The Kemp’s ridley, Lepidochelys kempi, are the smallest of the sea turtle species at about 60-70 cm long (2-2.5 feet). Their shell is oval or disk shaped, high browed and dull olive, gray or brown. Young animals usually have three longitudinal ridges on the carapace that become less evident with age.
They are restricted primarily to the Gulf of Mexico, with one consistent nesting beach in Mexico, where the entire breeding group of females come ashore at once to lay eggs (called an arribada). After hatching, they head out to sea. These hatchlings are primarily pelagic, drifting the open ocean, hiding and foraging for invertebrates in floating beds of algae. At about two years old, they change their habits, moving inshore along the Gulf to feed on a few species of crab including blue crab. At least part of the population of these juveniles actually slips out of the Gulf though, maturing as they hitch a ride on the warm Gulf Stream. Some are carried as far as Cape Cod, others to the Eastern Atlantic.
Are these animals truly lost, or can they find their way back to the Gulf with the onset of winter or nesting? So many Ridleys have stranded on North Atlantic shores that some parts of this area might be considered habitat for developing young and there is no reason to believe that Ridley’s lack navigational abilities. Unlike leatherbacks, Ridley’s are not cold tolerant. Cold currents can overtake individuals, slowing them down as they drift ashore. These cold stunned individuals can be rehabilitated and may help us understand some important questions. As the rarest of the sea turtles, any answers may help.
The loggerhead, Caretta caretta may be the most common sea turtle in the North Atlantic. Adults average about 100 cm (3.5 feet) but giants weighing above 445 kg (1,000 pounds) have been found. The carapace is high up front, sloping to the rear. The five or more costal shields are red or brown, edged with yellow (sometimes covered with algae and barnacles). Young animals usually have three ridges running the length of the carapace. The head is large in proportion to the body.
In the North Atlantic, nesting beaches stretch from Texas to New Jersey. Many of these beaches have been severely modified by development. After hatching, the young disperse into the Sargasso Sea, hiding in sargassum weed to escape predators and hunt for invertebrates. Adults are omnivorous, foraging into shallow or coastal areas, like Stellwagen, for plants like eelgrass, sponges, mollusks and urchins.
The hawksbill, Eretmochelys imbricata, is rarely seen on the Bank. It is mostly a tropical species, foraging around coral reefs for invertebrates, like sponges. Their beautifully patterned scutes, fashioned into “tortoiseshell” bric-a-brac, have toppled most populations. They show up on Stellwagen Bank as accidentals, carried by spin off of warm water currents from the south.
The green sea turtle, Chelonia mydas, unlike most other sea turtles, takes very little animal prey. They prefer to graze on marine plants, like turtle grass, in warm shallow areas. They are large animals, up to 60 cm (5 feet), with beautifully patterned heads and shell. The common name refers to the color of their highly sought after flesh. Populations nest in tropical and subtropical areas at well known beaches, making them very susceptible to over harvesting. When they do show up in this area, it is usually in late summer, but they are not cold adapted and may become cold stunned.
The leatherback, Dermochelys coriacea, is the only living representative of this unusual turtle family, the Dermochelyidae (all other sea turtles belong to the Cheloniidae). Most individuals in our area are about 2 meters long weighing about 450 kg. (the largest was over 900 kg). The structure of the carapace and plastron are reduced to a mosaic of fine bones and tough skin sculpted into five or seven long ridges that run the length of the back. Overall, they are dark with hints of red, green or blue, often with fine spots of white. The front flippers are very long and tapered.
Leatherbacks are found throughout the world’s oceans, often feeding in higher latitudes and nesting at night on tropical beaches. The females observed in the North Atlantic may nest every two to three years, during spring in Central America or northern South America. On Stellwagen, they are probably the most commonly seen sea turtle, especially in late summer and early fall. The diet of juvenile and adult leatherbacks is highly specialized when compared with other sea turtles: gelatinous invertebrates like jellyfish, salps and siphonophores. They do not have the ability to maintain a constant body temperature, but it does seem to be highly regulated by blood flow, thick skin, fat and sheer size (gigantothermy). These adaptations for thermoregulation allow them to forage in much cooler waters than all other sea turtle species and, help them cool down in warm nesting areas. While foraging they can make exceptionally deep dives of over 1000 meters to access the zooplankton of the deep scattering layer. Consequently, their dives tend to deepen with daylight.
Despite the adaptive differences between the species, it can be very difficult to tell them apart, especially at sea. Even when found on the beach, there can be drastic differences between different age classes within the species.
Only three species, leatherbacks, loggerheads and Kemp’s ridleys, are found on Stellwagen with any regularity. Another two, green and hawksbill, are only rarely seen. To distinguish between the species, first look at the general shape of the carapace, the arrangement of the costal scutes (modified scales arranged as a mosaic on the carapace) and the prefrontal scales on the head, between the eyes (especially important when identifying them at sea).
Leatherback – 5-7 Long ridges on Carapace – Smooth Skin – No Prefrontals
Loggerhead – Tapered Carapace – Five or more Costal Scutes – Two pairs of Prefrontals
Kemp’s Ridley – Heart-Like, Olive Carapace – Five Costal Scutes – Two pairs of Prefrontals
Green – Oval, Smooth Carapace – Four Costal Scutes – One pair of Prefrontals
Hawksbill – Tapered, Patterned Carapace – Four Costal Scutes – Two pairs of Prefrontals
Lutz, L.L., and Musick, J.A. 1997. The Biology of Sea Turtles. Boca Raton. CRC Press.
Ripple, J. 1996. Sea Turtles. Voyageur Press. .