DIAMONDBACK DILEMMA Like clockwork, the urge to procreate calls Maryland terrapins to shore and into harm's way

THE BALTIMORE SUN

Patuxent River, June 24, 8 a.m. No heads in sight.

The stage is set: the water tranquil, beach empty, sands beginning to bake in humid heat, already nearing 90; the steamy anomie of the bordering marsh is punctuated only by the piping of ospreys, wren songs and the flitting of swallows.

We are concealed in a cramped, makeshift blind along this Southern Maryland tributary of the Chesapeake Bay. But so far, since sunup, no heads; no sign of what we're prepared to spend the day -- or days -- to witness. It is a courtship between an animal and the river's edge, an evolutionary ritual whose astounding complexity is only beginning to emerge from eight years of unique study.

The animal is the diamondback terrapin.

This deep summer dance of the diamondbacks is teasing and secretive. Though it goes on for months, scattered throughout the estimated 9,000 miles of land-water edge around the Chesapeake and its 40-odd tidal rivers, you may live your life in such regions and never observe it.

9:45 a.m.

A head pops up, just off a little point the beach makes, about 200 feet from us, before it angles out of our line of vision behind the spartina grass and high-tide bush of the marsh. Two heads, three heads, four; black as coal against the reflective water. They belong to big female terrapins, all paddling hard now, closing fast on the nesting beach.

Relax, says Greg Bokor, a senior from Hood College who spends seven days a week in the blind on the "first shift," 6 a.m. until 2 p.m. Submerged except for their craning necks, the diamondbacks may flirt with the beach for hours, half-emerging, diving back in, disappearing, reconnoitering. Anything can spook them -- a dog barking, the bang of a distant farmhouse door, the shadow of a heron gliding across the shallows.

Sure enough, all four have disappeared. But wait. A head is moving just off the blind where Greg and I are concealed. The terrapin enters a little creek behind the blind, circling us, arching her neck, peering intently.

Does she know someone is watching? Most likely, Greg says. Female terrapins don't even reach sexual maturity until somewhere between 8 and 13 years, and quite possibly live for half a century or more, he explains. And with a precision rivaling that of spawning salmon, they return every summer to the same small stretch of beach to nest. It is not certain whether they use visual clues or, as salmon are thought to do, employ some exquisitely refined sense of smell; but there is little doubt that the old girl checking us out has a long and complex association with the piece of real estate on which we have intruded.

10 a.m. No heads.

An osprey alights on the point of beach, wades out a few feet and flaps and thrashes in the shallows, soaking itself and luxuriating in the cooling bath for a good five minutes.

10:30 a.m. Five heads.

Two more; here they come!

No heads.

A little green heron takes the osprey's spot, and progues for darting minnows.

Greg is reading "Silent Spring," Rachel Carson's 1962 classic on the perils of pesticides. I'm reading a draft of "Chesapeake Diamondback Terrapin Investigations," Willem Roosenburg's someday-to-be classic on the habits of more than 5,000 Patuxent River terrapins. He is Greg's boss, a young biology professor who began catching and marking terrapins here as a Ph.D. student in 1987. Using a system of notches and small holes drilled into the edges of the turtles' shells, he now can precisely identify and track thousands of the creatures.

He grew up on the Patuxent, son of a researcher at the University of Maryland's bay laboratory at Solomons; but it was not until the early 1980s that he caught "turtle fever" as a graduate student, working in Costa Rica with the late Archie Carr, a world authority on sea turtles and an early force for the preservation of the Everglades. Now, regular as the river's diamondbacks, Dr. Roosenburg returns to the Patuxent nesting beaches every summer.

10:40 a.m.

Some 200 feet away, a terrapin is wanting badly now to come ashore and lay down her burden of eggs. She crawls out, ducks back, re-emerges. Her thick dark neck is stretched to the limit, straining to see as much as possible. Down on the beach goes her head, as if smelling the sand. I have never seen a deer, or a fox, or a rabbit any more alert, soaking in every nuance of its surroundings, than this old, slow turtle.

What a terrible and lovely moment in nature this is, the beach powerfully beckoning -- also repelling -- the terrapin. What sights and scents of the land must draw her; and what urges within must propel her to be about her business -- nothing less powerful than the perpetuation of her species.

Yet, it is on land that she is supremely uncomfortable, most at risk to predators, her aquatic grace and camouflage turned instantly to plodding, clumsy vulnerability. Do the scents of fox and raccoon and human mingle revoltingly with the come-hither of the warm sands? And so, there she poises, beneath the hot June sun, balanced between individual safety and survival of the race.

And back into the water she goes.

10:55 a.m.

So fast we almost missed it, she has committed; skedaddled up the few yards of sand and into the spartina, legs spraddled with the weight of her eggs. In the cover of the grasses, she will find a spot to her liking and dig down several inches with her hind legs, depositing from eight to more than 20 eggs in the flask-shaped excavation. Fresh-laid, they are lovely, about the size of the first joint of a man's thumb, luminous with the semitranslucence of quartz, so soft they dimple when you brush the sand off one.

