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Creature Feature: The Kemp's Ridley Sea Turtle Faces an Uncertain Future
The Kemp's ridley may be little as sea turtles go, but its got big problems. It was already the world's most endangered marine turtle before the mammoth Deepwater Horizon oil spill in the Gulf of Mexico threatened to wreak havoc on its vital habitat.
These are perilous times for the Kemp's ridley sea turtle (Lepidochelys kempi). Having been reduced to a small fraction of its historic population, and now assailed by the impacts of the Deepwater Horizon oil spill, the slowly recovering L. kempi population remains too close to extinction for comfort. Much will depend on continuing efforts to save it. It's the most sweeping campaign yet mounted in behalf of a marine turtle species.
The Kemp's ridley was named for Key West fisherman Richard M. Kemp, who submitted the type specimens nearly a century ago. In some places this species is also called Atlantic Ridley, Gulf Ridley, or Mexican Ridley.
By whatever name you may call it, A. kempi is the smallest of the marine turtles. Its nearly round dorsal shell (carapace) typically measures only 2.0 to 2.5 feet in length, and while some marine turtles tip the scales at well over 700 pounds, few Kemp's ridleys exceed 100 pounds. A close cousin, the olive ridley (L. olivacea), is similarly small.
Kemp's ridley shells darken as individuals mature, distinguishing adults by color as well as size. Hatchlings are black or grey-black on both top and bottom. Adults, however, have a lighter grey-olive carapace and an underside (plastron) that is yellowish or creamy white.
Although Kemp's ridleys can at times be found at times in some nearshore and inshore waters of the Atlantic as far north as Nova Scotia, are also found along Venezuela's coast, and may turn up in odd places (including the Azores, Morocco, and the Mediterranean Sea), their primary habitat is the northern Gulf of Mexico.
Kemp's ridleys can be found feeding in or migrating through/near many national parks along the U.S. Gulf and Atlantic coasts, including, for example, Padre Island National Seashore, Gulf Islands National Seashore, Jean Lafitte National Historical Park and Preserve, Dry Tortugas National Park, and Everglades National Park on the Gulf of Mexico, and Biscayne National Park, Cumberland Island National Seashore, and Fire Island National Seashore on the Atlantic Coast.
Individuals spotted in the northerly Atlantic Coast reaches of the range are likely to be current-carried or wandering juveniles or subadults. Mature Kemp's ridleys are characteristically drawn to the rich feeding grounds of the estuaries and shallow inshore or near-shore waters of the Gulf, especially areas near the mouth of the Mississippi River and in Mexico's Campeche region.
Available food, suitable temperatures, and nesting habitat are the key considerations. Kemp's ridleys are shallow water feeders. They mainly feed on crabs (blue crabs are their favorite food), but they also eat clams, oysters, jellyfish, and occasionally fish, seaweed, and sargassum. During feeding and nesting migrations, individuals commonly travel hundreds of miles.
Since severe cold can stun or kill Kemp's ridleys, individuals foraging in northern waters must migrate south to Florida or the Gulf before winter sets in. For reasons not fully understood, adult males in some warm water feeding areas are disinclined to migrate.
The Kemp's ridley can live as long as 50 years. Females, which are usually at least 10 -12 years old before they begin breeding, have nesting habits strikingly different from other marine turtles. The nesting occurs in broad daylight instead of at night, is heavily concentrated at a single beach instead of scattered among numerous locations, and tends to occur in synchronized fashion with hundreds of females converging on the same beach the same day. Around 95 percent of the females lay their eggs on a single lengthy beach at Rancho Nuevo in the Mexican state of Tamaulipas. Minor nesting sites include Tepehuajes, and Barra del Tordo (both in Tamaulipas), Veracruz (Mexico) and the Texas coast. Rare instances have been reported in North Carolina, South Carolina, and the Gulf and Atlantic coasts of Florida.
At Rancho Nuevo, the undisputed hub of Kemp's riply reproduction, the beach is the scene of one of nature's more remarkable events. At intervals from late April to early July, females swarm ashore en masse -- "wave upon wave," as some have described it -- laying about 110 eggs in each shallow nest. Females come ashore more than once, at intervals of about 10-28 days, typically laying two or four clutches of eggs in a season. Some females do not nest every year.
It may seem hard to believe today, when the population of nesting-age female Kemp's ridleys is probably not more than 1,000, but episodes involving more than 40,000 individuals coming ashore to nest in a single day were documented at Rancho Nuevo as recently as the late 1940s. These synchronized nestings -- locally known as arribadas (aka arribazones) -- are believed to enhance reproductive success because coyotes, vultures, and other predators (including egg-gathering humans in historic times) are confronted with so many eggs and hatchlings that they can take only a fraction.
Although the synchronized nesting strategy hastened the demise of the passenger pigeon (whose enormous nesting flocks made easy pickings for humans), the startling decline in the Kemp's ridley population that occurred during the 1950s and 1960s cannot be attributed to excessive predation or market hunting. Instead, the main culprits for the post-World War II decline have been commercial fishing, habitat loss, and pollution. By the early 1970s, the Kemp's ridley was in deep, deep trouble.
Drowning or getting seriously injured in shrimp trawls has been, and remains to this day, the principal hazard for Kemp's ridley turtles. Annual losses number at least 500 animals, and since most turtle deaths go unreported, actual losses could easily be ten times that large.
