can be filtered at the approximate
rate of one liter per hour. The cellulose ester filters are dried in
vacuo , dissolved in acetone and absorbencies of the samples are read
with a Beckman DU spectrophotometer. Concentrations of chlorophylls a,
b and c as well as astacin and non-astacin carotenoids can then be
Calculated using formulae published by Richards and Thompson (1952).
At present, we collect one sample per station per day for four
consecutive days each week and analyze them individually for plankton
pigment concentrations. We consider these four -liter samples to be
valid aliquots of the millions of gallons of water flowing past each
station daily. The effectiveness of this apparatus for collecting
representative samples may be judged by comparing the average monthly
salinity of its samples with data obtained from another water sampler
used routinely at this laboratory (Collier et al. 1953)' This second
device collects a small sample of water at hourly intervals from the
continuously flowing salt water system of the laboratory. Although
salinity levels may vary from day to day during the month by as much aa
15 parts per thousand, average monthly data obtained using these two
collecting methods are in frequent agreement and, during the past year,
havenot differed by as much as one part per thousand .
We have been conducting this program of plankton pigment analyses
for several months now and find that initial results are consistent and
show characteristic trends at the two stations. Chlorophyll a appears to
be the most significant component of the pigment complex and ranges in
concentration from approximately 1.0 to 12.0 mg/M3. Both chlorophyll a
and £ fluctuate greatly from day to day, but changes in their average
concentrations seem to be directly related to changes in average water
temperatures.
-112-
Summary
The water collecting device described here has special features
which may be of value to other investigators. Its application is limited
to fixed installations such as docks. Its chief advantage lies in its
capacity to collect a relatively small aliquot from a large mass of water
during a period of one or more days. Such samples have obvious value
for estimating average concentrations of both particulate matter in the
plankton and dissolved ions including nutrient salts and trace elements.
Literature Cited
Butler, P. A. 1953* Importance of local environment in oyster growth.
Proc. Gulf & Carib. 1 Ish. Inst., 5th Ann. Session: 99-106.
Collier, A., S. M. Ray, A. W. Magnitzky, and J. 0. Bell. 1953- Effect
of dissolved organic substances on oysters. U. S. Fish and
Wildlife Service, Fish. Bull. 5^(84): 185-
Goetz, A., and N. Tsuneishi. 1951* Application of molecular filters
to the bacteriological analysis of water. Jour. Amer. Water
Works Assoc. 43 : 943-969.
Richards, F. A., and T. G. Thompson. 1952. The estimation and character-
ization of plankton populations by pigment analyses. II. A
spectrophotoraetric method for the estimation of plankton pigments.
Jour. Mar. Res. 11(2): I56-I72.
-113-
PUBLIC HEALTH SIGNIFICANCE OF PARALYTIC SHELLFISH POISON:
A REVIEW OF LITERATURE AND UNPUBLISHED RESEARCH
E. F. McFarren, M. L. Schafer, J. E. Campbell, and K. H. Lewis
Robert A Taft Sanitary Engineering Center,
Cincinnati, Ohio
E. T. Jensen
Milk and Food Program
Public Health Service
Washington, D. C, and
E. J. Schantz
Chemical Corps, Ft. Detrick, Frederick, Md.
Consultant to the Robert A. Taft Sanitary Engineering Center
The prevention of poisoning due to the ingestion of toxic shell-
fish has been a problem of mutual concern to public health and fishery
authorities in Canada and United States for many years and has been
recognized for over a century as a clinical entity. From the standpoint
of public health, paralytic shellfish poisoning or so-called "mussel
poisoning" cannot be classified as a major problem; however, it has
caused considerable concern because of its extreme toxicity and the
fact that there is no known antidote. Less than one millionth of a
gram is sufficient to kill a mouse, and the fatal dose for man is only
a few milligrams.
During the 19^5-^6 clam canning season, which was cut short by
the regulatory action of the Food and Drug Administration, Southeastern
Alaska operators produced packs of frozen and canned butter clams,
Saxldomus , valued at over $170,000. As this industry was a winter
operation, offering employment and income during an otherwise slack
season, it was of special importance to resident Alaskan economy. Like-
wise, the Maritime Provinces of eastern Canada are an important pro-
ducing area for soft shell clams, Mya , normally exporting about four
million pounds per year to the United States.
Along the Pacific Coast of North America and the Canadian
Atlantic Coast, as well as a few other parts of the world, mussels,
Mytilus , may also become poisonous. The chief danger in these areas is
that individuals may gather the shellfish and roast them on the beach.
Because of this popular summer sport of beach parties or "clam bakes"
and the commercial operations mentioned above, it is obvious that unless
adequate control measures are maintained mass intoxication would result.
-nil-
Of the many naturally occurring poisons, there are only two
general types which resemble shellfish poison in some respects. One of
these is the so called "waterbloom poisoning" (Fitch et al. 193^) which
may be elaborated by profuse growth of fresh water algae or by their
subsequent decay. Farm animals have died within an hour after drink-
ing from lakes where the plankton grows, and it has been possible to
demonstrate the poison in solution in the water. Deer and ducks and
other wild birds have also reportedly been killed by this poison in
various parts of the world. There axe no reported cases of humans being
poisoned by drinking water containing large quantities of algae. How-
ever, during the great droughts of the 1930' s there was a widespread un-
explained outbreak of gastroenteritis in several eastern cities. Some
investigators thought that this outbreak might have been related to
tremendous growth of algae which occurred in rivers used as a source of
raw water, even though the water was purified in efficient water treat-
ment plants and was heavily chlorinated.
The other related group of poisons is found in the flesh of
fish. Three different types of fish poisoning have been intensively
investigated by Halstead (l95l)> t»ut little is known concerning the
origin or nature of these poisons. One of the types. Ciguatera, is
common in the Caribbean and in several instances has been reported as
causing intoxications in Florida. The great barracuda is one of several
fish species involved, and is most frequently associated with poisoning
in Florida. A second type of fish poisoning, the Pacific, is found
throughout the South Pacific areas and is generally associated with the
coral belt. The third type of poison, Tetrodon, is found primarily in
the Japanese areas. Of the three types, the Tetrodon is the most deadly
and causes symptoms (Sommer and Meyer 1937) most similar to those of
shellfish poisoning in man and animals.
Source of the Poison
The original source of the poison in shellfish is certain species
of unicellular microscopic marine organisms of which the dinoflagellate,
Gonyaulax catenella is perhaps the best known (Sommer and Meyer 19^8).
It is a free-swimming organism, multiplying by formation of chains of
two, four> or even eight individuals of dark orange or greenish brown
color, and living like a true plant cell by photosynthesis. It is most
abundant in the summer. At times it may increase to kO million per liter.
At such times the water for miles is a deep rust color the so-called
"red water" in the day time and a beautiful luminescent spectacle at
night. Other dinof lagellates or diatoms reach similar population densi-
ties in the ocean without being poisonous. Gonyaulax catenella may vary
considerably in number and perhaps, in its poison content, because small
numbers which are not visible as red water may cause shellfish to become
poisonous.
Plankton serves as food for many animals of the seashore, and
various plankton feeders may at times become poisonous. There is only
-115-
one known case in which oysters (Hunter and Harrisoh. 1928) may have
been toxic. Scallops may become highly toxic, but the danger is not
great because ordinarily only the nontoxic adductor muscle (Medcof et
al. 19^7) is eaten. The principal species of edible shellfish which
reach dangerous levels of toxicity are mussels and clams. After the
mollusks ingest plankton, the poison tends to accumulate in the digestive
gland of mussels (Sommer et al. 1937) and clams, although gills of the
soft shell clam (Medcof et al. 19^7) are a secondary site of accumulation
and the siphons of butter clams (Chambers et al. 1952) have been found
to contain over 50 per cent of the poison. The poison evidently does
not harm the shellfish. Toxicity is proportional to the number of
Gonyaulax ingested and to their poison content. If a large number of
Gonyaulax is present in the water, the toxicity of the bivalves may
rise to dangerous levels within a few days. In the absence of the
organisms the stored poison is slowly eliminated.
The reasons advanced by Sommer et al (1937) for believing that
Gonyaulax catenella is the primary source of poison on the west coast
of the United States are: (l) In the stomachs of toxic mussels this
species of plankton was in considerable numbers, whereas it was either
absent or present in very small numbers in the stomach of nontoxic
mussels. (2) Years of investigation indicate that the yearly maxima of
certain species of the genus Gonyaulax occurs preceding and during each
poison period. (3) When poisonous mussels were kept in the laboratory
in clean aerated sea water without food, the toxicity of the mussels
dropped about one-half in 10 days. On the other hand, when mussels
were kept in the laboratory in fresh sea water at a time when Gonyaulax
catenella was abundant, the poison content rose as much as 20 times.
(h) When surface water to the amount of I50 liters was filtered through
a No. 25 net and the residue collected in a volim:e of 72 ml, a count of
the organisms revealed a total of 2,100,000 Gonyaulax catenella .
Extraction of these organisms with acid revealed that 2,050 of these
organisms yielded one lethal dose (mouse). Riegel et al. (19^9) describe
an experiment in which about 500,000 mouse units of poison were centri-
fuged from 5>000 liters of red sea water containing Gonyaulax .
In studying paralytic poisoning associated with mollusks from
the Bay of Fundy, Needier (I9U9) concluded that toxicity was caused by
Gonyaulax tamarensis . Koch (1939) found that another dinoflagellate,
Pyrodinum phoneus was responsible for extreme toxicity in Belgian mussels.
In contrast to mussels from California and New Brunswick, the toxic
Belgian mussels originated from estuaries and inner harbors, and it must
be assumed that an organism is responsible which has its habitat in
brackish waters. Further taxonomic studies are needed to establish the
relationship of these species to Gonyaulax catenella .
In an attempt to correlate shellfish toxicity with other periodic
manifestations, one naturally turns to the meteorological and oceano-
graphic data. From a study of the weather records in California it is
apparent that the maxima of shellfish toxicities occur in the summer at
times when the water and air are relatively cool (Sommer and Meyer 1937 )•
-116-
The temperatures of the water along the coasts of California and Oregon
indicate that there are upwellings of colder water to the surface.
Consequently the average temperatures of the water along the central
coast of California are 3 to 4° C lower than the average to be expected
from the latitude of the locality. In fact, average temperatures of the
water along the entire region in which mussel poisoning occurs, from
central California to Alaska, are remarkable similar in suminer time,
ranging from 10 to lU° C.
In regard to the tides (Soramer and Meyer 1937) no clear relation-
ship can be observed. As a general rule toxicity may be expected to
reach a maximum on or immediately after the second big tide in early
summer, but outbreaks have occurred at time of the aut\:imnal equinox
when tide differences were at a minimum. Evidently tides are not a
primary cause of variations in the toxicity of shellfish.
In studying the effect of water conditions on Gonyaulax fo\md
in the Bay of Fundy, records were kept showing stage of ■ he tide, time
of day, condition of the weather, and surface and bottom temperature of
the water. On these the only factor correlated with occurrence of
Gonyaulax tamarensis was the temperature of the surface water. Compari-
son of numbers of Gonyaulax tamarensis and water temperatures, especially
at the surface, indicate that Gonyaulax tamarensis may appear any time
after the surface water reaches 10" C. Small peaks in the counts of
Gonyaulax tamarensis often occur at the same time as temperature peaks
during late July or early August, but the highest count of Gonyaulax
tamarensis for any given year corresponds to the peak temperature
(13.9° C) in the latter half of August. Although these findings have
provided a useful basis for local control measures, specific relationships
between water temperature and toxic plankton are not characteristic of
the St. Lawrence River estuary and perhaps other areas.
In the Bay of Fundy the principal enemy of Gonyaulax is a
ciliate Favella ehrenbergii (Needier 19^9)- The ciliate occurs at about
the same time of year as Gonyaulax, sometimes in enormous nijmbers. It
was found feeding on small dinoflagellates, including Gonyaulax tamarensis ,
and Investigation showed a relationship between the counts of the two
species, large numbers of Gonyaulax tamarensis occurred only when Favella
ehrenbergii was rare or absent. A survey of the diatom production in this
area also indicated that the number of diatoms (Needier 19^9) inay have
some effect on the number of Gonyaulax tamarensis . It is suggested that
when many diatoms are present in late July or August they may compete
with Gonyaulax for food or reduce the light and so check production.
During the simimer of 19^9 the Hooper Research Foimdation of the
University of California cooperating with the Fishery Products Laboratory
in Ketchikan, Alaska, successfully identified Gonyaulax catenella in
waters from several areas of Southeastern Alaska (Magnus son and Carlson
1957). The organisms were never found in numbers even approaching the
concentration needed to cause a visible red tide. Red tides do occur
during the stunmer, but they have been foiind to contain concentrates of
-117-
other plankton which do not exhibit the toxic qualities of Gonyaulax .
