DRIFT OF SEA SCALLOP LARVAE PLACOPECTEN-MAGELLANICUS ON GEORGES BANK - A MODEL STUDY OF THE ROLES OF MEAN ADVECTION, LARVAL BEHAVIOR AND LARVAL ORIGIN

The drift and exchange of sea scallop larvae (Placopecten magellanicus ) on Georges Bank is investigated by tracking particles in three-dimen sional flow fields consisting of the semidiurnal tidal current and aut umn mean circulation on realistic topography. Three composite flow fie lds are considered, each forced by non-linear tidal current interactio ns, 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 ar e consistent with observations only in being generally weak. In most c ases it is unclear whether the discrepancies arise from observational uncertainties or from model approximations. In the simulations the par ticles are given the behavior and planktonic period expected of sea sc allop larvae. Particle star-ting positions correspond to the three maj or scallop aggregations: the Northeast Peak (NEP), the Southern Flank (SF), and the Great South Channel (GSC). Simulations are run to examin e the sensitivity of the particle trajectories and settlement numbers to aspects of larval biology (vertical distribution, ascent and descen t rates, search times, growth and mortality rates), and to various flo w field components. The pattern and extent of larval exchange and sett lement are most sensitive to the duration and depth of planktonic drif t, gyre strength, weak cross-isobath flow, and mortality rate. The sim ulations indicate significant larval exchange among the three aggregat ions, 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 wh ole (10-73% before mortality), Georges Bank scallops should be conside red self-sustaining.