Pacific Black Sea Turtle, Chelonia mydas agassizii
Pacific Black Sea Turtle, Chelonia mydas agassizii. Photograph taken on Floreana Island, Galapagos Islands, August 2009.
Pacific Black Sea Turtle, Chelonia mydas agassizii. Underwater photograph taken in coastal waters off La Jolla, California, May 2018. Photograph courtesy of Bob Hillis, Ivins, Utah.
Phylogeny: The Pacific Black Sea Turtle, Chelonia mydas agassizii (Linnaeus, 1758), is a member of the Chelonidae Family of Sea Turtles. The genus Chelonia is one of seven genera in this family, and Chelonia mydas is the only species in the genus. The Pacific Black Sea Turtle is a subspecies of Chelonia mydas. This species is also called the Galapagos Sea Turtle. In Mexico the Pacific Black Sea Turtle is known as tortuga marina negra. Some important sources do not recognize a taxonomic difference between the Green Sea Turtle, Chelonia mydas, and the Pacific Black Sea Turtle. We treat it as a subspecies because in the popular opinion of the local residents it is a subspecies. The Pacific Black Sea Turtle differs from the Green Sea Turtle in that the Green has a flatter carapace, a lighter color, and a larger head.
Morphology: The Pacific Black Sea Turtle has a smooth, oval, carapace that consists of 5 medial scutes, 4 pairs of lateral or costal scutes, and 11 pairs of marginal scutes. As they age, their carapaces become more elongated. The carapace is almost black in color. The plastron is dark gray or dark green. Hatchlings have a black carapace, a white plastron and a white margin. Their head is small and blunt with a short snout, strong beaks and serrated jaws. There is 1 claw visible per flipper. Unlike other Sea Turtles, the Pacific Black Sea Turtles have only 1 pair of large scales (prefrontals) between their eyelids. Pacific Black Sea Turtles can reach a maximum carapace length of 1.00 m (3 feet 3 inches) and 100 kg (220 lbs) in weight.
Habitat and Distribution: The Pacific Black Sea Turtle spends the majority of its time in coastal waters including bays and estuaries in tropical and sub-tropical waters. Most of their time is spent in shallow water where algae growth is greatest, but they can dive to depths in excess of 50 m (165 feet). In Mexico the Pacific Black Sea Turtle is a resident of the Pacific and found in all coastal waters. They are known to nest on the beaches of the State of Michoacán.
Diet: Pacific Black Sea Turtles are herbivores that primarily consume marine algae.
Predators: Pacific Black Sea Turtles are eaten by sharks. Juveniles and hatchlings are also preyed upon by octopuses, sea birds, and pelagic fishes .
Reproduction: Pacific Black Sea Turtles are either male or female, for life. Reproduction is sexual with fertilization occurring internally. After mating at sea, the female visits a wide beach, within a cove surrounded by rocky granite cliffs. She makes this visit at night. She clears an area of debris and digs multiple nesting holes, using her rear flippers. She selects one hole, then lays clutches of 70 to 100 eggs and covers them with sand. After the hours-long process, the female returns to the sea leaving asymmetrical tracks that are easy to identify. She will return multiple times with nesting intervals of twelve to fourteen days. Babies hatch at night within fifty days to fifty-five days. The babies instinctively crawl into the sea, under the cover of darkness; baby turtles that do not reach the water by daybreak are preyed upon by shore birds, shore crabs, and other predators. Studies conducted in Michoacán on the nests of black sea turtles reveal that nest temperatures below 27.1°C (81°F) do not produced females while temperatures of 31°C (88°F) or higher produced only females.
Ecosystem Interactions: Pacific Black Sea Turtles can host several types of internal and external parasites including: Sporochid flukes, protozoa, helminths, trematode eggs, and even ticks. At times they have commensal relationships with barnacles, crabs, shrimp, and algae.
Human Interactions: From a conservation perspective the Pacific Black Sea Turtle is currently considered to be ENDANGERED primarily due to exploitation by humans. Present population estimates vary from 5,000 to 10,000 individuals. They have slow growth rates, are slow to reach maturity and have slow reproductive rates. Major factors that affect their longevity include artificial lighting that affects their nesting locations, poaching of turtles and eggs, destruction of seagrass beds, entrapment in shrimp trawls and other bottom trawling devices, boat strikes, and plastic pollution. In addition, for human consumption turtle eggs and turtle meat have been exploited in many parts of the world. They are known to hibernate in the Northern Gulf of California where they are consumed by the indigenous Seri Indian population. At present major efforts are on-going to provide protection of sea turtles including the ban of their trade and sale, agreements to help conserve habitats, enhanced public awareness, enhanced scientific focus.
Synonyms: Chelonia agassizii