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 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.