Summary of the Grand Banks Otter Trawling Experiment (1993-1995): Effects on Benthic Habitat and Macrobenthic Communities
Donald C. Gordon, Jr., Kent D. Gilkinson, Ellen L. Kenchington, Cynthia Bourbonnais, Kevin G. MacIsaac, David L. McKeown, and W. Peter Vass
Abstract. A 3-year experiment was conducted to examine the effects of repetitive otter trawling on a sandy bottom ecosystem at a depth of 120–146 m on the Grand Banks of Newfoundland. Immediate effects were observed on habitat structure. However, these effects were relatively short-lived since the available evidence shows that the habitat recovered in about a year or less. Except perhaps for snow crabs Chionoecetes opilio and basket stars Gorgonocephalus arcticus, direct removal of epibenthic fauna by the otter trawl appeared to be insignificant because of its very low efficiency in catching benthic organisms. Immediately after trawling, the mean biomass of epibenthic organisms (as sampled with an epibenthic sled) was reduced by an average 24%. The most affected species were snow crabs, basket stars, sand dollars Echinarachnius parma, brittle stars Ophiura sarsi, sea urchins Strongylocentrotus pallidus and soft corals Gersemia spp. The immediate impacts of otter trawling on the infauna (as sampled by a large videograb) appeared to be minor and limited to a few species of polychaetes. Significant effects could not be detected on the majority of species found at the study site, including all mollusk species. All available evidence suggests that the biological community recovered from the annual trawling disturbance in a year or less, and no significant effects could be seen on benthic community structure after 3 years of otter trawling. The habitat and biological community at the experimental site are naturally dynamic and exhibited marked changes irrespective of trawling activity, and this natural variability appeared to overshadow the effects of trawling.