Turtle and Tortoise Newsletter, 2000, 2:1-3
© 2000 by Chelonian Research Foundation

Turtle and Tortoise Newsletter

A Too Brief and Woefully Incomplete Terrapin Primer

Don Lewis
Founding Partner, Cape Cod Consultants, P.O. Box 1054, South Wellfleet, MA 02663
Research assistant, Wellfleet Bay Wildlife Sanctuary, P.O. Box 236, South Wellfleet, MA 02663

Diamondback terrapins are elusive turtles of the Atlantic and Gulf seacoasts’ rich estuarine system of rivers, creeks, coves, bays and marshes. According to Turtles of the United States and Canada (Smithsonian Institution Press, Washington and London, 1994) there are seven formally described sub-species: Malaclemys terrapin terrapin from Cape Cod to Cape Hatteras; M. terrapin centrata from Cape Hatteras to northern Florida; M. terrapin tequesta on the Atlantic coast of Florida; M. terrapin rhizophorarun in the Florida Keys; M. terrapin macrospilota from the Florida Bay to the panhandle; M. terrapin pileata from the Florida panhandle to western Louisiana; and M. terrapin littoralis from western Louisiana to western Texas.

An important part of East Coast history and lore, diamondbacks were said to have fed our impoverished soldiers during the hard times of the Revolutionary War. Nearly harvested to extinction in the last century, terrapins were thought to be making a slow recovery, but today their numbers may once again be on the decline as pressures intensify on their fragile habitat from development, pollution and commercial activities. Vacation and retirement homes press deeper into terrapin environment as demand escalates for “waterfront” property. Accidental spills, hazardous debris and “ghost” equipment for seafood harvesting and farming, all take their toll on these turtles and their habitat. And commercial activities, whether directly targeted at terrapins or affecting diamondbacks only as a by-product of fishing other species, continue to threaten their long-term viability.

Even in Maryland, where the terrapin is a state icon and is still harvested commercially, they have acknowledged the species is “declining in population and requires concerted conservation efforts.” Maryland’s governor recently proclaimed May 13th, 2000 as Diamondback Terrapin Day to increase “public awareness for natural resources conservation and stewardship for this species.”

Diamond in the Rough
For this all too brief primer, though, I will focus on my paludal pals of the north, terrapins of the Land of Ooze, the salt marshes of Outer Cape Cod. These terrapins are medium size with distinct gender dimorphism. Mature females range from eight to nine inches long, weighing around three pounds, while males grow to almost five inches and about 2/3 of a pound. This pair captured last summer well illustrates the size difference between the sexes. The female [#697 on the left] also proved a surprising success story. Marked after nesting in June 1997, she was hit by a car the next year and given emergency treatment. Her cracked shell patched, she was returned to the creek with only a hope and prayer for recovery. But here she appeared on 13 September 1999, fully healed and engaged in normal mating with only a few bumps and scars to recall her unfortunate encounter with man.

Terrapins have a hingeless shell. The top or carapace has 13 scutes ringed like diamond facets, ten around the perimeter with three in the center — eight costals and five vertebrals. The bottom shell or plastron is symmetrically bisected with six sections on each side of the centerline. A turtle’s age can be estimated by annual growth marks, especially on the plastron, as demonstrated by this five-year old female. A terrapin’s shell smoothes with wear and tear and usually by ten years, a turtle’s age can no longer be easily determined. While we are not certain how long our Cape Cod terrapins live, we suspect they reach 40 or 50 years of age — at least.

Reproduction and Nesting
Males reportedly reach sexual maturity after the third year, while females wait until at least the sixth. Our nesting season, which varies in each geographical area, lasts from early June through mid July. Two clutches of pinkish white eggs, ranging in number from four to 18, are laid above the wrack line with remarkable nesting site fidelity. Last summer terrapin #145, a twenty-something female, was spotted digging her nest in tire tracks of a dirt road. She had been observed nesting at this identical spot a decade earlier on that very same date, 6 July.

Designed for the water, terrapins encounter their greatest risk when ashore for nesting. Predators, especially fox and raccoon, have been known to specialize in hunting this protein rich prey. But today, the worst danger comes from man. Trophy vacation homes ring their nesting sites; teetering at dune’s edge, these million dollar houses demand protective seawalls to delay the inevitable advance of the bay.

Other sites are lost to decorative landscaping, locking loose dune soil in lawns and invasive ground cover. Turtles are forced to march inland and search for less suitable locations, extending their vulnerability and decreasing the viability of hatchlings. Dirt roads, free of vegetation, offer a risky, but attractive alternative, and each year more and more turtles are hit either while nesting in roads or in transit to upland sites.

Not content with just any nest, turtles have been seen digging as many as ten test holes before finally depositing their offspring. Yet others have been considerably less fussy. Some dropped eggs in the hands of observers who interrupted their nesting a bit too prematurely. And then there was turtle #765. She became so impatient during processing last June that she laid a clutch of eggs on the Sahara colored rug of my jeep. A surprised surrogate mom, I located a secluded south-facing site several feet above the high water mark with ample loose soil surrounded by protective vegetation. I imitated a nesting female, dug a narrow vertical shaft, gently stacked the four eggs together, and covered and smoothed the hole. Having witnessed wholesale predation of terrapin nests throughout the summer, I decided to paint the site with human scent as a warning. As luck would have it, this nest escaped predators and on 27 September I became the proud virtual father of four infant hatchlings.

A Quarter Century of Research
Scratching out an existence at the absolute edge of their range, terrapins of the Outer Cape serve as a signal species within our coastal environment. Recognizing this importance, the Massachusetts Audubon Society’s Wellfleet Bay Wildlife Sanctuary has conducted research efforts since 1980 with informal observations stretching back to the mid-1970s. The core of its data collection program consists of capture, mark and recapture studies. From spring to fall, turtles are captured in creeks, coves, and bays by a variety of strategies: wading, canoeing, kayaking, netting, trapping and seining. During the nesting season, researchers and volunteers walk designated shorelines, observe and mark nests, and capture/recapture turtles after their eggs have been deposited. Each turtle is measured for carapace and plastron length and width, weighed, examined for general health and anomalies, individually marked and digitally photographed for follow-on study. Through this method, histories for many turtles have spanned several decades. Growth models can be constructed and demographic profiles of the Outer Cape population can be developed. And, by the percentage of marked and unmarked terrapins discovered in each capture event, population estimates can be obtained and trends can be followed.

The diamondback terrapin is a shy creature extremely sensitive to human disturbance. They are so rarely seen that most people are surprised to learn they share the same habitat with them. They are very hardy critters, though. We find a number of turtles with missing appendages, yet they seem to hold their own. One breeding female, which we affectionately dubbed Stumpy, has two missing forelimbs. Yet twice each year she drags herself onto the beach to nest.

But they can be killed. No matter how robust, terrapins must breathe to live. Trapped in pots or netting, turtles will drown. No matter how strong, terrapins can’t withstand the weight of a vehicle. And no matter how resilient as individuals, the species can’t survive if their environment is lost. As nesting sites and nurseries and foraging habitats disappear, so do diamondback terrapins.