Immediate Effects of Experimental Otter Trawling on a Sub-Arctic Benthic Assemblage inside Bear Island Fishery Protection Zone in the Barents Sea
Tina Kutti, Tore Høisæter, Hans Tore Rapp, Odd-Børre Humborstad, Svein Løkkeborg, and Leif Nøttestad
Abstract. Marine epibenthic fauna in a sub-arctic ecosystem have been studied at 100-m depths within the Fishery Protection Zone around Bear Island, Barents Sea. The immediate effects of intensive experimental otter trawling are described. A BACI (Before–After and Control–Impact) design was used to quantify the trawling impact. Replicate samples were collected using a Sneli epibenthic sled equipped with a video camera and an integrated trawl instrumentation positioning system. The benthic assemblage was characterized by a small-scale patchy distribution of the fauna. We found a numerical domination by ophiuroids, polychaetes, bivalves, cirripedes and echinoids, while echinoids and cirripedes dominated the biomass. Trawling seemed to affect the benthic assemblage mainly through resuspension of surface sediment and through relocation of shallow burrowing infaunal species to the surface of the seafloor, and 25 h after trawling, we found a significant increase in the abundance and biomass of a majority of the infaunal bivalves. The number of species sampled remained constant after trawling, as did the diversity based on numerical abundance. However, diversity based on biomass data was significantly higher after trawling. Although multivariate analyses indicated that the composition in the samples taken after trawling were somewhat different from the majority of those taken before trawling, no evidence of dramatic changes in the composition of the fauna due to trawling was found. Almost no dead or broken benthic animals were found in the epibenthic samples.