Impacts of Scallop Larva Behavior in the Surface Mixed Layer on Larval Transport and Settlement over the US Northeast Continental Shelf

An individual-based population dynamics model (IBM) of sea scallop was developed and was coupled with the Northeast Coastal Ocean Forecast System (NECOFS). Driven by the NECOFS-assimilated hourly flow and temperature fields, a set of the scallop IBM model experiments were conducted for scallop larvae spawn on Georges Bank over the period of 1978-2013. Two types of experiments were made for the cases with or without inclusion of diel vertical migration of early-stage scallop larvae in the surface mixed layer. The results indicate that timing and location of scallop larva settlement is very sensitive to the behavior in their early stages. Ignoring the thermocline-seeking behavior (without active vertical migration) reduced the resident time of larvae in the water column over Georges Bank and over-predicted larval transport to the Middle Atlantic Bight. Taking the thermocline-seeking behavior into account (with active vertical migration) resulted in a slow horizontal movement of larvae. As a result, the larvae, which were from adults spawning on Georges Bank, mainly circulate with the clockwise residual flow around the bank and eventually settled on the bank, with only a few flowing southwards towards the Middle Atlantic Bight. The connectivity of scallop larvae between Georges Bank and Middle Atlantic Bight varies interannually with variability of vertical stratification and cross-shelf temperature gradients. The model may be used to predict settlement of scallop larvae on Georges Bank and Middle Atlantic Bight, and their possible distribution.