In Alaska, however, shellfish are toxic the year around (Chambers et al.
1952) with a slight indication of a period of high toxicity in the fall
followed by a decrease during the winter and a rise again in the spring.
It is, therefore, probable that the water temperature does not fluctuate
so greatly in Alaska, and that there Gonyaulax are present most of the
time although the temperature never becomes high enough for blooms of
these organisms to occur.
Occurrence and Distribution of Toxic Shellfish
The first recorded death ascribed to paralytic shellfish poison
on the North American Continent occurred on June 15, 1793> on Vancouver
Island, British Columbia, when one of Captain Vancouver's seamen died
after eating roasted mussels. There is reason to believe that this was
not the first death due to paralytic shellfish poison, for Vancouver
wrote that his crew members had some idea of how to treat the stricken
seamen, thus indicating prior knowledge.
In 1799 a troupe of Aleut hunters from Unalaska and Kodiak
stopping at a place now known as Peril Way (near Sitka, Alaska), consumed
mussels and, according to Petroff (l884), 100 men died in less than two
hours.
In 1953 Meyer reported that the Hooper Foundation had collected
histories of more than 400 cases of mussel or clam poisoning recorded in
the literature (Sommer and Meyer 1937, Meyer et al. 1928, California
State Department of Public Health 1951, and Public Health Service 1951 ).
There were 35 deaths among the group. Most of these poisonings occurred
at irregular intervals along the central California coast with a sprinkling
of extensive outbreaks from Juneau, Alaska, to southern California. All
cases occurred between May 15 and October 26.
Medcof and his associates (19^7) and Needier (19^9) reported a
total of 28 cases of paralytic poisoning due to the soft shell clam in
the areas of the Bay of Fundy, New Brunswick, and Nova Scotia in 19^5 •
In 1936 Murphy reported five cases with two deaths caused by eating
mussels in Nova Scotia. Twenty-four cases (Fish and Wildlife Service
19^+6) were reported in Maine in 19^+3.
Several cases attributed to the ingestion of the white mussel
(Donax serra ) or the black mussel ( Mytilis edulis) have been observed
near Cape Town, South Africa (Saprika 19^+8, von Bonde 19^8). There
were 12 cases with four deaths due to these shellfish in Belgium (Koch
19^0),
Mussel poisoning has also occurred in New Zealand (Meyer 1953)
and before 1915 Germany, England, Ireland, and Frajice had reported over
a period of 20 years approximately 110 cases with 2h deaths (Meyer et al.
1928).
-118-
In 19^+8 two children died from eating mussels collected at Les
Boules, Quebec, on the south shore of the St. Lawrence River, and in
July 195^ two out of seven persons died from eating soft shell clams
collected at Metis Beach. (Tennant et al. 1955)»
One fatal case of shellfish poisoning was also reported in July
195^ at False Pass, Alaska (Meyers and Milliard 1955)* Six other eat-
ing mussels from the same source four days earlier became sick. A
summary of known outbreaks by geographical location, year of occurrence,
and number of cases is given in Table 1. The disastrous outbreak in
Alaska in 1799 has been omitted from the table because description of
the clinical manifestations is not sufficiently detailed to establish
conclusively that mussel poison was the cause of illness.
In the above cases of shellfish poisoning it has been assumed
that fresh mussels and mussels kept for a few days were equally toxic.
In California (Sommer and Meyer 193?) all of the mussels Mytilus cali -
fornianus were derived from the open shore of the ocean. Not a single
poisoning occurred from eating mussels of the species Mytilus edulis,
gathered in San Francisco Bay or other bays. On the west coast nearly
all clam poisonings were caused by Saxidomus nuttalli , Washington clam,
(Sommer and Meyer 1937) from Bodega Bay. However, Siliqua patula (razor
clams) on several occasions have contained only a little less poison
than mussels from a nearby source. The toxicity curve of sand crabs
has also been found to parallel that of mussels.
The data accumulated along the Pacific coast ( Sommer and Meyer
1937) of the United States indicates that the time of danger from shell-
fish poisoning is from May until October, with peak toxicity about the
middle of July. Variation in toxicity of mussels in a given bed is not
large, i.e., not more than t 50 per cent, and is negligible compared
with the variability in samples from different beds, which amounts to
as much as 1:3500' Severaly assays were also made of male and female
mussels and toxicity was always found the same within the limits of
experimental error. These constancies held, however, only if mussels
from approximately the same tide level were compared. Specimens gathered
from the lowest possible locations, which are swept by the waves most of
the time, are on the whole more poisonous than those from the upper limits
of their habitat where the water supply may be scarce.
In studying the presence of poison in the butter clam, Saxidomus
giganteus , in Alaska, it was concluded that the clams were toxic through-
out the year in certain areas, although there was slight indication of a
high toxicity period in the fall, followed by a decrease during the
winter and a rise again in the spring. In most cases there was no
significant difference in samples taken at the same time from high and
low plots (Chambers et al. 1952). It was further shown that bodies of
the clams do not vary greatly in toxicity from month to month but toxicity
of the siphons showed marked fluctuations.
-119-
Table 1. Known cases of paralytic shellfish poisoning 1798 to 195^
Location.
Years
of occurrence
No. of cases
No. deaths
California
1903,
'29,
'15,
'32,
'he,
'17,
•36,
'18,
'39, '
'5^
'27
'h3
373
30
Oregon
?, 1933
22
1
Vancouver, B.C.
1793
3
1
Alaska
193^,
'5^
19
3
Nova Scotia &
New Brunswick
1936,
'i^5
33
2
Maine
19^3
2k
-
Quebec
19^8,
'5h
9
k
England
1857,
'72,
■88,
190J+
7
k
Wales
1909
19
1
Scotland
I827
30
2
Ireland
1872,
■90
11
8
Norway
1901
5
2
Prussia
1885,
■87
22
5
France
1907
13
2
Belgium
l9i+0
.
12
k
South Africa
19^8
several
-
New Zealand
1951
TOTAL
several
-
602
69
-120-
In Alaska none of the beaches (Chambers and MagnusBon 1950) from
so-called outside waters contained toxic clams, but beaches on or near
the open water of the wide straits characteristic of southeastern Alaska
yielded the most toxic clams. As sampling was continued toward the head
of the bays toxicity decreased.
Poisonous shellfish gradually lose their toxicity if they are
put into sea water (Soramer and Meyer 1937) in nontoxic surroundings.
With strongly poisonous shellfish, excretion of the toxic subst'ance in-
to the water can be demonstrated directly. Experimental work in
California showed a drop to one-half of the original toxicity in 10 days
when mussels were kept in filtered aerated sea water at room temperature.
However, the Alaskan butter clarn (Magnusson and Carlson 1951) and the east
coast soft shell clam (Medcof et al. 19^7) lost their toxicity much more
slowly in transplantation studies. On the other hand, by transplanting
nontoxic shellfish to toxic areas, the shellfish become poisonous in three
to four days (Sommer and Meyer 1937)j in fact, some poison was detected
after 2k hours. In California, in one area, mussels showed a hundred-
fold increase in toxicity in about 12 days. At Metis Beach, Quebec on
the south shore of the St. Lawrence River it was shown in 195^ that with-
in six days toxicity of Mya arenaria increased from 5^2 to 26, 180 mouse
units per 100 grams (Tennant et al. 1955)' These facts indicate that
slightly poisonous shellfish may become dangerous in the course of a
few days and demonstrate the importance of the problem from the stand-
point of public health.
Physiology and Toxicology
Symptoms of poisoning (Meyer et al. 1928) in human beings are
primarily peripheral paralysis which may vary from slight tingling and
numbness about the lips to complete loss of strength in muscles of the
extremities and neck, and to death by respiratory failure. In a moder-
ately severe case the tingling, stinging sensation around the lips,
gums and tongue develops about five to thirty minutes after consumption
of the mussels. This is regularly followed by niimbness or a prickly
feeling in finger tips and toes, and within four to six hours, the same
sensation may progress to the arms, legs and neck, so that voluntary
movements can be made only with great difficulty. In all cases of
moderate severity this toxic weakness and stiffness of locomotion is
accompanied by a peculiar feeling of lightness. Some patients have
declared that they experienced a floating or flying sensation and even
heavy objects appeared to them very light. The reflexes are normal and
active. It is stated that in one of the fatal cases the deep reflexes
were affected. The mentality remains clear, although dizziness,
staggering, and drowsiness may be noted. A few patients complain of a
gripping sensation around the throat and slight respiratory distress.
Incoherence of speech was noted in one of the fatal cases. Vomiting is
an inconstant symptom, but diarrhea and abdominal pain have not been re-
corded in untreated cases. In fact, there is a tendency to constipation
which persists for several days. Records of carefully observed cases
-121-
show average temperature to be slightly subnormal (mean 98° F). The
pulse is firm and slightly accelerated (80-100 per min.). IXuring recovery
some patients have chilly sensations in their limbs and may feel slightly
stupefied or become easily fatigued for a number of days. The longest
recorded interval between eating poisonous shellfish and death is 10
hours and the shortest interval is three hours. Intoxications may be
mild or fail to develop in those who have consumed shellfish in conjunc-
tion with a heavy meal, have boiled the mollusks with rice and garlic,
or have fried them in oil. When shellfish are taken into an empty
stomach intoxication rate seems to be higher. As soon as intoxication is
recognized emptying of the stomach by an emetic and pxirging by brisk lax-
atives has been the usual practice, but in severe cases these measures
canot be relied upon to prevent adsorption of a fatal dose of poison.
As soon as difficult breathing develops artificial respiration should be
applied. Clinical observations indicate that even in severe cases this
procedure may prevent a fatal issue if extended over several hours.
The lethal dose of mussel poison for man was not known until
19^6, when an epidemiologic investigation (Meyers 1953) furnished lead-
ing information. In most instances the amount of poison eaten by victims
cannot be estimated reliably, but in this episode, involving two men
and a woman, the exact number of mussels eaten by each was known from
the number of empty shells left after the meal. Furthermore, adequate
samples of cooked and raw mussels for assay purposes were left over from
the beach picnic. It was estimated that one member of the party con-
sumed about ^2,000 mouse units; this man died in less than four hours.
The woman ingested about 22,000 mouse units, became seriously ill and
was put in a respirator for four and a half hours. This supportive
measure was probably responsible for her recovery. The second man, who
had eaten mussels containing about 17,000 units, had mild symptoms and
recovered. It this is an accurate estimate, the lethal dose for man is
probably between 20,000 and 40,000 mouse units.
A more recent epidemiological Investigation of an outbreak in-
volving seven persons at Metis Beach, Province of Quebec, gives further
information on the amount of poison which may be necessary to cause in-
toxication (Tennant et al. 1955)' One death resulted from the ingestion
of not less than 3>300 or more than 31^300 mouse units. A second
fatality resulted from ingestion of not less than 1,200 or more than
11,700 mouse units, but another person who ate a similar quantity survived.
Four other persons survived but had severe symptoms from ingestion of ^28
to 3^200 mouse units each.
Medcof et al. (19^7) also investigated clam poisoning in Canada
and concluded that people involved showed great variation in severity of
reactions to approximately equal doses. In general, however, those who
ingested the most poison suffered most. Mild poisoning, with symptoms
sometimes including numbness of legs and arms, arose from doses of poison
estimated at 2,000 to 10,000 mouse units. Those severely poisoned, who
suffered prostration and paralysis in addition to mild reactions, gen-
erally ingested 10,000 to 20,000 units. Respiratory difficulty resulted
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from Ingestion of heavier dosages estimated at about 30>000 units.
Inquiry further showed that picnickers (city people) eat clams only on
rare occasions. In contrast, people living in many of the shore com-
munities eat them frequently, especially in winter when other types of
protein food are often not readily available. The 88 different persons
for whom records of consumption of toxic shellfish were obtained in-
cluded 35 residents and 53 nonresidents of shore communities. One case
of poisoning arose in the former and 23 in the latter group. The maxi-
mum dosage ingested without producing any symptoms was estimated at
17,000 units, which is sufficient to produce severe illness in the most
susceptible persons. From these records (Medcof et al. 19^7) it may be
deduced that: (l) some people have a natural tolerance to the poison;
(2) some people in the shore communities who consume shellfish more or
less regularly may acquire a tolerance to doses of poison which would
produce severe symptoms in susceptible persons. The investigators were
unable to demonstrate development of tolerance in experiments with
guinea pigs and mice. Their research indicated that the poison is not
antigenic, and that repeated exposures do not increase resistance.
In connection with establishment of the human lethal dose, it
is of interest to compare estimates for man with results obtained using
various laboratory animals. In 19^5j 19^6, and 19^7 several shipments
of frozen clams from Alaska to Seattle, Washington, were detained by
the Food and Drug Administration (Woodward 1955) because they contained
shellfish poison. Toxicity tests were made to determine the LD^q for
several different animals. The comparative data in Table 2 were obtained
by using material from a commercially frozen pack containing from 800 to
2,000 mouse units per 100 grams. From ii0 to 80 animals of each species
were used, except for the monkeys and dogs, where smaller numbers were
tested.
