Diamondback Terrapin Research

Diamondback Terrapin populations have undergone drastic declines due to historic and contemporary threats. These are our only brackish dependent species of turtle and occur in coastal areas from Massachusetts to Texas. They also happen to be the state reptile of Maryland! Louisiana has approximately 653,000 ha of habitat that could be used by terrapins, the most of any state, and roughly 30% of available habitat within their entire range. However, their sustainability is negatively impacted by habitat loss and fragmentation, nesting mortality, and because their range largely overlaps with blue crabs (Callinectes sapidus), incidental capture and drowning in crab traps. We are trying to better understand terrapin within the state through multiple projects including long-term mark-recapture, nesting success, and bycatch mortality through the blue crab fishery.

Diamondback Terrapin Mark-Recapture

Since 2021, we have been conducting mark-recapture of terrapin at Elmer's Island and East Grand Terre, building upon work started by LDWF in 2012. Through our work, we've marked hundreds of terrapin and have begun to collect baseline data of terrapin demographics in Louisiana. From our work, we've noticed a significant bias towards adult females in our populations and that female terrapin in Louisiana are some of the largest throughout their range! We've also shown that terrapin in relatively isolated habitats have very high survival, while terrapin more closely associated with humans are more scarce.

Terrapin and Blue Crab Traps

Terrapin Interactions with Blue Crab Traps

Over the course of two years we ran crab traps in and around an area of known terrapin habitat to understand where and when terrapin are likely to interact with crab traps. Our research has found that terrapin and crab traps are more likely to interact with each other during the summer months and within tidal channels as opposed to open water habitats. This information can be really important for promoting a sustainable blue crab fishery and potential localized implementation of bycatch reduction devices!

Terrapin and Bycatch Reduction Devices

Numerous studies outside of Louisiana have shown the benefits of using Bycatch Reduction Devices (BRDs) to prevent the unwanted capture of non-target species in crab traps. We experimented with different placements and different materials to understand the potential impact of BRD usage in coastal Louisiana. We've found that not only do they prevent terrapin capture, but they also exclude hard head catfish, and importantly do not affect the size of blue crabs captured, which is really important for adoption by the commercial crab industry!

Terrapin Telemetry

Ultra-High Frequency Automated Telemetry

Our terrapin telemetry project uses a system of receivers (yellow) which continuously record terrapin tagged with UHF tags. Unlike traditional telemetry which requires either exhaustive active tracking or expensive satellite tags with low resolution our system is passive and has allowed us to accumulate thousands of GPS level precision locations for terrapin in their barrier island habitats! These data will allow us to answer really neat questions about terrapin behavior and ecology.

Terrapin Movement

Our telemetry data has allowed us to understand movements of terrapin at both the hourly and daily scale. From this, we know that terrapin our more likely to move during the mating and nesting season, when females are likely looking for nesting locations and males are looking for mating opportunities. We've also found out that our terrapin don't seem to rest during the winter and our likely active all year unlike their more northerly counterparts!

Terrapin Habitat Use

Our telemetry system has provided us with thousands of location data for many individual terrapin at a very fine resolution. We use these data and step-selection functions to look at preferred and selected for habitat in coastal Louisiana. Our data suggests that terrapin are more likely to use salt marsh and tidal channels over mangrove habitat, and mangroves are likely used at the highest of tides. Coastal Louisiana is predicted to increase in mangrove abundance and we look forward to investigating how terrapin may respond to this relatively new habitat!