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The sea scallop (Placopecten magellanicus) fishery in the Atlantic is assessed during annual surveys by using both dredging and surface-deployed imaging techniques. In this pilot study in the Mid-Atlantic Bight, we used an autonomous underwater vehicle (AUV) to photograph the seafloor and to evaluate its use for determining scallop density and size. During 22 surveys in 2011, 257 km of seafloor were photographed, resulting in over 203,000 color images. Using trained annotators and photogrammetric software, we determined scallop density and shell heights for 15,252 scallops. The inshore scallop grounds near Long Island (at depths <40 m) had a density of 0.077 scallops per m2, whereas the inshore grounds of the New York Bight had a density of 0.012 scallops per m2. Shell heights derived from images were found to agree well with measurements from scallops collected with a commercial dredge. We show that images obtained with an AUV can be used to reliably estimate both density and shell height consistent with direct sampling from the same area. Moreover, side-scan sonar images obtained with an AUV can be used to detect dredge scars and, therefore, can provide a simultaneous, relative estimate of fishing effort in that area. AUVs provide a highly accurate suite of data for each survey site and therefore allow the design of experimental studies of fishing practices. [ABSTRACT FROM AUTHOR]

The author discusses the disappearance of 10.4 billion sea scallops Placopecten magellanicus from the Mid-Atlantic between 2003 and 2004 and the hypothesis that the disappearance was caused by incidental fishing mortality particularly discard mortality where small scallops were captured, exposed to lethal surface water and air temperatures then discarded. He argues against claims of D. R. Hart and B. V. Shank who suggested that crab predation is the more like cause of the mortality. He maintains that discard mortality had a major role in the decrease of juvenile scallop abundance in the Mid-Atlantic between 2003 and 2004 and suggests real-time, spatially specific information and rapid responses by management to avoid similar losses.