Effects of Fishing on Gravel Habitats: Assessment and Recovery of Benthic Megafauna on Georges Bank
Jeremy S. Collie, Jerome M. Hermsen, Page C. Valentine, and Frank P. Almeida
Abstract. This study assessed the effects of disturbance to benthic communities and the rate of recovery in an area closed to bottom fishing. The study site was the gravel sediment habitat on the northern edge of Georges Bank, which is an important fishing ground and a nursery area for juvenile fish. On eight cruises to this area from 1994 to 2000, we collected dredge samples and photographs from sites of varying depths and with varying degrees of disturbance from otter trawling and scallop dredging. We assessed the megafaunal communities at two adjacent sites in Canadian waters, one heavily fished and the other only lightly trawled. The lightly trawled site (84-m water depth) had significantly higher numerical abundance and biomass of benthic megafauna than did the heavily fished site. There were also marked differences in community composition between the two sites: the undisturbed site was characterized by fragile species— shrimps, polychaetes, and brittle stars—that live in the complex habitat provided by colonial epifauna, which is not present at the disturbed site (80 m). We also monitored the recovery of a previously disturbed shallow area (47 m) that was closed to bottom fishing in January 1995. In the closed area (Closed Area II), we observed significant shifts in species composition and significant increases in abundance (4×), biomass (18×), production (4×), and epifaunal cover. Among the taxa that have increased are species of crabs, molluscs, polychaetes, and echinoderms. Species-dominance curves reversed following the closure, with species abundance progressively decreasing and species biomass progressively increasing, as large animals came to dominate the biomass. Results of this and prior studies have been used by the New England Fishery Management Council to designate and maintain a Habitat Area of Particular Concern for juvenile Atlantic cod Gadus morhua.