Density of the Commercial Spider Crab, Chionoecetes opilio, and Calibration of Effective Area Fished Per Trap Using Bottom Photography

Abstract

Bottom photography was found to be a more accurate method of censusing the commercial spider crab, Chionoecetes opilio, than trawling or sight counting from a submersible. Because of their highly aggregated distributions, estimating abundance of mature female crabs and immature crabs of both sexes was not practical by any method. The larger males (≥ 40 mm carapace width), including those of commercial value, approached a random distribution, however; and abundance estimates for four study areas ranged from 5.2 to 9.2 crabs/500 m2 and from 2.2 to 4.2 kg live weight/500 m2. To permit results of exploratory fishing with traps to be converted to crab density and size of crab stocks available to a commercial fishery, a commercial crab trap was calibrated for "effective" area fished. The effective fishing area per trap averaged 4100 m2 over four study areas.