Effect of proximity to the shelf edge on the diet of female Australian fur seals

The Australian fur seal Arctocephalus pusillus doriferus is a temperate latitude species with a breeding distribution restricted to Bass Strait, Australia. Recent studies of the foraging behaviour of female Australian fur seals indicated that they feed demersally in the shallow continental shelf waters, a behaviour that is in contrast to the epipelagic foraging of females of most other arctocephaline (Southern Hemisphere fur seals) species and akin to that observed in sea lions. These studies, however, were conducted at one colony (Kanowna Island) located in central northern Bass Strait, and it was suggested that the observed foraging behaviour may have been due to the distance of this colony from the continental shelf edge (180 km), making it inefficient to forage beyond it. Here, the diet of lactating Australian fur seals was compared between 2 colonies to test if differing proximity to the continental shelf edge resulted in differences in foraging behaviour. The 2 breeding colonies studied, Kanowna Island and The Skerries, were 180 and 25 km from the nearest shelf edge, respectively. We analysed a total of 917 scat samples collected at the 2 colonies between 1997 and 2001. From faecal analysis, 45 primarily demersal on-shelf species of fishes and cephalopods were identified. Only 4 species had a frequency of occurrence greater than 10%: redbait Emmelichthys nitidus, jack mackerel Trachurus sp., red rock cod Pseudophycis bachus, and Gould’s squid Nototodarus gouldi. No seasonal, annual or spatial differences were found between the 2 colonies, indicating that proximity to the shelf edge does not influence diet.