Due to a variety of factors including habitat loss, drowning in crab pots, and the predation of adult turtles and their eggs, diamondback terrapin (Malaclemys terrapin) populations have declined throughout much of their range. In Virginia, diamondback terrapins are classified as a Tier II species (“High risk of extinction or extirpation”) according to the Virginia Department of Game and Inland Fisheries. During summer 2015 we studied the nesting ecology of terrapins near Wallops Island, VA. More specifically, we compared nest success and nest predation between nesting areas located on Wallops Island proper (“mainland” sites) to small “isolated” island sites located in nearby saltmarsh. The purpose of this comparison was to determine the relative importance of these two nesting areas to population recruitment. We hypothesized that nest predation would differ substantially between these two areas due differences in the ability of nest predators (e.g. raccoon, fox, etc.) to access these areas. To compare nest predation, we systematically surveyed 11 mainland and 11 isolated sites over the majority of the nesting period. These sites were monitored approximately every 3 days for visual evidence of depredated nests.
Results/Conclusions
We found the average density of predated nests was greater for mainland nesting sites (372 nests/ha) than for sites located on islands (94.5 nests/ha); however this difference was marginally non-significant (T=2.075, P=0.06, n=11). Based on findings from previous years of research at this site, the probability of a nest becoming depredated is similar between isolated and mainland nesting areas (35%). Taken together these data suggest that the difference in the density of predated nests that we observed was a function of reduced nesting activity at the isolated sites relative to mainland sites, rather than differences in predation risk. Since isolated sites are poorly protected from heavy winds, storms, and spring tides as compared to mainland sites, isolated areas pose a greater risk of inundation from saltwater which could account for differences in nesting activity between these two locations.