Combined video-hydroacoustic survey of nearshore semi-pelagic rockfish in untrawlable habitats

New survey technologies are needed to survey untrawlable habitats in a cost-effective and nonlethal manner with minimal impacts on habitat and nontarget species. Here, we test the efficacy of integrating data from a suspended underwater camera with acoustic data to generate population estimates for nearshore Black (Sebastes melanops), Blue (Sebastes mystinus), and Deacon Rockfish (Sebastes diaconus). We surveyed Seal Rock Reef near Newport, Oregon, and compared our results to population estimates derived from a mark-recapture study conducted at the same reef. We compared fish density estimates from video deployments to those calculated from applying published target strength to length regression models to our acoustics data. Densities derived from the acoustics, using a generalized physoclist target strength to length model, were significantly different from densities derived from video; conversely, a rockfish-specific target strength to length model generated densities that were not statistically different from video densities. To assess whether, and how, fish behaviour was influenced by the presence of an underwater camera, we deployed our camera under the acoustic transducer. No statistical difference was observed in the acoustic density of fish before, during, or after camera deployment. Our work suggests that combining acoustic and stereo video data provided a similar population estimate to historic survey results, but an accurate acoustic density estimate was dependent on using the proper acoustic target-strength model. We contend that combining camera data with hydroacoustic data is effective for surveying rockfish in untrawlable habitats.

Automated summary

This study tests the effectiveness of integrating data from a suspended underwater camera with acoustic data to estimate the populations of nearshore Black, Blue, and Deacon Rockfish. The results show that combining camera data with hydroacoustic data can provide similar population estimates as historic surveys, but accurate acoustic density estimates depend on using the correct acoustic target-strength model.