Efforts to Conserve the Local Diamondback Terrapin Population
By Roz Herlands, Associate Professor of Biology
A visit to our Animal Care Facility in the F-wing Laboratory must include a stop in the "terrapin farm". It is here that nearly 2000 Northern diamondback terrapin hatchlings have spent their first nine to ten months of life. These are no ordinary baby turtles; they are turtle hatchlings brought to life after death. They are the result of a decade-long project that involves the recovery of viable eggs from crushed road-killed females and the incubation of these eggs in artificial nests in our Lab.
The diamondback terrapin, Malaclemys terrapin, lives in the coastal salt marshes along the Atlantic and Gulf of Mexico seaboards from Cape Cod to Texas. Of the 270 different species of turtles, diamondback terrapins are the only ones exclusively adapted to life in brackish (variably salty) water. The Northern subspecies is found from Virginia to Massachusetts. Terrapins spend most of their active lives swimming in water or foraging in the marsh vegetation in the intertidal zone. Only the females come out of this aquatic environment; they do so in late May, June and July to find a place above high tide to dig their nests, in which they usually deposit 8-12 eggs. Their usual nesting grounds are sand dunes. Unlike many turtles, terrapins nest during both the day and night. The diamondback terrapin has State protection in New Jersey, but that does not keep it from being harmed by human activities: its nests are destroyed by coastal development, thousands drown in commercial crab traps, and many adult females are killed crossing causeway or barrier island roads, especially at night, looking for nest sites to lay their eggs.
For the past eight years, my biology colleague Roger Wood and I have worked together on a long- term research and conservation project on these turtles. Dozens of Stockton students, summer college interns from the Wetlands Institute, and especially John Rosita (caretaker of the Animal Care Facility) have helped us. One of our efforts to conserve this species involves round-the-clock road patrols in Cape May County and early morning road patrols along the Longport and Margate causeways in Atlantic County during the annual terrapin nesting season. Students and local volunteers do most of these patrols. They recover intact eggs from the road-killed females and these eggs are brought to Stockton for incubation in artificial nests of moist vermiculate in large plastic containers. We maintain these eggs under controlled temperatures in laboratory incubators and monitor the eggs for developing embryos. Hatchlings emerge from the eggs about 7-10 weeks after their arrival at Stockton and are then 'head-started' in a special 26-27° C (about 80° F) room, known as the terrapin farm, where they remain active, eat regularly and grow rather than hibernate as their cousins do in the wild. By the following June, the hatchlings are large enough to be returned to their natural wetlands habitat with little likelihood of predation by sea guus.
We initially tried to incubate the eggs in a warm environment (Roger's garage attic at the shore) to produce females (to compensate in part for the road-ki11ed ones), because terrapins, like many other turtle species, have temperature-dependent sex determination; that is, their sex is determined by nest temperature, not at fertilization by the combination of sex chromosomes. The hatching success was, however, very low (9%) due to a long heatwave over the 4th of July weekend. To improve the hatching rate, we decided to incubate these "rescued" eggs in laboratory incubators under controlled and constant temperatures. We were able to raise the hatching rate to between 33% and 40%. This approach also allowed us to study the effect of incubation temperature on development and sex determination. We found that incubation temperatures of 30-32° C always produce only females and that incubation temperatures of 24-28° C produce only males.
