Estimating the Discard Mortality of Atlantic Cod in the Southern Gulf of Maine Commercial Lobster Fishery

Abstract The Gulf of Maine (GOM) commercial lobster fishery has approximately 3.5 million actively fished traps and captures several nontargeted groundfish species, including Atlantic Cod Gadus morhua, as bycatch, yet there has been limited research on the incidental mortality of groundfish in this fishery. Although the mortality of Atlantic Cod has been estimated in other GOM commercial fisheries, unaccounted discard mortality in the lobster fishery may impair recovery efforts for this stock. To help meet research needs, we assessed the discard mortality rate of Atlantic Cod captured in the Maine Lobster Management Zone G commercial lobster fishery using acoustic transmitters and observations of viability. From 2016 to 2017, 111 Atlantic Cod were captured in 18,853 individual trap hauls and were observed for viability. A subsample of 54 Atlantic Cod was externally tagged with acoustic transmitters and observed after release. The combined at-vessel mortality (9.3%) and model-based long-term discard mortality (17.1%) estimates indicated an overall discard mortality rate of 24.8% for Atlantic Cod captured in commercial lobster gear. Based on this finding and the low bycatch of Atlantic Cod in the lobster fishery, the commercial lobster fishery may not be responsible—to the extent previously assumed—for hindering the GOM Atlantic Cod stock’s regrowth.