Analysis of Bottom Trawling Impacts on Diversity and Community Composition of Benthic Epifauna in Hecate Strait, British Columbia

Bottom-trawl fishing can cause long-term physical effects on marine ecosystems through homogenization of seafloor habitat and subsequent reduction of the structural complexity and species diversity of the benthic environment.  Benthic epifauna such as corals, sponges, and sea pens create living habitat structures and help to maintain the diversity and abundance of numerous commercially important species, thus, there is growing interest in assessing and mitigating the impacts of bottom-trawl gear on seafloor communities. Sustainable fishing practices are also becoming increasingly recognized by organizations such as the Marine Stewardship Council (MSC) and quantitative estimates of fishing gear impacts on seafloor habitat are an important component of eco-certification assessments; however, there are currently no procedures or methods for performing these assessments on Canada's west coast.  Our study creates a framework to assess the regional scale impacts of bottom-trawl fishing practices on the diversity and community composition of benthic ecosystems in Hecate Strait, British Columbia. During a survey of Hecate Strait in August 2010, we used a remotely operated vehicle (ROV) to make video and photographic transects at varying depths that experience varying degrees of disturbance from bottom-trawl fishing.  A subset of still photographs from each transect were analyzed for substrate type and organism abundance with each organism identified to the lowest possible taxonomic level.  To assess the response of habitat-forming benthic communities to differing levels of trawling disturbance, species diversity measures were applied to the abundance data.  Exposure-response models were also created to look at the relationship between the degree of fishing disturbance at a particular area (exposure) and the diversity and composition of communities of sessile benthic foundation species (response).  AMOEBA plots examined the changes in the composition of habitat-forming benthic communities for each categorical definition of trawling intensity.  Results of this research will provide managers with a better understanding of how the diversity of benthic marine ecosystems changes as a result of past and current bottom fishing practices off of the coast of British Columbia.  This information will facilitate changes in current bottom fishing operations and management in order to reduce or remove the impacts to benthic ecosystems.  This study also provides important information necessary to support the eco-certification of the bottom fisheries of British Columbia.