Population, Breeding, Diet and Conservation of the Crozet ShagPhalacrocorax [atriceps] Melanogenisat Marion Island, 1994/95–2002/03

Abstract

The number of Crozet shags or cormorants Phalacrocorax [atriceps] melanogenis breeding at subantarctic Marion Island decreased by 68% from 841 pairs in 1994/95 to 272 pairs in 2002/03. The mean number of pairs at colonies also decreased and was significantly related to the overall number of birds breeding in any given season. The decreases coincided with a period of warming and reduced precipitation at Marion Island and with a decrease in the number of gentoo penguins Pygoscelis papua breeding there. Both these seabird species forage inshore and there is considerable overlap in their diets. Nototheniid fish and the decapod Nauticaris marionis continued to be important in the diet of Crozet shags, but a change in dominance among nototheniid prey suggests availability of prey to shags changed after the mid 1980s. Crozet shags breed for the first time when aged three years. It is probable that about 25% of the mature population did not breed in 1997/98, coincident with a strong El Niño Southern Oscillation event. In four seasons, breeding pairs on average fledged 0.30 chicks from first clutches, an amount thought inadequate to sustain the population. Crozet shags at the Prince Edward Islands should now be regarded as Endangered. Placing breeding colonies in the most highly protected zone on Marion Island, considering the establishment of an ex situ population and undertaking a genetic study of the specific status of the Crozet shag are recommended conservation measures.

The Prince Edward Islands: Land-Sea Interactions in a Changing Ecosystem

“…Macaroni Penguins are less constrained by a need for sheltered landing sites, breeding in more than 50 colonies at Marion Island and seven at Prince Edward Island, but some 80% breed at two sites on the east coast of Marion Island, at Bullard and Kildalkey (Crawford et al 2003c;Ryan et al 2003a), where they have removed some 3 x 10 5 m 3 of peat (Hall & Williams 1981). By comparison, more agile Rockhopper Penguins occur around the coasts of both islands, breeding along all but the most sheer of cliffs (Crawford et al 2003b;Ryan et al 2003a). They also penetrate further inland, at least locally, but do not venture as far from the coast as the small numbers of Gentoo Penguins breeding at both islands (Adams & Wilson 1987;Crawford et al 2003d;Ryan et al 2003a).…”

“…The islands support some 13% of King Penguins worldwide, 4% of Macaroni Penguins and only 0.5% of Gentoo Penguins (Woehler 1993;Williams 1995;Crawford & Cooper 2003). The population of Southern Rockhopper Penguins is about 5% of the world population (and 17% of the eastern race filholi), but this is affected by the rapid decreases observed at many colonies, including Marion Island (Crawford et al 2003b;BirdLife International 2004a). Penguins dominate the avian biomass at the islands, comprising some 97% of the biomass of breeding adults at Marion Island (9 200 tons) and 60% of the biomass at Prince Edward Island (750 tons).…”

“…Nel et al 2002c;Crawford et al 2003aCrawford et al , 2003bCrawford et al , 2003cCrawford et al , 2003d. Demographic parameters are estimated from individually-marked birds in several study colonies that have been followed since the early 1980s (Nel et al 2002c).…”

“…Breeding success has increased over the last decade, but appears to have been too low to maintain a stable population (Crawford et al 2003c). The decrease in the population of Rockhopper Penguins has been even more marked at Marion Island, falling by c. 40% in 14 years (Crawford et al 2003b). Most of the decrease occurred in the late 1990s, with the breeding population decreasing by an average of 12% per year from 1994/95 to 2001/02 (Crawford et al 2003b).…”

Conservation and management

“…The increase in sea-surface temperature may be related to a southerly shift in the mean position of the Sub-Antarctic Front, with the resultant advection of zooplankton and micronekton to the islands benefiting pelagic predators, but creating unfavourable feeding conditions for inshore feeders (Pakhomov & Chown 2003). Decreased food availability as a result of climate change has been implicated in the decline of three inshore-foraging species at the Prince Edward Islands: the Gentoo Penguin, Rockhopper Penguin E. chrysocome and Crozet Shag (Crawford et al 2003a(Crawford et al , 2003b(Crawford et al , 2004. Climatic perturbations on a global scale may also influence breeding by seabirds, as evidenced by a marked difference in the breeding success of inshore and offshore foragers in 1997/1998, a season coinciding with a major El Niño Southern Oscillation event (Crawford et al 2003c(Crawford et al , 2004.…”