A vessel-deployed passive postlarval collector to assess settlement of the American lobster Homarus americanus

Passive collectors are used widely in postlarval settlement and recruitment monitoring of spiny lobsters and crabs, but they have only been used in a limited way with clawed lobsters. For nearly two decades, diver-based suction sampling has served to monitor spatial-temporal patterns of American lobster (Homarus americanus) postlarval settlement and early juvenile abundance in shallow near-shore nurseries. Collectors could reveal settlement patterns in zones beyond the practical limits of diving. In 2005, we launched a fisher-scientist collaboration to evaluate the performance of passive collectors designed to extend the reach of sampling, and to be deployable from a vessel equipped with a standard pot-hauler. Building on previous designs, our collectors comprised wire mesh trays lined with fine screening on the floor and walls and filled with cobble to simulate natural nursery habitat. Results indicate that no newly settled lobsters were lost during the retrieval process, and densities of young-of-year lobsters found in the collectors were similar to those in directly adjacent natural cobble habitat sampled by divers with suction samplers. The collectors also proved to be effective samplers of juvenile fish and crabs, suggesting a possibility for wider application. This success bodes well for expanded deployment of cobble collectors to broaden our understanding of the recruitment processes of lobster and other cobble-dwelling fauna along the coast of New England, United States and Atlantic Canada.