Modelling the transport of lobster (Homarus americanus) larvae and postlarvae in the Gulf of Maine

We used a coupled physical–biological model to examine potential distances between hatching and settlement locations for lobsters in the Gulf of Maine. The physical model is based on a finite-element mesh and climatological averages of the seasonally evolving temperature and density fields. Larval trajectories from coastal and offshore hatching sites (21–224 m deep) were calculated for early, middle and late-season hatching by coupling temperature-dependent development rates and depth (the biological model) to the circulation. Model results showed large spatial differences in larval development times (from 18 to 38 days) and distances transported (19–280 km) for the early hatch. Development time and transport decreased markedly by mid-season at most sites, but strong spatial differences persisted. The eastern Maine coast appears to experience stronger removal and less resupply of larvae than other regions, consistent with observed lower recruitment. Inverse solutions of the model for larvae arriving in mid-coastal Maine indicate that they originate from a broad section of the eastern coast 'upstream', with those nearest the shoreline generally travelling the shortest distances. The postlarval stage is neustonic (living near the surface), and a simple inverse model demonstrates that a diurnal coastal sea breeze can contribute substantially to inshore movement during this final planktonic stage. Thus, offshore reproduction may be linked to inshore recruitment.