Sea Urchin Seeding in Japan
 

Sea Urchin Seeding in Japan


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Sea Urchin Seeding in Japan

Artificial culture of sea urchins began in Yamaguchi Prefecture in 1968, and Japan produced a total of about 3.5 million cultured seed in 1984. Techniques used to rear S. intermedius at the Hokkaido Institute of Mariculture have been detailed (Saito et aI., 1985; Saito, 1987). Many of the techniques appear to have been adapted from abalone culture; in fact, the Institute is converting an abalone hatchery at Shikabe, Hokkaido, to a sea urchin hatchery7 . Toole7 visited this laboratory in the spring of 1987 and reports that the sea urchin hatchery is slated to produce 5 million 5 mm seed a year.

Briefly, procedures followed in Hokkaido (Fig. 6; Saito et aI., 1985; Saito, 1987) allow females to spawn naturally, releasing eggs into a round 10 L tank. Sperm collected from several males is mixed and used for fertilization.

The zygotes are washed at least five times at 30-minute intervals and the fertilization rate assessed. The tanks are then left undisturbed until the larvae hatch at about 20 hours after fertilization. Larvae are transferred to 600 L larval culture tanks at 3 days and feeding is begun. The suitable temperature range is 15°-21°C. For larvae cultured at 18°C and fed a diet of Chaetoceros gracilis, metamorphosis and settlement begin on the 16th day after transfer to the larval tanks. Wave plates which have been coverd with a culture of Vlvella lens, a species of disk-shaped Chlorophyta, are installed in 5 m tanks to act as settlement substrates, and the water and swimming larvae are transferred (Fig. 7).

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Settlement of 70-80 percent of the larvae occurs within 3-4 hours, and the water can be exchanged within 24 hours. Toole7 reports about 60 percent sur-vival to metamorphosis. Seed up to a test diameter of 3-4 mm consume benthic diatoms on the wave plates. Once that size is attained, soft seaweed fronds (e.g., VIva) are placed on top of the wave plates for food (Saito et aI., 1985; Saito, 1987).

Sea Urchin Seeding in Japan

When the cultured seed reach a size of about 5 mm, they are placed into small mesh cages for intermediate culture in tanks on land or suspended in the sea, as is done with seed settled on collectors. Kelp or knotweed is provided as food. It is desirable to adjust sea urchin density and cage mesh size as the seed grow. Release size is 15 mm or larger. With fertilization in September-October and intermediate culture offshore, sea urchins reach release size the following autumn. In shore-based facilities where the water is heated during the winter, the seed are large enough to be released in 5 months (Saito et aI., 1985; Saito, 1987). Fishermen broadcast the seed over the fishing ground from the surface7.

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ami (1987) reported the results of seeding experiments using cultured S. intermedius in Hokkaido. In each of two tests, 40,000 seed were released into areas measuring 20 X 50 m in water depths of 3 m. Seed were spread uniformly over release sites by divers and from boats. Survival rates were assessed by divers with m2 sampling frames. Released sea urchins were generally distinguished from natives by test diameter. The survival rate after 622 days for the 1983 release group was 38.7 percent, and 92 percent of these had achieved the minimum legal size of 40 mm.

For the 1984 group, the survival rate after 597 days was 22.6 percent, and 91 percent were of fishable size. Other studies showed variation in survival rates between 10 and 40 percent, as well as in growth rates, in different areas. The seed spawning season was the same as that of the parent stock, which varies among different areas of Hokkaido, regardless of where they were planted. Agatsuma and Momma (1988) compared the growth of cultured and native seed. They found that the introduced seed grew faster than the native seed during the first 14 months, but that the cultured seed growth rate decreased there after and was lower than that of the native stock after 3 years.

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