Vol. 53 - Alaska Resources Library and Information Services

Using the diel feeding chronologies and the multi-compartmental
exponential decay function for the evacuation of stomach contents, the
daily rations of juvenile king crab were calculated to be 6.30 and 11.92
mg dry weight per g crab wet weight per day in June and August,
respectively.
Using several methods to determine dietary composition gave a more
complete picture of the crab's diet than reliance on one method alone.
Visual examination of stomach contents gave dietary composition by
frequency of occurrence. Measuring dry weights of the hard parts of prey
items and estimating soft tissue intake with appropriate ratios gave a
measure of dietary composition by bulk that was converted to dietary
composition in terms of caloric intake. The immunoassay determined the
extent to which readily digested prey items detectable immunologically
went undetected by visual examination.
Examination of stomach contents alone does not indicate relative
importance in the diet because such examinations are biased in favor of
prey items with long stomach residence times. For the juvenile king crab
correction of dietary composition for gut residence times profoundly
changes the perceived dietary importance of certain prey types. After
correction for gut residence times molluscs and echinoderms, whose hard
parts dominate stomach contents, become of lesser dietary importance
whereas soft bodied polychaete worms become the first-ranking dietary
item. The results indicate that future dietary studies involving crabs
will be obligated to consider and correct for gut residence times. More
experimental effort to determine gut residence times for more prey types
would have been desirable in this study.
For juvenile king crab (CL = 53-80 mm), floc, i.e., unidentifiable
amorphous organic matter, constitutes the major bulk of the stomach
contents. Assuming that this floc derived mainly from prey items whose
hard parts were weighed, and after correcting for gut residence times,
four taxa (two polychaetes, a sand dollar, and a clam) accounted for 92%
of the soft tissue dry weight in the diet. The immunoassay results
supported the reasonableness of the above assumption. Under this
assumption the caloric intakes were 17.5 and 42.2 calories per g crab wet
weight per day in June and August, respectively. Energetically two
polychaetes, Pectinaria sp. and a sabellid, constituted over 50% of the
caloric intake in June and August. The sand dollar, Echinarachnius parma,
constituted 36% of the caloric intake in June but only 2% in August.
Bivalves constituted 3% of the caloric intake in June but 25% in August.
The major bivalve in the August diet was a small, thin-shelled clam,
Tellina sp. Juvenile king crab appear to be predators of small, poorly
motile benthic organisms living at or just beneath the sedimentary
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