Intra-specific Niche Partitioning in Antarctic Fur Seals, Arctocephalus gazella

Competition for resources within a population can lead to niche partitioning between sexes, throughout ontogeny and among individuals, allowing con-specifics to co-exist. We aimed to quantify such partitioning in Antarctic fur seals, Arctocephalus gazella, breeding at South Georgia, which hosts similar to 95% of the world's population. Whiskers were collected from 20 adult males and 20 adult females and stable isotope ratios were quantified every 5 mm along the length of each whisker. Nitrogen isotope ratios (delta N-15) were used as proxies for trophic position and carbon isotope ratios (delta C-13) indicated foraging habitat. Sexual segregation was evident: delta C-13 values were significantly lower in males than females, indicating males spent more time foraging south of the Polar Front in maritime Antarctica. In males delta C-13 values declined with age, suggesting males spent more time foraging south throughout ontogeny. In females delta C-13 values revealed two main foraging strategies: 70% of females spent most time foraging south of the Polar Front and had similar delta N-15 values to males, while 30% of females spent most time foraging north of the Polar Front and had significantly higher delta N-15 values. This niche partitioning may relax competition and ultimately elevate population carrying capacity with implications for ecology, evolution and conservation.