Tidal-front entrainment and retention of fish larvae on the southern flankof Georges Bank

From a grid of stations across the southern flank of Georges Bank in May 19 97, larval haddock and cod were observed to be concentrated across the tida l front in a band 10-20 km wide. Several cross-bank CTD and acoustic Dopple r current profiler (ADCP) sections indicated a narrow ( < 10 km) but signif icant tidal-front jet with residual currents moving southwest along the 60- m isobath at 10-20 cm/s in the upper water column ( < 35 m), consistent wit h a satellite-tracked drifter that logged a mean residual velocity of 13 cm /s for over a week. The tidal-front jet moved laterally with the strong M2 tide, but generally occurred in the region of maximum cross-bank density gr adient. Evidence is provided for a two-cell secondary circulation pattern, with upwelling flow on the mixed side of the front and a surface convergenc e and downwelling on the stratified side. A surface convergence zone was ob served with drifters and also predicted from a modeled flow field within 10 km of the jet on the stratified side, which generally coincided with the h ighest concentration of larvae. Model simulations, initialized with observe d density structure from a CTD survey, suggest that larvae located in the c onvergence zone could be advected onto the shoals, under the jet in the nea r-bottom ( > 35 m), cross-isobath residual flow (0.6-1.2 cm/s). (C) 2000 El sevier Science Ltd. All rights reserved.