Drift of sea scallop larvae Placopecten magellanicus on Georges Bank: a model study of the roles of mean advection, larval behavior and larval origin

Abstract The drift and exchange of sea scallop larvae ( Placopecten magellanicus ) on Georges Bank is investigated by tracking particles in three-dimensional flow fields consisting of the semidiurnal tidal current and autumn mean circulation on realistic topography. Three composite flow fields are considered, each forced by non-linear tidal current interactions, seasonal-mean density gradients and seasonal-mean wind stress. The around-bank flow rates are in approximate agreement with the observed residual gyre, while the cross-isobath currents in the flow fields are consistent with observations only in being generally weak. In most cases it is unclear whether the discrepancies arise from observational uncertainties or from model approximations. In the simulations the particles are given the behavior and planktonic period expected of sea scallop larvae. Particle starting positions correspond to the three major scallop aggregations: the Northeast Peak (NEP), the Southern Flank (SF), and the Great South Channel (GSC). Simulations are run to examine the sensitivity of the particle trajectories and settlement numbers to aspects of larval biology (vertical distribution, ascent and descent rates, search times, growth and mortality rates), and to various flow field components. The pattern and extent of larval exchange and settlement are most sensitive to the duration and depth of planktonic drift, gyre strength, weak cross-isobath flow, and mortality rate. The simulations indicate significant larval exchange among the three aggregations, with self-seeding possible for the GSC and NEP, and unlikely for the SF. Given the high retention of particles on Georges Bank as a whole (10–73% before mortality), Georges Bank scallops should be considered self-sustaining.