As indicated in Table 2, these workers, using a crude acid
extract of clams, found an oral LD50 for rats of 1,060 mouse units per
kilo. After a supply of purified paralytic shellfish poison became
available to the Public Health Service, the LDcq °-^ this solution was
determined at the Sanitary Engineering Center, Cincinnati, Ohio. In one
experiment with ^0 white albino rats from Hamilton Laboratory Animals,
Inc., Cincinnati, Ohio, an oral LD50 for male and female animals weighing
IOO-I5O grams was 1,715 mouse units per kilogram. In another experiment,
with 80 adult male and female albino rats of the Sprague-Dawley strain
weighing 200-250 grams, the oral LD50 dose was established as 3>270 mouse
units (Davis and Campbell 1956) per kilogram of body weight. In still
another experiment, in which 90 rats of the Sprague-Dawley strain were
pretreated with a nonlethal conditioning dose of 1,000 mouse units per
kilogram two weeks prior to determination of the LD50 ^ose for these
rats, the LD50 dose was 4,718 mouse units per kilogram. From these pre-
liminary results summarized in Table 3> it can be concluded that the
oral LDcQ dose for rats may vary, depending upon strain and/or weight of
rats used, and that a nonkllling oral dose of paralytic shellfish poison
renders rats less sensitive to subsequent doses. If a comparison can be
made between the LD50 for rats determined by the Food and Drug
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Table 2. ID50* °^ shellfish poison for various animals
Animal
Oral II150
per kilogram**
Estimated lethal dose
for adult animal**
Pigeons
Mice
Rats
Rabbits
Guinea Pigs
Cats
Dogs
Monkeys
Man
500
25c
2,100
63
1,060
320
1,000
3,500
640
260
1,400
3,500
1,000 approximately
11,000
2,000 to 4,000
15,000
500
36,500
* Woodward. I955
** In mouse units.
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Table 3« Variation in response of rats to oral doses of
paralytic shellfish poison
Weight Conditioning
Strain g No. tested dose* Oral LD50*
Hamilton IOO-I5O
Sprague-Dawley 200-250
Sprague-Dawley 200-250
* In mouse units
ko
1,715
80
3,270
90
1,000
4,718
-125-
Adminstration and the LDcq determined by the Sanitary Engineering Center,
it would appear that an LD50 dose determined by using purified shellfish
poison is higher than when a crude extract of poison is used. This
latter result would seem to confirm the finding of an effect of salt
(Schantz et al. ) on the bioassay of clam meat extracts. It would appear
that salt in the extract lowers the bioassay by causing a decrease in
the rate of adsorption of the poison when injected intraperitoneally in-
to mice or fed orally to rats.
A number of physiological and pharmacological studies have been
made on shellfish poison in order to investigate its mode of action.
In autopsies on humans (Meyer et al. I928) no significant findings were
recorded in the abdominal or chest cavities except a slight pulmonary
congestion. In every case folds of the stomach were studded with small
hemorrhages.
Injection of small or intermediate amounts of mussel poison into
dog or rabbit (Prinzmetal et al. 1932) causes a definite slowing of
respiration with gradual recovery. In the dog there is a fall in blood
pressure followed by a secondary rise. With respiratory depression, a
secondary slowing of the heart occiirs. Large doses cause an immediate
speeding up of the heart followed by marked secondary slowing. When
fatal doses are given, the heart continues to beat after respiration
has stopped. In one rabbit the heart beat ^5 minutes after respiration
had stopped, and when the thorax had been opened, it was found that the
auricles were beating three to five times faster than the ventricles.
It is thought that this heart block is probably due to the direct action
of the poison on the heart muscle.
In a study of the excretion (Prinzmetal et al. 1932) of the
poison, urine was taken from a dog which had been fed 100 mouse units
over a period of two hours. Of the 100 mouse units, kO were recovered
in the urine. It was concluded that excretion takes place probably
almost as fast as absorption, thereby preventing a high concentration
of the poison in the body fluids.
Frogs (Prinzmetal et al. 1932) are quite resistant to shellfish
poison. Only a slight transitory stimulation of the respiratory move-
ments is caused by 7-5 mouse units. Fifteen mouse doses are required to
cause severe symptoms. The general symptoms resemble closely those caused
by curare and consist of progressive paralysis, which is quite general,
with the exception of the heart action. Respiration is slowed and may
stop, and the heart is slowed, but the animal may recover after several
days depending upon its individual resistance and environmental conditions.
On macroscopic examination of the central nervous system of
poisoned animals, softening and edema of the brain was observed with
moderate congestion of surface vessels (Covell and Whedon 1937). There
was no evidence of hemorrhages into the spinal cord or brain. The lungs
revealed large and small areas of hemorrhage, and the abdominal viscera
were congested with blood. Microscopic examination of the organs revealed
-126-
the usual changes accompanying agonal death (Covell and Whedon 1937).
Acutely poisoned animals revealed no alterations in the nerve cells
of the central nervous system. The large nerve cells of the ventral
horn of the spinal cord and the ganglion cells of the medulla of the
chronically poisoned animal showed alterations in certain cytologic
constituents. The only striking evidence within the organs is the
altered condition of mitochondria of the convoluted tubules of the
kidney. The gradual elimination of the poison by the kidneys may be
responsible for this effect.
From a group of experiments on frog muscle and nerves, Kelloway
(1935) concludes that shellfish poison is a neurotoxin with central
effect upon the cardiovascular and respiratory centers and peripheral
effect upon the nerve endings, both motor and sensory.
Fingerman et al. (1953)* however, conclude that shellfish poison
has a strong effect on both peripheral nerves and skeletal muscles of
the frog. Action of this poison on muscle is similar to that of curare.
Furthermore, shellfish poison has an even more general action than curare,
for it not only decreases excitability of muscle to direct stimulation
but also blocks nerve conduction. In view of these actions, this poison
must be considered a neuromuscular toxin rather than a neurotoxin.
Characteristics of the Poison
On the occasion of the Wilhelmshaven mass intoxication in 1885*
Salkowski (I885) classified mussel poison as belonging to the group of
the chemical poisons of the highest potency. Stability to heat, in-
stability to alkali and solubility in alcohol were established. At the
same time, Brieger (I889) isolated a gold salt of the base C6H15NO2
called "mytilotoxin" which he considered a quaternary ammonium base and
the pure poisonous principle. According to Muller (1935)* Thesen in
1902, although obviously dealing with the same type of toxin, could not
identify his poison as "mytilotoxin".
Muller in 1935 also attempted to repeat Brieger 's method for
Isolation of "mytilotoxin" but concluded that even in highly concentrated
and purified solutions no precipitate of the poison could be formed by
either gold or platinim salts. As a result, Muller was inclined to
believe that the toxic properties of Brieger 's mytilotoxin were simulated
by traces of poison adherent to an inactive substance. Muller 's experi-
ment supports the opinion that "mytilotoxin" does not, as stated in many
textbooks, represent chemically pure poison responsible for pajralytic
type of shellfish poison.
Mussel poison has been shown to be soluble in water, methanol,
ethanol, glacial acetic acid, and aqueous acetone (Meyer et al. I928).
Effectiveness of these solvents for extracting the poison appears to be
increased if small amounts of hydrochloric acid are added. The poison
is insoluble in ether, chloroform, ethyl acetate, butanol, and toluene.
-127-
It cannot be extracted from an aqueous solution by any of these solvents.
The isolation of betaine from a partially purified extract of mussel
poison indicated that the properties of betaine and the poison were
enough alike that the substances tended to accompany each other. This
fact and the solubility behavior suggested that it might be a nitrogenous
base.
Muller (1935) further characterized shellfish poison as being
of relatively small molecular weight. The purified poison did not give
any color reactions for alkaloids and was not removed from solution by
the customary precipitants. The poison was purified by the following
steps. Drying of the toxic organs, extraction of lipoids with ether,
extraction of the poison with acid methyl alcohol, adsorption of impuri-
ties and pigments on Norit A, adsorption of poison by permutit, elution
by KCl, separation from inorganic salts by the alcohols, acetone, or HCl-
ether, and precipitation of poison by rufianic and reinecke acids. The
most purified preparation had a potency of 590 mouse units per rag of
solids but still contained 35 per cent ash. Analysis of this piorified
preparation showed it to contain 10.73 per cent carbon, 5*31 per cent
hydrogen, and 8.59 per cent nitrogen. Two atoms of nitrogen were present
for each tliree atoms of carbon. The preparation also gave negative
carbohydrate and protein tests, was dialyzable, and was not affected by
ultraviolet irradiation. Catalytic hydrogenation, as well as attempts
at methylation did not change the physiological activity, but acetylation
completely inactivated the poison. Hydrolysis in moderate concentrations
of mineral acid did not affect the poison. Boiling in strong acid solu-
tion destroyed its potency. Oxidants attacked the poison in acid solu-
tion only at high temperatures causing instantaneous destruction at
100° C when treated with H2O2. No adsorption of the poison on aluminum
hydroxide occurred at various pH values. Kaolin adsorbed about 50 per
cent of the poison from an aqueous solution. Brief shaking with Lloyd's
reagent removed the poison quantitatively from aqueous or acid alcohol
solutions, but no satisfactory method for elution was found. Common
sea sand, washed free of electrolytes, adsorbed approximately 90 per
cent of the poison from aqueous solution and practically none from
alcoholic solution. Diatomaceous earth did not adsorb the poison or
pigments from a crude extract .
Bendien and Sommer (19^1) investigated the use of chromatography
for further purification and found active carbon the most satisfactory
adsorbent. In preliminary tests to determine optimum conditions for
chromatography, four different carbons were tested. Of these Norit A
(Sommer et al. 19^8) seemed to be most suitable. Mussel poison was not
adsorbed completely from solutions containing less than 1.0 N acid.
Traces of ethanol in the extract also prevented complete adsorption of
the toxic material. The mussel poison hydrochloride was retained by the
carbon, and the major portion of the inorganic, as well as organic,
contaminants passed through at once. The use of distilled water to
develop the chromatogram was sufficient to carry the poison through in-
to the filtrate. By repeated treatment, as above, the ash content of
highly toxic material obtained from carbon columns was reduced to three
-128-
or four per cent. By chromatography on carbon of a concentrate obtained
by ion exchange on Decalso, a mussel poison hydrochloride was obtained
with a toxicity greater than 1,000 mouse units per mg of solids (Soramer
et al. 19^8).
Mussel poison extracts, even after preliminary purification,
retain varying amounts of other bases. Choline was found in Decalso
eluates. After chromatography of the eluates on Norit A, it was found
in the primary acid filtrates. Betaine was also found in acid filtrate
from the chromatography of crude extracts on Norit A. A study of the
nitrogenous bases (Riegel et al. 19^9) was made because their presence
in partially purified poison indicated they possessed chemical properties
similar to the poison, and because the removal of these bases would be
made easier if they were identified. In addition to betaine and choline,
homarine, taurine, and tyrosine have been isolated and identified. Cho-
line and hornarine, both quaternary bases, remain closely associated with
the poison through the preliminary steps in its purification. An addi-
tional base has been detected by its characteristic ultraviolet absorp-
tion spectrum but has not been identified.
Recently, Schantz et al. and Mold et al. have obtained the
poisons from California mussels and Alaska butter clams in pure form.
These poisons were purified by adsorption on Amberlite IRC-50 followed
by chi'omatography on XE-64 and on acid washed alumina. The potency of
the preparations obtained in this way ranged between 5>500 and 6,000
mouse units per mg of solids. The purified poisons were subjected to
frontal analysis and counter-current-distribution and were pure.
Repeated chromotography on alumina and recrystallization of the poisons
as a helianthate did not produce a product of higher toxicity. The
chemical and physical properties of the two poisons indicate that they
are identical.
Studies (Sommer et al. 19^8) were also made of the effect of
pH and temperature on the stability of the poison in aqueous solution
as measured by its toxicity. The decrease in toxicity with increases
in pH and temperature, as illustrated in Figure 1, shows that the poi-
son must be handled in acid or, under certain conditions, in neutral
solution, and that the temperature should be kept low. For example,
there is a loss in toxicity of only six per cent in six days at 25° C,
but at a pH of 6.6 this loss increases to 35 per cent, and to 7^ per
cent at pH 11.5- Likewise an increase in temperature from 25 to 100° C
at a pH of 5'0 results in increased loss in toxicity from six per cent
in six days to 85 per cent in one day. No change in toxicity of shell-
fish poison is observed in aqueous solution at room temperature if the
solution is more acid than pH ^.5> nor in 3 N hydrochloric acid solutions
up to a temperature of 55° C. These studies, on the other hand, indicate
that commercial processing of clams and mussels by heating above 100° C
may be expected to reduce the toxicity considerably unless the product
is acidic.
