Sea Turtle Overview

Sea Turtles - Overview

• Sea turtles have existed for 200 million years with minimal changes.
• The earliest fossil records date back 150 million years, which indicates links to an extinct lizard-like reptile lineage.
• Fossil evidence suggests a marsh-dwelling species origin.
• There were 4 families by the Cretaceous Period (70-60 million years ago): Toxochelidae, Protostegidae, Cheloniidae, and Dermochelyidae.
• Toxochelidae and Protostegidae are now extinct.
• Aside from a few sea snake species, they are the only reptile group living entirely in water.

General characteristics

• Shells contain a carapace (upper shell) and the plastron (lower shell), which are joined by cartilage.
• Carapace are covered in keratinous scutes (scales) in most species.
• The quantity and pattern of scutes play a role in species identification.
• They don't have teeth; instead, their jaws have evolved into modified "beaks" for crushing, tearing, and biting.
• Eardrums are covered by skin because they lack external ears.
• Can hear lower frequencies better
• They have a keen sense of smell
• Underwater vision is good, but vision is poor out of water.
• They spend most of their time submerged, but they must come to the surface to breathe.
• Lungs are adapted for rapid oxygen transfer and prevention of gas entrapment during deep dives.
• Typically dive for 4-5 minutes and breathe for 1-3 seconds.
• Can rest or sleep for several hours underwater, but activity or stress reduces this time.

Temperature

• Sea turtles are cold-blooded reptiles.
• At water temperatures below 59°F, they become lethargic and seek warmer water or burrow into the mud. -Hibernation in sea turtles was discovered in the 1970’s
• Water temperatures dropping below 41°F for more than 12 hours are lethal.
• Overheating is as dangerous as cold and sunlight can cause an 18°F temperature increase during nesting.

Sea Turtle Species

• There are 8 known species in 6 genera.
• Genera is plural for genus

Genus Caretta - Loggerhead Sea Turtle (Caretta caretta)

• Hatchlings are 2" long, growing to 200-350 pounds and 30-40" in carapace length.
• Head size may reach up to 10" in diameter with powerful muscles that crush clams, crustaceans and encrusting animals.
• For extra predator protection, the carapace is thickest towards the back.
• Sexual maturity is reached between 12 and 30 years of age.
• They live in temperate and subtropical coastal waters.
• Feeds in the shallows and gather when food is plentiful.
• Nesting sites include Oman (Middle East) which has 30,000 nests and beaches in the Southeast U.S. which has 25,000 nests.
• Florida has 14,000 of the U.S. nests.
• Florida nesting happens from March to June.

Genus Eretmochelys - Hawksbill Turtle (Eretmochelys imbricata)

• Small turtle, 30-36" in carapace length and 89-133 pounds in weight.
• Possesses a strong, hooked beak and an arrow-shaped head
• Carapace is a dark amber color with brown or black stripes, has thick overlapping scutes and is strongly serrated along the posterior border.
• Are a source of natural tortoiseshell.
• They are the most tropical sea turtles and are found in Florida, the Florida Keys, the Bahamas, and throughout the Gulf of Mexico.
• Adults forage at around 330', while juveniles forage at around 66'.
• Few vertebrates consume sponges (some sponges are toxic due to spicules, but there have been no explicit adaptations identified in Hawksbills).
• Spicules have been discovered inside the intestines of hawksbills.
• They prefer to nest alone or in small groups, an adaptation to prevent poachers.
• Approximately 5 nests are laid per season every 2-3 years in the Eastern Caribbean.
• 150 eggs are laid in an average clutch.
• Hatchlings are light to dark brown and have a pelagic voyage; after reaching 10", they become benthic feeders and move further towards deeper reefs as they increase in size and dive deeper for sponges.

Genus Dermochelys - Leatherback Turtle (Dermochelys coriacea)

• They are larger, dive deeper, and favor colder waters more than other species.
• Grow up to 800 pounds and 64" in carapace length.
• Carapace is made of thick, oily cartilaginous material with thousands of tiny bones.
• Pacific leatherbacks grow only to 600 pounds.
• The largest recorded was 10' from tip of beak to tip of tail.
• Anterior-to-posterior with 7 narrow ridges.
• Carapace, head, and flippers have white spots and are all black.
• Plastron is soft, ridged, and white with black spots
• Their flippers lack scales or claws.
• Hatchlings are 2.5" long with flippers as along as their shell
• They are the most widely distributed of any turtle species.
• Nest 4 - 10 times per season; nest cavity is deeper, and eggs have a longer incubation period
• Each nest contains 80 - 90 eggs
• Exclusively consume jellyfish using their scissor-like and deeply notched jaws.
• Can maintain a consistent internal body temperature
• Can dive to 3300' to forage for food because their plastron and lungs compress; only elephant seals and sperm whales can dive as deep.

