Abstract
- Trends in diamondback terrapin (Malaclemys terrapin) abundance and demography suggest that crab pot bycatch mortalities may be contributing to population declines and demographic shifts of this estuarine turtle. Designing effective regulations to minimize terrapin-crab pot interactions requires information on the spatial ecology and seasonal behavior of terrapins. Thus, our goals were to 1) identify spatial and temporal aspects of terrapin-crab pot overlap and 2) assess the likelihood of encounters (bycatch risk) based on densities and distribution of crab pots and terrapins as well as terrapin behavior in North Carolina. We radio-tracked 29 terrapins and documented their locations and behavior, as well as the locations of nearby crab pots, in sounds where crabbers have observed terrapin bycatch. The potential for interactions between terrapins and crab pots was determined using a spatially-explicit predator-prey model to assess their spatial overlap based on seasonal distribution and activities. This model has been used in previous studies to predict areas of high bycatch by comparing the density and distribution of fishing effort (predator) to that of the marine bycatch species (prey) and describes the degree to which the spatial correlation of predator and prey deviates from the random expectation under uniform spatial distributions. Results indicate that spatial overlap is greatest in warm months when terrapins are active and using the same shallow, near-shore habitat as blue crabs. This pattern suggests higher bycatch risk for terrapins in the Spring and Summer, which is corroborated by our observed bycatch data. However, we also found when seasonal and semi-aquatic behavior of terrapins is incorporated into the spatial overlap model, bycatch risk is reduced.