Medcof et al. (19^7) reported the effects of domestic cooking
-129-
lUU
ir^^^^r" — ' —
1 I
90
K ^^^\
pH 5.0 _
80
-\\
^^^-^^5*'C
70
A ^^"--.
pH 5.0 _
>-
O
X
o
1-
60
\ ~~
_25^C
pH 6.6
2
UJ
o
UJ
Q.
50
] ^.
—
40
^^^
30
A
^'""-^25*'C
20
\ lOO'^C
pH 5.0
1 1 1
pH 11^
1 1 1
3 4
TIME IN DAYS
Fig. 1. pH and temperature effects on shellfish poison in aqueous
solution (Sommer et al. 19I+8).
.130-
on toxicity. Their results show that ordinary cooking of shellfish in
a little water, even for brief periods, provides the consumer with some
degree of protection. On the average, 100 grams of steamed, boiled, or
pan-fried meat contained only about 30 per cent of the poison in 100
grams of raw meat . Cooking may actually reduce toxicity of the meat by
considerably more than 70 per cent because part of the poison is expressed
in the juices. However, when clams are steamed or boiled, varying amounts
of the juices may be ingested with the meats, either in the form of
bouillon or broth. Temperatures involved in pan frying are considerably
higher than in steaming or boiling and seem to be somewhat more effective
in destroying the poison even though none of the extractives is discarded.
In 19kk and 19^+5 a cannery (Medcoff et al. I9U7) processed I5
different lots of poisonous clams following its established procedure.
This involved precooking for 15 to 20 minutes in barrels with loose-
fitting heads into which live steam was fed. The clams were then shucked,
siphons trimmed off, meats washed in warm fresh water, and packed in cans.
Next a portion of the hot bouillon resulting from steaming was used to
completely fill the cans. The bouillon was seasoned with vinegar lowering
the pH from about 8.2 to 6.5. The cans were sealed without being
exhausted and were retorted at 250° F for k^ minutes. The results showed
that linder the alkaline condition of steaming and the slightly acid con-
ditions in cans during retorting, 8^+ to 9^ per cent of the poison is
destroyed. Presumably canning without adjustment of the pH by addition
of vinegar would result in even greater destruction of the poison, since
it is less stable in alkaline than in acid media. Further tests showed
that the bouillon contains considerable poison. In commercial canning
preliminary cooking with steam produces much more bouillon than is
ordinarily used to fill the cans, and surplus has to be discarded. Thus,
much of the poison present in raw clams never enters the commercially
canned product. To illustrate this point, raw shellfish meat was packed
in cans without adjustment of pH, sealed and processed by two methods
retorting at 230° F for 55 minutes and in a boiling water bath for three
hours. The lesser reduction in toxicity (6^+ to 8^ per cent) in these
tests indicated that drainage of bouillon from meats is highly important
in producing the low toxicities consistently observed in commercial packs.
It was concluded that precooking clams with steam for 10 minutes reduced
the poison content by about 9O per cent, but extending the period pro-
duced no significant additional reduction. Retorting at 250° F for 45
minutes lowered toxicity only by an additional three per cent.
Although perhaps not true of the soft shell clam, it should be
pointed out that with the Alaska butter clam the commercial practice of
removing the siphon is highly significant in reducing the toxicity of
the canned product, since about one-half to two-thirds of the poison
contained in the butter clam is found in the siphon.
Numerous studies on transplanting and on storage in air, on ice,
and in the frozen state have been conducted in an effort to find a means
of detoxification of raw shellfish. None of these methods has resulted
in development of feasible industrical practices. Studies have also been
-131-
made of variations in commercial canning and processing in an effort to
find ways to destroy all of the poison. Until more effective methods
are found for detoxifying clams and mussels, commercial exploitation of
this valuable food supply is not possible in many areas. Recently,
preliminary experiments on destruction of shellfish poison by ionizing
radiations have been conducted cooperatively by the Robert A. Taft
Sanitary Engineering Center and the Massachusetts Institute of Technology.
Through the courtesy of Dr. B. E. Proctor, Head of the Department of Food
Technology at M.I.T., both toxic clam meat and the purified poison have
been exposed to 3,000,000 roentgen-equivalents-physical. Although the
data now available are too limited to be conclusive, the poison appears
to be so little affected that irradiation offers no ready means of
detoxifying shellfish on a commercial scale.
Prevention and Control
Prevention of shellfish poisoning involves education and legis-
lation in addition to technical control measures. The plain fact that
any type of clam or mussel may be a potential source of poison should
be readily understood. Along the Pacific shore of North America and the
Canadian Atlantic Coast a safe rule is: Do not eat the viscera (dark
meat) of mussels or the siphons of clams, or drink the juice of mussels,
clams, and scallops from the open coast unless the shellfish from that
specific area have been tested recently. The white meat must be
thoroughly washed before cooking. The addition of baking soda to cooking
shellfish has been advocated to help reduce the toxicity, but it is no
safeguard against poisoning if highly toxic whole shellfish are prepared,
and it may reduce their palatability.
During the poison season of 1939 in California (Sommer and Meyer
19^8) it was shown that warning signs posted along the beaches and across
the highways at county lines are effective in reducing the number of
persons who dig clams. The same applies to publicity in the local press
and through radio stations along the coast. The health officer or local
physician has an excellent opportunity to dispel in the minds of the
people the many erroneous notions (Sommer and Meyer 19^8) concerning the
cause of the shellfish poisoning. Among the points to be emphasized are
the following: (l) Paralytic shellfish poison is not a post-mortem pro-
duct of decomposition. (2) Temporary exposure to the sun does not harm
living shellfish, nor does it make them poisonous. (3) Mussels below
the tide lines are, if anything, more poisonous than those above water.
(h) Copper in the rocks, oil on the beaches, and stagnation or pollution
of the water are in no way connected with paralytic shellfish poisoning,
although they may render the shellfish otherwise unfit as food. (5)
Toxic mussels or clams cannot be distinguished from normal shellfish
without laboratory tests. (6) Discoloration of a piece of garlic or of
a silver spoon in the pot is no indication of poisonous shellfish. The
plain story of the chain of intoxication from the microscopic plant
through the bivalve to man should be clearly understood by people along
the coast, in order that they may avoid exposure to this type of food
poisoning.
-132-
As for legislative control, various food and drug, fishery, and
public health agencies in both Canada and the United States have taken
measures for many years to prevent the occurrence of shellfish poisoning.
Wherever poisonous clams are known to exist, digging is prohibited when-
ever tests demonstrate the meats to be toxic. In Alaska this may include
nearly all seasons, because clams in certain localities remain toxic the
year around. In California, mussels, being the most common soxirce of
the poison, are put under quarantine by the State Department of Public
Health (Sommer and Meyer 19^8) from May 1 to November 1 and at such
other times as laboratory tests show them to be dangerous.
During the last war, commercial canning of clams in Alaska
grew rapidly from a negligible operation to one of significance to the
territory (Mangnusson and Carlson 1951)' During the 19^+5-19^6 season
the operation was cut short when poison was found in packs of frozen
clams. In January 19^9 a tolerance level (Magnusson and Carlson 1951)
was established for the amount of toxin in whole and minced claji.s . As
modified in February 1951> marketing of fresh, frozen, or canned clams
is permitted only when they have an average toxicity of less than 400
mouse units per 100 grams of contents (Magnusson and Carlson 1951) • No
individual unit package is permitted to exceed 2,000 mouse \inits per 100
grams. In the case of minced or chopped claiiis, which are subject to
less variation, the average toxicity must be less than 2,000 mouse units
per 100 grams of contents and no unit package should materially exceed
that figure.
Canning of clams in Canada around the Bay of Fundy and the mouth
of the St. Lawrence River has also been practiced for many years. Almost
5,000 toxicity tests (Public Health Service 1955) have been made in this
region since 19^3^ and the indicate that most of the growing areas in the
Bay of Fundy can be readily classified for control purposes. Class I
areas are not affected by paralytic shellfish i^oison at all. Class II
areas are affected only in late suminer for a short period each year, if
at all. Class III areas are usually affected the year around. Further-
more, there is a consistent order in the time of appearance of poison in
different areas. Mussels in areas exposed to the open Bay of Fundy
regularly show poison about 10 days before first traces appear in the
tributary inlets. Accordingly, regular sampling at a "key station"
shows when the time has come to impose quarrantine.
Up to and including 19^5 canning of soft shell clams was permitted
in Canada at all seasons, but when toxicities of raw stock were above hOO
mouse units per 100 grams the pack was released for sale only after
systematic sampling showed that it contained not more than 200 units per
100 grams of canned meat (Medcof et al. 19^7)* Since processing normally
destroys about 70 per cent of the poison, such a product was regularly
obtained (Medcof et al. 19^7) from raw shellfish containing 1,000 mouse
units or less per 100 grams. After U. S. authorities relaxed their
restrictions in 1951 on packs of whole Alaskan butter clams, Canadians
again adopted the UOO mouse unit quarantine level and now permit the
marketing of clams (fresh, frozen, or canned) when average score of
■13
o .
representative samples from each shipment are less than ^00 and scores
of all samples are less than 2,000 mouse units per 100 grams (Public
Health Service 1955)-
Commercial harvesting of mussels of any species from the Bay of
Fundy (Medcof et al. 19^7)> either for canning or for sale as raw food,
has been prohibited at all seasons since the autumn of 19^3> when their
toxicities were found to be several times higher than those for clams.
Likewise the marking of beaches or quarantine of an area to prevent
local residents and tourists from digging clanis or mussels has been
generally instigated when toxicity of the shellfish exceeds 400 mouse
xinits per 100 grams of meat .
These restrictions have interferred seriously with the shell-
fish industry in Nova Scotia, New Brunswick, and Alaska (Medcof et al.
19^7) • Nevertheless, they have proved necessary and do provide signifi-
cant protection, as shown by the fact that sufficient poison (1,000 to
5,000 units) to produce the mildest symptoms in the most susceptible
persons would require an individual to eat a whole can, about 300 ml of
meat and bouillon combined, with a toxicity of 300 to 1700 units per
100 ml.
For control purposes, the present accepted technique for deter-
mining toxicity of shellfish is a bioassay using mice; briefly, this
method (Medcof et al. 19^7) involves the following steps. Clams are
shucked, washed in fresh water, drained on a sieve for five minutes
and minced in a meat grinder. A 100 gram portion of the ground meat is
suspended in 100 ml of 0.1 N hydrochloric acid and boiled gently for
five minutes with continuous stirring. The mixture is cooled, adjusted
to a pH of k.O or 1+.5 by addition of a few drops of 5 N acid or 0.1 N
sodium hydroxide, and then made up to 200 ml with distilled water. The
supernatant liquid is clarified by settling or centrifuging and used
for injection into a few test mice to obtain a preliminary estimate of
potency. With high toxicity clams, dilutions of the extract may be
necessary to obtain solutions which give death times within the desired
range. The death times corresponding to various numbers of mouse units
may be determined by referring to Sommer's Table*. When injection of
1 ml into each of three mice produces a mean death time of 10 to 20
minutes, each milliliter is said to contain one mouse unit. The toxicity
per 100 grams of meat is the number of mouse units contained in 1 ml of
extract multiplied by 200, which is the total volume of 100 grams of
meat plus 100 ml of dilute acid.
In 19^9 the Fishery Products Research Laboratory sponsored a
collaborative study (Public Health Service 1955) on the assay of toxic
clam extracts. This study indicated considerable variation when several
♦Furnished by Sommer to other workers in this field. These tables are
based on graphs (Soramer and Meyer 1937) recorded in the literature.
The essential portions have been reproduced for distribution by the
Public Health Service (1956).
-I3ii-
strains of mice are used, and that results from one laboratory may
differ from the assays of another by as much as 60 to 70 per cent under
these circumstances.
In 1950 some changes in the assay procedure (Public Health Service
1950) were suggested, and further progress was made in 1955 when the
Public Health Service sponsored a one-day conference to discuss the most
recent developments in assay of shellfish poison. At the conference,
the use of a purified shellfish poison as a reference standard was
proposed by Dr. E. J. Schantz. Dr. Schantz and his associates at Fort
Detrick have been engaged in this field of research for several years
and have succeeded in isolating (Schantz et al.) the poison in pure
form (Mold et al.). On the basis of the information presented at the
conference, the conferees agreed: (l) that purified poison should be
used as a reference standard for obtaining uniform bioassays, and (2)
that results of future bio-assays should be reported in terms of weight
of the poison. As a result of the conference, the Robert A. Taft
Sanitary Engineering Center cooperated with Dr. Schantz in determining
practical requirements for use of the purified poison as a reference
standard. Briefly, it was found (Schantz, McFarren et al.) that: (l)
a median death time between five and seven minutes gives the most
reliable estimate of potency; (2) in using the reference standard to
determine the factor for conversion (CF value) of mouse units to micro-
grams of poison, the results should not vary by more than t 20 per cent;
(3) the CF value obtained in one laboratory may differ significantly from
that obtained in another laboratory through the use of different strains
of mice or variations in technique of assay, but once the CF value has
been determined in each laboratory it is expected that comparable results
will be obtained in separate laboratories assaying clams if CF values
are used to calculate micrograms of poison; (h) in assaying low-toxicity
clams containing around UOO mouse units per 100 grams, which is the
present level of acceptability, the bioassay procedure may underestimate
total toxicity by as much as 60 per cent.
