Blubber fatty acids reveal variation in the diet of male Australian fur seals

Top-order predators play an important role in the structure and function of marine ecosystems. Optimal foraging theory predicts that predators will utilise foraging strategies that maximise their net energetic intake, and consequently, individuals within a population may utilise alternate strategies to target different prey resources. The present study investigated variation within the diet of 41 male Australian fur seals (Arctocephalus pusillus doriferus) using quantitative fatty-acid signature analysis (QFASA) of blubber. The study was conducted during the pre-breeding seasons of 2012 and 2013 and the non-breeding seasons of 2013 and 2014 at a colony on Kanowna Island (39°10′S, 146°18′E) in northern Bass Strait, southeastern Australia. QFASA models revealed that while males consumed prey commonly reported within the diet of Australian fur seals, elasmobranchs were more important than previously reported. Prey composition also varied between males which may reflect individuals using different strategies to target different resources, which ultimately broadens the trophic niche of a species and reduces intra-specific competition. Furthermore, substantial temporal variation in male diet was apparent presumably reflecting variation in the distribution, availability, and abundance of prey resources within Bass Strait at the time of sampling. Given that the energetic content of prey is expected to differ between species, temporal variation in dietary composition presumably has important implications for the growth and reproductive success of males.