The diet of the subantarctic fur seal Arctocephalus tropicalis at Marion Island

Abstract

Scats of subantarctic fur seals Arctocephalus tropicalis at Marion Island were collected from 1996 to 2,000, to examine temporal variability in the diet, factors affecting the variability and how the diet differed from that of the Antarctic fur seal A. gazella in the same period. For A. tropicalis, 19 prey species, of which 18 were fish and one a cephalopod, were identified in 213 scats. Fish were the main prey, occurring in 98.1 % of scats, whereas the cephalopod was present in only 1.4 % of scats. Amongst fish species, Myctophidae were most abundant, with Gymnoscopelus piabilis, G. fraseri and Electrona carlsbergi being the commonest prey items. Other fish families present in the diet in small numbers were Channichthyidae, Paralepididae, Nototheniidae, Microstomatidae and Notosudidae. Fish eaten ranged in size from Protomyctophum bolini and Krefftichthys anderssoni of standard length (SL) 25 mm to a single Dissostichus eleginoides of SL 249 mm. Differences in the diet existed between summer and winter. However, prey type accounted for most variability in the diet. In previous studies based on scats, a dominance of fish in the diet of A. tropicalis was also found at Possession Island (Iles Crozet), Amsterdam Island and Macquarie Island, but the dominant prey species differed between the various localities, also suggesting that prey availability is a major determinant of diet. At Marion Island, from 1996 to 2000 the diet of A. gazella comprised similar prey to that of A. tropicalis, but the proportional contribution of prey types differed in instances.