Final Report on Surveys of the Arboreal and Terrestrial Snail Fauna of American Samoa

Miller, Stephen

The native land-snail fauna of Pacific islands is under assult by introduced predators. Some of these predators are intentional introductions aimed at controlling the agricultural pest AchatinajWica. Their ability to control this pest snail is questionable. However, these predators, and rats, are partly responsible for large decreases in the abundance and diversity of land snails throughout the Pacific basin. The surveys reported here evaluated the extent to which introduced snails have spread throughout the four main islands of American Samoa and qualitatively assessed the status of the four endemic partulid tree snail species and several other native and endemic snail species. The giant African snail Achatina fulica was introduced into American Samoa prior to 1977, and populations rapidly increased. In an effort to eradicate the giant African snail, two carnivorous snails, Gonaxis kibweziensis and EugJOJUlina rosea, were introduced in 1977 and 1980, respectively. Results of our surveys showed that A. folica and E. rosea have spread throughout the main island of Tutuila. Gonaxis. ldbweziensis is present on Tutuila but seems to be in decline. Achatinafolica and E. rosea were also found on the northwest corner of Ta'u, but were absent from Ofu and Olosega. Our surveys showed that several species of native or endemic snails are endangered. One emdemic species of partulid tree snail is extinct, and the three remaining partulid species were seen in small numbers at only three of the 17 sites surveyed. Comparison to an earlier (1975) survey showed that other species of native arboreal and terrestrial snails have also greatly declined in abundance. Some native and endemic snails were not found during the 1992 surveys. Overall, the land-snail fauna is endangered with several species on the verge of extinction. Immediate action is needed if the remaining snail fauna of American Samoa is to be saved. The declines and extinctions of native snails have resulted from loss of habitat to agriculture and hurricanes. and predation by introduced carnivorous snails and rats. Several recommendations are given to help mitigate the causes of the continuing decline in snail abundance and diversity. Most importantly, two refugia that are free of introduced snails have been identified in this report. Endangered populations of snails should be moved to these refugia and periodically monitored.