Estimates of adult survival and migration for diamondback terrapins: conservation insight from local extirpation within a metapopulation

Abstract

As a case study we analyze a recent extirpation within a metapopulation of diamondback terrapins (Malaclemys terrapin) in a South Carolina salt marsh. Survival and migration probabilities were estimated by means of a multistratum approach in Cormack–Jolly–Seber mark–recapture models to obtain transition probabilities among four tidal creeks adjoining a river. Terrapins showed high fidelity to each subpopulation and the low migration rates were insufficient for recolonizing a creek that had suffered extirpation. Annual survival rates for adult female terrapins averaged 0.84 across all creeks, ranging from 0.748 to 0.971. Survival rates were converted to instantaneous mortality rates (M) for the purpose of calculating the mean life-span as 1/M. When re-expressed in terms of mean life-span, the results confirmed that the average female terrapin did not survive to its estimated age at maturity, as might be predicted if additional mortality of females in crab pots was implicated. The results emphasize that incidental mortality of terrapins in crab pots is a conservation concern. Simple modifications of crab-pot design, such as an entrance reducer, can successfully mitigate this threat to the survival of terrapin populations.