When the female finishes laying, she will cover the nest so adroitly that only a trained eye can detect it. Within a day, after wind and rain have put the final touches on the turtle's work, not even the most skilled human could find a terrapin nest except by luck.

Others can, though. Raccoons, also some foxes and the occasional otter, have this year located and destroyed every one of the nests observed by Dr. Roosenburg's team on this and one other beach in the terrapin study. Predation has destroyed about 95 percent of more than 400 observed nests during the eight-year study. All the same, his trapping is turning up what appears to be healthy numbers of juvenile terrapins along the river, Dr. Roosenburg says. Some biologists, however, suspect that predation has increased in modern times.

11:10 a.m.

It takes a diamondback about 20 minutes to complete its nest. Greg, once he sees them go ashore, waits 15 minutes and heads up the beach. His mission is to capture the female and find and mark her nest. Turtle, eggs, depth of nest, temperatures of the sand -- everything will be weighed, measured and recorded, then released or covered back up. But this one diamondback has eluded him. He searches and searches for clues -- the surprisingly dainty, five-toed footprints, the thin tracery of a tail dragged in the sand; but after half an hour, no turtle, no nest.

Then, a flicker of movement another 100 feet along the beach. The diamondback has used a finger of marsh extending almost to the water for cover, and scrambles from behind it for the river, as Greg races full tilt to grab her. He almost does, grasping her shell some 20 feet offshore; but this is her medium. With a powerful spurt, she is gone. This is why it takes about 40 hours of observer time for every nest that is located.

Then we get lucky. Another large female, one we never saw come up, crawls out of the marsh, an easy capture. Probing her abdomen through the hind-leg openings of her shell, Greg can tell she has deposited her eggs; but where? We will never know. With luck, a thunderstorm will rake the beach this afternoon and wash away even the traces of scent a coon needs to find the nest.

Our captive is an old familiar of Dr. Roosenburg's, known as 1R8R1L10L. He first captured and marked her in 1988. The letters and numbers refer to the distinct compartments, or "scutes," that surround the edges of a terrapin shell. There are 12 on a side; thus, ours has been marked on the first and eighth right-hand scutes, and the first and tenth left-hand ones. The system affords about 10,000 unique identifications.

Her records show that she's been caught nesting eight times in the last six years (females lay up to three clutches of eggs a year, losing nearly a third of their body weight during the June-July nesting season). She is just a teen-ager still, barely in .. her prime, the records show. Like virtually all the nesters in the study, she exhibits remarkable fidelity to the same small piece of sand, returning there and only there, year after year.

That information -- and something just emerging that is perhaps even more intriguing -- holds profound implications for conserving the bay's terrapins, Dr. Roosenburg says. He and his wife, Kate Kelley, a Ph.D. candidate, are sorting and marking terrapins at the trailer they rent amid the farm fields of Cremona. The historic St. Mary's County estate, with its extensive shoreline, is where the bulk of the nesting studies are done.

The two spend hours each morning running more than 20 bank traps for a local waterman. In return, Dr. Roosenburg gets all the terrapins, plus 25 percent of the crabs, whose sale helps finance him and Kate and the six students working with them.

He thinks the close bond between terrapin and beach may be unbreakable. He's seen females lay eggs, vainly, right in the water against a bulkhead, installed unthinkingly by property owners on a nesting shore. "She may have been coming there for 20-30 years," he says. To incubate properly, eggs must be laid in the warm sand, above the tide's reach. Two months or more can elapse before the tiny hatchlings break free and crawl into the water.

In the long run, shorefront development around the bay may pose the greatest threat to the terrapins. The most immediate threat, Dr. Roosenburg says, is the recreational crab pots that waterfront owners all too often leave untended (illegally) in the water, for days at a time. The pots catch and drown the smaller, male terrapins, and younger females. (Older ones are too big to enter.) He has seen dozens dead in a single pot, and thinks

unattended recreational pots could be killing thousands of Chesapeake terrapins annually. He has even designed and promoted -- so far with only local success -- a special pot of his own design. Tall enough to break the surface of the water, it gives trapped terrapins a way to enter its upper chamber and breathe, and a way to submerge periodically at low tide to keep from dehydrating in the sun.

It is only a dream now, he says, to think of identifying for protection all the terrapin nesting beaches around the bay. Because of a study he did for the state, officials have closed May, June and July, the prime nesting season, to any commercial harvest. Meanwhile, Dr. Roosenburg is beginning to research a new and crucial twist to the matter of terrapin beaches: whether the bay might be divided among male beaches and female beaches. It has to do with ESD, or Environmental Sex Determination.

ESD is believed to be ancestral in most turtles, crocodiles and some snakes and fish. It means sex is not determined by X and Y chromosomes, as in humans; rather by outside factors -- in the case of turtles, the temperature of the sands in which the eggs incubate.

