Evaluation of Bycatch Reduction Devices on Diamondback Terrapin Bycatch in Alabama Salt Marshes

Fishery bycatch represents a major anthropogenic threat currently decimating numerous marine species' populations.  Gear modifications have been successfully implemented in a variety of fisheries to address bycatch issues.  However, to be widely accepted by all stakeholder groups, modifications need to reduce the capture of bycatch individuals without significantly diminishing the total catch of targeted species.  Crab pot mortality has been largely recognized as threatening the survival of diamondback terrapin (Malaclemys terrapin) populations throughout its range.  This obligate estuarine turtle is a top level predator directly contributing to the overall health of vital salt marsh ecosystems.  Bycatch reduction devices (BRDs) were developed to decrease the funnel openings of crab pots so terrapin entry would be prevented without affecting crab ingress.  The efficacy of this gear modification was evaluated on the Gulf Coast of Alabama from 2007-2009 in Cedar Point Marsh, which supports the largest aggregation of terrapins in Alabama.  For the study, a side-by-side comparison of crab pots fitted with BRDs and not fitted was completed.  Both terrapin and crab catch were analyzed.  In addition, the size of captured crabs was estimated and compared between the two pot types.  Terrapin bycatch was significantly higher in crab pots not fitted with BRDs.  But, total crab catch along with the catch of marketable sized crabs were significantly lower in pots fitted with BRDs, although the study’s crab sample size paled in comparison to other studies that showed no significant decrease in crab catch or even a higher catch with BRDs.  Therefore, BRDs appear an effective tool to prevent crab pot mortality in diamondback terrapins.  Recent surveys have indicated that the Alabama population of terrapins has experienced a historical decline mostly due to crab pot mortality.  This threat requires adequate management to ensure the population’s future viability.  In the wake of the Deepwater Horizon oil spill, baseline data obtained from Alabama terrapins will be crucial in understanding the disaster’s ecological consequences from more heavily impacted terrapin populations along the Gulf Coast.