| Diamondback terrapins (Malaclemys terrapin) are distributed along the US east coast from Massachusetts to Texas in brackish water habitats. This long-lived, sexually dimorphic turtle is subject to both terrestrial and aquatic threats. For example, terrapins comprise a large component of bycatch species in the commercial fishery for blue crabs (Callinectes sapidus), and females are subject to roadkill when they come ashore to nest. Until now, no clear population definition had been established for this continuously-distributed species, so effective conservation efforts to mitigate population-level threats have not been realized.; To determine ecologically and evolutionarily relevant management units, I used molecular techniques (i.e., microsatellite DNA) to test the hypothesis that M. terrapin comprise one single, homogeneous population. To assess the magnitude of the threat that actively-fished commercial crab pots pose for terrapins, I conducted experimental fishing studies with crab fishers in North Carolina and tested the ability of several bycatch reduction devices (BRDs) to exclude terrapins but retain valuable blue crabs. I also used elasticity analyses to rank different BRDs among several management options. Finally, to estimate adult survival rate, capture probability, and abundance for mangrove terrapins, I conducted a mark-recapture study in the Big Sable Creek (BSC) complex of the Florida Everglades and analyzed individual encounter histories.; Results indicate that M. terrapin exists as at least six distinct metapopulations or regional management units (MUs), which do not coincide with previous morphologically-based subspecies designations. Additionally, microsatellite analysis revealed that male-biased dispersal exists in M. terrapin. Next, field studies revealed that terrapin interaction with blue crab fishery activity primarily occurs in the early spring, close (i.e., <250m) to shore. Terrapin bycatch in crab pots can he mitigated by using BRDs, although some BRDs still allow adult males to enter. Larger (i.e., 5.0 cm) BRDs did not significantly affect catch rates of crabs, but smaller (i.e., 4.5 and 4.0 cm) BRDs did ( p < 0.001). Finally, I established the first adult survival rate (ϕ = 0.79) and population estimate (mean N = 1545 individuals) for mangrove terrapins, and I determined that their distribution within Big Sable Creek lies largely in unsurveyed habitat. |
