Foraging site fidelity in male Australian fur seals

Abstract

Optimal foraging theory predicts that predators will employ strategies that maximise their net energetic return. Foraging site fidelity (the re-use of a prior foraging area) is assumed to be beneficial, because it facilitates direct travel to foraging areas and familiarity with a foraging area may confer energetic advantages over the lifetime of an animal. In the present study, foraging site fidelity was investigated in 16 male Australian fur seals (Arctocephalus pusillus doriferus) from Kanowna Island (39°10′S, 146°18′E), in northern Bass Strait, south-eastern Australia, during the winters of 2013 and 2014. Male Australian fur seals used several haul-out sites and made relatively short foraging trips (3.4 ± 0.2 days) to nearby foraging areas. Males behaved like central place foragers and foraged exclusively on the continental shelf (modal dive depth range: 70.5–85.5 m). Presumably, short foraging trips enabled males to minimise the metabolic costs of transit, while maximising their net energetic intake. Site fidelity varied considerably between individuals (site fidelity index ranged 0.1–0.6). However, the degree of site fidelity was unrelated to individual morphology parameters (such as body length). While long-term fidelity could make some individuals susceptible to increased environmental variability, the intra-variability in site fidelity reported in the present study suggests that males maximise their fitness by optimizing the time spent in different foraging areas. Variability in male foraging site fidelity highlights behavioural flexibility within Australian fur seals, which could help to reduce intra-specific competition or be a response to environmental variability.