Predicting the relative risk of grey seal (Halichoerus grypus) bycatch based on habitat suitability and fishing activity

Abstract

Bycatch poses a global challenge to the sustainable management of fisheries. In Irish waters, the risk of grey seal (Halichoerus grypus) bycatch in commercial fisheries is highest with large mesh static nets. There is a need to understand the spatial distribution of this conflict to effectively prioritise mitigation actions and facilitate long-term coexistence between commercially viable fisheries and healthy seal populations. Such efforts are hampered by limited data on bycatch and critical gaps in tracking data for fishing vessels <12 m in length. Here, we combine intensive observer and fisher-reported bycatch data, high-frequency vessel tracking data, and a seal habitat suitability model to predict the spatial relative risk of seal bycatch surrounding the Blasket Islands, Ireland. Areas of high suitability for grey seals were concentrated in shallow waters around known haul out sites, such as the Blasket Islands. Our relative risk model demonstrated high predictive accuracy, with 90 % of the observed bycatch events occurring within high or very high risk bins. In contrast, low and very low risk bins included only 2.4 % of bycatch events, despite comprising almost half of the modelled area. We put forward a replicable and effective risk analysis approach for the spatial prioritisation of bycatch mitigation measures at broad spatial scales. By quantifying risk, we offer a tool to guide management that supports both seal conservation and sustainable fisheries. This approach represents an effective conservation tool that is scalable and can be applied to other species at risk of bycatch where relevant spatial data are available.