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Turtle and Tortoise Newsletter, 2000, 2:8
© 2000 by Chelonian Research Foundation

Turtle and Tortoise Newsletter

Terrapin research at Gateway National Recreational Area

Russell L. Burke and Jeremy Feinberg
Dept. of Biology, Hofstra University, Hempstead, NY, 11549;
E-mail biorlb@hofstra.edu

The Gateway National Recreation Area (GNRA), managed by the National Park Service (NPS), is a large estuarine park in the mouth of the Hudson River, thereby constituting New York Harbor. GNRA is comprised of four “units” encompassing a total of 26,000 acres. The three New York units are “Jamaica Bay”, “Breezy Point”, and “Staten Island”; the New Jersey unit is “Sandy Hook”. All four units are located in the Hudson-Raritan Estuary, the southernmost section of the Hudson River Watershed.

Jamaica Bay Wildlife Refuge (JBWR), the largest unit of GNRA, has been the main focal point of our study so far. JBWR is a 9,155-acre estuarine wildlife refuge located at the southwestern corner of Long Island, New York. The refuge runs through the boroughs of Queens and Brooklyn, and consists of a main island called Rulers Bar Hassock and several smaller islands. JBWR has at least 100,000 visitors each year, while GNRA as a whole had 6.4 million visitors in 1996. As the fifth most highly visited national site in the United States, GNRA has about the same number of visitors as Yosemite and Yellowstone National Parks combined. Thus GNRA provides an invaluable service by creating opportunities for the public to learn about and interact with estuarine ecosystems and their inhabitants.

We began studying diamondback terrapin (Malaclemys terrapin) nesting ecology at the Jamaica Bay Wildlife Refuge in 1998. We advertised generally for help with terrapin research and found a number of interested volunteers, mostly from New York City and Long Island. With their help we found populations of nesting terrapins at three different locations at Gateway National Recreation Area in 1998. We made estimates of activity levels based on evidence such as depredated nests, turtle egg shell fragments, dead adult female terrapins found in upland regions, hatchlings, false nests, and tracks leading inland from the water.

Female terrapins nested from 3 June through 23 July (51 days), and laid up to two clutches per season, depositing an average of 10.9 eggs per nest. Nesting activity increased with daily high temperature and high tide. Seasonal activity levels peaked three times during the nesting season, on 17-20 day intervals. The majority of females were captured when there was 25-75% cloud cover. The majority of nests were counted in shrub-land, mixed-grassland, and dune habitats, but nest density was highest in non-vegetated habitats such as a man-made, sandy trail and beaches.

Previous research at JBWR showed that until the mid-1980s, there were no major mammalian predators inhabiting the Refuge, leading to extremely low nest predation and extremely high nest and hatchling survivorship. A raccoon population appears to have become established in the late 1980s and early 1990s. We discovered that raccoons depredated 92.2% of terrapin nests (n=77) in 1999. We counted 1,319 and 1,840 depredated nests in 1998 and 1999, respectively, at the Refuge. An overall nest survivorship rate of 5.2% was determined (n=77), and hatchling survivorship in successful nests (n=3) was 54%. We also found the carcasses of 23 female terrapins that were apparently killed by raccoons as the terrapins came on land to nest.

Our research at Gateway is now branching into four different directions. We are now surveying several more nesting beaches in GNRA, in an attempt to learn more about other important nesting beaches and how predation rates vary among them. To that end we are focussing on smaller islands that do not support raccoon populations, but apparently are used by nesting terrapins. We also expect to begin work at the Sandy Hook unit of GNRA, where the nesting population appears to be at least as large as at JBWR, and raccoons have been predating nests all along. We will also be studying JBWR nesting in greater detail, looking at the importance of predation by plant roots, while at the same time monitoring nest temperatures and resulting hatchling sex ratios. We are beginning a raccoon study at JBWR, in which we will determine the size of the raccoon population, use night vision and radio telemetry to document movements during and after the terrapin nesting season, and attempt to use taste aversion training to modify raccoon behavior. Finally, we just received funding to begin radio tracking 20 terrapins in Jamaica Bay, as well as begin a major mark-recapture study throughout GNRA.