I

STOMACH CONTENTS

OF THE BERING SEA KING CRAB

SPECIAL SCIENTIFIC REPORT-FISHERIES Na 291

UNITED STATES DEPARTMENT DP THE INTERIOR
FISH AND WILDLIFE SERVICE

SPECIAL NOTE

The North Pacific Fisheries Commission, established in 1953
by the International Convention for the High Seas Fisheries of the
North Pacific Ocean, coordinates the research of the member nations:
Japan, Canada, and the United States. The resulting investigations
provide data to the Commission for use in carrying out its duties in
connection with fishery conservation problems in the'-North Pacific
Ocean. Publication of this scientific report has been approved by the
United States Section of the Commission.

United States Department of the Interior, Fred A. Seaton, Secretary
Fish and Wildlife Service, Arnie J. Suoraela, Commissioner

STOMACH CONTENTS OF THE BERING SEA KING CRAB

by

Patsy A. McLaughlin and James F. Hebard
Fishery Research Biologists
Bureau of Commercial Fisheries

Contribution No. 6 to research conducted with
the approval of the United States Section of the
International North Pacific Fisheries Commission,

United States Fish and Wildlife Service
Special Scientific Report — Fisheries No. 291

Washington, D. C.
April 1959

The Library of Congress catalogue card for this publication
is as follows:

McLaughlin, Patsy A

Sloniacli contents of the Bei'inp Sea kinp ci'ab, by Patsy
A. McLaughlin and James F. Hebard. Washington, I^. S.
Dept. of the Interior, Fish and Wildlife Service, 1959.

ii, 5 p. illus., map, tables. 27 ciii. (U. .S. Fish and Wildlife
Service. Special spientific report — fi.sherips, no. 29] ) ,

"Contribution no. 6 to research conducted with the approval of
the United States Section of the International North Pacific Fisheries
Commission."

Bibliograpliy : p. .5.

1. Paralithodes camtschatica. i. Hebard, James F., joint author.
II. Title. (Series)

rSHll.A335 no. 291] Int 59-64

U. S. Dept. of the Interior. Library

for Library of Congi-ess

The Fish and Wildlife Service series, Special Scientific
Report — Fisheries, is catalogued as follows:

U. S. Fish and Wildlife Service.

Special scientific report : fisheries, no. 1-
[Washington, 1949-

no. illus., maps, diagrs. 27 cm.

Supersedes in part the Service's Special scientific report.

1. Fisheries — Research.
SH11.A335 639.2072 59-60217

Library of Congress

11

aXOMACH CONTENTS OF THE BERING SEA UNG CRAB

by

Patsy A. McLaughlin and James F. Hebard

U. S. Fish and Wildlife Service

Seattle, Washington

ABSTRACT

This preliminary study of the stomach contents of Bering Sea king crabs indicates that the major
food items of these crabs are molluscs and echinoderms. The frequent occurrence of echinoderms in the
stomachs in large amounts is in contrast to the findings of Russian workers who feel that echinoderms
play only a very minor dietary role ia the king crabs of the Kamchatka region. Differences in food pre-
ferences apparently do not exist between the sexes.

This report is the result of the
cinalysis of king crab stomachs collected
during the summer of 1957 in southeastern
Bering Sea by biologists of the King Crab
Investigation of the U. S. Fish and Wildlife
Service. A study of the food habits of the
crab is of considerable importance because
food availability and utilization may play
important roles in the distribution, migra-
tion, and molting patterns of the crabs.

Very few reports on the food habits
of the King crab, Paralithodes camtschatic
(Tilesius), are found in the literature.
Among the available papers, the work
of C. F. Feniuk (1945) is the most
recent and perhaps the most complete.
For the most part, his methods were
used in this analysis. Quantitative
studies on the species of food of
the crab are made exceedingly diffi-
cult because, in contrast to fish
which for the most part swallow food
whole, the crab breaks up his food
with the chelae before ingesting it;
hence reconstruction of individual
organisms is usually impossible.
Methods which are used in quantita-
tive food studies of vertebrates
which masticate their food are not
adaptable to the food studies of
crabs, since the quantity of crab
stomach contents is usually small.
As yet, no suitable method of quan-
titative analysis of these stomach
contents has been devised.

Because of this lack of an
applicable method, the smallness of
samples from any one area, and the
limited scope of available related

data, this report intends primarily to
indicate the types of organisms which con-
tribute to the diet of the crabs, however
it will show quantitatively the fullness of
the stomachs examined. More intensive
studies designed to compensate for the in-
adequacies noted here will be pursued in
1958.

