Population status of diamondback terrapins on the Catlett Islands

Abbi Belvin and Justin Mitchell, 2020

We completed a mark-recapture study of terrapins from the Catlett Islands on the York River in Virginia (part of the Chesapeake Bay National Estuarine Research Reserve). Our objective was to estimate the size and determine the demographics of the terrapin population from a location that had not been studied previously. From May 30^th to July 26^th 2019, five crab pots were placed at two locations around the Catlett Islands. Each pot was modified with a 120-cm chicken wire chimney to allow trapped terrapins access to the surface for air. The pots were baited with menhaden on Mondays and Wednesdays each week, then cleared of crab catch and terrapins Tuesday-Friday (pots were left open on the weekends). The carapace length, width, and shell depth of each terrapin was recorded, and their shells were notched for identification in case of recapture. Over the 9-week study, 78 turtles were caught, with 0 recaptures (Figure 1). On average ± SD, terrapin captures were greater on the first day following baiting than the second day, but not significantly so (2.5 ± 3.7 vs 1.8 ± 2.0 terrapins d^-1). Of the turtles captured, 34 were females and 44 were males.  Age ranged from 2 years to 9+ years, and carapace length ranged from 6.7 cm to 20.6 cm. None of the females was gravid, based on abdomen palpitation. Five terrapins were found with leg or foot injuries, and one was found deceased in a pot with a wound to its neck, likely from the concomitant catch of crabs (on average, 2.1 crabs pot^-1 d^-1). Despite the loss of 30 terrapins drowned in a ghost pot prior to the start of the study, the population of diamondback terrapins from the Catlett Island ecosystem appears robust. No recaptures in a 9-week period within the same location is unusual (Table 2) and points to an abundance of terrapins. We doubt that terrapins are leaving the island complex as transients or behaviorally are avoiding a second capture.