Vol. 53 - Alaska Resources Library and Information Services

juvenile king crabs may depend on clams, especially Spisula polynyma, to a
greater extent than data here indicate. First, juvenile king crabs were
directly observed scraping the flesh from bivalve shells rather than
ingesting shell along with the flesh. Secondly, whereas most of the shell
of small clams, such as, Cyclocardia cebricostata were observed in the
gut, only bits of the shell margin of Spisula polynyma were found.
Thirdly, the immunoassay detected Spisula sp in the stomachs of the larger
juveniles where visual examination did not. Given the rapid clearance
rate for clam soft tissue determined in shipboard experiments and the
three considerations above, the contribution of Spisula to the crab's diet
is probably underestimated here.
COMPARISON OF VARIOUS METHODS FOR DETERMINING DIETARY COMPOSITION
For the June, August, and overall diets of juvenile king crab (CL = 53
to 80 mm) comparisons of dietary composition determined by visual
examination, dry weights and caloric intake appear in Tables 31, 32, and
33. The major problem in all estimates of dietary composition from
stomach analysis is that what is found in the stomach is not directly
representative of what occurs in the diet. Corrections done here were
designed to estimate the relative contribution of prey items to the diet
rather than just to the contents of stomachs.
The findings here agreed with Hyslop (1980) that the frequency of
occurrence method gives only a crude qualitative view of dietary
composition, suffers greatly when food items are not readily identifiable,
and is not an indicator of the amount or bulk of food consumed. Perhaps
the most fruitful way to view the frequency of occurrence data is to see
it as indicating whether a given prey is consumed by most, some, or only a
few of the juvenile crab population.
In contrast to the frequency of occurrence method, the gravimetric
approach using dry weights, although more tedious and time consuming,
gives the best indication of the amount of food consumed and is necessary
for determination of caloric intake (Hyslop, 1980). In interpreting the
relative importance of prey items in the diet, more credence was given to
rankings of dietary importance based on dry weights and calories than
those based on frequency of occurrence.
Perception of what prey were most important changed after correction
for gut residence times, estimation of soft tissue dry weights and
conversion to caloric equivalents. The major effect of such corrections
was to show that, excluding floc, molluscs and echinoderms dominate
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