Population Dynamics of the Wandering Albatross, Diomedea exulans, of the Crozet Islands: Causes and Consequences of the Population Decline

Abstract

Between 1966 and 1985 breeding populations of wandering albatrosses on three islands of the Crozet group decreased at annual rates of 2.6, 4.9 and 6%, but with a rapid decline, at all except one colony, between 1969 and 1975. For the whole study period, the mean age at first breeding was 11.2 yr in females and 12.1 yr in males. Since 1973 birds have bred at younger ages. Breeding success did not vary significantly over time but was correlated with the survival of breeding birds; it was the same for experienced breeders and for birds attempting a first breeding. Adult survival was 90.5% per year during the rapid decline period and 94.4% afterwards. Females appeared to have a higher mortality than males. Immature survival was low (71.5% per year between fledging and 5 yr old) but increased from 1966 to 1980: it was 91.8% per year between ages 6-11 yr. The high adult mortality appears to be the major cause of population decline and is assumed to result from accidental deaths in fishing tackle and from deliberate trapping or shooting by fishermen. Differential survival between males and females is probably due to their distribution when at sea, females foraging more frequently than males in waters where fishing activities occur. Likewise, immatures foraging in similar waters to females have suffered a high mortality. The consequences of the decline for the future of albatross populations in the southern hemisphere is discussed.