Industry-independent video survey of commercial scallop ( Pecten fumatus ) densities in Great Oyster Bay – May 2017 survey

A towed underwater video camera was used to assess scallop densities north of the commercially fished beds in the Great Oyster Bay Shark Refuge Area in May 2017. The primary objective was to determine the presence or absence of a large spawning biomass of scallops outside of the commercially fished zone. Twenty one video tows were conducted over a range of depths and locations. Results show that throughout offshore areas of Great Oyster Bay (>2km from shore) there is general trend of decreasing scallop density with shallowing depths north of the commercial beds, while isolated pockets of high density scallops exist inshore. The video survey did not detect extensive, high density, scallop beds north of the fished area in Great Oyster Bay. Results of the video survey were comparable with the commercial pre-season dredge survey. A concurrent towed video survey of recreational scallops in the D’Entrecasteaux Channel, which allowed direct comparison with quantitative diver transect methods, indicated a high level of accuracy in scallop density estimates from towed video footage. Comparisons of size structure indicated some bias in the video derived data, in particular in defining the cohort structure in the smaller size classes. The towed video proved to be a very-cost effective and low impact technique for the rapid assessment of scallop abundance, provides an indication of relative size structure, and hence is an effective methodology for fishery-independent biomass estimation.