Lab and Field Tests of Terrapin Release Hatches

Lindsey Dillard ’24

 

The objective of this project was to design and complete lab and field tests of a “terrapin release hatch” to be used on commercial-style crab traps in the extensive blue crab fishery along the Atlantic and Gulf coasts of the U.S. We designed and lab tested approximately 15 separate prototypes of release hatches that ostensibly were to be operated by terrapins (the bycatch) and not by blue crabs (the target species). Tests were completed in a swimming pool filled with estuarine water, and terrapins were filmed attempting to escape traps fitted with the different release hatch designs. From hundreds of hours of videos, none of the designs was effective, primarily because terrapins were unable to operate the release hatches. Our most recent hatch design, however, is simply an opening in the top of the trap that we cover with parallel lengths of elastic cord. We have video evidence from the pool that terrapins are able to push through the elastic cords to escape the trap. We have no field evidence yet that documents terrapin escape from traps set in estuarine water. We have, however, documented that marketable sizes of the target species (blue crabs) do not use the release hatch, whereas the smaller crabs are able to exit traps through the hatch. We are encouraged that this elastic hatch design seems to preferentially retain larger blue crabs and lets smaller, non-marketable crabs out.