From University of Rhode Island
Analysis of impact studies reveals how bottom fishing affects seafloor denizens
Fishing gears used to catch bottom-dwelling fish and shellfish often disturb both the seabed and the organisms living within or on it. The potential impact of this disturbance has become a subject of heated debate because of the widespread use of bottom fishing gear and the ability to visualize its effects with underwater photography. To address this controversy, a team of international scientists, including University of Rhode Island fisheries oceanographer Jeremy S. Collie, analyzed data from a number of separate fishing impact studies and have come to some surprising conclusions. The results of Collie’s meta-analysis, which is the summary of multiple, independent studies to detect general relationships, are reported in a recent issue of the Journal of Animal Ecology. The scientific team found 57 different observations from 39 separate studies on the effects of fishing disturbance on seafloor organisms around the world.
The study reveals that the type of fishing gear used has a significant effect on the degree of disturbance to sediment organisms. Inter-tidal dredging has the most negative impact, followed by scallop dredging and inter-tidal raking. Otter trawling and beam trawling are less negative, which is not surprising as dredges tend to penetrate deeper into the sediments than trawls.
Habitat type was also considered with the most negative impacts occurring in muddy sand and gravel habitats. Surprisingly, the least impact is observed in mud habitats, not sand. The studies revealed that beam trawling in sand habitats has less impact than the other gear types and other habitats. As expected, largest negative impacts occur in biogenic habitats, which are largely composed of relatively slow growing species, such as sponges and corals.
The populations affected by bottom fishing range from corals, sea anemones, lobsters, shrimp, and crabs being most negatively affected, to starfishes and aquatic earthworms being the least affected. While populations respond differently to disturbance, on average none of the effects were positive and no species increased in abundance in response to fishing disturbance.
"Despite our efforts to predict the outcome of fishing activities for existing seafloor communities, we are often unable to determine the original composition of the fauna because data gathered prior to the era of intensive bottom fishing are sparse," said Collie. "This is an important consideration because recent analyses of the few existing historical datasets suggest that larger bodied fish and invertebrates were more prevalent prior to intensive bottom trawling."
Collie’s analysis also considered the species’ patterns of recovery. Recovery of any species was rarely less than 100 days, with most species recovering in closer to 500 days. The most rapid recovery occurs in sand, indicating that the species in this habitat could withstand 2-3 incidents of physical disturbance per year without changing markedly in character. On the other hand, intensively fished areas are likely to be maintained in a permanently altered state, inhabited by organisms adapted to frequent physical disturbance.
The article also cites studies that suggest that recovery rates for sponge and coral habitats off the western coast of Australia may exceed 15 years.
"Our initial theories about how bottom fishing affects species living in the sediments or near the bottom of the ocean are generally supported by this analysis," said Collie. "There are still substantial gaps in the available data that urgently need to be filled."
The study arose from a joint initiative by the International Council for the Exploration of the Sea and the Scientific Committee for Oceanic Research. Other members of the scientific team include Stephen J. Hall of the Flinders University of South Australia, Michel J. Kaiser of the University of Wales School of Ocean Sciences, and Ian R. Poiner of Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO).
Collie has been invited to present the results of this study and his own Georges Bank research at the Second Marine Conservation Biology Symposium in San Francisco on June 22, 2001.
The URI Graduate School of Oceanography (GSO) is one of the country's largest marine science education programs, and one of the world's foremost marine research institutions. Founded in 1961 in Narragansett, RI, GSO serves a community of scientists who are researching the causes of and solutions to such problems as acid rain, global warming, air and water pollution, oil spills, overfishing, and coastal erosion. GSO is home to the Coastal Institute, the Coastal Resources Center, Rhode Island Sea Grant, the Slater Center for Ocean Technology, and the National Sea Grant Library.