Canoeing for Terrapins

My name is Scott Morris.  I am a junior here at the College and plan to attend medical school following my years here.  I am majoring in Biology and conduct research in that department.  I have worked since freshman year for Dr. Randy Chambers, the Director of the Keck Environmental Field Laboratory doing a number of projects, ranging from lab analysis of soil samples from the Everglades to conducting water quality tests in the College Creek Watershed.  This summer, I am doing research that I will continue for the next year and a half which will culminate in a senior honors thesis.

This summer, I am collecting data on the diamondback terrapin population at Goodwin Islands, a 300 acre chain of islands owned by the College and operated by the Virginia Institute of Marine Science.  The Keck Lab believes that terrapin populations in Chesapeake Bay are threatened, but as of now no data exists to show this.  At Goodwin Islands and in the greater bay, terrapins are negatively impacted in two major ways: bycatch in commercial crab-pots and by subsidized nest predation.  Commercial bycatch occurs when a terrapin becomes trapped in a crab-pot and drowns because it can’t escape.  I mainly focus on the subsidized predators, which are animals that move into an area after human interference.  In this case, raccoons, which live in the trees of the Western Island (the largest and only island with living tree cover), predate terrapin nests on the other islands, hiding by day and searching by night, using their keen sense of smell to find the nests.  When they find a nest, they simply dig it up and crack open the eggs to drink the protein-rich egg.  As raccoons offer the chief form of subsidized predation following human interference, their actions as recorded at Goodwin Islands, is valuable data.  It is logical to think that if all nests deposited at Goodwin are predated (or a very large percentage of them) then the terrapin population should be aging each year, without sufficient recruitment into the next generation.  It is then logical to suppose that if the predation continues on such a large scale for many generations, eventually, the females returning to nest (which show very high fidelity to deposit their nests in the place of their birth) will grow older, and eventually die off.  If this trend continues, it is not improbable that a local extinction event will take place on the islands.  The major goal then of the project is to present data to encourage the State Government of Virginia to trap the raccoons of the Western Island to limit nest predation and allow sufficient recruitment of terrapins into the next generation.  If this could be shown to be successful at Goodwin Islands, then similar action could be encouraged at other sites.

In order to assess the age of female terrapins nesting on the islands, I do a couple of things.  The first and most obvious means of assessing age is to physically catch a female nesting on the beach and determine her age, done simply by counting the number of concentric rings on her shell (kind of like growth rings on a tree).  But, this method cannot be counted upon to be sufficient as the chance of catching a female laying a nest is very small.  The other way I assess the female population age presents more data but is not as accurate as the first way: I count the number of eggs in a predated nest and hope that my count is close to the number of eggs that were actually deposited.  It is assumed in this manner that the older females will have larger clutch sizes than younger females, thus on the beaches with a higher average number of eggs per clutch, I would expect older females to have deposited the eggs.  The age data will be used, hopefully, to support a hypothesis which states that raccoons are preferentially disturbing nests closer to their homes.  Thus it would be expected that the larger clutch sizes would be found on beaches closest to the trees of the Western Island, and decreasing as one goes further outward.  This is what I am hoping to show with my project, presenting data that would predict a local extinction of the terrapins nearer to the trees, then radiating outward to the Eastern Island.

I hope that in reading my project you have gotten a taste of what I do and maybe spurred you interest in diamondback terrapin research.  My project is just one of a couple that are currently ongoing at the Keck Lab that involve diamondback terrapin research, and I would encourage you, if you are interested in conservation research, to stop by and talk to Dr. Chambers or myself and see what’s going on down at the Keck Lab.  If you would like to do conservation research, but maybe terrapins aren’t right for you, still come by: professors and graduate students out of the Keck Lab work on everything from birds in the Shenandoah Valley to amphipod collection and storm-water management techniques in the College Creek Watershed, and they are always looking for help.