Reprint Series No. 3

PADILLA BAY DUNGENESS CRAB, CANCER MAGISTER, HABITAT STUDY

Paul A. Dinnel, Russell 0. McMillan, David A. Armstrong, Thomas C. Wainwright, Anthony J. Whiley, Richard Burge and Richard Baumgarner

1986

Bibliographic Citation
Dinnel, Paul A., Russell 0. McMillan, David A. Armstrong, Thomas C. Wainwright, Anthony J. Whiley, Richard Burge and Richard Baumgarner. 1986. Padilla Bay Dungeness crab, Cancer magister, habitat study. Report to NOAA/OCRM/MEMD by University of Washington, Fisheries Research Institute. 78 pp. Seattle, Washington. Padilla Bay National Estuarine Research Reserve Reprint Series No. 3.

Abstract
Dungeness crabs, Cancer magister, were sampled in Padilla Bay from May 1985 to August 1986 using four sampling methodologies. A small beam trawl was used to sample 19 intertidal and subtidal channel stations. Commercial crab pots modified with small-mesh screen to retain small crabs were fished at a subset of 9 of the trawl stations. Diver transect surveys were conducted side-by-side with some of the trawls in an attempt to quantify the efficiency of the trawls. Finally, intertidal quadrat samples (0.25 m2) were collected along 6 transects in Padilla Bay and 2 transects at March Point.

The results showed that each sampling methodology selected for different size classes of crab. The trawls caught the widest size range of crab but caught relatively few large crab (>140 mm) compared to the crab pots. The pots, however, rarely caught crabs <60 mm in size. Comparisons between diver transects and the trawls indicated that the divers were also missing small crabs. Intertidal quadrat sampling sampled very small young-of-the-year crab very well but rarely caught crabs >3O mm in size.

Habitat preferences for each of the age classes were different. Typically, 0+ (young-of-the-year) crabs (up to about 30 mm size) preferred intertidal or shallow subtidal areas with algae (especially Ulva) or eelgrass cover, although cobble and gravel substrates were also favored with or without plant cover. The 1+ age class (crabs entering their second year of growth) crabs preferred the shallow channels, moving out to the deeper channels as they grew to 2-year-old crabs. Gravid females were essentially absent from Padilla Bay, probably migrating to areas near deep water for mating and egg production.

Historical patterns of Dungeness crab abundances within Puget Sound and near Anacortes show that major fluctuations in abundance can be expected, probably due to natural (but unknown) causes.