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Marine Turtle Newsletter 33:2-3, © 1985

Green Turtle Research Program in Ogasawara

Hiroyuki Suganuma
Research Staff, Ogasawara Marine Center, Marine Environmental Association of Tokyo, P.O. Box 404, Chichi-jima, Ogasawara-mura, Tokyo 100-21, Japan

Four species of marine turtles are known in the Ogasawara Islands: the green turtle, (Chelonia mydas) , hawksbill (Eretmochelys imbricata), loggerhead (Caretta caretta) and leatherback (Dermochelys coriacea). Only green turtles breed in the Ogasawara Islands, one of the northernmost (latitude ca. 27 N) rookeries of this species in the Western Pacific Ocean. Nesting commences during the middle of May, reaches its peak between late June and early July, and declines to a very low level by the middle of August. A few hawksbills, mostly juveniles, are also found around the islands. Loggerheads are captured incidentally by longline fishing vessels; they are rarely encountered around the islands. Leatherbacks seldom or never appear in the waters adjacent to the Ogasawara Islands.

Around the year 1880, about 1,500 adult green turtles were caught by islanders annually. Since the 1920s, the Ogasawara population of green turtles has been much smaller. Nowadays, we can find at most only about 200 annual migrants.

The experimental hatchery program was previously conducted by the Ogasawara Fisheries Center, Tokyo Metropolitan Government (1975-1981: 61,528 hatchlings released). In April, 1982, the Ogasawara Marine Center, Marine Environmental Association of Tokyo, was founded as a museum with the special objective of studying and conserving marine turtles. Therefore, the hatchery program was transferred to us. We have released 36,601 hatchlings over the past three years (Table 1).

Table 1: Hatchery Statistics for 1982-1984, Ogasawara Marine Center

Eggs for the hatchery are collected from turtles that are held captive temporarily. These turtles are caught by fishermen during mating season (March-May), bought by the Ogasawara Public Office and kept in a pond with a fence enclosing an artificial nesting beach. After nesting, they are tagged with plastic tags and released.