A comparison of size selectivity and relative efficiency of sea scallop, Placopecten magellanicus (gmelin, 1791), trawls and dredges

摘要

During August and September 1997 and May 1998, three comparative fishing experiments were conducted aboard commercial sea scallop trawl and dredge vessels to assess the efficacy of gear restrictions found in Amendment 4 to the Sea Scallop Fishey Management Plan (SSFMP). This amendment involved certain gear restrictions including minimum mesh and ring sizes and maximum gear widths and was intended to equate the performance of sea scallop trawls and dredgest with respect to size selectivity and efficiency. Statistical analysis indicated that selectivity and efficiency were not equal for the two gear types. While absolute gear size selectivity could not be estimated, there was clear evidence of differential relative size selectivity between the two gear types. While absolute gear size selectivity could not be estimated, there was clear evidence of differential relative size selectivity between the two gears. Relative harvest efficiency values shifted at 90 to 95 mm shell height. Trawl vessels were more efficient capturing sea scallops less than 90 mm, and dredge vessels were more efficient capturing sea scallops greater than 90 mm. This shift in relative harvest efficiency coupled with an observed cull size at 70 to 75 mm shell height resulted in the trawl vessels being more dependent on age 3 sea scallops with shell heights of 70 to 90 mm. Operational differences observed between the two year types restricted sea scallop trawl vessels to areas of smooth substrate. Large differences in both relative efficiencies and operational requirements will present considerable impediments to the desired outcomes of having equivalent performance between gear types.