Northern quahog (Mercenaria mercenaria) larval transport and settlement modeled for a temperate estuary

Evaluating marine species' population connectivity through larval transport can provide insight into the reliance of geographically separated areas on each other's recruitment and metapopulation resiliency. Using larval transport modeling, we assessed the significance of different regions in supporting the Narragansett Bay Northern quahog (Mercenaria mercenaria) population. We aimed to identify how areas with varying adult quahog biomass and implemented management strategies (based on water quality and commercial harvest) contribute to the overall stock's larval supply. Larval trajectories were modeled by integrating the currents from a realistic physical circulation model with quahog larval behavior applied to particles during spawning periods of 2006, 2007, and 2014. Modeled larval transport suggested that settlement occurs throughout Narragansett Bay, with 35% of spawned larvae swept out of the Bay to the coastal ocean and leaving the stock bounds. Quahogs in areas where shellfishing is prohibited due to water quality concerns produce a significant portion of the Bay's spawned larvae, theoretically serving as de facto spawning sanctuaries. The Providence River, located at the head of the Bay with high mature quahog biomass and currently closed to fishing due to water quality, is a significant source of quahog larvae for the stock. Simulated larval quahog settlement locations corresponded predominantly to sandy bottoms, with less spatial correspondence to commercial fisheries landings. Our work provides insight into the population connectivity of quahogs in Narragansett Bay and highlights the importance of considering oceanography and species' life history characteristics when constructing effective fisheries management plans.