Spatiotemporal analysis provides solutions to mitigate bycatch of southern Gulf of St. Lawrence Atlantic Cod in an expanding Redfish fishery

Bycatch mortality threatens ecosystem health and fisheries sustainability worldwide. In this study, we assessed potential impacts of an expanding Redfish (Sebastes spp.) fishery on a depleted stock of Atlantic Cod (Gadus morhua) in the southern Gulf of St. Lawrence, Canada. Spatiotemporal modelling of fisheries landings and scientific surveys indicates that Atlantic Cod have shifted into deeper water over time, placing them in closer proximity to Redfish than historically observed. Presently, some differences persist in depth use and spatial distribution during May to October. During November to April, seasonal migration patterns and overwintering behaviour make spatial predictions difficult, but suggest that sporadic, large bycatch events can occur. Combined, these results identify specific times, areas, and depths that could be targeted for bycatch mitigation strategies. Nevertheless, Atlantic Cod bycatch limits could be rapidly met depending on the scale of the Redfish fishery. We also caution that continued shifts of Atlantic Cod into deeper water could make them increasingly vulnerable to this expanding fishery, as well as existing fisheries currently responsible for the majority of bycatch. Although this study primarily focused on bycatch of one species in the context of a single fishery, our methods could be expanded to consider additional species and fisheries. Based on existing literature, our proposed solutions to mitigate cod bycatch will also help protect other vulnerable groundfish with similar geographic distributions and depth profiles.