AFSC/RACE/GAP/McConnaughey: Trawlex Chronic Effects: Trawlex (1996) Macrofauna CPUE (weight/hectare)

The eastern Bering Sea has experienced rapid and intensive development of commercial trawl fisheries. Because of good record keeping and the relatively brief history of fishing it is possible to reconstruct the spatial and temporal patterns of exploitation. Previously unfished (UF) areas can be identified and directly compared with heavily fished (HF) areas to investigate long-term consequences for the benthos. Using this approach, macrofauna populations in a shallow (48 m average) soft-bottom area were studied during 1996.

Benthic communities are structured by dynamically interacting factors that determine habitat quality. Since benthic macrofauna demonstrate strong and often narrowly defined affinities, forces altering (or disturbing) the environment will be of considerable importance to their distribution and abundance. Commercial fishing with mobile gear, such as bottom trawls and dredges, and the physical disturbance that results, is widespread in continental shelf areas. Because of its prevalence and the potential for adverse effects, there have been numerous attempts to quantify sea-floor exposure at various spatial scales. The well documented development of commerical fisheries in the eastern Bering Sea (EBS) since 1954 presents a unique opportunity for studying trawling impacts. The Crab and Halibut Protection Zone 1 (CHPZ1; also known as management area 512), located north of the Alaska Peninsula in Bristol Bay, has a long and complex history of trawl prohibitions that extend from 1959 to the present. Using detailed accounts of closures and fishing activity, it is possible to reconstruct historical effort and identify essentially pristine areas immediately adjacent to areas that have been heavily fished with bottom trawls. This physical arrangement permits an examination of chronic disturbance by bottom trawls, without confounding environmental effects that result from geographic separation. Sampling locations were preselected on the basis of historical fish effort. Starting positions for commercial bottom trawls (n=392 743 through July 1996) were spatially joined with a 1 nm2 grid to calculate total number of trawls per nm2, and thus identify heavily fished (HF) and unfished (UF) areas along the boundary of the CHPZ1 (NORPAC fishery observer database maintained at the NMFS Alaska Fisheries ScienceCenter, Seattle, Washington). HF and UF cells on opposite sides of the boundary line were paired a priori on the basis of spatial proximity and were generally separated by 1 nm to allow for prior navigational discrepancies. A total of 42 pairs was identified at the northeastern corner of the CHPZ1. Catch data were spatially joined to line segments which were created from the start and ending trawl positions for each haul.

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Effects of Chronic Bottom Trawling on the Size Structure of Soft-Bottom Benthic Invertebrates. American Fisheries Society Symposium 41:425?437, 2005

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