A Field Study of a Vanishing Species, Achatinella mustelina (Gastropoda, Pulmonata), in the Waianae Mountains of Oahu

Abstract

A population of Achatinella mustelina occupying four trees within a 5 x 5-m quadrat on a ridge in the Waianae Mountains of Oahu, Hawaii, was studied by mark-recapture techniques. Between September 1974 and December 1975, 222 snails were individually marked and measured. Recapture analyses indicate that the standing population consisted of about 220 snails, of which an average of 40 percent were large enough to be sexually reproductive. Growth of A. mustelina was found to be slow, averaging about 2 mm increase in length per year from a birth size of 4.50 mm to a size at terminal growth of 18.44 mm. Maturity is estimated to occur at an age of 6.9 yr. During the course of the study, snails belonging to the introduced predatory species Euglandina rosea were found progressively nearer the study site. In August 1979, shells of E. rosea were abundant in and about the study area and no living specimens of A. mustelina or any other arboreal snail species could be found. We conclude that E. rosea was responsible for the destruction of the population under study and that species with life histories similar to that of A. mustelina stand little chance of surviving the ravages of such introduced predators.