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

Abstract

Faecal analysis (n = 806 scats) was employed to examine the diet of the Subantarctic fur seal Arctocephalus tropicalis at Marion Island (46° 54’S, 37° 45’E) over a period of six years (April 2000 – March 2006). Identifiable prey remains (fish otoliths, cephalopod beaks) were extracted from the faeces and analyzed. The number of individuals of each prey group identified was determined, and the size of individuals was estimated by applying appropriate regression formulae to measurements of the prey remains. Despite the biases associated with the method, useful information was gained on seasonal and inter-annual fluctuation in the presence of prey species in the diet. The indices used to investigate these variations were percentage numerical abundance, percentage frequency of occurrence and reconstituted body size (mass and length) of prey species taken. The diet was diverse and myctophid species predominated. Cephalopods were minor prey species in scats (n = 39). The five main prey species were Gymnoscopelus bolini, G. piabilis, G. fraseri, G. nicholsi and Protomyctophum tenisoni. In all respects G. bolini predominated throughout the study period, although in most comparisons no statistically significant differences in the relative contribution amongst the main prey species in the diet were found. Seasonal and inter-annual variations in the contributions of these species to the diet presumably resulted from changes in the relative abundance and distribution of prey.