A vessel‐deployed passive postlarval collector to assess settlement of the American lobsterHomarus americanus

Abstract

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 fisherscientist 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.

The geography and bathymetry of American lobster benthic recruitment as measured by diver-based suction sampling and passive collectors

“…Each collector is fitted with a bridle to permit lifting in a horizontal position, which is important to retaining collections during retrieval. In previous pilot studies, we demonstrated that losses of organisms were negligible when the collectors were retrieved in this way (Wahle et al 2009b). Once on deck, the wire mesh covers are removed from the collectors.…”

“…Collectors were primarily designed to evaluate lobster settlement in locations that are either unsafe or impractical for diver sampling, although they have become the preferred sampling device, even in shallow water, in some regions. Details of their design and method of deployment are provided in Wahle et al (2009b). Collectors are made of 10-gauge vinyl-coated wire with a 38-mm (1.5 inch) mesh.…”

“…Passive, vessel-deployed postlarval collectors were recently developed as an alternative to suction sampling (Wahle et al 2009b). Collectors were primarily designed to evaluate lobster settlement in locations that are either unsafe or impractical for diver sampling, although they have become the preferred sampling device, even in shallow water, in some regions.…”

“…Our aim here is to describe patterns of young-of-year and older juvenile lobster abundance along the coast, and by depth, using the two quantitative tools currently in use within the collaborative programme: diver-based suction sampling and passive postlarval collectors. We also use this opportunity to build on our previous preliminary studies (Wahle et al 2009b) comparing the performance and size-selectivity of the two methods, and evaluating species interactions in collectors that may bias abundance estimates.…”

“…In a cooperative research project with the US lobster fishing industry in 2005, vessel-deployed passive postlarval collectors, consisting of wire mesh trays filled with cobble, proved to be a viable alternative to suction sampling as means of quantifying lobster settlement (Wahle et al 2009b). Collectors, therefore, provided the opportunity to evaluate settlement in locations that were either unsafe or impractical for divers.…”