Getting to the bottom of fishery interactions with living habitats: spatiotemporal trends in disturbance of corals and sponges on the US west coast

• Published in: Marine ecology. Progress series (Halstenbek) 2017-07, Vol.574, p.29-47
• Main Authors: Barnett, Lewis A. K., Hennessey, Shannon M., Essington, Timothy E., Shelton, Andrew O., Feist, Blake E., Branch, Trevor A., McClure, Michelle M.
• Format: Article
• Language: English
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps12195

Despite evidence that mobile bottom fishing gear causes physical damage to habitatforming organisms on the seafloor, likely indirectly affecting associated fishes, it is difficult to determine how conservation and management policies influence such effects because researchers do not typically systematically quantify the extent and intensity of gear–habitat interactions. Here, we estimated spatiotemporal trends in bottom trawling in areas containing biogenic habitat (sponges and corals) on the US west coast to evaluate the effect of spatial closures, catch shares, and vessel buybacks. We predicted highest probabilities of biogenic habitat occurrence in moderate to deep depths north of Cape Mendocino and off southern California, and highest gear–habitat interaction frequencies in moderate depths off Oregon and Washington. Temporal trends in total biogenic habitat contacts tracked changes in fishing effort, mostly declining between 2003 and 2014 (declines between start and end year ranged from 51–55% across taxa). However, the predicted frequency of contacts per unit effort increased by 17–56% across taxa from 2003–2009, coinciding with implementation of spatial closures, and our results indicate this was due to effort displacement and shifting spatial distribution of fishing. These relative interaction rates then declined by 10–34% after implementation of catch shares. Thus, although spatial closures may protect habitat within protected areas, without complementary policies, spatial closures may increase gear−habitat interactions in adjacent areas due to changes in fisher behavior and fishing effort displacement.