Estimating efficiency of a scientific clam survey dredge: Strategies for an improved experimental approach

Objective Fishery stock surveys are used to estimate stock abundance and detect changes over time. The success of fishery-independent surveys can be enhanced by evaluating the capture efficiency of survey gear, which allows for absolute rather than relative estimates of stock abundance. Estimating capture efficiency empirically can be challenging, costly, and time consuming; however, methods to improve experimental success in real time would improve the efficacy and success of these experiments. We evaluated the catch efficiency of a new clam survey platform that was designed for scientific surveys using an experimental approach that provided more information with which to evaluate experimental success in real time at sea. Methods Dredge selectivity was evaluated by direct comparison to an established survey dredge that is used in the federal management of surfclam stocks, and capture efficiency was estimated from several depletion experiments. Results Although the density estimates that were produced by the two gears were similar, the size frequency of the catch differed significantly, with the smaller scientific dredge showing higher selectivity for smaller (<90 mm) and larger (>145 mm) surfclams. Dredge efficiency was estimated to be 0.65, consistent with the efficiency that is estimated for the survey dredge used in federal management. Conclusions These results will support the integration of data that are collected on this new survey platform with previously collected data sets and improve our ability to investigate regional patterns in population dynamics.