The largest and one of the most ancient reptiles on Earth, the endangered leatherback turtle is a survivor and a creature of immense contradictions. With a leathery skin covering its carapace rather than a shell, this turtle braves freezing polar waters, migrates further than any other sea turtle, grows huge on a diet of jellyfish, and seems to disappear from its maiden scramble to the sea until the female returns to nest on tropical beaches.
It is this lost period that has frustrated scientists for decades, for without knowing where hatchling and juvenile leatherback turtles go and how they spend their time, a big chunk of these turtles' lives remains a mystery-and remains unprotected. Furthermore, biologists have no way of determining how fast leatherbacks grow, how long it takes a leatherback to reach reproductive maturity, and how long the turtles live-critical facts for their conservation. These facts enable conservationists to gauge a turtle population's potential productivity. And conservation of this ancient species is desperately needed, especially for the Pacific population.
Development and pollution have claimed many nesting beaches, poachers have taken virtually every egg from certain beaches, hunters have harpooned the adults for their oil and meat, and leatherbacks have drowned on longlines or in fishnets or have died from eating plastic bags they mistook for jellyfish. As a result, the Pacific population of endangered leatherback turtles has plummeted from an estimated 91,000 individual nesting females in 1980 to fewer than 1,500 females in 2002.. In the Pacific, one must assume that many females only nest once, their lifetime productivity cut short by entrapment in fishing gear.
There are some bright spots, however. Both at Parque Marino Las Baulas on Costa Rica's Pacific coast, and on St. Croix, starting in 1998 and 1991 respectively, Earthwatch-supported scientists noticed a surprising influx of smaller nesting leatherbacks without any tags. They wondered if these turtles might be hatchlings released a decade or more from these beaches, now returning to nest for the first time. As tantalizing as it would be to finally pin an age-to-maturity figure on the most pelagic of all sea turtles, no scientist is ready to do it yet. Several factors confound making a definitive pronouncement.
As yet, there is no safe and reliable way to mark a leatherback hatchling so one could identify it as an adult. Moreover, since estimates are that fewer than one in one thousand hatchlings reaches maturity, any identification method devised would likely be costly and labor-intensive. Dr. Peter Dutton (National Marine Fisheries Service), one of the former lead scientists for Saving the Leatherback Turtle on St. Croix, however, is conducting DNA analysis on leatherbacks from a number of sites, comparing blood samples from older nesters with that of purported first-timers to try to find a match. Finding relatives (mother or daughter) among identified animals with nesting records is the key to establishing the turtles' earliest reproductive age. It's a slow and laborious process that may yield definite conclusions only when the next generation of leatherbacks comes ashore to nest, because researchers have only been able to reliably identify first-time nesters since 1992.
Another related puzzle in the leatherback nesting picture is that no one is quite sure how faithful a leatherback is to her natal beach. Most sea turtles, it was thought, return to the same beach on which they hatched, but leatherbacks, especially in the Atlantic, may not slavishly follow this pattern. Earthwatch-supported biologists have recorded the same leatherbacks nesting in one season both on St. Croix and on nearby Culebra, Puerto Rico. Bill McLarney (ANAI), who led Earthwatch teams studying leatherback nesting on Costa Rica's south-Atlantic coast, believes the 932 leatherbacks that nested there are part of a "metapopulation" that nests at various beaches throughout the region. If this is the case, then, to ensure this endangered species' survival, it may be necessary to protect all nesting beaches-no small goal. And it makes it more difficult to determine if a given first-time nester is really a hatchling from that particular beach.
A further complicating factor in the case of the Pacific leatherback population may be the El Niño-La Niña cycle, periodic warming and cooling of Pacific waters. Data from Parque Marino Las Baulas suggest that La Niña can increase food supplies, possibly triggering leatherbacks to nest earlier than expected and thus abnormally increasing productivity one year and decreasing it the next. While it is still too early to state that climate definitely affects leatherback reproduction, Dr. Richard Reina (Monash University) and his colleagues are continuing to study the effects.