Site use and connectivity of female grey seals (Halichoerus grypus) around Wales

Abstract

Grey seals (Halichoerus grypus) are a qualifying feature of three special areas of conservation (SACs) in Wales, yet relatively little is known of their site use along this coastline. Since 1992, many individuals and organisations have contributed to a grey seal photographic identification database held by Natural Resources Wales, which is one of the largest and oldest of its kind, providing key information from grey seal haul-out sites around the Celtic and Irish Seas. Here, we investigated spatial connectivity of haul-out sites and fidelity of adult females to breeding sites. The minimum number of adult female grey seals using the area between 1992 and 2016 was 2688. Individual capture histories and relative spatial transition probabilities (P ij) between pairs of location groups were calculated. Adjacent locations were highly connected (e.g. Lleyn Peninsula and Bardsey, P ij = 0.7) but connections spanned the entire region, up to 230 km apart (e.g. Skomer and Dee Estuary, P ij = 0.004). Resights were recorded within SACs (e.g. Lleyn Peninsula and Bardsey [Lleyn Peninsula and the Sarnau SAC], P ij = 0.7), between SACs (e.g. Bardsey and Skomer [Pembrokeshire Marine], P ij = 0.03), between SACs and non-designated areas (e.g. Skerries and Bardsey, P ij = 0.09) and between sites outside any protected area (e.g. Dee Estuary and Anglesey, P ij = 0.5). While inter-annual fidelity to breeding sites was high (P ij = 0.82-1), individual female grey seals moved throughout the region. This evidence of extensive site use beyond protected areas is important for the management and conservation of grey seals around Wales.

Climate causes shifts in grey seal phenology by modifying age structure

“…Given the time lag with SST, it seems that such competition would be for limiting resources such as prey availability earlier in the year, rather than access to beaches during the pupping season. However, it is known that Welsh seals can travel widely throughout the Irish Sea and as far as southwest England, France and Ireland [30,[76][77][78]. Therefore, a wider study of other pupping sites around the region would be needed to really understand the processes driving dynamics in such a mobile and open population.…”

“…[23][24][25][26][27][28][29]. Like many other seal species, grey seals are iteroparous capital breeders with a high degree of site fidelity [30]. They start breeding at around 5 years old and reproduce annually for potentially several decades, resulting in populations with overlapping generations [31,32].…”

“…In closed populations, describing the stable age structure may be enough to understand dynamics, brought about through local demographic processes, such as changes to fecundity and differential survival across age classes. However, along with many age- or stage-structured species, grey seals are known to roam widely [ 54 – 56 ] and even where site fidelity is high, local populations are open to immigration and emigration as a further source of changes to age structure [ 30 ]. In grey seals, younger adults have been found to be more likely to remain resident and have smaller home ranges than older adults [ 57 ].…”

Pinnipeds, people and photo identification: the implications of grey seal movements for effective management of the species

“…Most PID projects have focused on female grey seals (e.g. Karlsson et al ., 2005; Hiby et al ., 2007; Paterson et al ., 2013; Langley et al ., 2018) due to their distinctive patterns. Male grey seals also have fur patterns but with fewer, simpler markings (Vincent et al ., 2001; Paterson et al ., 2013), providing contrasting challenges between the sexes for PID.…”

“…If undertaken as part of a long-term structured research programme, PID can allow longitudinal studies of individuals over a lifetime of reproductive output, aid an assessment of cumulative threats and provide insights into individual behaviour (Loughlin et al ., 2010; Macleod et al ., 2010). PID has been used on a range of marine species in the North-east Atlantic to track long-term movements and residency behaviour for bottlenose dolphins ( Tursiops truncatus ) (O’ Brien et al ., 2009), killer whales ( Orcinus orca ) (Beck et al ., 2014) as well as grey seals in the Baltic Sea (Karlsson et al ., 2005), Ireland (Kiely et al ., 2000), Wales (Kiely et al ., 2000; Beaumont & Goold, 2007; Boyle, 2011; Langley et al ., 2018) and France (Gerondeau et al ., 2007).…”