Diamondback Terrapin

Experiments were completed in SE Virginia during June–July 2014 and 2015 to examine the responses of blue crabs (Callinectes sapidus) and diamondback terrapins (Malaclemys terrapin) to commercial-style crab pots modified in visual and other ways that might attract and retain crabs while excluding terrapins as by-catch. In a seawater tank, far fewer crabs entered crab pots fitted with red plastic by-catch reduction devices (BRDs), relative to pots without BRDs. Crab retention times, however, were significantly longer in pots fitted with red BRDs. In a second experiment, fewer terrapins entered crab pots with funnels painted red relative to black. From a field pilot study, the legal crab catch from pots with red BRDs was similar to pots without BRDs, and terrapin by-catch was reduced. Relative to those treatments, fewer crabs and more terrapins were captured in pots with orange BRDs and blue BRDs, and in pots with a magnetic field directed into the funnel openings. Based on these results, a final field trial yielded comparable crab catch from 15 pots without BRDs and 15 pots fitted with red plastic BRDs. Of a by-catch of 68 terrapins, 58 were from pots without BRDs. The structure and color of BRDs can exclude most terrapins; because crab retention rates are high, the net effect of BRDs on crab catch is relatively minor, even though fewer crabs may enter pots fitted with BRDs.

Human development can impede wildlife moving between complementary habitats,
particularly in highly disturbed coastal ecosystems. Coastal barriers may affect the behavior of diamondback
terrapins (Malaclemys terrapin), a salt-tolerant estuarine turtle that requires access to complementary upland
habitat for annual nesting. We used telemetry to quantify terrestrial and aquatic movements of 78 nesting
female terrapins in response to coastal barriers at 2 sites in Barnegat Bay, New Jersey, a heavily developed
estuary. Nesting female terrapins traveled significantly greater distances with more tortuous paths or spent
significantly more time in the water when their movements were obstructed than females nesting at beaches
with no obstructions. We hypothesize that the additional effort and displacement associated with
reproduction where obstructions exist will reduce terrapin fitness and potentially contribute to population
declines. Our study demonstrates a unique approach to quantifying effects of barriers on organisms requiring
complementary habitats, and improves our understanding of the impacts of shoreline hardening on estuarine
wildlife threatened by encroaching coastal development.