Effects of Bottom Trawling on Soft-Sediment Epibenthic Communities in the Gulf of Alaska
Robert P. Stone, Michele M. Masuda, and Patrick W. Malecha
Abstract. The goal of this study was to determine if chronic bottom trawling in some of the more heavily trawled areas in the central Gulf of Alaska has altered soft-bottom marine communities. Spatial distribution and abundance of epifauna were examined at two sites that overlapped areas open to trawling and closed areas where bottom trawling had been prohibited for 11–12 years. Video strip transects of the seafloor were collected at each site from a manned submersible. Transects were bisected by the boundary demarcating open and closed areas. The positions of 155,939 megafauna were determined along 89 km of seafloor. At both sites, we detected general and site-specific differences in epifaunal abundance and species diversity between open and closed areas, which indicate the communities in the open areas had been subjected to increased disturbance. Species richness was lower in open areas. Species dominance was greater in one open area, while the other site had significantly fewer epifauna in open areas. Both sites had decreased abundance of low-mobility taxa and prey taxa in the open areas. Site-specific responses were likely due to site differences in fishing intensity, sediment composition, and near-bottom current patterns. Prey taxa were highly associated with biogenic and biotic structures; biogenic structures were significantly less abundant in open areas. Evidence exists that bottom trawling has produced changes to the seafloor and associated fauna, affecting the availability of prey for economically important groundfish. These changes should serve as a “red flag” to managers since prey taxa are a critical component of essential fish habitat.