The diet of Antarctic fur seals Arctocephalus gazella (Peters) during the breeding season at Heard Island

Abstract

Abstract:Between September 1987 and February 1988, Antarctic fur seals Arctocephalus gazella (Peters) at Heard Island fed mainly on fish with an average 95.2% of scats in monthly collections containing fish remains. Pelagic myctophids constituted more than 50% of fish taken by fur seals at the beginning of the summer season and again at the end when there was an influx of non-breeding male seals. During the middle period from October to December, fish from the surrounding shelf area comprised the bulk of the diet. These included various benthic nototheniid species, the bentho-pelagic ice fish Champsocephalus gunnari Lonnberg and skate (Bathyraja spp.), the latter being found in over 60% of scats in October and November. The population of Antarctic fur seals at Heard Island is increasing at about the same rate as at South Georgia. There the increase is thought to be due to the high availability of krill E. superba, but in the present study no euphausiid remains were found, so the increasing population at Heard Island has been supported on a diet of fish. Whether this population increase can be sustained in future on a diet of fish is arguable. Trial fishing around Heard Island indicates that one of the major dietary items of the seals (C. gunnari) is of probable commercial importance and therefore any plans for the establishment of a fishery on Heard Island grounds must be considered in this light.

Prey of the Antarctic fur seal Arctocephalus gazella at Marion Island

“…The estimated size and mass classes of the fish species consumed by A. gazella in this study (2.71-37.16 cm and <1 to 438.28 g) was similar to that found for the period 1989-1995(Klages and Bester 1998, although the average prey was slightly smaller in the previous study. The size range of prey taken by A. gazella at Marion Island was relatively narrow compared to that found at South Georgia (Reid and Arnould 1996) and Heard Island .…”

“…Similar to this study, highly seasonal patterns in the consumption of fish species, particularly of myctophids, have been documented for A. gazella at Heard Island (Green et al 1989), South Georgia (Reid and Arnould 1996) and previously at Marion Island (Klages and Bester 1998). Such patterns may depend on seasonal differences in the availability of prey species (Lea et al 2002b).…”

“…Such patterns may depend on seasonal differences in the availability of prey species (Lea et al 2002b). As for other sites, Heard Island and South Georgia, there was no discernable seasonal pattern in the intake of cephalopods (Green et al 1989;Reid 1995;Reid and Arnould 1996;Cherel et al 1997).…”

“…However, the two species breed sympatrically at three localities just to the north of the APF, namely Macquarie Island (Goldsworthy 1999), Iles Crozet (Guinet et al 1994) and the Prince Edward Archipelago (Condy 1978). The annual rate of growth of the Antarctic fur seal population at Marion Island (Prince Edward Archipelago) increased from about 11% between 1981-1982and 1988-1989(Wilkinson and Bester 1990 to about 17% for the period 1988-1989to 1994-1995(Hofmeyr et al 1997. Breeding occurs at ten sites on Marion Island; the largest breeding colony is found at Watertunnel Stream on the south coast.…”

“…The feeding ecology of A. gazella has been studied at numerous locations throughout its range, namely South Georgia (Bonner 1968;North et al 1983;North 1996;Reid 1995;Reid and Arnould 1996), Heard Island (Green et al 1989(Green et al , 1991), the South Shetland Islands (Daneri 1996;Casaux et al 1998;Osman et al 2004), the South Orkney Islands (Daneri andCoria 1992, 1993), Macquarie Island (Goldsworthy et al 1997), Iles Kerguelen (Cherel et al 1997;Lea et al 2002a), Bouvet Island (Klages et al 1999;Kirkman et al 2000) and the Antarctic Peninsula (Casaux et al 2003). Krill and various fish species constitute the bulk of the diet, with the relative importance of the different prey species varying with geographic location, season and the sex of individuals .…”