Mitigating bycatch of Southern Gulf of St. Lawrence Atlantic Cod (Gadus morhua) in NAFO Divisions 4T - 4Vn (November-April)

Abstract

The primary management measure proposed in the southern Gulf of St. Lawrence (sGSL) Atlantic Cod (Gadus morhua) rebuilding plan is to keep removals to the lowest level by introducing new and/or stricter management measures in all fisheries that intercept sGSL Atlantic Cod. In this study, we assessed spatial and temporal patterns of bycatch risk in four fisheries. Three of these fisheries, Atlantic Halibut (Hippoglossus hippoglossus), Greenland Halibut (Reinhardtius hippoglossoides), and Witch Flounder (Glyptocephalus cynoglossus) have been responsible for the majority of sGSL Atlantic Cod bycatch in recent years. The fourth fishery, Redfish (Sebastes spp.), was assessed because it was also noted for having relatively high bycatch levels, and because the commercial fishery reopened in 2024, potentially increasing bycatch impacts on Atlantic Cod. To assess bycatch risk, we used both fisheries-independent and fisheries-dependent data in species distribution models, and we compared model predictions under different fishing scenarios to develop fishery-specific considerations for Fisheries and Harbour Management. Occurrence and density of Atlantic Cod in Northwest Atlantic Fisheries Organization (NAFO) 4T were associated with depth, making the adoption of depth-targeted strategies an important component of bycatch mitigation. In addition to depth, area-targeted mitigation strategies also offered solutions to lower bycatch rates. As noted elsewhere, winter distributions of Atlantic Cod in NAFO 4Vn may be more difficult to predict due to dense overwintering aggregation behaviour. In NAFO 4Vn, area closures may help mitigate bycatch in fisheries that operate there. In addition to existing fisheries management practices, the best scenarios to minimize bycatch in each fishery include the following recommendations: (i) area- and depth-associated mitigation for the NAFO 4T Atlantic Halibut fishery, (ii) area-associated mitigation for the NAFO 4Vn Atlantic Halibut fishery, (iii) depth-associated mitigation for the NAFO 4T Witch Flounder fishery, (iv) depth-associated mitigation combined with a revised latitude limit for the NAFO 4T Greenland Halibut fishery, (v) area- and depth-associated mitigation for the NAFO 4T Redfish fishery, and (vi) either maintaining a winter closure of NAFO 4Vn to Redfish fishing, or applying area-associated mitigation combined with a latitude limit in the winter.