Effects of Gear Modifications on the Trawl Performance and Catching Efficiency of the West Coast Upper Continental Slope Groundfish Survey Trawl

mensions, variation in trawl dimensions, and door attitude) and to determine if catch rates in terms of weight and number of DWC species and invertebrates were affected by the gear modifications. Trawl performance was highly variable for the historically used standard trawl configuration. Improvements were observed with the addition of either a 2-bridle door or lighter ground gear. Changes in scope length had relatively little effect on trawl performance. The interaction of door bridle and ground gear weight had the most effect on trawl performance. In spite of the standard trawl’s erratic performance, catch rates of all four DWC species and invertebrates were not significantly different than the 2-bridle/heavy combination, which did the best in terms of engineering performance. The most important factor affecting DWC catch rates was ground gear. Scope length and the type of door bridle had little effect on DWC catch rates. Subsequent revisions to survey gear and towing protocol and their impact on the continuity of the slope survey time series are discussed. ment and Conservation Engineering (RACE) Division of the NMFS Alaska Fisheries Science Center (AFSC), initiated a pilot groundfish bottom trawl survey of the upper continental slope (Raymore and Weinberg, 1990). Compared to the shelf, the west coast upper continental slope (WCUCS) is a challenging environment in which to do a trawl survey because of the extreme depths (183‐1,280 m), steep and irregular bathymetry, submarine canyons, and muddy bottom. The survey was motivated by the need for information on the commercially important species inhabiting the slope region. These species, referred to as the deep-water complex (DWC), include Dover sole, Microstomus pacificus; sablefish, Anoplopoma