Evaluating the condition and discard mortality of winter skate, Leucoraja ocellata, following capture and handling in the Atlantic monkfish (Lophius americanus) sink gillnet fishery

Abstract

Abstract Discard mortality (DM) estimates are vitally important to fisheries management. Commercial fishery DM estimates, for example, can help calculate total fishing mortality and biologically acceptable catch limits. The winter skate, Leucoraja ocellata, is the only species within the US portion of the western North Atlantic that is targeted in the skate wing fishery. However, due primarily to fishery regulations, this species is also routinely discarded at sea when daily quotas are reached. While already examined in mobile fishing gears (i.e. bottom otter trawls), DM has not been addressed for the western North Atlantic skate species captured in the sink gillnet fishery, and a conservative 50% DM is used across the species of the skate complex in the management processes. Given this data gap, we estimate the DM of winter skate in sink gillnets under standard commercial fishing conditions. The study methods employed address the issue of cryptic mortality (drop out of dead skates from the gear and depredation prior to retrieval), which can bias DM estimates low for bycatch in passive gear. The degree of injury sustained during capture and handling was found to be a statistically significant predictor of mortality. Overall mean DM rates reached an asymptote within 170 h of captivity, with estimates of 11% and 17% for females and males, respectively. Based on these results, the species appears more resilient to sink gillnet capture and release than previously thought. However, cryptic fishing mortality appeared to be high for extended soak times and likely represents an important focus of future research and management actions.