Interannual variability in coastal Washington Dungeness crab (Cancer magister) populations: larval advection and the coastal landing strip

Abstract

ABSTRACTSubstantial and unexplained variations in abundance characterize US west coast populations of Dungeness crab, Cancer magister. It is likely that this variability reflects oceanic advection of larvae given the dynamics of the California Current system, the protracted (4–5 months) pelagic larval phase and the restrictive nature of juvenile habitat requirements. We compare 40 years of Ekman transport vectors during January‐May (1947– 1986) with time‐lagged and stratified commercial landings for coastal Washington (1951–1990). Persistent landward and net northward flow characterized the circulation of near‐surface waters during the larval periods studied. A mechanism for progressive seaward transport of larvae through ontogeny, as proposed by others, was not apparent. Overall, above‐ (below‐) average year classes were associated with relatively weak (strong) northward transport and, to a lesser degree, strong (weak) landward transport. Based on these analyses and in consideration of the prevailing coastal circulation, we propose that the relative magnitude of C. magister juvenile recruitment and, hence, incoming year class strength, reflects: (1) the proportion of larvae retained within a relatively narrow (≤ 15 km) and heterogeneous ‘coastal landing strip’, (2) the availability of suitable substrate within the coastal landing strip at time of settlement and (3) the magnitude of downstream advective losses (export) of larvae from the California‐Oregon‐Washington coastal system. Based on a consideration of the physics of the California Current system and the larval biology of the species, significant linkage of Dungeness crab populations along the west coast of North America is likely.