Genus Lepidochelys - Kemp’s Ridley (Lepidochelys kempii)

• The smallest sea turtles are 24-28" in carapace length and weigh 78-100 pounds.
• Adults have olive green tops and yellowish bottoms.
• Has a huge head with powerful jaws.
• Hatchlings measure 1.5" long.
• Mexico is home to 95% of the nesting population.
• Only 400 adult females remained in 1993, whereas the population was approximately 40,000 in 1947.
• Consume crabs, clams, mussels, and snails.
• In Cape Cod, Massachusetts, lies the "Lost" East Coast nesting population.

Olive Ridley (Lepidochelys olivacea)

• Carapace is 22-30" long and weighs less than 100 pounds.
• Olive green carapace with a yellowish plastron that has a heart shape.
• Hatchlings measure 1-1.5".
• Are the least threatened species of sea turtles
• Nesting takes place all year long in Central America.
• Around 100 eggs are laid in each clutch (nest).
• They forage for shrimp, crabs, snails, tunicates, sea urchins, and jellyfish up to 500' deep.

Genus Chelonia - Green Sea Turtle (Chelonia mydas) and Black Sea Turtle (Chelonia agassizi)

• The color of its fat gives the green turtle its name and is the turtle that is most well-known.
• Carapace is greenish, brown, black, or gray in color and the plastron is white or yellowish
• Green turtles in Florida have an average carapace length of 3.3 feet and weigh 303 pounds.
• Hatchlings have the size of a half dollar.
• Black turtles possess a more angled carapace and varying pigmentation.
• Diet includes jellyfish, mollusks, crustaceans, sponges, algae, and sea grasses.
• Black turtles are found in the Galapagos Islands.
• Mature around 15 - 50 years.
• They lack Vitamin D in their diets, leading them to frequent bask in the sun by lingering at the surface or laying on the beach (white sand, steady wind, partly cloudy).
• Green turtles nest throughout the world, but black turtles only do so in the Galapagos.
• Sea turtles are vulnerable to fibropapillomas.
• Fibropapillomas may be caused by external parasites, warmer water temperatures, excessive solar radiation, and chemicals
• Loggerheads and olive ridleys are also contracting papilloma-like illnesses.

Genus Natatar - Australian Flatback Turtle (Natatar depressus)

• Believed to be the most primitive of all Cheloniidae.
• Only inhabits Australia.
• Produces 1/2 the amount of eggs as other sea turtles.
• Hatchlings are non-pelagic.
• Carapace length is 30–38" and weighs 156 pounds makes it a medium size
• The females are larger than the males.
• The head and neck area are olive gray on top, whereas cream color is on bottom.
• Flattened carapace is olive gray, greasy to the touch, oval in shape, and upturned at the edges.
• They can bleed if you scratch the turtle with your fingernail because the keratin that covers the carapace and flippers is so thin.
• They feed on sea cucumbers, jellyfish, and crustaceans.
• Nests in November and December
• Nests average 56 eggs and they lay 4 nests per season.
• Hatchlings are 2"+

Growth Rates

• Growth rates vary with species.
• They can live for 75 - 100 years.
• Juveniles grow quickly whereas adults grow slowly (0.2 - 0.4” per month versus 13 mm per year).

Other Facts

• Have magnetite in their heads to aid in navigation.
• Humans are their most dangerous predator.
• Eggs are sometimes consumed as food and aphrodisiacs.
• Green Turtles are used for their meat (often put into soup).
• Olive Ridleys are consumed for their skin from their necks, shoulders, and flippers (for accessories)
• Shells are used for decorations
• Leatherbacks are used for their oils (for lamps and some cosmetics).
• "Living tag" - pieces of the carapace and plastron are switched to aid in identification for tracking
• No heteromorphic sex chromosomes
• TSD - temperature dependent sex determination
• Temps below 82.4 F produce 90% - 100% males
• Temps between 83.3 F - 86.4 F produce mixed nests
• Temps above 86.9 F produce 94% - 100% females
• Some beaches are known for hatching only certain sexes