Estimating the Discard Mortality Rate of Sea Scallops Following Capture and Handling in the Commercial Dredge Fishery

Discard mortality can represent a significant source of removals.  These removals represent an unobserved component of fishing mortality and can go unaccounted for presenting difficulties in accurately assessing the stock and setting appropriate annual fishery specifications. The sea scallop, Placopecten magellanicus, supports the most valuable single species commercial fishery in the U.S. Northwest Atlantic Ocean, with an estimated ex-vessel value of over 467 million U.S. dollars in the 2013 fishing year.  However, despite the importance of the fishery, scallop discard mortality has received little recent attention.  The current study attempts to understand the processes related to the short-term survival of commercially captured scallops, with estimates conditional on shell damage and reflex impairment indices. We evaluated the various factors that influence survival, utilizing a series of field (eight cruises over two years) and laboratory experiments.  Overall findings suggest that the mortality of discarded scallops is both increased for smaller animals exposed to air for extended durations at high temperatures and irrespective of size, for animals suffering shell damage during the capture and handling process.  Results will be discussed in the context of impacts to the scallop stock assessment and the development of best management practices for the fishing industry.