POPULATION DYNAMICS OF THE WANDERING ALBATROSS DIOMEDEA EXULANS AT MARION ISLAND: LONGLINE FISHING AND ENVIRONMENTAL INFLUENCES

  • D C NEL BirdLife International Seabird Conservation Programme, BirdLife South Africa, P. O. Box 1586, Stellenbosch 7599, South Africa. <br>Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
  • F TAYLOR Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
  • P G RYAN Percy FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa
  • J COOPER Avian Demography Unit, University of Cape Town, Rondebosch 7701, South Africa
Keywords: <i>Diomedea exulans</i>, longline fishing, Marion Island, population dynamics, Prince Edward Islands, Subantarctic, wandering albatross

Abstract

The subantarctic Prince Edward Islands (Marion and Prince Edward) support the largest breeding population of the Vulnerable wandering albatross Diomedea exulans. The number of birds breeding at Marion Island has fluctuated over the past three decades apparently as a result of both real changes in the size of the population and changes in the proportion of the population that attempts to breed in a given year. Changes in several demographic parameters that appear to be influenced by both environmental and anthropogenic effects are described. From 1994–2001, the proportion of first-time breeders in the population was positively correlated with the maximum ENSO (Niño 3) index, whereas from 1984–2000 the annual survival rates of breeding adults were negatively correlated with Japanese pelagic longline fishing effort in the southern Indian Ocean. Adult survival rates were significantly correlated with those on neighbouring Possession Island, Crozet Islands, but differed from those at South Georgia, suggesting common factors operating at an ocean-basin scale. The average survival rate of adult females was lower than that of males. Males who lost partners took 40% longer than females to find a new mate, suggesting a male-biased population. Survival rates of juvenile males and females did not differ. The age distribution of first-time breeders shifted progressively towards younger birds during the 1990s. Higher than expected survival rates of breeding adults during the late 1990s may be linked to large amounts of supplementary food being made available by the initiation of a longline fishery for Patagonian toothfish Dissostichus eleginoides close to the islands at this time. Overall, breeding success was better than recorded at other localities, indicating that breeding conditions at Marion Island were comparatively favourable. The early implementation of both international and national conservation initiatives to reduce the impact of longline fishing on this species and improve its conservation status is encouraged.

Afr. J. mar. Sci. 25: 503–517
Published
2005-05-12
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X