The crabs from which stomach samples
were taken were from catches made by the
chartered trawler Mitkof during the months
of June and July 1957 (fig. 1). Of the 329
stomachs obtained, the sexes were almost

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\ ;

SOUTHEASTERN
BERING SEA

.O^Vl

««•>

PACIFIC OCEAN

Hgure 1. — Stations at which stomach samples
were taken during 1957.

equally represented — 160 females and 169
males. Sizes ranged from 63 mm. to 193 ram.
in carapace length. All types of presently
recognized shell conditions were also re-
presented, as the Scimples varied from newly
molted, soft-shelled crabs to those having
bcirnacle-encrusted very old shells. The
majority of the crabs, however, possessed
hard new shells indicating a molt within
the season.

Anatomically, the stomach of the king
crab is divided into two sections, referred
to as the cardiac and pyloric sections.
(Marukawa 1933). This conventional nomen-
clature will be used in this report. How-
ever, as pointed out by Pearson (1908),
these terms may technically be misnomers
when applied to the Malacostraca since the
cardiac section of the stomach is farthest
from the heart, and lies under the region
of the carapace defined as the gastric re-
gion (fig. 2) by Marukawa. Figure 3 shows
the position of the stomach, with relation
to the carapace and the rest of the body.

in 4 percent formalin in an individual
cloth bag. The pyloric section and the
intestine were not used in this study.
Anatomically the cardiac section of the
stomach is divided into two parts. The
anterior part, which comprises the largest
area of the entire stomach, is guarded at
its entrance by a hairy filter and at its
exit by the teeth of the gastric mill.
The smaller part of the cardiac stomach
lies between the teeth of the gastric mill
and the pyloric valve which is the entrance
to the pyloric section of the stomach.
When the stomach is filled to maximum capa-
city in both sections, the ratio of the
amount of food in each of the three parts
is 6:2:1 respectively (Feniuk 1945). Each
percentage of fullness was assigned a coded
index (table 1). Each part was considered
individually and the fullness estimated
visually:

Table 1. — Code for relative fullness
of stomachs.

The cardiac section of the stomach
was dissected out of each crab and preserved

Percentage of
fullness

Index (k„)

Figure 2. — Carapace of king crab (after
Marukawa) G.R. , Gastric region; C.R. ,
Cardiac region; B.R., Bramchail region.

Empty
Trace of food

1-20
21 - 40
41 - 60
61 - 80
81 -100

0
1
2
3
4
5
6

In order to eliminate variations due
to the different sizes of the parts of the
stomach, a common index of K^. was obtained
for each part by multiplying its index of
fullness (kx) by its factor taken from the
ratio of the parts to the whole. The total
K factor represents the sum of the Kx fac-
tors, i.e., K = 6kj^ + 2k2 (+ lk3 not used
in these samples). With the entire cardiac
stomach filled to maximum capacity, the
maximum K obtainable in our samples if 48
units. The percentcige of fullness of the
stomach, both parts considered, is thus
calculated from this K factor. The quan-
tity of food present in the stomachs varied
considerably; however, only 7.6 percent of
the stomachs were found to be completely
empty. Table 2 shows the distribution of
stomach fullness.

Cardiac region of carapace

Post cardioc stomoch

Anf. cordioc stomach

Gostric region of carapace

«^

«?<^

Figure 3. — Left side of sagittal section of a king crab.

Table 2. — Distribution of stomach fullness
in 329 crabs.

Stomach fullness

Upper
limit of K

Equivalent
percentage

Number of crabs
(in percent)

0

Empty

7.6

8

Trace

14.4

16

1-20

42.7

24

21 - 40

18.6

32

41 - 60

10.0

40

61 - 80

4.9

48

81 -100

2.4

The contents of each stomach were
examined microscopically. Although the
components occasionally were completely
unidentifiable masses of torn tissues, for
the most part, relatively large pieces of
recognizable materials were present in the
cinterior part of the cardiac stomach: for
example, pelecypod shell fragments, legs
and dactyls of crabs, gastropod shell frag-
ments and opercula aind legs of brittle
stars. Occasionally, complete individuals
were found — among these, small brittle
stars and amphipods were the most common.
Remains in the posterior part of the car-
diac stomach were often still recognizable
but were more finely broken from the action
of the teeth of the gastric mill. Because
no bottom fauna from the sampling area was

collected or available for species identi-
fication and comparison with organisms pre-
sent in the stomachs, these organisms in
most cases were identified only to the class
or order level. We express our appreciation
to Dr. Paul Illg of the Department of Zool-
ogy of the University of Washington for his
verifications of many of our identifications
of the food organisms. Remains of organisms
which apparently, because of decomposition
rather than digestive action, had been dead
prior to being ingested by the crabs, as
well as the remains of animals which were
alive prior to capture, were found in the
stomachs .

