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.

The Pacific Black Sea Turtle, Chelonia mydas agassizii (Linnaeus, 1758), is a member of the Chelonidae Family of Sea Turtles and is known in Mexico as tortuga marina negra. Some individuals do not distinguish between the Green Sea Turtle, Chelonia mydas, and the Pacific Black Sea Turtle but they are treated as separate species herein.

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 marg. Hatchlings also have white marginal coloration.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.

The Pacific Black Sea Turtle spends the majority of its time in coastal waters including bays and estuaries in tropical and sub-tropical waters. Adults are herbivores that primarily consume marine algae. In turn they are preyed upon by octopuses, pelagic fishes and sharks. After mating at sea, females visit a wide beach in coves surrounded by rocky granite cliffs during the night, clear an area of debris and dig multiple nesting holes before selecting one using their rear flippers, then lay clutches of 70 to 100 eggs and cover 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 12 to 14 days. Babies hatch at night within 50 days to 55 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) produced 0 percent females while temperatures of 31°C (88°F) or higher produced only females.

In Mexico that 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.

The Pacific Black Sea Turtle is often confused with the Green Sea Turtle, Chelonia mydas  (flatter carapace and lighter in color; larger head) and recognized by many to be one and the same species.

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 coral reefs and seagrass beds, entrapment in shrimp trawls and other bottom trawling devices, boat strikes and fertilizer runoff 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. In the Hawaiian islands they are known to crawl out of the shallow water and lay along the rocks and sand in the bright sunlight, uncommon sea turtle behavior. This behavior has created a new eco-tourism niche for the Hawaiian islands. 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.