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Gregory R. Mann, Ph.D. {ret.}

Kemp’s Ridley Sea Turtle

“Lepidochelys kempii”

Kemp’s Ridley Sea Turtles are a close relative of Olive Ridley Sea Turtles and are one of the smallest sea turtles. These turtles are called Kemp’s Ridley because Richard Kemp of Key West, Florida was the first to send a specimen to Dr. Samuel Garman at Harvard University however, the etymology of the name “Ridley” itself is unknown. Adult generally weigh 45 kilograms with a body length of 65 centimeters. The shells are broad and light gray-olive in color. They are off-white to light yellow underneath which is called their plastron. Juvenile turtles have gray-black carapaces (top shells) and plastrons. Hatchlings have lighter gray-olive carapaces and plastrons. There are 2 pairs of prefrontal scales on the head, 5 vertebral scutes (back plates), 5 pairs of costal scutes (belly plates) and 12 pairs of marginals (rimming plates) on their carapace. Four scutes perforated by a pore are found on each bridge joining the plastron to the carapace. The pore is the opening of their Rathke’s gland which secretes a substance of unknown function. Male Kemp’s Ridley Sea Turtles resemble the females in size and coloration but have secondary sexual characteristics including a longer tail, more distal vent, re-curved claws and during breeding, a softened mid-plastron. Although Kemp’s Ridley Sea Turtles cannot withdraw their heads into their shells, the adults are protected from predators by their shells, large size and thick scaly skin on their heads and necks.

Kemp’s Ridley Sea Turtles spend almost all their lives submerged but must breathe air for the oxygen needed to meet the demands of vigorous activity. With a single explosive exhalation and rapid inhalation, sea turtles can quickly replace the air in their lungs. Their lungs are adapted to permit a rapid exchange of oxygen and to prevent gasses from being trapped during deep dives. The blood of Kemp’s Ridley Sea Turtles can deliver oxygen efficiently to body tissues even at the pressures encountered during diving. Kemp’s Ridley Sea Turtles can rest or sleep underwater for several hours at a time but submergence time is much shorter while diving for food or to escape predators. Breath-holding ability is affected by activity and stress, which is why turtles drown in shrimp trawls and other fishing gear within a relatively short time. Because sea turtles are difficult to study in the open ocean, scientists are just beginning to learn about the life history of Kemp’s Ridley Sea Turtles. Today, radio transmitters attached to nesting Kemp’s Ridley Sea Turtles help track the sea creatures on their travels and provide valuable information.

The major nesting beach for Kemp’s Ridley Sea Turtles is on the northeastern coast of Mexico. This location is near Rancho Nuevo in southern Tamaulipas. The species occur mainly in coastal areas of the Gulf of Mexico and the northwestern Atlantic Ocean. Newborn Kemp’s Ridley Sea Turtles feed on the available sargassum and associated animals or other epipelagic species found in the Gulf of Mexico. In post-pelagic stages, the turtle is largely a crab-eater with a preference for swimming crabs. Age at sexual maturity is not known but is believed to be approximately 7-15 years, although other estimates of age at maturity range as high as 35 years. Kemp’s Ridley Sea Turtles reach sexual maturity between 11-35 years. Females lay eggs that measure 34-45 millimeters in diameter and weigh 24-40 grams. Incubation lasts between 48-62 days. Hatchlings range from 42-48 millimeters in straight line carapace length, 32-44 millimeters in width and 15-20 grams in weight. Although Kemp’s Ridley Sea Turtles move swiftly in the ocean, they are slow and defenseless on land. Males almost never leave the water. Female Kemp’s Ridley Sea Turtles leave the ocean only to lay eggs and for most species, nest only at night. Females of most species may nest every 2 to 3 years. The female Kemp’s Ridley Sea Turtle has a unique nesting behavior known as the “arribada” or arrival in Spanish. Females congregate in the shallows and all emerge at once to lay eggs on the beach. Nesting season for Kemp’s Ridley Sea Turtles lasts from April-July.

Nesting can take between 1 to 3 hours. After a female turtle drags herself up the beach, she hollows out a pit with her back legs and deposits between 50-200 eggs the size of golf balls. When the last egg is laid, the turtle covers the eggs with sand, tamps down the sand with her plastron and flings more sand about with her flippers to erase any signs of the nest. After about 2 months, the hatchling Kemp’s Ridley Sea Turtles emerge at night. The light reflected off the water from the sky guides them to the sea. These days, car headlights, street lamps or lights on buildings near the beach cause some Kemp’s Ridley Sea Turtle hatchlings to travel in the wrong direction. Waiting Herons make fast meals of other hatchlings. Any babies still on the beach in the morning, are easily picked off by predators or die in the hot sun. It is thought that when the surviving Kemp’s Ridley Sea Turtles reach maturity, they return to the beach where they hatched to lay their eggs.

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