MEPS 516:209-227 (2014)  -  DOI: https://doi.org/10.3354/meps10975

ABSTRACT: Sea scallops Placopecten magellanicus on Georges Bank in the northwest Atlantic exhibit semi-annual spawning phenology, where the autumn spawn is dominant and the spring spawn is smaller and more variable. The spring spawn is thought to contribute little to total annual larval settlement on the Bank because fecundity is lower, larval development is slower and off-Bank transport is higher during spring. We tested the hypothesis that larval settlement during spring is negligible compared to autumn by incorporating spatially and temporally explicit information about spawning and larval mortality into a coupled biological-physical larval tracking model to investigate dispersal and connectivity during each spawning period. To accomplish this, we assimilated field data on adult density-at-size and seasonal fecundity-at-size as initial conditions into the model. We discovered that larval production varied in time (spring production on the Bank is half that of autumn) and space (spawners are concentrated along the advective pathway of the along-Bank gyre). Particle settlement and connectivity was reduced, but not negligible, during spring compared to autumn due to stronger dispersal off-Bank and into uninhabitable areas during spring. When mortality was made constant in space and time, lower larval production combined with slower growth during spring resulted in a minimal contribution of the spring spawn to annual settlement. When mortality was correlated with environmental variation in time and space, the spring spawn contributed up to one-third of the total annual larval settlement between the immediate upstream-downstream connected aggregations. We conclude that the spring spawn can make a substantial contribution to total annual larval production, and that settlement on Georges Bank and should be given more attention in field studies. Larval mortality has a strong influence on settlement during spring and autumn, and future field studies should focus on quantifying space and time variation in mortality in relation to the environment.

KEY WORDS: Sea scallop · Placopecten magellanicus · Georges Bank · Connectivity · Larval tracking model