Mixed up in fishy business: Using drift models and correlation with fishing activity to evaluate the strandings of common dolphins (Delphinus delphis) in Irish waters.

Common dolphin stranding around Irish coasts have been reported in recorded-breaking numbers for the last decade.  Since low cases of bycatch were observed aboard fishing vessels, despite concerns by ICES for the region, we examined reverse drift modelling of stranding data as an alternative method for calculating fisheries’ involvement. After collecting photographic and post-mortem data of the stranding events, a hydrodynamic model for the North-East Atlantic was used on Opendrift to backtrack carcasses' movement from their stranding point and simulate the predicted location of each dolphin’s death. Their spatial distribution was then correlated with fishing effort of eight active fisheries trough General Additive Modelling. Significant overlaps were identified for demersal and pelagic trawling of all flags and gillnetting of Irish vessels, all targetting either predatory fishes or prey of common dolphins, pelagic shoaling fish. Consequently, current monitoring practices need to be improved, include inshore effort, and homogenised for the North Atlantic. Combinations of mitigation options are proposed with high emphasis on reduced fishing effort, i.e., spatio-temporal closures. The co-occurrence demonstrated the existence of a previously neglected risk, identified the gears that need further investigation, and showed the potential of drift modelling as a tool for alternative calculations of bycatch impacts.