The success of the terrapin farm is a testament to the ingenuity and perseverance of John Rokita and Jimmy Grant (NAMS' own lab mechanic and carpenter); it is a genuine Rube Goldberg invention. It has 16 old lab sinks that serve as the large tanks for the hatchlings; each sink is equipped with its own faucet for adding clean brackish water and a drain pipe to take away dirty medium, and a large brick for the hatchlings to bask under a 100-watt light. There is a large, 155 gallon tank to mix and store the brackish water with pipes leading to the faucets of each of the tanks. [I should mention that this set-up has been copied for a similar care facility at the Philadelphia Zoo.] There are also two large exhibit tanks and two plastic swimming pools that house adult terrapins which are recovering from human-caused injuries. In addition to our hatchings and the injured adults, the terrapin farm also cares for terrapins brought in by local citizens or found by the Marine Mammal Stranding Center. John and his student helpers in the Animal Care Facility take care of all the terrapins; this work entails daily feedings (including Saturdays, Sundays, and all holidays), frequent tank cleanings, and preparation of the brackish water. This conservation project would not be possible without the tender loving care provided by John and the students. Roger and I also appreciate the commitment that Stockton has made to this project; it costs a lot to maintain this facility, to feed the animals, and to make, the salt water medium.
When the hatchlings emerge from the eggs, they are the size of a quarter, with soft shells and a large yolk sac still attached to their belly. John Rokita and I have found after some trial and error what kinds of transitional environments the hatchlings need before they enter the larger tanks. Our efforts have substantially reduced early hatchling deaths. Over the next nine to ten months, the hatchlings increase in size (from about 3cm to 8cm) and their shells harden. They become voracious eaters. With the help of local school groups, we return the hatchings to different salt marsh areas in June. We hope that they are strong and big enough to survive. They certainly swim off eagerly as if ready for a new adventure. But we do not know what actually happens to them after their release. This kind of information is certainly important for our conservation efforts. We have tried marking them by filing notches in the margins of the carapace, but such notches disappear within a year in growing terrapins so we have abandoned this marking approach. We have tried to tag the hatchlings by inserting a tiny microchip, whose number can be easily be scanned, into the loose tissue in front of the right hindlimb. This method is expensive but is more permanent and seemingly harrnless, so we plan to mark as many hatchlings this way as we can this summer before their release.
Another focus of our conservation efforts is to decrease the number of adult terrapins caught in crab traps. Terrapins and crabs inhabit the same back bay habitats. The bait in the traps attracts both terrapins (who are real carnivores) and crabs. However, unlike the crabs who breathe through gills, terrapins have lungs and so need to come to the surface to get their oxygen. Roger and the student interns at the Wetlands Institute in Stone Harbor have found that even when the traps are checked every day, about a quarter to a third of the turtles caught in them drown. The number of commercial traps in New Jersey has increased exponentially over the past 15 years, from about 20,000 per year to over 60,000 per year, and so the number of terrapins that drown in these traps has also increased.
We estimate that 15,000 or more adult terrapins die each year in commerical crab traps in New Jersey alone. Roger and the student researchers have developed a simple excluder device (about 2 by 4 inches) that fits over the openings to crab traps and lets in crabs but excludes about 90 percent of adult size terrapins; moreover, traps fitted with the excluder device tend to catch more marketable- size crabs. Similar research by the New Jersey Division of Fish, Came and Wildlife and by Willem Roosenberg on the Chesapeake Bay population has confirmed Roger's crab trap data. New Jersey now requires the excluders on all commercial crab traps.
Around a hundred years ago, terrapins were considered a gourmet food item and a dozen females brought the modern equivalent of $1700 at the markets in Philadelphia and Baltimore. Not surprisingly, the terrapins were hunted to near extinction in the mid-Atlantic region. Prohibition led to a decrease in available sherry, an essential ingredient in terrapin stew, and food fads changed, so the terrapin populations did rebound in the middle part of this century. With the help of a number of Stockton biology students, I have also started a project to measure the extent of the genetic variability in the local terrapin population. This kind of information tells us what the terrapin populations long-term evolutionary survival might be. Although the actual size of the local population today is unknown, several indicators suggest that is has steadily declined over the past 25 years. The question remains whether the local population has the necessary variability in its gene pool to meet environmental challenges in the long-term.
We realize that our efforts are not keeping pace with the number of terrapins lost locally each year to human activities, but we hope that our efforts and continued public interest in and awareness of the plight of the terrapins will keep them from becoming an extinct species.