Reprint Series No. 14

FISH PREDATION ON DUNGENESS CRAB IN PADILLA BAY, WASHINGTON

Paul A. Dinnel, Janet A. Armstrong, Robert R. Lauth Karen Larsen and David A. Armstrong and Stephen Sulkin

 

December 1990

Bibliographic Citation
Dinnel, Paul A., Janet A. Armstrong, Robert R. Lauth, Karen Larsen, David A. Armstrong and Stephen Sulkin. 1990. Fish predation on Dungeness crab in Padilla Bay, Washington. Report to NOAA/OCRM/MEMD by University of Washngton, Fisheries Research Institute (FRI - UW - 9001). 69 pp. Seattle, Washington. Padilla Bay National Estuarine Research Reserve Reprint Series No. 14.

Abstract
Dungeness crab, Cancer magister, and marine fish were sampled in Padilla Bay, Washington, from June 1987 through September 1988 using a variety of sampling gear. Dungeness and related crab species were sampled with a 3-m beam trawl on 7 occasions at 9 stations (3 each, intertidal eelgrass, subtidal eelgrass and subtidal channel) during an annual period and with shovel and screen at 2 intertidal stations. The resulting data on crab abundance and distribution have been added to a long-term data series on Dungeness crab to help define relationships between juvenile yearclass strengths and future fisheries. Marine fish were sampled by beam trawl, trammel net and beach seine. Forty-one species of fish were collected, 12 of those being previously unreported for Padilla Bay. Stomach content analyses of 18 species of fish indicated that only staghorn sculpin, Leptocottus armatus, had an index of relative importance greater than 3% for crab. The diets of sculpin were variable but reflected a preference for amphipods, isopods and crabs. Pea crabs (Pinnixa spp.) were the foremost crab prey item, and megalopae and juvenile Dungeness crab accounted for <1% of the average diet. Staghom sculpin showed a gradual shift in feeding preferences with growth, switching to larger prey, including fish, at lengths of >120 mm. Laboratory studies of sculpin feeding on Dungeness crab showed that 70- to 90-mm sculpin could consume crab megalopae at an average rate of 17 megalopae/day under controlled lab conditions. Similar tests showed that 88- to 102-mm fish could consume an average of 15 new juvenile crab/day, and that larger sculpin preferred to feed on larger crab (up to 37 mm carapace width). Gut evacuation experiments showed that sculpin digested meals at the rate of about 50% in 12 h and 95% in 48-72 h, depending on size of fish and its meal.