Kemp's Ridley Sea Turtles

Description

Adult Kemp's ridleys, considered the smallest marine turtle in the world, weigh on average around 100 pounds (45 kg) with a carapace (top shell) measuring between 24-28 inches (60-70 cm) in length. The almost circular carapace has a grayish green color while the plastron (bottom shell) is pale yellowish to cream in color. The carapace is often as wide as it is long and contains 5 pairs of costal "scutes". Each of the front flippers has one claw while the back flippers may have one or two.

Similar to olive ridleys, Kemp's ridleys display one of the most unique synchronized nesting habits in the natural world. Large groups of Kemp's ridleys gather off a particular nesting beach near Rancho Nuevo, Mexico, in the state of Tamaulipas. Then wave upon wave of females come ashore and nest in what is known as an "arribada," which means "arrival" in Spanish.

There are many theories on what triggers an arribada, including offshore winds, lunar cycles, and the release of pheromones by females. Scientists have yet to conclusively determine the cues for ridley arribadas. Arribada nesting is a behavior found only in the genus Lepidochelys.

Female Kemp's ridleys nest from May to July, laying two to three clutches of approximately 100 eggs, which incubate for 50-60 days. After incubation, hatchlings emerge weighing about half an ounce (14 g) and measuring about 1.5 inches (3.8 cm).

Reproduction and Development:

Nesting occurs from April to June during which time the turtles appear off the Tamaulipas and Veracruz coasts of Mexico. Precipitated by strong winds, the females swarm to mass nesting emergences, known as arribadas or arribazones, to nest during daylight hours. Clutch size averages 110 eggs. Some females breed annually and nest an average of 1 to 4 times in a season at intervals of 10 to 28 days. Age at sexual maturity is believed to be between 7 to 15 years.

Range and Population Level:

The range of the Kemp's ridley includes the Gulf coasts of Mexico and the U.S., and the Atlantic coast of North America as far north as Nova Scotia and Newfoundland. Most Kemp's ridleys nest on the coastal beaches of the Mexican states of Tamaulipas and Veracruz, although a very small number of Kemp's ridleys nest consistently at Padre Island National Seashore, Texas. Hatchlings, after leaving the nesting beach, are believed to become entrained in eddies within the Gulf of Mexico, where they are dispersed within the Gulf and Atlantic by oceanic surface currents until they reach about 20 cm in length, at which size they enter coastal shallow water habitats.

The Kemp's ridley is the most seriously endangered of the sea turtles. Its numbers have precipitously declined since 1947, when over 40,000 nesting females were estimated in a single arribada. The nesting population produced a low of 702 nests in 1985; however, since the mid-1980's, the number of nests laid in a season has been increasing primarily due to nest protection efforts and implementation of regulations requiring the use of turtle excluder devices in commercial fishing trawls. During the 1999 and 2000 nesting seasons, more than 3,600 nests and 6,000 nests, respectively, were deposited on the Mexico nesting beaches.

Habitat:

Outside of nesting, the major habitat for Kemp's ridleys is the nearshore and inshore waters of the northern Gulf of Mexico, especially Louisiana waters. Kemp's ridleys are often found in salt marsh habitats. The preferred sections of nesting beach are backed up by extensive swamps or large bodies of open water having seasonal narrow ocean connections.

Adult Kemp's primarily occupy "neritic" habitats. Neritic zones typically contain muddy or sandy bottoms where prey can be found. Their diet consists mainly of swimming crabs, but may also include fish, jellyfish, and an array of mollusks.

Depending on their breeding strategy, male Kemp's ridleys appear to occupy many different areas within the Gulf of Mexico. Some males migrate annually between feeding and breeding grounds, yet others may not migrate at all, mating with females opportunistically encountered.

Female Kemp's have been tracked migrating to and from nesting beaches in Mexico. Females leave breeding and nesting areas and continue on to foraging zones ranging from the Yucatn Peninsula to southern Florida. Some females take up residence in specific foraging grounds for months at a time, leading scientists to suggest that females have a goal-oriented migration, opposed to the suggested wandering strategy employed by olive ridleys. Kemp's ridleys rarely venture into waters deeper than 160 ft (50 m) (Byles and Plotkin, 1994).

