Fragmentation and Demography as Causes of Population Decline in Seychelles Freshwater Turtles (GenusPelusios)

Abstract

In the Seychelles islands, all 3 endemic freshwater turtle taxa are either extinct (Pelusios seychellensis) or critically endangered (Pelusios castanoides intergularis and Pelusios subniger parietalis). These turtles are threatened by habitat loss, and monitoring of populations since 1996 has identified significant ongoing population declines. Drainage of wetland sites has reduced the number of populations, but even surviving sites are mostly reduced in area and quality. Only 5 Pelusios subniger parietalis and 3 Pelusios castanoides intergularis populations showed evidence of reproduction within the last 10 years. Longevity records suggest that Pelusios species may live for at least 40 years, and captive breeding data indicate that sexual maturity may be comparatively early in these taxa (ca. 2 years). Populations can persist for decades after reproduction has ceased, resulting in effective population extinction, even when environmental conditions stabilized. This is a characteristic that is shared with other long-lived species, and demography should be an essential component of recovery plans for any such species. Conversely, improvement in habitat may allow rapid population recovery, as has been demonstrated in Pelusios subniger parietalis on Fregate Island.