The Public Health Service has recently issued an interim plan
(Public Health Service 1956) for standardization of the bioassay and
has secured a quantity of purified poison from the Chemical Corps for
use as a reference standard. These items are now ready for distribution,
and individuals or organizations desiring to obtain them should address
their requests to the Department of Health, Education, and Welfare, Public
Health Service, Washington 25^ D. C, attention, Shellfish Sanitation
Section.
As the result of determination of the micrograms of poison
equivalent to one mouse unit, and the information, also presented at
the conference in May 1955> that the poison gives a color reaction
(Schantz, Mold, and Lynch) in the Jaffe Test, a chemical method for
the quantitative determination (McFarren et al.) of the poison has been
devised. Briefly, this method (Fig. 2) consists of making an acid ex-
tract of clam meats, adsorption of the extract on an ion-exchange resin,
elution of the poison and measurement of it colorimetrically by the
Jaffe Test.
■135-
Extraction of 100 grams of clam meat with
100 ml of 0.5 N trichloroacetic acid
I
Adjust 100 ml of filtrate to pH 5-0
i
Adsorb on XE-6k at pH 5.0
i
Wash column with 200 ml of
pH 5-0 buffer and 200 ml of
water
i
Elute with O.5 N
trichloracetic acid
i
Apply Jaffee Color Test to eluate
Fig. 2. Flow Bheet for chemical assay of
paralytic shellfish poison
-136-
Table k. Comparison of the bioassay with the chemical assay
foi- detei-inination of the toxicity of olatns
Clam Bioassay Chemical assay
sample ug/lOO g ug/lOO g
A 115 159
B 1U7 198
c 160 207
D 328 337
E 1093 IO5J+
■137-
In Table '+ are presented some data comparing the toxicitleB of
various clam samples as determined by chemical and bioassay procedures.
The data indicate that in testing low-toxicity clams the bioassay may
underestimate the poison content by a considerable amount. This is as
to be expected, since, as mentioned previously, in recovery studies in
which poison was added to non-poisonous clams, the bioassay underesti-
mated the toxicity by as much as 60 per cent. In assaying clams of
greater toxicity the bioassay becomes progressively better, until at
high toxicities the recovery appraoches 100 per cent. In this case, as
can be noted in Table k, the bioassay agrees with the chemical assay.
The chemical test may not be suitable for use in the field, but in the
laboratory has accuracy equal to or greater than that of the bioassay,
and should be useful as a control test particularly in areas where it
is difficult to obtain and keep mice.
Literature Cited
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Arch. f. path. Anat. 115: 483-
California State Department of Public Health. 1951. Manual for control
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Chambers, J. S., H. J. Craven, and D. M. Galerman. 1952. Technological
studies on the Alaska butter clam; additional studies on the
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Chambers, J. S., and H. W. Magnusson. 1950- Seasonal variations in
toxicity of butter clajiis from selected Alaska beaches. Spec.
Sci. Kept. - Fish. No. 53, Fish & Wildlife Service, Washington
25, D. C.
Covell, W. P., and W. F. Whedon. 1937. Effects of the paralytic shell-
fish poison on nerve cells. Arch. Path. 2k: J+ll-4l8.
Davis, R. K., and J. E. Campbell. 1956. Unpublished data of Robert A.
Taft Sanitary Engineering Center, Cincinnati, Ohio.
Fingerraan, M., R. H. Forester, and J. H. Stover. 1953. Action of
shellfish poison on peripheral nerve and skeletal muscle. Proc.
Soc. Exptl. Biol. Med. 8^+: 6^3-6^6.
Fish & Wildlife Service, Dept . Interior. Aug. 6, 1946. Report of a
conference on mussel poisoning.
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Fitch, C. P. et al. igS'^- Cornell Vet. 24: 30.
Halstead, B. W. June 1951* Poisonous fish - a medical -military problem.
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Hunter and Harrison. March 1928. Tech. Bull. No. 6k, U.S. Dept. Agr.
Kelloway, C. H. 1935 • The action of mussel poison on the nervous
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Koch, H. J. 1939- La Cause des enpoisonneraents paralytiques provoque
par les moules. Assoc. Franc. I'avanc. Sci., Sean. Sess. 63:
65i+.
Koch, H. J. 19^0. Dinoflagellate als ooruoak van verlammend
mooseluergiftiging, Natuurw. Tijdschr. 22: 96.
Magnusson, H. W., and C. J. Carlson. September 1951« Technological
studies on the Alaska butter clam - review of problem of
occurrence of a toxin. Tech. Rept. No. 2, Fish. Exptl. Coram.
Alaska. Fish. Products Lab., Ketchikan, Alaska.
Medcof, J. C, A. H. Lain, A. B. Needier, A. W. H. Needier, J. Gibbard,
and J. Naubert. 1947- Paralytic shellfish poisoning on the
Canadian Atlantic Coast. Bull. Fish. Res. Bd. Canada 75: 1-32.
Meyer, K. F. 1953- Food poisoning. New England Jour. Med. 2^9:
848-852.
Meyer, K. F., H. Sommer, and P. Schoenholz. I928. Mussel poisoning.
Jour. Preventive Med. 2: 365-394.
Meyers, H. F., and M. S. Hilliard. 1955- Shellfish poisoning episode
in False Pass, Alaska. Public Health Reports. 7O: 419-4-20.
McFarren, E. F., E. J. Schantz, J. E. Campbell, and K. H. Lewis.
Chemical determination of paralytic shellfish poison. Un-
published date of Robert A. Taft Sanitary Engineering Center,
Cincinnati, Ohio.
Mold, J. D., E. J. Schantz, et al. Evidence for the purity of the
poison isolated from toxic clams and mussels. Unpublished data
of Chemical Corps. Fort Detrick, Frederick, Md.
Muller, H. 1935. The chemistry and toxicity of mussel poison. Jour.
Pharm. Exptl. Therap. 53: 67-89-
Murphy, A. L. 1936. Mussel poisoning in Nova Scotia. Canadian Med.
Assoc. Jour. 35: 4l8-4l9.
-139-
Needier, A. B. 19^9- Paralytic shellfish poisoning and Gonlaulax
tamerensls . Jour. Fish. Res. Bd. Canada 7: 490-505"!
Petroff, I. 188^. Report on the population, industries, and resources
of Alaska. Tenth Census of the U.S.A. 8: 123.
Prinzmetal, M., H. Soinraer, and C. D. Leake. 1932. The pharmacological
action of "mussel poison". Jour. Pharra. Exptl. Therap. k6:
63-73.
Public Health Service. November 19j 19^3 • Tentative standard procedure
for the determination of shellfish (mussels or soft clams)
poison. Mimeographed copy of procedures with suggestions of
1950, k pp., Washington 25, D. C.
Public Health Service. October 2, 1954« Communicable disease summary.
Natl. Office Vital Statistics, Washington 25, D. C.
Public Health Service. May 26, 1955- Conference on shellfish toxicology.
Mimeographed copy of proceedings. 35 PP', Washington 25, D. C.
Public Health Service. May 7, 1956. Interim plan for the standardizing
of the bioassay of paralytic shellfish poison by use of a
reference standard, 9 PP-, Washington 25, D. C.
Riegel, B., D. W. Stanger, D. M. Wikholm, J. D. Mold, and H. Sommer .
1949' Paralytic shellfish poison. IV. Bases accompanying
the poison. Jour. Biol. Chem. 177: 1-6.
Salkowski, E. 1885 . On the poison of edible mussel ( Mytilus edulis ).
Arch. Path. Anat . 102: 578-592.
Saprika, N. 19^8. Mussel poisoning. South African Med. Jour. 22:
337-338.
Schantz, E. J., et al. A procedure for the isolation and purification
of the poison from toxic clams and mussel tissue. Unpublished
data of Chemical Corps, Fort Detrick, Frederick, Md.
Schantz, E. J., J. P. Mold, and J. Lynch. Color tests given by shell-
fish poison. Unpublished data of the Chemical Corps, Fort
Detrick, Frederick, Md.
Schantz, E. J., E. F. McFarren, M. L. Schafer, and K. H. Lewis. Studies
on the bioassay for paralytic shellfish poison using crude and
purified preparations. Unpublished date of the Robert A. Taft
Sanitary Engineering Center, Cincinnati 26, Ohio.
Soraraer, H., and K. F. Meyer. 1937. Paralytic shellfish poisoning.
Arch. Path. 2^+: 56O-598.
-li+0-
Sommer, H., and K. F. Meyer. 19^8. Mussel poisoning a summary.
A manual for the control of communicable diseases of California.
Calif. Sta. Dept. Public Health.
Soramer, H., R. P. Monnier, B. Riegel, D. W. Stanger, J. D. Mold, D. M.
Wikholm, and E. S. Kiralis. 19^8. Paralytic shellfish poison.
I. Occurrence and concentration by ion exchange. Jour. Amer.
Chem. Soc. 70 : 1015-1018.
Sommer, H., B. Riegal, D. W. Stanger, J. D. Mold, D. M. Wikholm, and
M. B. McCaughey. 19^8. Paralytic shellfish poison. II.
Purification by chromatography. Jour. Amer. Chem. Soc. 70:
1019-1021.
Sommer, H., W. F. Whedon, C. A. Kofoid, and R. Stohler. 1937. Relation
of paralytic shellfish poison to certain plankton organisms of
the Genus Gonyaulax. Arch. Path. 2k: 537-559.
Tenneint, A. D., J. Naubert, and H. E. Corbeil. 1955 • An outbreak of
paralytic shellfish poison. Canadian Med. Assoc. Joior. 72:
436-U39.
Thesen. 1902. Arch, f . exper. path. u. Pharmakol. ^7: 31I.
von Bonde, C. 19^8. Mussel and fish poisoning. South African Med.
Jour. 22: 76O-763.
Woodward, G. May 26, 1955* Conference on shellfish toxicology. Public
Health Service, Washington 25, D. C.
-141-
SHELLFISH TECHNOLOGY
and
PUBLIC HEALTH ASPECTS
-li+2-
THE EFFECT OF AUREOMYCIN^ CHLXDRTETRACYCLINE
IN THE PROCESSING AND STORAGE OF FRESHLY SHUCKED OYSTERS
Anthony Abbey
A. Richard Kohler
Sidney D. Upham
American Cyanamid Company
Fine Chemicals Division
Princeton, New Jersey
Abstract
The use of Aureomycin chlortetracycline, in concentrations
from one to 30 ppm, was evaluated in the processing and storage of
freshly shucked oysters. Several trials were conducted in cooperation
with commercial processors using production facilities and schedules
whenever possible. The proportions of oysters and treating solutions
and the exposure times were varied. Although unfavorable storage con-
ditions were usually employed, microbial counts and organoleptic tests
favored the oysters processed with Aureomycin chlortetracycline.
.Ik3-
FREEZING AND PROCESSING SOUTHERN OYSTERS
This topic was organized for the Convention in the forms of a
panel discussion moderated by Charles F. Lee. Abstracts of the dis-
cussions are recorded in the following section.
INTRODUCTION TO PANEL DISCUSSIONS
Charles F. Lee
U. S. Fish and Wildlife Service, College Park, Maryland
The first technological project approved under the Saltonstall-
Kennedy Act was for research on Southern oysters. "Southern" oysters
as here defined refers to the product of the Gulf Coastal States, North
and South Carolina, Georgia, and Florida. Problems of handling these
oysters differ considerably from those of the oyster industry north of
North Carolina.
The necessity for working with such a highly perishable product
as raw oysters required work to be done by contract groups located near
the producing area. Research teams located at Florida State University
in Tallahassee, Florida; Tulane University in New Orleans, and Louisiana
State University in Baton Rouge, Louisiana, received these contracts in
February 1955* All of these contracts were renewed and research is well
advanced in the second year. The results of this research will be pre-
sented by representatives of each group.
The Fish and Wildlife Service has coordinated the work and pro-
vided liaison between the groups. The staff of the Fishery Technological
Laboratory at College Park, Maryland, has also determined the dry solids,
protein, fat, ash, chlorides, and carbohydrates (by difference) of a
large number of samples of raw shucked oysters collected throughout the
season and in most of the states in the area.
