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Friday, Nov. 8, 2002


Loggerhead turtle

* Japanese name: Ao-umigame
* Scientific name: Caretta caretta
* Description: Turtles are reptiles with limbs modified into swimming paddles. Loggerhead turtles have a characteristically large head, but they don't have a big brain: It's their jaws that are large. The reddish-brown carapace of adults is 70-100 cm long, and they weigh around 165 kg. Adult males can be distinguished from females by the tail, which extends well beyond the carapace. Loggerheads may live for more than 50 years.
* Where to find them: Loggerheads prefer tropical and subtropical waters, but they are the only species of sea turtle that will nest in temperate areas. In Japan they live south of Ibaraki Prefecture on the Pacific Ocean side, and south of Noto on the Sea of Japan side. Only the females ever leave the sea -- about 3 or 4 times a year in spring and summer -- to lay their eggs on quiet beaches or in grassy vegetation. However, because of intense predator pressure, few baby turtles survive. Loggerheads are a threatened species, due to human use of nesting beaches, beach pollution and the accidental trapping of turtles in shrimp nets.
* Food: Loggerheads are omnivorous, but with such powerful jaws it's not surprising to learn that crustaceans such as horseshoe crabs, oysters, mussels and clams form an important part of the diet. Loggerheads also eat sponges, jellyfish, fish, seaweed and sea grass.
* Special features: Humans and most other animals have sex chromosomes. This means (for humans) that if you have a Y and an X chromosome, you are male. If you have two X chromosomes, you are female. But like many other reptiles (including most snakes), loggerhead turtles don't have sex chromosomes. Instead, the temperature at which the eggs are incubated determines the sex of the offspring. This means that egg clutches laid in southern, tropical climes tend to produce more female turtles than clutches laid in northern, cooler climes. The optimum sand temperature for loggerheads is 29 degrees.

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