Vol. 53 - Alaska Resources Library and Information Services

obtain sufficient weights all the stomachs at a station were pooled into
one sample. Dividing the dry weights of individual prey items by the
total dry weight of all items and multiplying by 100 gave dietary
composition as a percentage of total dry weight. Because floc and sand
proved a substantial proportion of the dry weight, calculations were done
both including and excluding floc and sand.
CALORIC INTAKE
To determine caloric intake the dry weights for each item needed to be
converted to caloric equivalents. However, simple conversion of dry
weights of stomach contents to calories was not possible without an
estimate of the intake of soft tissue. Caloric values are determined on
the soft tissue of marine invertebrates after the shell or other hard
parts have been removed. Because the dry weights of prey items were
determined almost exclusively by weighing hard tissue, such as shell,
estimating the dry weight of soft tissue ingested from the dry weights of
hard parts was necessary before conversion to calories was possible. For
a number of potential prey items collected from the Bering Sea, the soft
tissue was separated from the hard tissue, and both dried at 60 C in tared
containers to constant weight. Soft tissue/hard tissue conversion factors
were calculated by dividing the dry weight of the soft tissue by the dry
weight of the hard tissue. Conversion factors for prey items not
determined experimentally were estimated by their similarity to those
items for which data exists. Floc was assumed to be essentially soft
tissue and assigned a soft tissue/hard tissue ratio of 1.000.
To obtain dietary composition on the basis of soft tissue dry weights,
the dry weight for each prey item was multiplied by its soft tissue/hard
tissue ratio, the resulting soft tissue dry weights summed to obtain a
total, and the percentage of the diet calculated based on that total.
Correction for gut residence time followed the same procedure described
above for dietary composition as percentage of all occurrences.
To obtain the energetic contribution to the diet made by each prey
item, the corrected percentage of diet on the basis of total soft tissue
dry weight was multiplied by the daily ration (mg/g crab wet weight) to
yield the soft tissue dry weight for each item. Then these soft tissue
dry weights were multiplied by the calcric values (calcries/mg dry weight)
to obtain the calcries ingested from each prey item. Caloric values came
either from the literature or from new determinations done on specimens
collected from the Bering Sea. These new determinations of caloric value
were done by standard bomb calcrimetry with benzoic acid standards at
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