The Decline of Rockhopper Penguins Eudyptes chrysocome at Campbell Island, Southern Ocean and the Influence of Rising Sea Temperatures

Abstract

Rockhopper Penguin Eudyptes chrysocome numbers at Campbell Island have declined by 94% since the early 1940s. Many breeding colonies have disappeared and the remaining nine major colonies have all shrunk in size. We estimate there were 103 000 breeding Rockhopper Penguins in 1985, compared with approximately 1.6 million in 1942. The decline had started by 1945, was greatest during the next ten years and coincided with substantial changes in sea temperatures. The mean December-February sea-surface temperature rose from 9.1°C in 1944 to peaks of 9.7°C in 1948-49 and 9.6°C in 1953-54. It declined to 8.6°C by 1965, rose rapidly to 10.2°C by 1970, and has averaged 9.7°C since then. In one colony, Rockhopper Penguin numbers temporarily increased after the cooler seas in the 1960s. We consider that rising sea temperatures are associated with the decline, which may have been caused by changes in the penguins' food supply; there is no evidence that terrestrial factors have been responsible.