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Turtles, eggs, and nesting: A simple primer

By JEFFREY GOLDING

My quest for information about turtle nesting grew out of a concern about off-road vehicle and even pedestrian access to our beaches at Cape Hatteras National Seashore Recreation Area toward the end of summer and into the fall fishing season, one of the most active and economically important times of the year. Without a doubt, the terms of the consent decree mandate closures that may have an impact far beyond closures for piping plovers and could, in fact, close access to some favorite beaches, especially Cape Point, if only for a short time. And it’s all about location and timing.

The vast majority of nests that occur at the seashore are those of loggerheads. Growing to almost four feet in length and weighing up to 400 pounds, they crawl from the sea and make their nests which usually contain from 75 to 150 eggs. Once hatched, the new turtles return to the ocean to make quite a swim to the Sargasso Sea where they mature and eventually set forth to breed and lay their nests. Sounds simple but it’s not.

When I began to ask questions, I talked to Michelle Baker Bogardus, the lead turtle biologist for the seashore, and Matthew Godfrey, senior turtle biologist with the North Carolina Wildlife Resources Commission.

Our turtles, as it turns out, are some very complex critters. Apparently unlike say, piping plovers, they don’t return to nest yearly and, in fact, will go for up to three years between returning to shore. Godfrey explains that this is a function of regaining nesting strength, which correlates to the availability of food sources. These turtles are pelagic, meaning they migrate great distances to both breed and nest. Most males return to the same oceanic vicinity, perhaps spread out over thousands of miles to mate, while the females sometimes, but not always, will return to the same general area in which they were hatched to nest. Bogardus says that the females don’t always show anywhere near the nest fidelity, returning to the same spot, as a lot of people are taught. In fact, the have been known to nest far away from their beach of origin.

Loggerheads and their other turtle buddies have been around for quite a while. Estimates range upwards of 110 million years and more. Rather impressive. They’ve survived tens of thousands of hurricanes, the Jurassic period and beyond when the predators swimming about the world’s oceans would have considered even the greatest of currently living sharks to be a joke. They have survived ice ages, extremely warm periods, and, if modern theory is to be believed, even the phenomenal comet impact that left a huge crater centered at the Yucatan Peninsula in Mexico, blamed for the demise of 90 percent of life on earth, including the dinosaurs.

Currently, the loggerhead turtles are considered threatened, though Godfrey says that there is a push to move the North Atlantic sub-population up a notch to endangered status, based primarily on the nesting numbers in Florida. These turtles nest worldwide -- from Japan, Australia, Brazil, the Arabian Peninsula, throughout the Gulf of Mexico, Africa, and beyond. Last year 45,084 nests were found in Florida, down from previous years. It’s important to note that that figure, though down, cannot be used to determine trends.

What makes that true also means that the assertion of Derb Carter, attorney for the Southern Environmental Law Center, at a recent Senate subcommittee hearing that the consent decree and its ban on night driving are responsible for the increase in nests at the seashore cannot be accepted as a fact at this point.

Here’s the science:

Loggerheads account for almost all of the sea turtle nesting at the seashore in 2008. Of the record 106 nests, reported as of Aug. 11, only three were not loggerheads. They were green turtle nests. Loggerheads nest on average only once every three years. Each turtle lays an average of five nests per season at sometimes 100 eggs per nest. The nests are laid about 14 days apart and can sometimes tie to lunar cycles. In a year like this one in which water temperatures warmed earlier, allowing for earlier nesting, some turtles will lay as many as seven nests.

Based on their nesting cycle, comparing last year’s numbers to this year’s is like comparing apples to oranges. While it’s true that numbers are up this year – last year there were 82 nests on the seashore – it is premature to say that this is a result of the consent decree and the ban on night driving, seashore officials say.

This argument is further bolstered by the fact that turtle numbers are up all along the North Carolina coast and in South Carolina and Georgia as well. Pea Island has had a record number of nests this year. It’s likely that an increase will also be noted in Florida at season’s end.

Derb Carter also said at the Senate subcommittee hearing that the consent decree will not interfere with fall fishing, which may not be the case. Bogardus says there are about 15 turtle nests that will force full beach closure as a result of the consent decree on Sept. 16, including nests at the Point.

