Use of oyster shell to enhance intertidal habitat and mitigate loss of dungeness crab (Cancer magister) caused by dredging

Citation

Dumbauld, B. R., D. A. Armstrong, and T. L. McDonald (1993). “Use of oyster shell to enhance intertidal habitat and mitigate loss of dungeness crab (Cancer magister) caused by dredging”. In: Canadian Journal of Fisheries 20, pp. 381-390. DOI: 10.1139/f93-043.

Abstract

Juvenile Dungeness crab (Cancer magister) recruit to intertidal areas in estuaries along the Pacific Northwest coast of the United States in May and June of each year and survive best through their first summer in shell or eelgrass habitat. Experiments were initiated in Grays Harbor, Washington, to investigate the potential of using shell to enhance intertidal crab habitat as a means to augment the crab resource and mitigate losses from the subtidal population that occur during dredging. Experimental plots (225 m2) were constructed prior to crab settlement at each of three intertidal locations using three configurations of oyster shell (heavy layer, light scattering, and small piles of shell). Resulting crab densities were comparable with those found in naturally occurring shell with high numbers (20–60 crab∙m−2) observed during settlement that declined to a relatively stable density of 10 crab∙m−2 in July and August. Crab survival was highest in both heavy and pile configurations, but the heavy shell configuration remained intact the longest. This enhancement experiment has become the impetus for a large-scale (8 ha) mitigation program in 1992 as part of a dredging project completed in 1990 in Grays Harbor.