Content area
Full Text
When sympatric top predators of conservation concern compete for food, space, or have predatory interactions with each other, there may be the potential for conservation conundrums, particularly on how to best manage protected species (Stirling & Archibald, 1977; Crawford et al., 1989; Williams et al., 2004; Butler et al., 2006; Margaritoulis & Touliatou, 2011). The grey seal (Halichoerus grypus) and the harbour porpoise (Phocoena phocoena) are both species of considerable local, national, and international conservation interest that co-exist across most of their range within northern European waters (Reid et al., 2003; Baines & Evans, 2012; Special Committee on Seals [SCOS], 2013) and feed on similar prey (Hammond et al., 1994; Santos & Pierce, 2003; Gosch et al., 2014). Both species are listed under Annex II of the European Union Habitats & Species Directive (Council Directive 92/43EEC), which requires spatial management through the creation of Special Areas of Conservation (SACs). The harbour porpoise, as with all cetaceans, is also given strict protection as a European Protected Species under Annex IV of this Directive. Central to this Directive is the requirement to maintain or restore listed species and habitats to "Favourable Conservation Status."
Approximately 4% of the United Kingdom's grey seal population breed in Wales (Duck, 2009), where most are found in Pembrokeshire, the largest breeding population in the Irish Sea and southwest Britain at approximately 5,000 seals (Baines et al., 1995; Strong et al., 2006; Duck & Thompson, 2007). Here, grey seals are the primary feature of the Pembrokeshire Marine/Sir Benfro Forol SAC, with Ramsey Island being the main breeding site (Baines et al., 1995; Strong et al., 2006). The area is also locally known for its high density of harbour porpoises that make use of the strong tidal races around the island for foraging (Pierpoint, 2008). Harbour porpoise abundance is thought to be higher in summer than in winter, and there is a high proportion of juveniles during this time (Pierpoint et al., 1998; Baines & Evans, 2012)
Grey seals are generalist feeders, taking a wide variety of fish, mollusc, echinoderm, crustacean, and cephalopod prey (Bowen & Harrison, 1994; Hammond et al., 1994; Strong, 1996; Brown et al., 2012; Smout et al., 2013, 2014; Gosch et al., 2014). Other marine mammals are not a usual...