MEPS 443:249-263 (2011)  -  DOI: https://doi.org/10.3354/meps09392

ABSTRACT: We examined the movement characteristics and seasonality of feeding behaviour for an endemic Australian otariid, the Australian sea lion Neophoca cinerea. By combining tracking data and stable isotope analysis of serially subsampled vibrissae from 20 adult females at 7 colonies, we were able to characterise individual foraging specialisation across 80% of the species range. Adult females expressed long-term temporal consistency in both foraging site (offshore vs. inshore) and prey selection. When seasonality in foraging behaviour was detected (n = 7), there was no consistency in variation of isotope ratios between individuals or colonies. Offshore-foraging sea lions fed at higher trophic levels than inshore foragers. Potentially, inshore foragers could be subdivided into those which targeted heterogeneously distributed seagrass meadows or calcarenite reef systems for different payoffs. This data highlights the importance of understanding individual specialisation and the dangers of generalising behaviour at the colony level. Individual specialisation in foraging behaviour may be a mechanism that reduces intra-specific competition, but its effectiveness will be a function of the temporal stability of individual differences. The present study is the first to identify multi-season consistency of individual foraging behaviour for any otariid. Given the long-term stability of adult female foraging behaviour, categorising individuals using a proxy measure such as whisker isotopic signature appears robust, economical, and appropriate. Such data is critical to modelling population response to anthropogenically driven fine-scale habitat modification.

KEY WORDS: Stable isotopes · Otariid · Niche specialisation · Sea lion · Whiskers · Tracking · Individual variation · Australian sea lion