Study on Diamondback Terrapins in the Catlett Islands on the York River: By Justin Mitchell

September 10, 2019

This summer my research partner Abbi Belvin and I, along with some help from our friends GuruBandaa Khalso, Adrianna Gorsky, and Professor Randolph Chambers, monitored the Diamondback Terrapin population within the Catlett Islands on the York River to look at the population’s distribution and dynamics as well as nesting ecology within the islands.  Following the recent research of ENSP’s Honor student Holy Funkhouser developed a GIS-based model of terrapin occurrence in the Chesapeake Bay, that predicted the Catlett Islands would be a suitable nesting habitat and environment for Diamondback Terrapins. The Catlett Islands site is one of 29 sites in the National Estuarine Research Reserve System (NERRS) and is administrated by the Commonwealth of Virginia and the National Oceanic and Atmospheric Administration and is managed daily by the Virginia Institute of Marine Science (VIMS). Terrapins had been known to inhabit this island complex, but no formal studies had been conducted in the area on the species. Since the area was a protected by the NERRS and was controlled by VIMS, it gave us the perfect location to test a prediction from the GIS model and to gain a greater understanding of the terrapin population in the islands. We sought to gain a greater understanding of this species as it is a crucial part of the Chesapeake Bay ecosystem and to most who call the Bay home.

On our initial paddle around the islands in May we discovered something shocking, a lost crab pot that had been swept into a cove in the islands. It contained 30 dead terrapins that had drowned in the trap. It certainly wasn’t the way we wished to start off our survey of the Diamondback Terrapin population there, but it served as a reminder of why this research was important. This species was previously listed as endangered or threated along much of the East Coast, as it was almost hunted to extinction in the early 1900’s as it was considered a delicacy. The population is slowly recovering but it still faces many threats today from human development and as potential bycatch.

From the beginning of May until the end of July we took to the waters of the York River and attempted to see how many turtles we could survey. We set up 5 modified crab pots turned terrapin pots around the islands in order to catch individuals for our survey. Each pot was modified with a chimney that poked out high above the water to allow the turtles to come up and breath air if caught in the traps. Each day we would paddle out to the traps and measure the length, width, and depth of the turtles within. We would notch their shells for identification incase they were recaptured before releasing them back into the wild. We also explored the islands looking for potential beaches for terrapin nesting sites, but we only found a few small beaches that would allow for terrapin nesting.  All the beaches were easily washed over by storms and what nest we found were raided by predators, making these islands an extremely hard location to nest in. Abbi and I also got the unique opportunity to assist in a study on the unique species of diatom that is only found on the back of whales, manatees, and sea turtle. We would assist by taking swabs of algae samples off the backs of our turtles and shipping them out for analysis in order to identify if this species was also found on the back of terrapins.

After three months of hot sunshine, bug bites, and terrapin catching, we managed to identify a total of 78 individual terrapins. We had caught 34 females and 44 males in our traps, with surprisingly no recaptures over the entire three-month period.  Terrapins have a small home range of .5 to 3.5km2and are often recaptured in surveys such as this, but our zero recaptures points to the possibility of a large population of turtles within this small set of islands, or just a population of ones who didn’t want to be recaptured. The data collected shows that our terrapin population was doing well in the Catlett Islands, even after the loss of the 30 turtles in the beginning. There are still some questions to be answered, and we are still conducting analysis on some of the data we collected, but signs are positive for this valuable population of York River turtles. We are preparing a presentation for a conference with the Diamondback Terrapin Working Group in October in Wilmington, North Carolina and hope to share our results with the rest of the Diamondback Terrapin scientific community.

Abbi_Measuring_a_Terrapin Our_Terrapin_Pots Diamondack_Terrapin_Photo Justin_Holding_a_Female_Terrapin




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