Juvenile Dungeness Crab (Cancer magister) Recruitment Variability and Oceanic Transport during the Pelagic Larval Phase

Abstract

The influence of environmental variability on Cancer magister year class strength was examined using trawl survey data from the Washington coast, 1983–88. Average June–September estimates of early instar abundance within two coastal estuaries and the adjacent nearshore are compared with alongshore and cross-shelf transport vectors during the preceding 4- to 5-mo pelagic larval phase. Settlement in the study area varied interannually by nearly 40-fold and was inversely related to net alongshore (northward) transport during January–May. Settlement was confined to a relatively narrow band along the coast and in estuaries; new recruits were rarely encountered beyond 46 m depth, corresponding to a distance of ~15 km from shore. We found no evidence for sustained westward Ekman transport to account for progressive seaward transport of zoeae, as proposed by other authors. Rather, persistent landward transport of near-surface waters will tend to minimize advective loss of larvae to seaward while promoting retention in proximity to suitable juvenile and adult habitat nearshore. Temporal and spatial continuity of northward transport during the winter months, coupled with proximity to high-risk areas downstream, suggests that Washington C. magister populations are frequently dependent on larvae originating to the south for recruitment.