Co-occurrence of seal foraging behaviour and offshore set-net fisheries in the north-east Atlantic

Data used in modelling of seal-fisheries interactions in the paper: Co-occurrence of seal foraging behaviour and offshore set-net fisheries in the north-east Atlantic. Please refer to README file. ABSTRACT 1. Interactions between marine predators and fisheries are an issue from both a commercial and conservation perspective, as animals are known to depredate fish catches and can also become entangled as bycatch. 2. Here, we examine fine-scale co-occurrence of grey seal (Halichoerus grypus) foraging and offshore set-net fisheries (>5 km from the coast) using high resolution (GPS) tracking data from 164 individuals tagged across the UK, Ireland, and France. Seal foraging behaviour was inferred using Hidden Markov Models (HMM’s) and linked to information on the locations of set-net fisheries from global Automatic Identification System (AIS) data. To assess if seals directly target fishing nets or encounter them more opportunistically due to coincidental proximity and subsequent co-occurrence, two sets of models were run using: (1) concurrent fishing activity, and (2) seasonal fishing persistence. 3. Grey seals were increasingly likely to switch from travelling to foraging behaviours in or near areas of high fishing activity. This relationship was stronger for males than females. However, only 4.5% of seal foraging occurred within 5km of potential set-net locations, and model performance improved with the use of seasonal persistence rather than contemporaneous presence. Moreover, 33-41% of seals (dependent on scale/sex) that passed within 5-10 km of concurrent fishing activity did not transition to foraging behaviour at these locations/times (i.e. were never detected foraging in co-occurrence/proximity to contemporaneous fishing activity). 4. Synthesis and applications: Together, these results suggest co-occurrence of seal foraging and fishing activity is limited to a small proportion of seal foraging time, and varies between individuals and sexes. Rather than supporting the assertion that seals target nets to depredate, we suggest nets are encountered more opportunistically while foraging in areas also targeted by set-net fisheries. This provides important context for seal-fisheries interactions, supporting the use of targeted fisheries-based management (e.g. deterrents, fishing/gear modification, and area closures) to reduce/mitigate opportunistic net attendance and subsequent conflicts such as depredation and bycatch. Future work should assess relationships at inshore locations, which requires fishing effort data from the smaller vessels operating in these areas.