Impacts of mobile fishing gear: The biodiversity perspective

The increasing concern about impacts of bottom trawling, scallop dredging, and other mobile fishing methods has focused primarily on effects on commer cial fisheries, but these fishing activities also act more broadly on benth ic biological diversity. Because the seabed is erroneously envisioned as a featureless, nearly lifeless plain, impacts of commercial fishing gear have long been underestimated. Structures on and in the seabed, including bioge nic structures (reef corals, kelp hold-fasts, shells, tubes, and tunnels), create a diversity of habitat patches. They provide refuges from predation and feeding places for demersal fishes and other species. Benthic structura l complexity is positively correlated with species diversity and postsettle ment survivorship of some commercial fishes. Mobile fishing gear disturbs t he seabed, damaging benthic structures and harming structure-associated spe cies, including commercially important fishes, although some other commerci al fish species can persist where seabed structures have been removed. Bott om trawling is therefore similar to forest clear-cutting, but it is far mor e extensive and is converting very large areas of formerly structurally com plex, biologically diverse seabed into the marine equivalent of low-diversi ty cattle pasture. In contrast with the U.S. National Forest Management Act , which governs use of living resources in federally owned forestlands, the 1996 Magnuson-Stevens Fishery Conservation and Management Act does not pre vent ecosystem "type conversion" and ignores the need to maintain biologica l diversity. Preventing further loss of marine biodiversity and key fisheri es will depend on our willingness to protect marine areas from effects of m obile fishing methods.