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Effects of Trawling and Dredging on Seafloor Habitat
entine et al., 2001; Wakefield et al., 1998) but even these are small relative to the areas involved in many fishery management decisions. In general, habitat maps have been compiled only on an ad hoc basis for small areas. This is due partly to the lack of an accepted classification scheme for seafloor habitats in the United States.
Several classification systems have been proposed (Allee et al., 2000; International Council for the Exploration of the Sea, 2001; Roff and Taylor, 2000). These systems are hierarchical: they start at a large scale (1000 km) consisting of permanent physical features and scale down to microhabitat. Each system includes enduring physical features of the environment, such as bottom relief, substrate, temperature, stratification, and exposure. Natural physical features are relatively stable over time and can be measured with broad-scale surveys. Physical features alone, however, do not define habitat. Biologic features, the presence of seagrass beds, kelp forests, and coral reefs, for example, also define habitats.
World Wildlife Fund Canada has sought to apply the concepts of terrestrial habitat mapping to Canadian marine waters (Roff and Taylor, 2000). The Canadian classification scheme is based on enduring physical features of the environment. It is especially important to use physical features compatible with broad-scale surveys in Canada and the United States because of the very long coastlines. The rationale is to delineate relationships between biologic community composition and physical variables that can be measured more readily over large areas. This World Wildlife Fund approach has been used to identify representative and distinctive habitats off the coast of Nova Scotia, and it is being used by the Conservation Law Foundation to characterize habitats in the Gulf of Maine.
A parallel approach has been taken to map and classify marine habitats in European waters. The European Nature Information System (EUNIS) has been developed for the European Environment Agency (International Council for the Exploration of the Sea, 2001). European marine habitats are defined by geographic, abiotic, and biotic features, whether entirely natural or partially modified. This broader definition recognizes that habitats can be defined by biogenic features and that marine habitats have been shaped by human activities (e.g., artificial reefs and shipwrecks). The EUNIS classification has five hierarchical levels (Box 4.1).
The difference between the Canadian and European
Box 4.1European Nature Information System Classification
The European Environmental Agency has been developing a common parameter habitat classification framework for marine and terrestrial systems. This forms an integral part of EUNIS. The marine component was derived from the BioMar project (Connor et al., 1997) and has five basic levels, based on the following criteria: 1) marine and coastal habitats versus freshwater and terrestrial habitats, 2) depth zone, 3) substrate type, 4) biologic features, and 5) dominant species.
Because of differences in biotic communities, the ecotypes used in Levels 4 and 5 are not broad enough to account for the diversity of marine habitats present in U.S. waters. The general features of this classification system are consistent with those developed for the United States (Allee et al., 2000).
approaches is largely in available data. In part because of the more uniform geography of European waters, habitats have been mapped more thoroughly, allowing more detailed classification. The U.S. situation is more similar to Canada because the United States has an extensive coastline that encompasses an even greater variety of habitat types. Mapping the entire U.S. exclusive economic zone even by substrate type (EUNIS Level 3) is not possible with existing data. Habitats in the U.S. exclusive economic zone range from arctic to tropical, making it difficult to construct a standardized classification scheme for all habitats. Spatial management is at the km2 scale and requires mapping of sediment type (EUNIS Level 3). Although the ecological effects of bottom fishing have been documented at the scale of square meters (EUNIS Levels 4 and 5) concerns about anthropogenic effects are at the much larger scales of ecological communities. Therefore, the International Council for the Exploration of the Sea Working Group on Ecosystem Effects of Fishing Activities recommended identification of habitats influenced by human activity and inclusion of biologic characteristics in the EUNIS classification system.