Characteristics of benthic sediments from areas open and closed to bottom trawling in the Gulf of Alaska

Abstract

This report documents the sedimentary, biogeochemical, and infaunal characteristics of sediments from areas that were open or closed to bottom trawling in the central Gulf of Alaska. Sediment samples were collected from three sites during two cruises in 1998 and 1999. Bottom trawling had been prohibited in the closed areas for 11-12 years. Trawling intensity in the open areas was estimated at 11%-29% of the seafloor per year for the 5 years preceding this study. We found evidence that the sedimentary and biogeochemical characteristics of the seafloor have been altered to some degree by ambient levels of bottom trawling. Total organic carbon was higher in open areas at Site 1-1998 and at Site 2. Median grain size differed between open and closed areas at Sites 2 and 3, as did sediment sorting at Site 3. Grain size analysis at Site 3 provided evidence of a natural habitat gradient that may have been present prior to the closure in 1987.

No significant differences in infauna measures of community structure were found between open andclosed areas, other than a higher Simpson’s index of dominance in the open area at Site 2. Differences in sediment characteristics were subtle and minor, and no clear, repeated pattern of effects occurred among the three sites. Our results indicate that the effect of mobile fishing gears (i.e., otter trawls and scallop dredges) on sediment properties and infaunal communities at the three sites examined and at present levels of fishing is minor and not cause for serious concern at the present time. These results, used in conjunction with those on the effects of trawling on the epifaunal component of these communities, will provide resource managers with some insight into how current trawling activities in the Gulf of Alaska are affecting this important habitat. Infauna data appendices are included.


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