Seal bycatch in gillnet and entangling net fisheries in Irish waters

Abstract

A dedicated observer programme was carried out in gillnet and entangling net fisheries off the west and southwest coasts of Ireland to monitor interactions with seals. No seals were observed as bycatch in gillnet fisheries suggesting the risk of bycatch in observed gillnet fisheries is low. Grey seals (Halichoerus grypus) and to a lesser extent harbour seals (Phoca vitulina) were observed as bycatch principally in large mesh tangle nets targeting crawfish (Palinurus elephas). Observed bycatch levels, proximity of grey seal colonies to crawfish fisheries and similar habitat preferences suggest that the risk of seal bycatch in tangle net fisheries for crawfish on the west and southwest coasts of Ireland is high. Factors affecting bycatch in tangle nets were modeled to investigate potential bycatch mitigation measures. Crawfish and monkfish (Lophius spp.) catches, depth of gear deployment and larger mesh size were significantly positively correlated with seal bycatch. Development of mitigation measures such as improved net visibility, use of smaller mesh size and reintroduction of pots has major potential to reduce seal bycatch in the observed tangle net fishery. Growing seal populations in regions where tangle netting for crawfish is most prevalent could be related to factors such as benefits accrued from depredation and possible immigration from adjacent populations in the UK. More explicit conservation objectives will likely be needed to provide an impetus for development of proposed mitigation measures and bycatch reductions in Ireland. Results of this study also have broader ramifications for management of pinniped bycatch in large mesh gillnet and entangling net fisheries, which are widespread but poorly studied in European Community waters.