Samples of shucked oysters, as prepared for market by the plants
as well as samples of unwashed oysters shucked from the shell into the
sample can were obtained in most instances. This material has been pub-
lished in Southern Fisherman , Vol. l6, April 1956 and in Commercial
Fisheries Review , Vol. 18, July I956.
A large degree of variability for all constituents was found as
a result of the seasonal, plant process, and geographical differences in
the samples, making interpretation of the results a somewhat difficult
matter .
.Ikk-
An impression of the degree of variability may be obtained from
listing the ranges in average values obtained for the various constituents
with the shell samples only. Dry solids ranged from 7 to 17 per cent, so
for better comparison, all other data have been converted to a dry basis.
Protein on a dry basis ranged from 35 to 65 per cent; fat 5«5 to 15.5 per
cent; mineral matter 5 to 35 pei" cent; chlorides (salt) 2.5 to 29 per
cent; and carbohydrates (by difference) 8.5 to 45 per cent.
The data for shell samples indicated that dry solids and fat in-
creased from low values in September and October to maximum values in
March and April, then decreased rapidly to low summer values during the
spawning season. On the other hand, mineral matter and salt content of
the oyster decreased at a uniform rate from October to a seasonal low in
March and April and increased during the summer months.
The carbohydrate content increased irregularly as the oyster
season advanced, and exhibited quite a marked inverse relationship to
the protein content: when one was low the other was high.
The problems of the southern oyster industry are numerous and
there is no promise of simple or rapid solution. The research groups
have completed the preliminary stages of acquiring familiarity with the
industry, and accumulating basic information concerning its product
and problems. During the coming oyster season they expect to concentrate
to a greater extent on practical phases of the problems and anticipate
results of both interest and value to the industry.
-l45-
INVESTIGATIONS OF THE BODY FLUID AND "BROWN-SPOTTING" OF THE OYSTER
Milton Fingerman and Laurence D. Fairbanks
Tulane University, Louisiana
Since January 1955 the study of oyster biology at Tulane Uni-
versity has been concerned chiefly with the physiology of the body
fluid and the phenomenon of "brown-spotting" in the American oyster
( Qrassostrea virginica).
Several experimental approaches have been utilized in this
study. Physical stimuli such as shucking, wedging open of the shells,
and heat cause considerable fluid losses. As much as hO per cent of the
oyster weight may be lost within 30 minutes after shucking. A compari-
son of oysters in March 1956 from New Jersey and Maryland with oysters
from Louisiana has shown that there is no difference in weight losses
following shucking at this time. In the fall, however, Louisiana oysters
lost 26.6 per cent more body weight than Delaware Bay oysters.
Oysters exposed to heat above kl° C lost body weight progressively
with increase in temperature. Mortality closely paralleled body weight
losses. However, death appeared to be due to the direct effects of heat
and not to any certain percentage weight loss of fluids. No significant
weight loss or death occurred at temperatures below 35° C. Oysters could
be killed by short exposure to high temperatures (^5-55° C) or long
exposure to lower temperatures (^^0-^2° C). Apparently the lethal tempera-
ture varies with the conditions of the experiment.
Elimination of water and conservation of chloride ions are effected
in great extent by excretion of a hypotonic urine through the organ of
Bojanus by way of the pericardium. Determinations of chloride concentra-
tion of fluid from the mantle cavity (shell fluid), mantle tissues
(mantle fluid), pericardial fluid, blood, and fluid from the organ of
Bojanus indicate that the latter fluid generally has a chloride concen-
tration about 18 millimoles per liter below that of any of the other
body fluid components of oysters in estuarine water (chloride concentra-
tions of 2^1 to 270 millimoles per liter). The average chloride con-
centrations of the other fractions of the body fluid generally remain
about the same as that of the environment in the range of 2^1 to 270
millimoles per liter.
Determinations of concentrations of proteinaceous material of
oyster body fluids in June and July I956 showed that the blood has an
average concentration of 1.93 per cent; mantle fluid, I.56 per cent;
pericardial fluid, O.96 per cent; and shell fluid, O.3O per cent. A
correlation between concentrations of chloride ion and proteinaceous
material was evident. Oysters with greater concentrations of protein-
aceous material tended to have greater concentrations of chloride ion.
-IU6-
Average blood cell counts of fractions of the body fluid of
individual oysters are as follows: blood, 1,715 cells per cubic milli-
meter; mantle fluid, 1,048; shell fluid, 535; and pericardial fluid, 3^8.
Centrifugation of the blood cells showed that they constitute no more than
0.10 per cent of the blood and generally much less than this. Apparently
the blood cells contribute very little directly to protein concentration
of the body fluids.
Microscopic observation of histological sections of "brown-
spotted" oyster tissues showed that the "brown-spot" material is composed
of numerous golden brown granules restricted to the epithelial cells of
the mantle. The brown material may be easily scraped from the surface of
the mantle. The pattern of spotting found on the mantle often matches the
pattern of coloration on the inner side of the shell against which that
particulajT part of the mantle lies, suggesting that the colored material
is laid down in the shell by the overlying mantle. The intensity of
coloration on both the mantle and shell ranges from light tan to intense
purple and black. Often the intensity of coloration on the mantle matches
the intensity of coloration on the shell. Sectioning of a shell whose
inner surface is colored may reveal that the coloration extends two to
three millimeters into the prismatic layer from the inner surface of the
shell. There may or may not be deeper layers of pigment, indicating
that the formation of "brown-spot" material need not be a continuous
process.
Oysters receiving implants of "brown- spotted" oyster tissue and
oysters maintained for a week in sea water containing homogenized "brown-
spotted" oyster tissues showed no significant increase of intensity of
"brown-spotting". There seems to be no particular time of year when
"brown-spot" is more frequently found and no particular size of oysters
that is more frequently spotted.
■ Ihl-
RESEARCH ON HAM)LING AND PROCESSING
SOUTHERN OYSTERS
Arthur Novak and E. A. Fieger
Louisiana State University
Baton Rouge, Louisiana
In the first series of experiments extra-select oysters were
frozen. Treatments prior to freezing included the following:
1. Water washed, packed in Marathon cartons with overwrap of
Tyton.
2. Washed with either water or salt solution, packed in
Marathon cartons, and after freezing glazed with water or
salt solution.
3. Washed with water or with salt solution and vacuum packed
in sealed cans.
All samples were stored at F.
Brief summary of results:
1. Rancidity developed in the overwrapped samples after six
months storage, in the glazed samples after eight months storage.
Vacuum packing gave the best product and rancidity was not evident until
after nine months frozen storage. We believe, therefore, six to nine
months is the maximum storage life under the conditions of our experi-
ment s .
No loss of protein or glycogen occurred during frozen storage,
while the pH of the drip and of the meats decreased slowly.
Bacterial counts increased during the first eight months and then
remained constant .
Although the frozen oysters retained a satisfactory flavor during
six to nine months frozen storage, other changes occurred which will have
to be prevented if freezing is to become a satisfactory means of preserv-
ing oysters on a commercial scale.
Detrimental changes:
1. During the first two months of frozen storage the loss in
weight upon cooking increases and after two months storage
fluctuated between 50 and 60 per cent. Accompanying this
change is a pronounced decrease in the size of the cooked
-li+8-
oyster in comparison with cooked oysters which had not been
frozen. We are of the opinion neither the institutional
trade nor the housewife would continue to buy frozen oysters
unless this change in size upon cooking can be greatly
reduced.
2. The second change we noted was the development of a black
to green spot on the body of the oyster. These spots varied
in intensity of color and size and generally after several
months of frozen storage were about the size of a dime.
Upon cooking, these spots remain as dark spots. Again we
believe this condition will have to be corrected before
frozen oysters can be successfully marketed commercially.
3. When frozen oysters are exposed to air, as is the case with
an overwrapped package, or through improper glazing, the
surface of such oysters become lemon-yellow in color, and
when cooked become an intense orange color. Also such oysters
have a definite rancid flavor.
k. A definite darkening of the edges of the mantle occurs during
frozen storage. While not too serious it does decrease the
attractiveness of the product.
5. A small percentage of the oysters developed a pink discolora-
tion which spread out from the edge of the adductor muscle.
We have not been able to associate this discoloration with
yeasts or molds.
6. With increasing length of storage the thawed product becomes
very fragile and must be carefully handled to prevent tearing.
The above results were obtained with extra-select Louisiana
oysters. Similar results are being observed on select Mississippi and
Alabama produced oysters.
In late June we undertook experiments to determine whether it
would be possible to decrease the loss in weight and reduce the shrinkage
upon cooking. It is too early to predict the outcome of this work.
In a brief summary on this phase of the work we can only say we
have shown what detrimental effects must be overcome or solved before a
Batisfactory frozen oyster can be had.
Analysis of Louisiana Oysters Supplied by the
Louisiana Wild Life and Fisheries Coirimission
Samples were obtained monthly from several beds located both
east and west of the Mississippi River. Samples from both high and low
salinity areas were obtained.
-li+9-
A summary of the results follows:
The amount of solids, fat, and glycogen decreased during the
summer and reached a minimum during September -October . With the advent
of cool weather in the fall the amounts of all these constituents in-
creased. The content of the B complex vitamins was quite variable and
decreased slightly in late summer and early fall. The salt content of
the oyster meats was quite variable and tended to parallel the salt
content of the water from which they were dredged. The pH of freshly
shucked oyster meat samples varied between pH 6. 17 and 5»80 and, there-
fore, precludes its use as a test of quality of commercial stored samples.
The Use of Chlorotetracycline for the Preservation
of Freshly Shucked Oysters
Freshly shucked oysters were washed in water or in a solution
containing 10 ppm of the antibiotic chlorotetracycline (aureomycin).
After draining they were placed in pint cans and stored in ice. The
oysters washed in antibiotic had lower bacterial counts from the 8th to
the 15th day of storage than the water washed samples, with extension of
storage life by about five days, or from 10 to 15 days. No loss of B
complex vitamins occurred during I9 days storage for either series of
samples, the pH of the meats decreased progressively with increasing
length of storage.
-150.
OYSTER RESEARCH FROM FLORIDA STATE UNIVERSITY"^
Betty Watts, Harvey Lewis, Mark Schwartz
Florida State University, Tallahassee
I. CORRELATION OF pH AND QUALITY SHUCKED SOUTHERN OYSTERS
The spoilage pattern of raw whole Southern oysters stored at 5°
C has been found similar to that reported for oysters in other locations.
This spoilage is characterized by a gradual and continuous decrease in
pH and the development of a sour odor. A seasonal variation in pH,
initially and after storage, has been observed, with the values being
lowest during the summer (June 6.02) and the highest during the winter
(February 6.38).
The initial pH values of liquors, both after shucking and after
washing, were higher than those of oyster meats. However, the pH of the
liquors fell much faster than that of the meats, presumably because of
the lower buffer capacity of the liquor.
It was possible to produce the characteristic sour odor during
storage with very little or no fall in pH by heating the oysters just
enough to partially inactivate the enzyme catalase.
II. DETERIORATION OF COOKED OYSTERS
The type of spoilage occurring in cooked oysters (immersed in
water at 90-95° C for 2^ minutes) in which the enzyme catalase is com-
pletely inactivated is different from that which occurs in uncooked
oysters. A characteristic "sour" odor develops in uncooked oysters
stored at i+ C. The type of spoilage occurring in cooked oysters stored
at U C appears to be of an oxidative type characterized by a "rancid-
flsh" odor. The addition of various antioxidants, including butylated
hydroxyanisole (BHA), nordihydroguaiaretic acid (NDGA), and commercial
liquid smoke, to the cooking water has retarded this type of spoilage.
Weight losses during cooking were influenced more by length of
cooking time than by any of a number of types of cooking methods used.
Further losses of liquid took place upon subsequent storage (4 c) of
the cooked oysters. The total weight losses of cooked oysters ranged
from 17 to 59 per cent, whereas uncooked oysters held under the same
conditions lost 10 per cent.
1
This report is a brief summary of work reported in greater detail
elsewhere (Gardner & Watts I956, Gardner & Watts 1957^ Schwartz
& Watts 1957, Gardner & Watts, in press).
-151-
III. QUANTITATIVE MEASURE OF RANCIDITY IN OYSTERS - THIOBARBITURIC ACID
TEST
The thiobarbituric acid test has been applied to oysters in an
attempt to establish a rapid objective test for the determination of
oxidative rancidity. This test was selected for two reasons. First,
it can be applied directly to the oyster tissue without the necessity
of extracting the fat. Second, the fat decomposition product responsible
for the test is obtained in much greater amounts from highly unsaturated
fatty acids such as are present in marine fats.
The test measures oxidation products of unsaturated fatty acids.
