A Spatially Explicit Open-Ocean DeLury Analysis to Estimate Gear Efficiency in the Dredge Fishery for Sea Scallop Placopecten magellanicus

Abstract

The translation of survey data into estimates of absolute abundance hinges on the availability of an accurate estimate of gear efficiency. In many fisheries, however, a wide range of estimates exists and research directed at quantifying this critical parameter has focused on relatively small, fishery-independent data sets. In the present study, a technique was developed to utilize the copious amounts of data available from an open-ocean fishery for sea scallops Placopecten magellanicus in a spatially explicit depletion model. In June 1999, Georges Bank Closed Area II was opened to the commercial scallop fleet after a 5-year multispecies fishing ban. During the 5-month opening, the spatial distribution and magnitude of fishing effort was tracked through vessel monitoring systems, and a relatively small but still substantial number of catch observations were made aboard vessels from the commercial fleet. A spatial analysis of both catch and effort data was utilized to select areas consistent with the assumptions of a DeLury analysis. Maximum likelihood estimation was then used to generate a single estimate of the catchability coefficient (and thus efficiency), while simultaneously estimating the initial abundance in each area. The gear efficiency of the New England-style scallop dredge used during the fishing season was estimated to be 42.7%. A sensitivity analysis of model results shows a potential range of 35.5–52.5%, depending on model assumptions.