NESTING, RELOCATION, AND OVERWASH

Nesting turtles are driven instinctively to try and ensure the survival of their species just like any other animal. When they climb from the sea, they will nest in somewhat of a “shotgun” pattern. They will lay some nests close to shore, others farther away, and even some nests into the dunes. Like alligators, it’s the nest temperature that will determine the sex of the hatchlings. Our relatively cooler sands, as opposed to Florida’s, mean that on average, 60 to 70 percent of the hatchlings in this area are male. This can vary, depending on how early the nests are laid. Earlier nesting this year may very well result in more male hatchlings, as the early nest would have been perhaps a few degrees cooler, longer. Currently, turtle biologists are conducting a three-year temperature survey to better understand sex ratios in our area and others. In each nest, a small egg like temperature sensor is inserted that records, at different intervals, changes in nest temperature.

Turtle nests are considered within their hatch window when they are 50 days old. Most will hatch within a week or two. Nest placement can also affect hatch rates and incubation times. Nests laid in the toe of a dune generally have a high success rate and shorter incubation times than a nest laid on a flat beach because of nest temperatures, according to both Godfrey and Bogardus.

Moving a nest is a very complex and time-consuming affair. Part of that complexity, as you might expect, is policy. The Park Service is issued a permit annually by the North Carolina Wildlife Resources Commission (NCWRC), which, in turn, is permitted by the U.S. Fish and Wildlife Service through the Endangered Species Act. There seems to be a bit of the “do as I say, not as I do” effect going on here because as of mid-July, USFWS had moved over half the nests (11 of 17) on Pea Island National Wildlife Refuge. Bogardus said on Aug. 6 that only about 18 nests had been relocated on the seashore, mostly because they were below the high tide line.

What makes moving them so difficult is a function of the eggs themselves.

Within each egg, there is the yolk and an air bubble. As the eggs are laid, the air bubble and embryo both migrate to the top of the egg. Initially, this allows for a quick relocation of the nest but within nine hours of being laid, the embryo will attach itself to the top of the egg and utilize the air bubble to breathe. Rotating the egg after that nine-hour window will cause the embryo to drown since the bubble will move but the turtle-to-be cannot. Once that nine-hour window passes, relocation becomes extremely risky. This is further complicated by any change in temperature the nest will experience in the moving process.
Policy dictates that nests are not moved after the window has passed. Policy also dictates that nests are never moved closer to shore but always away from it, precluding the creation of access corridors behind a nest laid close to the dune line.

Overwash, as it turns out, is a tricky situation as well. As the eggs develop, they begin to rely less on the diminishing air bubble and more on aspiration. This is where air that permeates the eggshell provides a significant portion of the oxygen needed for continued development. Overwash can, in some circumstances, be beneficial to the nest, as it forces an exchange of air and tends to rid the nest of fungus that reduces hatch rates. Total inundation for an extended period, however, often will drown a nest. What seems to be a dominant factor in whether harm comes to the nest is its stage of development. The older the nest, the more mature the embryo, the greater the oxygen requirement. Godfrey explains that because of that even a heavy rain can drown a nest as it approaches its hatch date.

As you can clearly see, turtle nesting is a very complex situation and was long before the consent decree and its rules were set in place. Clearly the Park Service is not at fault for the closures now present at the seashore, since park officials don’t dictate policy, but are forced to follow the regulations set forth by others in the decree.

It will take a good deal more study before anyone can say what the effect of the consent decree has been on turtle nesting this year.

(Jeffrey “Wheat” Golding has been a visitor to the Outer Banks for 30 years and moved to Buxton in 2007 after he was disabled in a work accident. He works at Red Drum Tackle and has long worked for beach access. Golding grew up near the York River and Chesapeake Bay and lived next to National Colonial Historic Park. He attributes his interest in the natural sciences to his mother, who was a teacher, and his father, who worked for the Virginia Department of Health and Department of Water Programs. He worked for 17 years as an interpreter, presenting and teaching history, at Colonial Williamsburg.)