It depends upon the spectrophotometric estimation of a pink-red compound
produced when the acidified sample is heated in the presence of 2-
thiobarbituric acid.
As measured by this test, refrigerated cooked oysters have a
definite induction period during which the TEA values do not increase
over those for freshly cooked samples. At the end of the Induction
period there is a very rapid increase in the TEA values which corre-
sponds closely with the development of "rancid-fish" odors.
The "rancid-fish" odor, typical of oysters, cooked enough to
inactivate catalase, has been retarded by the addition of an antioxidant
added in sufficient quantity to give a final concentration of 0.1 per
cent butylated hydroxyanisole (BHA) in the cooking water. Other experi-
ments, using a variety of antioxidants on frozen cooked oysters, are
now being carried out.
IV. DEVELOPMENT OF FROZEN PREPARED OYSTER PRODUCTS
A. Fried Oysters
Breaded oysters may be frozen either raw or after frying. In
either case it was found necessary to dip the oysters in a batter before
breading. Direct coating with breading mixtures, without the use of
batters, resulted in poor adherence.
Problems encountered with breaded raw frozen oysters are mainly
concerned with exudation of liquor during preliminary stages of freezing
and during thawing. This results in clumping. The problem of clumping
was less pronounced when the product was subjected to quick freezing
(-30 to -40° C).
The chief disadvantage of the prefried frozen oysters was the
relatively rapid development of an oxidative type of deterioration in
the freezer, resulting in stale or rancid fish odors and flavors within
a few weeks. Experiments on preventive measures for this type of
deterioration are now in progress.
■152-
B. Oyster Stew
The problems encountered in oyster stews are those of excessive
shrinking of the oyster and curdling of the milk.
The use of raw oysters to overcome the excessive shrinkage
problem in frozen oyster stews is presently being explor.-d. A number of
different types of milks, (homogenized, evaporated, and dried) have been
used in an effort to overcome curdling. In the results so far obtained
dried milk yields the most suitable product. Presently, alkaline phos-
phate is being used in an attempt to inhibit undesirable changes.
Past experiments have shown that cooked oysters utilized for
stew yield a tough product, and after a few weeks of storage in the
freezer development of an oxidative type of spoilage results.
V. NUTRITIVE VALUE
Oysters from Apalachicola Bay were assayed for niacin, riboflavin,
and total solids from February 1955 through August 1956. Several relation-
ships between vitamin contents and other factors were found.
Total solids varied from period to period during the study. An
inverse relationship was found between niacin content and total solids
during the siAmmer months. The seasonal changes in niacin values were
almost the inverse of the changes in riboflavin content. Riboflavin
content tended to decrease as spawning activities increased. An increased
need for riboflavin in spawning may account for the decreased storage of
the vitamin during the spring and summer months.
Some factor in oyster homogenate was found to destroy thiamine
during freezer storage. A loss of 6h per cent was observed in two
samples studied for four weeks. This loss is believed to be caused by
the enzyme thiaminase.
Ranges of vitamins present in mg per 100 gm dry matter were
niacin, 6.9 to 15-9; riboflavin, 0.5 to 1.87; and thiamine O.36 to 1.02.
VI. PRESERVATION WITH IONIZING RADIATIONS
Although much investigation of food preservation by cold sterili-
zation through ionizing radiations is now in progress, no one has yet
reported any such investigation with oysters. The present study was
undertaken to determine whetlier or not preservation of oysters can be
effected by radiation treatment. This involved the determination of
whether or not oysters can be irradiated at dosages high enough for
partial or complete sterilization without producing undesirable side
reactions and also the determination of the extent to which souring
and pH changes may be inhibited by irradiation of the oysters.
-153-
Irradiation of rav oysters with sterilizing doses of gamma rays
produced an odor described as "grassy". Neither free sulfhydryl groups
nor catalase activity were noticeably reduced. Subsequent souring and
fall in pH occurred both in irradiated and unirradiated controls.
The irradiation of cooked oysters produced a somewhat different
type of odor described as "oxidized". The off odors were not eliminated
by the addition of various antioxidants and free radical acceptors.
The most acceptable irradiated products from an odor standpoint
were those irradiated raw but subsequently heated sufficiently to destroy
enzymes. The heating eliminated the grassy odor and prevented subsequent
enzymatic souring. However, the small size of samples which could be
irradiated with the limited source available precluded adequate storage
studies.
Literature Cited
Gardner, E. A., and B. M. Watts. 1956. Correlation of pH and quality
of shucked southern oysters. Comm. Fish. Rev. 18 (H): 8.
Gardner, E. A., and B. M. Watts. 1957- Deterioration of cooked southern
oysters. Food Technol. 11: 6.
Gardner, E. A., and B. M. Watts, (in press) Radiation preservation of
oysters. Food Technol.
Schwartz, M. G., and B. M. Watts. 1957. Application of the thiobarbituric
acid test as a quantitative measure of deterioration in cooked
oysters. Food Res. 22: 1.
-I5i^-
ASSOCIATION
AFFAIRS
-155-
ASSOCIATION AFFAIRS
ANmJAL CONVENTION
The 1956 Annual Convention of the National Shellfisheries
Association was held jointly with the Oyster Growers and Dealers Associa-
tion of North America and the Oyster Institute of North America, July
30-August 2, at the Algiers Hotel, Miami Beach, Florida. A special
feature of the program consisted of a "Symposium on the Production and
Utilization of Seed Oysters", and a panel discussion on the "Freezing and
Processing of Southern Oysters". In addition there were two half -day
sessions of contributed papers, the majority of which have been published
in this volume of the Proceedings.
OFFICERS OF THE NATIONAL SHELLFISHERIES
ASSOCIATION FOR THE YEARS
1955-1956, 1956-1957
President
Vice-President
G. Francis Beaven
Maryland Department of
Research and Education
Solomons, Maryland
Melbourne R. Carriker
Department of Zoology
University of North Carolina
Chapel Hill, North Carolina
Secretary-Treasurer
L. Eugene Cronin
Maryland Department of
Research and Education
Solomons, Maxyland
Executive Committee
G. Francis Beaven, Chairman
Melbourne R. Carriker
L. Eugene Cronin
Alphonse F. Chestnut
Philip A. Butler
Harry C. Davis
-156-
COMMITTEE APPOINTMENTS FOR I956-I957
Joint Program Committee ; J. L. McHugh, Chairman; Carl N. Shuster, Jr.,
Robert Dow, Charles R. Chapman, David H. Wallace.
Editorial Committee : Melbourne R. Carriker, Editor (1 year); Thurlow
C. Nelson, Associate Editor (2 years); Jay D. Andrews, Associate
Editor (3 years).
Nominating Committee : Walter Chipman, Chairman; Harold H. Haskin, Carl
n7 Shuster, Jr.
Auditing Committee : Frederick G. Deiler, Chairman, James L. McConnell,
Hugh J. Porter.
Joint Resolutions Committee : J. Richards Nelson, Chairman; Gordon Gunter,
Dexter Haven.
Joint 19^7 Convention Committee : James N. McConnell, and Thurlow C.
Nelson.
Biology-Public Health Relationships Committee: Eugene T. Jensen, Chair-
man; Winston Menzel, Harold Udell, Joseph B. Glancy, Robert L.
Dow, A. F. Chestnut.
Research Committee : (serving jointly with four members of the Oyster
Institute of North America) David H. Wallace, Chairman; John B.
Glude, G. Robert Lunz, Melbourne R. Carriker, Victor L. Loosanoff,
J. G. Mackln.
-157-
EDITORS' NOTES
The cost of typing dupliraat masters for VolLuiies k'^ and U6 of the
Proceedings was borne by the Oyster Institute of North America, and
preparation of plates of illustrations and final publishing of the volumes
was performed by the Fish and Wildlife Service, U. S. Department of the
Interior. The present publication, Volume U7, was handled in the same
manner, except that an improved method reproduction, the "Xerox Process"
was employed.
Some 500 copies of the Proceedings are published each year for
distribution to Association members and to marine laboratories and other
institutions concerned with research in marine biology in the United
States. A number of scientists and institutions abroad have also requested
copies and have been placed on the Association mailing list. This past
year the Secretary-Treasurer of the Association distributed copies of
Vol\ime kG of the Proceedings to 55 libraries in this country and abroad
without charge. This makes the Proceedings available in at least this
many permanent key locations. Papers appearing in the Proceedings are now
regularly abstracted in Biological Abstracts .
The Editorial Committee has functioned smoothly in its task of
reviewing all papers submitted to it for publication in the Proceedings
during the past year. In some cases the aid of additional reviev;ers was
Bought. In most instances papers were returned to authors for rewriting
before final acceptance for publication. We believe this procedure has
materially improved contributions. Proofs were distributed to authors
for final proof reading before publication. Reprints are available to
authors at cost.
INFORMATION FOR CONTRIBUTORS
Scientific papers delivered at the Annual Association Convention
and additional papers submitted by members of the Association will be
considered for publication, in entirety or in abstract form. Papers
appearing in print elsewhere are not acceptable.
Manuscripts will be judged on the basis of the original data,
ideas, and interpretations which they contribute. They will be examined
by the Editorial Committee and by other competent reviewers. Each paper
should be ready for publication before submission to the Editorial Com-
mittee.
Manuscripts should be typewritten and double -spaced; carbon
copies are not acceptable. Tables should appear fiii separate sheets;
most footnote material should be incorporated in i ' .■ text. Scientific
names should be underlined. Use the following sL^,le in lists of litera-
ture citations: "Galtsoif, P.S. 1955* Recent advances in the studies
of the structure and formation of the shell of Crassostrea virginica.
-158-
Proc. Natl. Shellfish. Assoc. 45: II6-I35". Reference to literature
citations in the text should be made as follows: "Loosanoff (1955)".
Abbreviations for the names of serial publications will be patterned
after those employed by Biological Abstracts (for special list see
Biol . Absts . 29(5): v-xxxv, 1955). Abbreviations for units of weight
and measure, and fundamental rules for the use of these, will be
patterned after those given in the Handbook of Chemistry and Physics ,
36th. Edition, pages 3108-313^ • The present publication should be used
as a guide for general format .
Illustrations should be reduced to a size to fit on paper 8 x
lO^- inches with ample margins; photographic copies of high quality are
preferred to originals. Illustrations smaller than page size should be
loosely attached to plain white paper with rubber cement, and the legend
typed in the propei- position under the illustration. More than one
illustration may appear on a sheet. If the illustration is page size,
the legend, properly spaced, should be typed (jn a separate sheet of paper.
No illustrations should appear on text pages.
Every paper should be accompanied by an author's suinmary, com-
plete in itself and understandable without reference to the original
article, for submission to Biological Abstracts by the Editors. Address
all irianuscripts and correspondence concerning editorial matters to the
Editor, M. R. Carriker, Department of Zoology, University of North Caro-
lina, Chapel Hill, North Carolina. All manuscripts should reach the
Editor prior to October 1 for inclusion in the Proceedings of that year.
Masters used in the reproduction of the Proceedings will be
retained for one year. Reprints can be made at cost, expense to be
borne by the author. Authors desiring reprints should communicate
directly with Mr. J. Nelson Callahan, Head, Duplicating Department,
Bingham Y, University of North Carolina, Chapel Hill, N. C.
-159-
TITLES OF OTHER TECHNICAL PAPERS PRESENTED AT THE CONVENTION
Augello, Williajn. The fishery exemption one of your industry's most
valuable possessions.
Engle, James B. Design and function of a suction drill dredge for small
boats.
Glancy, Joseph B. The supply of seed oysters in the New England-New York
area.
Haskin, Harold H. The seed supply in Delaware Bay.
Ingle, Robert M. Florida's potential beckons.
Janowitz, Edward. Further studies in the attraction of Uro salpinx
by oysters.
Mackin, J. G. Effects of graded dosage on infection and rate of
development of fungus disease of oysters caused by Dermocystidium
mar i num .
Mackin, J. G. Miscellaneous new diseases and parasites of oysters.
Menzel, Winston, N. C. Hulings, R. R. Hathaway. Oyster reseeirch in
Apalachicola Bay, Florida.
St. Amant, Lyle S. Some trends in the biological investigations of
various oyster problems in Louisiana.
Udell, Harold F. Handling of southern oysters for sale in New York
market s .
-160-
DIRECTORY OF MEMBERS OF THE NATIONAL SHELLFISHERIES ASSOCIATION
(To March, 1957)
Aldrich, F. A., Assistant Curator of Limnology, Academy of Natural
Sciences, 19th & The Parkway, Philadelphia 3, Pa.
Allen, J. Francis, Department of Zoology, University of Maryland,
College Park, Md.
Andrews, JayD., Oyster Biologist, Virginia Fisheries Laboratory,
Gloucester Point, Va.
Atlantic Biological Station, Fisheries Research Board of Canada, St.
Andrews, N. C, Canada.