Newly emerged hatchlings inhabit a much different environment than adult turtles. After emerging from the nest, hatchlings enter the water and must swim quickly to escape near shore predators. There is strong evidence that many sea turtle species employ an open ocean developmental stage because encounters with healthy, neonate sea turtles are extremely rare in near shore waters. Some hatchlings remain in currents within the Gulf of Mexico while others may be swept out of the Gulf, around Florida, and into the Atlantic Ocean by the Gulf Stream.

Juveniles of many species of sea turtles have been known to associate with floating sargassum seaweed, utilizing the sargassum as an area of refuge, rest, and/or food. This developmental drifting period is hypothesized to last about two years or until the turtle reaches a carapace length of about 8 inches (20 cm). Subsequently, these sub-adult turtles return to neritic zones of the Gulf of Mexico or northwestern Atlantic Ocean to feed and develop until they reach adulthood (Collard and Ogren, 1990).

Population Trends

The Kemp's ridley has experienced a historical, dramatic decrease in arribada size. An amateur video from 1947 documented an extraordinary Kemp's ridley arribada near Rancho Nuevo. It has been estimated that approximately 42,000 Kemp's ridleys nested during that single day! The video also provided evidence of Kemp's ridley egg collection. Dozens of villagers are seen on the beach excavating the nests and subsequent interviews have suggested that 80% of the nests, about 33,000, were collected and transported to local villages (Hildebrand, 1963).

This video has also served to measure the species' collapse. Twenty years after the video was filmed, the largest arribada measured was just 5,000 individuals. Between the years of 1978 and 1991 only 200 Kemp's ridleys nested annually. Today the Kemp's ridley population appears to be in the early stages of recovery. Nesting has increased steadily over the past decade. During the 2000 nesting season, an estimated 2,000 females nested at Rancho Nuevo, a single arribada of 1,000 turtles was reported in 2001, and an estimated 3,600 turtles produced over 8,000 nests in 2003. In 2006, a record number of nests were recorded since monitoring began in 1978; 12,143 nests were documented in Mexico, with 7,866 of those at Rancho Nuevo.

On the Texas coast, 251 Kemp's ridley nests were recorded from 2002-2006. For the 2007 nesting season, 127 nests have been recorded in Texas, with 73 of those nests documented at Padre Island National Seashore. Those 127 nests are a record for the Texas coast, passing the 2006 record of 102 nests.

Threats

Kemp's ridleys face threats on both nesting beaches and in the marine environment. The greatest cause of decline and the continuing primary threat to Kemp's ridleys is incidental capture in fishing gear, primarily in shrimp trawls, but also in gill nets, longlines, traps and pots, and dredges in the Gulf of Mexico and North Atlantic. Egg collection was an extreme threat to the population, but since nesting beaches were afforded official protection in 1966, this threat no longer poses a major concern.

For more information, please visit our threats to marine turtles page

Management and Protection

The recent nesting increase can be attributed to full protection of nesting females and their nests in Mexico, and the requirement to use turtle excluder devices in shrimp trawls both in the United States and Mexico. In 1966, conservation efforts for the Kemps ridley were initiated on the beach near Rancho Nuevo in Tamaulipas, Mexico. This locale is the only place in the world where large nesting aggregations of this sea turtle were and are known to occur. From 1966 to 1987, conservation efforts focused on the area of Rancho Nuevo with one turtle protection camp. In 1978, the U.S. joined with Mexico at Rancho Nuevo in a bi-national effort to prevent the extinction of the Kemps ridley. In 1988, this bi-national program expanded to the south and another camp was added. In 1989, a third camp was established when the program was expanded to the north of Rancho Nuevo. By 1997, a total of seven camps had been established along the Tamaulipas and Veracruz coasts to allow for increased nest protection efforts.

The Mexico government also prohibits harvesting and is working to increase the population through more intensive law enforcement, by fencing nest areas to diminish natural predation, and by relocating all nests into corrals to prevent poaching and predation. While relocation of nests into corrals is currently a necessary management measure, this relocation and concentration of eggs into a "safe" area is of concern since it makes the eggs more susceptible to reduced viability due to movement-induced mortality, disease vectors, catastrophic events like hurricanes, and marine predators once the predators learn where to concentrate their efforts.