Nesting Site Migration Route for Green Turtle

Orientation Cues to Open Ocean

Orientation Cues to Open Ocean

Seaturtle migration routes and orientation cues. (Illustration by Patricia Ferrer)

3. magnetic orientation ■ I

wave direction

Seaturtle migration routes and orientation cues. (Illustration by Patricia Ferrer)

Habitat

Coastlines on the continental shelves, where feeding and nesting sites are most abundant. Hatchling and small juveniles of most species apparently are mostly pelagic.

Behavior

Seaturtles (males and females) often make extremely long migrations between feeding and nesting grounds (at least 190 mi [300 km] in some cases). Some species congregate off the sandy nesting grounds and then nest en masse in large groups called "arribadas." Most nesting is done at night, but one species is a diurnal nester. Seaturtles enter temperate seas during the summer but usually either migrate to warmer waters or bury themselves in the mud in shallow coastal areas for the winter.

Feeding ecology and diet

All but one species of seaturtles are primarily carnivorous, feeding on sponges, mollusks, crustaceans, barnacles, sea urchins, or fish. The green seaturtle is primarily herbivorous, feeding mainly on sea grasses.

Reproductive biology

Female seaturtles migrate to nesting beaches in one- (rare) to three-year cycles. Seaturtles nest primarily on tropical

Seaturtle swimming strokes. (Illustration by Patricia Ferrer)

beaches, producing as many as seven or more clutches in a season at intervals of 10-30 days. The eggs are leathery and spherical and measure 1-2 in (30-60 mm) in diameter. Clutches usually contain 90-130 eggs, although maximum clutch size can approach 250. Incubation is generally quite short, only 40-70 days. All species exhibit temperature-

dependent sex determination. Warm temperatures produce mostly females, and cool temperatures produce mostly males.

Conservation status

Five species of seaturtles are classified as Threatened, with two listed as Critically Endangered, three as Endangered. The remaining species is listed as Data Deficient.

Significance to humans

Despite international legislation to protect them, seatur-tles and their eggs are still eaten locally around the world. The shells of some species, particularly the hawksbill (Eretmochelys imbricata), are used for making trinkets. Many more turtles are accidentally killed in fish and shrimp nets. Turtle excluder devices placed on these nets are known to reduce seaturtle drowning by at least an order of magnitude and are legally required by many countries, but universal use is sorely needed. Increasing numbers of seaturtles are being found with fibrous tumors (fibropapilloma) up to 12 in (30 cm) in diameter on the skin, in the mouth, and on the internal organs. More than 70% of the turtles in some areas are infected. The cause of this mysterious disease is not yet fully understand, although it is contagious and certainly linked to human pollution. The long-term effects of these tumors on seaturtle populations are unknown.

A hawksbill (Eretmochelys imbricata) over coral near the Solomon Islands. (Photo by Fred McConnaughey/Photo Researchers, Inc. Reproduced by permission.)

1. Kemp's ridley turtle (Lepidochelys kempii); 2. Loggerhead turtle (Caretta caretta); 3. Green seaturtle (Chelonia mydas). (Illustration by Patricia Ferrer)

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