Vol. 53 - Alaska Resources Library and Information Services

Estimating an appropriate residence time for shell fragments appears
problematic but a reasonable estimate is possible. Carter and Steele
(1982) found that shell fragments remained in lobster stomachs 90 to 180 d
(2160 to 4320 h). Hill (1976) observed no decrease in the weight of shell
fragments in the stomachs of the crab, Scylla serrata, during 8 days of
observations while soft tissue fell to 5% of its initial level in 12 h and
fishbone, to less than 5% in about 3.5 days (about 84 h). Here barnacle
tissue reached 5% of its initial dry weight at 3.0 x 10[superscript]4
h, i.e., 1250
days. Hard tissue, such as barnacle plates and molluscan shell fragments,
appear to remain indefinitely in crab stomachs. Hill suggests that crabs
regurgitate shell rather than evacuate it into the lower digestive system.
Pearson and Olla (1977) and Pearson et al (1979) have seen captive blue
crab, Callinectes sapidus, and Dungeness crab, Cancer magister,
periodically regurgitate shell when held on an ad libitum diet of blue
mussels. During shipboard holding of juvenile king crab regurgitation of
shell and sand dollar test fragments was observed. These observations
suggest that shell fragments and other hard tissue remain indefinitely in
crab stomachs accumulating to some threshold volume at which point the
crab regurgitates the entire volume. If so, the problem becomes one of
determining the time frame within which the regurgitation will normally
occur. On shipboard juvenile king crabs held without food regurgitated
shell beginning 4 days after capture and continuing each night until the
crabs were used in an experiment at 12 days after isolation. Five crabs
sacrificed 7 days after isolation had no visible shell fragments in their
guts, but dry weights of stomach contents for these individuals were not
determined. Both Hill's (1976) data and that presented here indicate
shell fragments have a longer stomach residence time than fish bone. In
light of the available information, a stomach residence time for hard
tissue such as shell fragments appears to be more than 5.4 days and could
be on the order of 135 days for crustaceans continuing to feed on soft
tissue. The shipboard observations on regurgitation and visual
examination of the stomachs would indicate a residence time between 4 and
7 days. The exponential model would indicate one of 1250 days. The
harmonic mean of these four estimates is 10.7 days. This latter value was
used in corrections for gut residence times.
SHIPBOARD OBSERVATIONS OF FEEDING BEHAVIOR
On shipboard, juvenile king crabs selectively ingested only certain
parts of some prey. Crabs ate the fleshy portions of the shrimp and
juvenile fish, leaving the heads. Similarly, crabs ingested little of the
barnacle plates and mussel shell. Crabs scraped the soft tissue from the
196