Symposium Abstract: A Comparison of Habitat Structure in Fished and Unfished, Mobile and Immobile Sand Habitats on Georges Bank (Northwest Atlantic)
J. B. Lindholm, P. J. Auster, and P. Valentine
Fishing has been described as the dominant anthropogenic impact to marine ecosystems worldwide. One subset of impacts is caused by fishing with mobile bottom-contact gear (e.g., scallop dredges, bottom trawls) on seafloor habitat and associated taxa. Mobile fishing gear reduces seafloor habitat complexity through the removal of emergent fauna that provide structure (e.g., erect sponges), the removal of structure-building megafauna that produce pits and burrows (e.g., crabs, fish), and the smoothing of bedforms (e.g., sand waves). In this study we compared the relative abundance of microhabitat features (the scale at which individual fish associate with seafloor habitat) inside and outside of a large closed area on Georges Bank (closed in December 1994 and sampled in June 1999). A total of 32 stations were selected in a paired sampling design inside and outside of the closed area in sand habitats. Video and still photographic transects were conducted at each station using the Seabed Observation and Sampling System. Seven common (i.e., flat sand, rippled sand, sand with emergent fauna, bare gravel, gravel with emergent fauna, shell, shell fragment) and two ‘rare’ (sponges, biogenic depressions) microhabitat types were compared separately. Analyses were conducted for ‘mobile sand’ habitats (< 60 meters water depth) and for ‘immobile sand’ habitats (> 60 meters). Results showed no significant differences in the relative abundance of the common microhabitat types between fished and unfished areas in mobile or immobile sand habitats. However, in immobile sand habitats sponges and biogenic depressions were numerically more abundant inside the closed area.