In addition to the estimation of per-
centage of fullness, tabulations were made
of the frequency of occurrence of the majox
food groups. In the determination of this
frequency, each food group present in a
stomach, even when represented by several
organisms, was considered to have had an
occurrence of one.

Among the food groups represented,
molluscs, present in 69.0 percent of the
stomachs examined, are the major food item —
pelecypod remains dominating those of gas-
tropods. Echinoderms rank second, appearing
in 42.2 percent of the crabs. Representa-
tives of the phylum include asteroids,
ophiuroids, and echinoids of the sub-order
Clypeastrina. In contrast to reports in the
available literature, no regular echinoids
(Hyman 1955) were present. This lack may
be only coincidence, as regular echinoids
are most commonly found in rocky areas, and
the majority of our samples were not taken
from these areas. The third most abundzint
food group is the decapod crustaceans, which
were present in 22.8 percent of the stomachs,
primarily represented by the sub-order
Reptantia. Other groups in the order of
their abundaince include polychaete worms
(17.5 percent), algae (14.3 percent, crusta-
ceans, excluding decapods, (16.0 percent),
and coelenterates (3.0 percent). Foramini-
fera, nematode worms, tunicates, echiuroids ,
fish and other groups were present occasion-
ally but not often enough to be considered,
on the basis of present information, foods
of any relative importance. Possibly these
organisms in some instances had been carried
into the crab stomachs as food of other food
organisms.

present in many of the stomachs. At least
with regard to king crabs of southeastern
Bering Sea, this causes us to question his
proposition that algae occur only as a food
of other organisms. Sand, which appeared
in practically all of his samples, was pre-
sent only occasionally in our samples, thus
leading us to believe that sand may not be
a chosen item, but rather one of coinci-
dence. Also, Feniuk's report indicates
that the echinoderms play only a minor role
in the diet of the king crab of the Kam-
chatka region, which is in contrast to our
data on the southeastern Bering Sea crabs.

Our study, like Feniuk's, shows that
the sexes exhibit no food preferences.
Table 3 gives the percentages of frequency
of occurrence of food groups for males and
females .

Table 3. — Frequency of occurrence of food
groups in 169 male and 160 female crabs.

Percentage

of

frequency

Food group

of occurrence

Male

Female

Mollusca

76.9

60.6

Echinodermata

48.5

35.6

Decapod crust acea

Polychaeta

Algae

Other Crustacea

26.0
18.3
12.4
11.8

19.4
16.9
16.3
15.6

Coelenterata

0.5

5.6

Contrary to the findings of Feniuk,
we found relatively large amounts of alga

ae

Chi-square tests show no statistically
significant differences in the frequency of
food group occurrence between the sexes
with the exception of the Coelenterata, and
this exception cannot be considered reli-
able because of the smallness of the sample.
Limitations of this preliminary study pro-
hibit further comparison of food preferences,
if any, exhibited by newly molted crabs and
crabs approaching the molt, or by various
size groups of crabs.

SUMMARY

It appears that the major food items
of the southeastern Bering Sea king crabs,
of the sizes studied, are molluscs and
echinoderms. On the basis of sex, these
crabs do not seem to show a differential

preference for particular food items. This
preliminary study indicates that a number
of differences in feeding habits exist be-
tween the southeastern Bering Sea king crabs
jind those of the Kamchatka region. More
complete studies are planned to answer the
many remaining questions pertaining to the
food habits and needs of the king crab.

FENIUK ,
1945.

LITERATURE CITED

Analysis of stomach contents of
Kamchatka Crab. (In Russian)
Tikhookeanskii nauchno-isslodo-
vatel' skii institut rybnogo
khoziaistva i okeanografii (Bladi-
vostok), Izvestia, Vol. 19, pp.
71-78.

HYMAN, LIBBIE H.

1955. The invertebrates: Echinodermat a.
Vol. IV, McGraw-Hill Book Co.,
763 p.

MARUKAWA, H.

1933. Biological and fishery research

on Japanese king-crab Paralithodes
camtschatica (Tilesius). Journal
of the Imperial Fisheries Experi-
mental Station (Tokyo), No. 4,
(Paper 37). 152 p.

PEARSON, JOSEPH

1908. L.M.B.C. Memoirs on typical Bri-
tish marine plants cuid animals.
XVI. Cancer. Liverpool Marine
Biology Committee. London,
Williams and Norgate. 209 p.

INT.DUP. ,D.C.59- 55815

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