Developing a two-step fishery-independent design to estimate the relative abundance of deepwater reef fish: Application to a marine protected area off the southeastern United States coast

Reliable data on reef fishes inhabiting the southeastern United States (North Carolina to Florida) continental shelf large marine ecosystem are difficult to obtain; catch quotas and time and area closures limit the collection of fishery-dependent samples. Further, unbiased fishery-independent samples are expensive to collect with conventional fishing gear. Consequently, stock assessments are often data-limited, especially for deepwater reef species. We estimated the relative abundance of deepwater reef fish with a double sampling approach using fisheries acoustics and conventional fishing gear (hook and line and chevron traps). Double sampling occurred within the newly-created Snowy Wreck Marine Protected Area and a nearby control site. Reef fish concentrations were identified by a single-beam Simrad ES60 transceiver with a transducer operating at 38 kHz. Hook and line samples were collected at 73 acoustic events, and chevron trap samples were collected at 20 acoustic events. The relationship between fisheries acoustic data and catch-per-unit-effort (CPUE) data was examined to develop a model to predict species-generic CPUE at unfished locations. Akaike's Information Criteria (AIC) found equal support for linear, exponential, and power relationships between acoustic backscatter and CPUE for each conventional fishing gear. Further model development would be aided by refining acoustic target information and applying complimentary fish sampling gears (i.e., split-beam fisheries acoustics gear, underwater video). Given further development, a double sampling design should be useful to estimate the relative abundance of important deepwater reef species over a wide area of the shelf break off the southeastern United States, utilizing either survey vessels or vessels-of-opportunity to rapidly collect acoustic samples.