Cross-seasonal foraging site fidelity of subantarctic fur seals: implications for marine conservation areas

Abstract

Marine top-predators show fidelity to foraging areas with predictable high-quality food patches.Areas of predictable prey yield are of conservation importance and telemetry data aid in identifying such areas. This study examined colony specific and intra-individual foraging site fidelity of lactating Subantarctic fur seals (Arctocephalus tropicalis) from Marion Island (46°54"S, 37°45"E) during summer and winter, comparing commitment to foraging areas across seasons. Thirty-one females were tracked in 2009-2013 resulting in 111 foraging trips for analyses. Inter-annually, preferred foraging areas in summer were consistently ≈200 km due east of Marion Island towards the Gallieni Rise. Summer individuals' core utilization areas overlapped by an estimated 32.84% (CI: 24.53% -41.94%). Seals responded to a decrease in regional productivity in winter by foraging in more distant alternative areas. In winter, individuals changed their travelling direction to north-east of Marion Island and foraged further afield, around the Del Caño Rise and along the South-west Indian Ridge. Despite preferring some foraging areas in winter, there was a low amount of overlap 6.03% (CI 4.02% -9.16%) of individual core utilization areas. The foraging grounds identified in this study have not been included in prior conservation assessments and are important in conserving for this globally 1 significant, and currently declining, population of Subantarctic fur seals and perhaps other toppredators breeding at Marion Island as well. Differences between winter and summer preferred foraging areas highlight the importance of sampling during different seasons when using telemetry data for the identification of potential pelagic conservation areas.

Overlap and temporal variation in the diets of sympatric Antarctic and Subantarctic fur seals (Arctocephalus spp.) at Marion Island, Prince Edward Islands

“…Our results do show that dietary overlap is substantially higher during summer, when the foraging range of both species is more restricted and their atsea spatial segregation is likely lower (Wege, Tosh et al 2016); any potential competition between the species will be greatest during this time. Potential competition between the two species could be minimized through the segregation of at-sea foraging grounds, as seems evident from recent tracking studies.…”

“…Potential competition between the two species could be minimized through the segregation of at-sea foraging grounds, as seems evident from recent tracking studies. Subantarctic fur seals forage primarily east and north-east or west and north-west of Marion Island and its neighbour Prince Edward Island (De Bruyn et al 2009;Kirkman et al 2016;Wege, Tosh et al 2016). In contrast, winter tracking data show that Antarctic fur seals have a more southerly foraging distribution (Arthur et al 2015;Arthur et al 2016;Arthur et al 2017), although there may be some overlap between the species to the east and northeast of Marion Island.…”

“…Numerous dietary studies throughout the range of both these fur seal species have shown that there are substantial dietary differences seasonally, among populations and between species, and it appears that the specific diet of Antarctic and Subantarctic fur seals is largely determined by local conditions and prey availability (e.g., Bester & Laycock 1985;Boyd et al 1994;Iverson et al 1997;Lea et al 2002;Casaux et al 2003;Reid et al 2006;De Bruyn et al 2009;Kernaléguen et al 2012). This is amplified by the fact that the potential foraging range of individuals changes throughout their annual breeding season (De Bruyn et al 2009;Wege, Tosh et al 2016). Generally, however, Subantarctic fur seals feed mainly on myctophid fishes (Myctophidae: lanternfishes) (e.g., Robinson et al 2002;Beauplet et al 2004;Luque et al 2007;De Bruyn et al 2009), with the notable exception of Gough Islandthe site of their largest populationwhere they feed primarily on cephalopods (Bester & Laycock 1985).…”

A cross-validation-based approach for delimiting reliable home range estimates

“…Recent empirical studies utilizing the T-LoCoH algorithm for delineating home ranges illustrate the subjectivity involved in parameter value selection [40,41,42]. While many studies rely upon the guidelines set forth in the Tutorial and Users Manual provided by the creators of the 'tlocoh' package in R [22], there was some variation among studies regarding the selection of s values (i.e., choosing different proportions of hulls that are considered time-selected) and whether the k or a approach was used for selecting nearest neighbors.…”

Assessing the importance of Isle of Man waters for the basking shark Cetorhinus maximus

“…Many animal taxa, including birds, fish and mammals, seasonally migrate to make use of natural fluctuations in available resources that are needed to support growth and reproduction, and to avoid harsh environmental conditions and predators (Hawkes et al 2011, Hopcraft et al 2014, Hammerschlag et al 2015, Leroy et al 2016, Peiman et al 2017. Moreover, many species display site fidelity, returning to the same area annually in search of profitable re -sources (Wege et al 2016). Although major gains have been made in understanding the movements of many terrestrial (Kays et al 2015) and marine taxa (Godley et al 2008, Hussey et al 2015, Hays et al 2016, some large marine vertebrates present a challenge to study due to the difficulties of tracking species that spend extensive periods of time underwater.…”