Document Type

Article

Date of Original Version

2008

Department

Oceanography

Abstract

Trawling and dredging on Georges Bank (northwest AtlanticOcean) have altered the cover of colonial epifauna, as surveyed through in situ photography. A total of 454 photographs were analyzed from areas with gravel substrate between 1994 and 2000 at depths of 40–50 m and 80–90 m. The cover of hydroids, bushy bryozoans, sponges, and tubewormswas generally higher at sites undisturbed by fishing than at sites classified as disturbed. The magnitude andsignificance of this effect depended on depth and year. Encrusting bryozoans were the only type of colonial epifauna positively affected by bottom fishing. Species richness of noncolonial epifauna declined with increasedbottom fishing, but Simpson’s index of diversity typically peaked at intermediate levels of habitat disturbance.Species that were more abundant at undisturbed sites possessed characteristics that made them vulnerable tobottom fishing. These characteristics include emergent growth forms, soft body parts, low motility, use of complexmicrohabitats, long life spans, slow growth, and larval dispersal over short distances. After the prohibitionof bottom fishing at one site, both colonial and noncolonial species increased in abundance. Populationsof most taxa took two years or more to increase after the fishing closure. This finding indicates that bottom fishing needs to be reduced to infrequent intervals to sustain the benthic species composition of Georges Bank at a high level of biodiversity and abundance.

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