Pacific Black Sea Turtle
Chelonia mydas agassizii
IUCN Listing Status: Threatened - Endangered (depending on location)
Adult Pacific black sea turtles have an almost black coloration to the carapace. The carapace is dramatically tear-drop shaped at the posterior. The plastron is generally dark gray or gray-green. Adult black turtles weigh as much as 220 pounds (100 kilograms) and measure up to 39 inches (100 centimeters) in carapace length.
Hatchling Pacific blacks have a black carapace and white plastron. Hatchlings also have white marginal coloration.
Some experts do not distinguish between the Atlantic green and Pacific black as separate species. At Sea Turtle, Inc. we consider them two different species. Physical similarities between the Atlantic greens and Pacific blacks include one pair of prefrontal scales on the head. Also, both have 4 costal scutes (along the spinal column). The head size of the Pacific black is comparatively smaller than that of Atlantic green sea turtles.
Habitat and Distribution
This turtle is found primarily in coastal waters, bays and estuaries in tropical and subtropical latitudes. Iverson (1992) lists the distribution of this turtle in the eastern Pacific Ocean from southern California, USA to Chile, west to the Galapagos Islands, Hawaii and Papua New Guinea. According to Alvarado and Figueroa (1986) the primary nesting beaches of Mexico include: Colola, Maruata, Mexiquillo, Chimapa, and Motin de Oro.
Present population estimates vary from 5,000 to 10,000 individuals. This turtle feeds primarily on marine algae.
Pacific blacks primarily nest at night. A typical clutch is 70-100+ eggs. Nesting intervals range from 12-14 days. The eggs typically incubate from 50 to 55 days prior to hatching. Nest sites are usually on wide beaches in coves surrounded by rocky granite cliffs. The nesting process takes between 1-3 hours. This includes emerging from the water, selecting a site, digging, egg laying and covering the eggs with sand. Both black and green sea turtles may dig several nests before laying a clutch of eggs.
Sexual maturity is probably attained between 16-30 years of age in this species. Studies conducted in Michoacan 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. Temperature-dependent sex determination (Bull,1980) is comparatively well defined in many sea turtle populations today.
Unique Traits of Pacific Black
Pacific black sea turtles are well known for presenting a basking behavior along the Hawaiian islands, particularly the French Frigate Shoals. These sea turtles will crawl out of the shallow water and lay along the rocks and sand in the bright sunlight. This is not a common sea turtle behavior. Scientists do not agree on the reason for the basking - some think that this unique basking behavior has something to do with temperature regulation, or it may be a way for them to rest without fear or predation. Many species of reptiles bask on a regular basis to regulate body temperature. This behavior has created a new eco-tourism niche for the Hawaiian islands. Volunteers are trained to spot and protect the sun bathing sea turtles. Tourists are encouraged to respect the space of the sea turtles and enjoy an odd behavior which allows for close up viewing of these usually aquatic animals.
Current Threats and Historic Reasons for Decline
Although this turtle enjoys a protected status in the Galapagos Islands, some portions of this population nest in coastal Ecuador where they are being exploited. In Mexico, despite laws to protect them, the turtles continue to be captured and sold by local Nahuatal people on the black market. According to Alvarado and Figueroa (1986) offshore poaching with shark gill nets and incidental capture in shrimp trawls are the main factors contributing to this species decline. In the 1960s, turtle hide hunting intensified in Mexico as a result of a ban on the export of crocodile skins to the international markers. The black turtle is known to hibernate in the Northern Gulf of California where it is consumed by the indigenous Seri India population.