An Optical Assessment of Weathervane Scallop Density and Abundance Off Kodiak Island, Alaska

Abstract

Since 2000, information to support the sustainable management of the weathervane scallop Patinopecten caurinus in the Gulf of Alaska is largely derived from fishery-dependent observations from a small fleet (≤8 vessels total). As a supplement to this information, the Alaska Department of Fish and Game collected more than one million high-resolution underwater photographs of the sea floor in five previously unsurveyed scallop beds off Kodiak Island during the spring of 2014. Weathervane scallop distribution, abundance, and size composition in these beds were assessed by analyzing more than 150,000 images subsampled in 50-image strips (stations) using a 100-m grid. In addition, the influence of local abiotic habitat features, including depth, substrate, and shell remains, on weathervane scallop distributions was explored. An estimated 26.8 [95% confidence interval (CI) = 23.5–30.7] million scallops in the five beds, with densities ranging from 0.08 (95% CI = 0.067–0.084) to 0.26 (95% CI = 0.221–0.297) ind.•m–2 among the beds. Shell size compositions differed significantly despite the relative proximity of the beds. Weathervane density was positively related (in order of influence) to gravel, shell debris, shell hash, mud, and cobble. Optical assessment of these five previously unsurveyed scallop beds in the Gulf of Alaska demonstrates the efficacy of this approach for weathervanes and suggests that the expansion of optical survey coverage to include other known beds as a viable path to overcoming the limitations of fishery-dependent information for scallop assessment and management in Alaskan waters.