The loss and disturbance of nesting habitat is also a very serious threat, especially since nearly all nesting is concentrated along a single strip of beach on the Mexican coast. Some mortality is due to pollution, including oil spills (fouling, toxic effects) and the ingestion of marine debris. Together, these and other factors put the Kemp's ridley population into a decline so steep that protective measures became necessary and extinction loomed as a distinct possibility.
The extent of the decline is evident in the nesting data. Whereas more than 40,000 Kemp's ridleys were observed nesting at Rancho Nuevo on a single day in 1947, the number had dropped to about 5,000 by 1968. During the 1970s and 1980s the nesting tallies rarely exceeded 200. The numbers have fluctuated over the years. During 1995, for example, there were 1,429 Kemp's ridley nests at Rancho Nuevo. In some recent years the tallies were in the neighborhood of 300 to 350 nests.
All of this is certainly not to say that the Kemp's ridley is doomed. In fact, things have been looking up for the species. Over 6,000 nests were counted in 2000, and while that's nowhere near the 40,000+ of the historic arribadas, it's 30 times the number recorded in the 1970s and 1980s. The total population of mature Kemp's ridleys is now thought to be in the neighborhood of 8,000. Full recovery is no longer just a dim prospect.
International efforts in behalf of the Kemp's ridley and other sea turtles have clearly paid dividends. Mexico extended limited protection to the Kemp's ridley in the 1960s, and the U.S. followed with endangered species designation in 1970. Important strides were made in the 1970s when Mexico declared Rancho Nuevo a Natural Reserve (in 1977) and initiated programs to protect the nesting beach and individual nests, minimize poaching, and reduce the natural mortality of eggs and hatchlings.
The U.S. began partnering with Mexico at Rancho Nuevo in 1978, and the Kemp's ridley recovery campaign in Mexico has since been a bi-national effort. By the late 1990s, the Bi-National Kemp's Ridley Recovery Plan had established seven camps along the Tamaulipas and Veracruz beaches for nest protection, law enforcement, and related activities.
Fencing nests and moving eggs to protected hatcheries has greatly decreased predation. Annual hatchling releases (reaching 50,000 by 1978) have greatly increased reproductive success.
Much credit for the rebound is owed to the use of Turtle Excluder devices (TEDs) by commercial shrimp boats in both the U.S. and Mexico. The devices, which enable trawlers to catch shrimp without drowning very many turtles, were developed in the 1970s and are now used in 15 countries around the world. The U.S. government made their use mandatory in U.S. waters in 1989 and stipulates that countries selling shrimp to the U.S. must require them as well.
TEDs are not 100 percent effective (especially for large species like the loggerhead and leatherback), and some animals who survive encounters with TEDs are seriously injured. Moreover, some shrimpers refuse to use the devices because they make trawling less productive. Dead turtles continue to wash ashore, sometimes in depressingly large numbers, in areas of intensive commercial shrimping.
In the United States, where the Kemp's ridley is federally protected, the recovery plan for the species has an interim goal of upgrading the Kemp's ridley from Endangered to Threatened status. Towards this end, the Sea Turtle Restoration Project has been monitoring nesting on Texas beaches (80 nests so far this year) and spearheading a campaign to establish a marine preserve along the Texas coast to protect the Kemp's ridley.
The recent slow-but-steady progress of Kemp's ridley recovery has offered encouragement, but now there is a wild card in the mix. Scientists fear that the Deepwater Horizon oil spill now fouling huge areas of the Gulf of Mexico might seriously retard or even prevent the Kemp's ridley's recovery. History, common sense, and marine science all provide a basis for concern. Sea turtles and oil just don't mix well. The 140 million gallon blowout of the Ixtoc 1 rig, which smothered the Rancho Nuevo nesting beach in 1979, provided good evidence of that.
Since the Kemp ridley's two primary feeding grounds in the Gulf are near major areas of oil production, oil spills have been a constant threat. Now the Deepwater Horizon spill has the makings of the nightmare scenario that marine biologists have always feared in the northern Gulf. The scale of the spill is gigantic, fragile ecosystems of crucial value are right in the bullseye, and the timing of the spill couldn't be worse.
Because the Kemp's ridley population is so heavily concentrated in the Gulf of Mexico, it is inherently more vulnerable to the long-term impacts of the Deepwater Horizon spill than the other large marine animals found there. As the oil slicks spread into the rich feeding areas along the Louisiana coast and beyond, what will happen to the crabs, clams, and oysters on which the Kemp's ridley subsists? Juveniles and adults turtles now safe in the waters off the Texas and Mexican coasts will sooner or later be heading into the areas most affected by the oil slick. How many of them will sicken and die from toxic oil exposure, the ingestion of tar balls (juveniles will eat anything that looks like food), oil pollution-related diseases, and other problems? As oily residues reach the beaches, how much Kemp's ridley nesting habitat will be rendered useless? In general, how serious will the Kemp ridley losses be?
We will eventually know of course. Meanwhile, we can monitor tagged turtles, perform necropsies on beached turtles, protect the nesting beaches as best we can, and conduct protection and recovery programs with an extra measure of zeal. We can also cross our fingers and hope that this oil spill is not as menacing as it appears.
The Kemp's ridley sea turtle has been around for millions of years. Will it now come to the end of the line on our watch?
Postscript: So far, necropsies performed on Kemp's ridleys recently beached in the Gulf of Mexico have revealed little or no evidence of oil poisoning. How long it will be before oil-related mortality is confirmed remains a matter of speculation.