Ayers, Robert J., Oregon Fish Commission, 1236 W. Marine Drive, Astoria,
Ore.
Ball, Eric T., 212 Summit Street, New Haven 13, Conn.
Baptist, John P., U. S. Fish & Wildlife Service, Shellfish Laboratory,
Beaufort, N. C.
Beaven, G. Francis, Oyster Biologist, Maryland Department of Research
& Education, Solomons, Md.
Berry, W. R., Bureau of Shellfish Sanitation, 57O9 Sellger Drive,
Norfolk 2, Va.
Blake, John W., Department of Zoology, University of North Carolina,
Chapel Hill, N. C.
Brittain, G. J., Jr., Shellfish Consultant, 56^3 Flamingo, Houston 21,
Tex.
Butler, Philip A., Chief, Gulf Oyster Investigations, Shellfish Laboratory,
U. S. Fish & Wildlife Service, Gulf Breeze, Fla.
Carriker, Melbourne R., Department of Zoology, University of North Caro-
lina, Chapel Hill, N. C.
Carver, Thomas C, Jr., Fishery Research Biologist, U. S. Fish & Wildlife
Service, Gloucester Point, Va.
Chanley, Paul E., Fishery Research Biologist, U. S. Fish & Wildlife
Service, Biological Laboratory, Milford, Conn.
Chapman, Charles R., Fishery Research Biologist, U. S. Fish & Wildlife
Service, Shellfish Laboratory, Gulf Breeze, Fla.
-161-
Chestnut, A. F., Director, University of North Carolina, Institute of
Fisheries Research, Morehead City, N. C.
Chipman, Walter, Director, Fishery Radiobiological Laboratory, U. S.
Fish & Wildlife Service, Beaufort, N. C.
Collier, Albert, Fishery Research Biologist, U. S. Fish & Wildlife Ser-
vice, Fort Crockett, Galveston, Tex.
Cronin, L. E., Director, Maryland Depajrtment of Research & Education,
Solomons, Md.
Currier, Wendell, Ass't. to Vice President, Research & Development,
Campbell Soup Co., Camden, N. J.
Darling, J. S. & Son, P. 0. Box iil2, Hampton, Va.
Dassow, John A., Technological Laboratory, U. S. Fish & Wildlife Ser-
vice, 2725 Montlake Blvd., Seattle 2, Wash.
Davis, Harry C, Fishery Research Biologist, Biological Laboratory,
U. S. Fish & Wildlife Service, Milford, Conn.
Dawson, C. E., Biologist, Bears Bluff Laboratory, Wadmalaw Island, S. C.
Deiler, Frederick G., Biologist, Freeport Sulphur Co., Port Sulphur, La.
Dow, Robert L., Director, Marine Research, Department of Sea and Shore
Fisheries, Vickery-Hill Building, Augusta, Me.
Dumont, William H., U. S. Fish & Wildlife Service, Department of
Interior, Washington 25, D. C.
Dunnington, Elgin W., Oyster Biologist, Department of Reserach & Educa-
tion, Solomons, Md.
Edwards, Malcolm B., Pacific Coast Oyster Growers Association, South
Bend, Wash.
Engle, James B., U. S. Fish and Wildlife Service, Clam and Chesapeake
Oyster Investigations, 800 Dreams Landing, Annapolis, Md.
Fahy, William, University of North Carolina, Institute of Fisheries
Research, Morehead City, N. C.
Fingerraan, Milton, Newcomb College, Tulane University, New Orleans, La.
Florida State Board of Conservation, W. V. Knott Building, Tallahassee,
Fla.
Flower, Frank M. & Sons, Growers of Pine Island Oysters, Bayville, Long
Island, N; Y.
-162-
Fox, Leo, Associate Sanitary Biologist, Department of Public Health,
511 A State House, Boston 33* Mass.
Galtsoff, Paul S., Director, Shellfish Laboratory, U. S. Fish & Wildlife
Service, Woods Hole, Mass.
Ganaros, Anthony E., Fishery Research Biologist, Biological Laboratory,
U. S. Fish & Wildlife Service, Mllford, Conn.
Glbbs, Harold N., A-71 Sowams Road, Barrington, R. I.
Girard, John G., State Department of Health, Smith Town, Seattle, Wash.
Glajicy, Joseph B., Shellfish, Inc., Box 212, West Sayvllle, Long Island,
N. Y.
Glude, John B., Chief, Clam and Chesapeake Oyster Investigations, U. S.
Fish & Wildlife Service, P. 0. Box I5I, Annapolis, Md.
Grice, George D., Fish and Wildlife Service, Juneau, Alaska.
Gunter, Gordon, Director, Gulf Coast Research Laboratory, Ocean Springs,
Miss.
Gustafson, Al, Professor Biology, Bowdoln College, Brunswick, Me.
Hanks, James E., Department of Zoology, University of New Hampshire,
Durham, N. H.
Hargis, William J., Jr., Associate Biologist, Virginia Fisheries Labora-
tory, Gloucester Point, Va.
Harrison, George T., President The Tllghman Packing Company, Tllghman,
Md.
Haskin, Harold H., Director, New Jersey Oyster Research Laboratory,
Department of Zoology, Rutgers University, New Brunswick, N. J.
Haven, Dexter, Virginia Fisheries Laboratory, Gloucester Point, Va.
Hedrick Brothers Oyster Company, 730 Auster City Street, New Orleans, La.
Hewatt, Willis G., Biology-Geology Department, Texas Christian University,
Fort Worth, Tex.
Heydecker, Wayne D., Atlantic States Marine Fisheries Commission, 22 West
First Street, Mount Vernon, N. Y.
Hofstetter, Robert P., Rt . #1, Box I32, La Porte, Tex.
Hopkins, Sewell H., Biology Research Laboratory, Texas A & M Research
Foundation, College Station, Tex.
-163-
Huber, L. Albertson, Hydrographic Engineer, 297 E. Commerce Street,
Bridgeton, N. J.
Hulings, Neil C, Oceanographic Institute, Florida State University,
Tallahassee, Fla.
Jensen, Eugene T., U. S. Public Health Service, Sheilrisn Branch,
Washington 25, D. C
Kahn, Archie M., Executive Director, Texas A & M Research Foundation,
College Station, Tex,
Kelly, C. P^, S;ic-Llfisii Sanitation Laboratory, U. S. Public Health
Servic.-, j.:if Breeze, Fla,
Lamson, P. (1., ''.blisher, "ntiantic Fisherman", Goffstuwn, N. H.
Lednum, J, M., 1o/;n Engineer, Town of Islip, N. Y.
Lester & 'I'oii.:/, .'.nc, c/o Royal Toner, 208 Front Street, Jc-w York 38,
N. y.
Lindsay, (>;cl.'-io. Director, Shellfish Laboratory, Fisheries Department,
Wa!;ui h-^ton State, Quilcene, Wash.
Littlefortl, i;obert A., Seafood Processing Laboratory, Crlsfield, Md.
Loesch, Harold, Marine Biologist, Alabama Department of Conservation,
Bayou La Batre, Ala.
Logie, R. R., Department of Zoology, Rutgers University, New Brunswick,
N. J.
Loosanoff, Vlotor L. , Director U. S. Fish and Wildlife Biological
Labor-alory, Milford, Conn.
Lunz, G. HoborL, Director, Bears Bluff Laboratories, Wadmalaw Island,
S. C.
Mackin, J. G-, Direct.or, Marine Jjaboratory, Texas A & M Research
FourKl,j.tion, Galveston, Tex.
Macomber, Roii-ild, 11 Pi'escott Avenue, Montclair, N. J.
McConnell, James L., P. 0. Box 103^, Bay Toweing & Dredging Company,
Mobile, Ala.
McConnell, James N., Director, Division of Oysters and Water Bottoms,
Department of Wildlife and Fisheries, 126 Civil Courts Building,
New Orleans lb, La.
■It
McHugh, J. L., Director, Virginia Fisheries Laboratory, Gloucester Point,
Va.
Manning, Joseph H., Clam Biologist, Chesapeake Biological Laboratory,
Solomons, Md.
Mansueti, Romeo, Fishery Biologist, Maryland Dept . of Research & Education,
Solomons, Md.
Marshall, Nelson, Dean of Liberal Arts, Alfred University, Alfred, N. Y.
Menzel, R. Winston, Oceanographic Institute, Florida State University,
Tallahassee, Fla.
Nelson, J. Richards, The F. Mansfield & Sons Co., 6lO Quinnipiac Ave.,
New Haven, Conn.
Nelson, Thvirlow C, 8 North Main St., Cape May Court House, N. J.
New Jersey Department of Conservation, Trenton, N. J.
Pellissier, Carroll E., Editor of Fishing Gazette, 46l Eighth Ave., New
York 1, N. Y.
Perlmutter, Alfred, Senior Aquatic Biologist (Marine), D.-J. Fish Research
Unit, New York Conservation Department, 65 West Sunrise Highway,
Freeport, N. Y.
Pomeroy, Lawrence, Marine Biology Laboratory, Department of Biology,
University of Georgia, Sapelo Island, Ga.
Porter, Hugh J., University of North Carolina, Institute of Fisheries
Research, Morehead City, N. C.
Price, T. J., Fishery Radiobiological Laboratory, U. S. Fish & Wildlife
Service, Beaufort, N. C.
Pritchard, Donald W., The Johns Hopkins University, 121 Maryland Hall,
Baltimore 18, Md.
Quayle, Daniel B., Nahcotta, Wash.
Ray, Sammy M., 3127 Avenue R, Galveston, Tex.
Rice, Theodore R., Fishery Radiobiological Laboratory, U. S. Fish &
Wildlife Service, Beaufort, N, C.
Rego, John L., Director, Department of Agriculture & Conservation,
Veterans Meii,orial Building, 83 Park Street, Providence 2, R. I.
Ropes, John W., U. S. Fish & Wildlife Service, 29 Linden Street, Salem,
Mass.
-165-
Ruseeli, Henry D., Springdale Avenue, Dover, Mass.
Sangree, John B., Glassboro State Teachers College, Glassboro, N. J.
Sayce, Clyde S., Fishery Biologist, Box 205, Ocean Park, Wash.
Sellmer, George, Department of Biology, Upsala College, East Orange,
N. J.
Shuster, Carl N., Director, Meirlne Laboratory, Depeirtment of Biological
Sciences, University of Delaware, Newark, Del.
Sleling, Fred W., Department of Research & Education, Box 186, Snow
Hill, Md.
Silliraan, KaJph P., Chief, Section of Anadronous Fish, Interior Department,
U. S. Fish & Wildlife Service, Washington 25, D. C.
Smith, F. G. Walton, Director, The University of Miami Marine Laboratory,
Coral Gables kC, Fla.
Sollere, Allen A., 1305 Park Avenue, Baltimore 17, Md.
Sparks, Albert K., Chief Biologist, Assistant Director, Box 203,
Thibodaux, ia.
Spraguo, Victor, lllawussee, Ga.
St. Amant, Lyle S., Wildlife and Fisheries Commission, 126 Civil Courts
Bull dill;;, New Orieana lb, L-i.
Stern, JoseiJli A., Scliool of Fiuherles, University of Washington, Seattle,
Wach-
Trezlse, William R., Fishery Aide, 318 - 12th Street, Raymond, Wash.
Trultt, Reginald V., Great Neck Fai^m, Stevensvllle, Md.
Udell, Harold, N. Y. Conservation Dexiartment, Bureau of Marine Fisheries,
Freeport, long Island, N. Y.
Virginia Commission of Fisheries, Newport, News, Va.
Wallace, Dana E., Department nf Sea & Shore Fisheries, Vlckery-Hlll
Building, Augusta, Mc .
Wallace, David II., Director, Oyster Institute or North America, 6 Mayo
Avenue, Bay Ridge, Annapolis, Md.
Webster, John R., U. S. KiBh i'. Wildlife Service, P. 0. Box 151, Annapolis,
Md.
-la-
Weiss, Charles M., Department of Sanitary Engineering, School of Public
Health, University of North Carolina, Chapel Hill, N. C.
Welch, Walter R., U. S. Fish & Wildlife Clam Investigations, R.F.D.,
Boothbay Harbor, Me.
Westley, Ronald E., Fishery Biologist, Washington State Department of
Fisheries, Shellfish Laboratory, Quilcene, Wash.
Whaley, Horace H., The Johns Hopkins University, 121 Maryland Hall,
Baltimore 18, Md .
Wilde, Frank W., Box 5, Shady Side, Md.
Woelke, Charles E., Fishery Biologist, Box 323 > Quilcene, Wash.
Wolman, Abel, The Johns Hopkins University, Whitehead Hall, Baltimore
18, Md.
Wurtz, Charles B., 6lO Commercial Trust Building, Philadelphia 2, Pa.
-167-
INT.-DUP. SEC, WASH., D.C. iiit2
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