The Fluctuating Abundance of Endangered Mammals on Bernier And Dorre Islands, Western Australia - Conservation Implications.

Abstract

Bernier and Dorre Islands in Shark Bay, Western Australia, provide refuge to populations of five species of threatened mammals that are extinct on the mainland other than as reintroduced or captive populations. This paper provides estimates of changes in population size of four species over three years from 1988-9 to 1991-2. The period from November 1986 to March 1989 was one of below average rainfall intensifying to severe drought on the islands; the period from mid 1989 to 1992 was one of average to above-average rainfall. Three of the four species (L. hirsutus, B. lesueur and P. bougainville) showed substantial and significant increases and one species (L. fasciatus) showed a small but non-significant increase in abundance. Combined estimates of minimum population size for both islands in 1991-2 vary from c. 4,000 P. bougainville to c. 10,000 L. fasciatus. If these densities are regarded as typical of average rainfall years then the drought in the late 1980s reduced populations of P. bougainville by up to 75%, B. lesueur by 65%, and L. hirsutus by up to 60%. Combined estimates for the four species give densities for the community of medium-sized mammals which vary between 160 km-2 in drought and 260 km-2 in years of average to above average rainfall.