Allen R. Place, a biochemist for the Center for Marine Biotechnology in Baltimore, has worked with Dr. Roosenburg on what makes a little Chesapeake terrapin a girl or a boy. The key, says Dr. Place, is a surprisingly small variation in incubation temperature. If the sands of a beach average 88 F, all females hatch; at 81 F, all males result. "You're talking about a very narrow critical temperature range," he says. "It's thought the dinosaurs may have been like that, and possibly it is why they went extinct. . . . a relatively minor lowering in global temperature resulted in not enough females."

So far, Dr. Roosenburg has confirmed only that there seem to be all-male beaches. Of 400 hatchlings he has examined during the last three years from one of his test beaches, 399 were male. He thinks there may be other, all-female beaches, whose solar exposure or lower water table results in hotter sands. Because the number of mature females is most critical to the health of the population, such hotter, female-favoring beaches, if identified, would be high priority for protection.

The terrapins' dependence on bay beaches is just one more reason why the thousands of sand-fringed marshes and shorelines of the Chesapeake, though small in acreage, constitute one of the bay's richest and least recognized habitats. Especially where they are undisturbed, those sand slivers also have nesting terns, skimmers, pelicans, oystercatchers and a variety of gulls and other birds; also nesting horseshoe crabs and perhaps giant sea turtles.

The science of the bay's terrapins must necessarily be dispassionate; but almost no good scientist lacks passion for his work, and Dr. Roosenburg is no exception. He says he has developed a deep respect for the diamondback's intelligence and the elegance of its evolutionary adaptations.

It is not unusual to hear him or an assistant mention a terrapin "catching my eye," with the clear implication that something, more felt than measurable, passed between researcher and subject. (I have heard watermen recount such moments of momentary eye contact with terrapins or even fish, and sometimes that creature is set free as a result.)

Dr. Roosenburg has corresponded for a few years now with a Smith Islander who is adept at locating the terrapins' secret winter hibernating places. (He does not locate them for science, but for a market, mostly in New York, that is estimated, very roughly, to take 10,000 terrapins a year from the Chesapeake.)

Between the two, scientist and waterman, they probably know more than everyone else on the bay about the habits of terrapins. It has been a delicate dance, the researcher wanting to pry out where the turtles spend the winter; the harvester a bit too interested for Dr. Roosenburg's liking in where all those terrapins are in the Patuxent. He does not mind the terrapin, within limits, being a resource for the bay's beleaguered watermen. He has often thought that, if he had another life to live, he would try it as a waterman: "If I've had any success, it's because I'm persistent; I like to catch things and I don't give up." If watermen needed a slogan, that would do nicely.

He says no one knows how healthy bay terrapin populations are, though the several thousand subjects of his research appear to be maintaining themselves. And certainly things are better than they were in the early part of the century, when the terrapin's huge popularity in fancy restaurants pushed wholesale prices to $120 a dozen. But by 1930, old watermen say, one might search a week to catch a single terrapin. The turtles were saved more by falling demand during the Great Depression than by conservation. Prohibition also helped because it deprived cooks of sherry, a prime ingredient in preparing terrapins for the table. They never regained their popularity, and by the 1960s populations had rebounded in many areas.

Given his interest, and the long lives terrapins lead, there seems no end to Dr. Roosenburg's terrapin study, if finances permit. A classic piece of research by someone else on the painted turtle took 25 years. He hopes eventually to do what that study did, to develop a "life table" for the terrapin, much the same as insurance actuaries do for humans, showing a schedule of survivorship and reproduction for each age class. That, in turn, -- forms the basis for understanding, managing and conserving a species.

He also envisions building an environmental education curriculum around the terrapin project. And mysteries remain about the relationships of turtles and shoreline: Where are the female beaches? Do nesting terrapins know how to select beaches by temperature, to produce male or female offspring?

Now it is 5:30 p.m. A thunderstorm looks to be looming across the Patuxent. Perhaps more terrapins have nested; the second shift of students out in the blinds will be recording them. Maybe the rain will wash away the scent, foiling the coons; and come August, some little hatchlings will crawl magically from the marsh.

How nice to think that a few of them, if we have not bulkheaded and paved everything by then, will be out here 50 summers from now, romancing the sandy edges of this old river of their birth.

F: TOM HORTON is the environmental columnist for The Sun.

Diamondback terrapin

Name: Malaclemys terrapin. It is called the diamondback terrapin for the roughly diamond-shaped rings on its carapace -- its upper shell or back.

Size: Females grow substantially larger than males. A large female measures 9 inches on her plastron. An average male is perhaps half that size. Terrapins can live half a century or more.

Coloration: The upper shell is dark -- olive, gray, brown, black; the plastron, or undershell, is light -- yellowish, amber.

Habitat: Maryland's brackish and saltwater marshes and tidal edges. The terrapin ranges throughout the bay and much of the East and Gulf coasts.

Diet: minnows and small fishes, snails, crabs, worms, insects.

Nesting: Terrapins lay up to 21 eggs and may nest three times in a summer. Nesting in the Chesapeake region is mainly during June and July. Hatchlings crawl out in August and September.

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