Ecological Studies at a Seed Oyster Production Aaea-II
Studies on the Spawning Condition of the Pacific Oyster in Matsushima Bay
1972 Volume 38 Issue 12 Pages 1315-1324
Details
1972 Volume 38 Issue 12 Pages 1315-1324
Seed oyster (Crassostrea gigas) production at Sendai Bay in well known because its source of supply not only to the domestic but also to foreign markets. Collectig seed oyster in Sendai Bay depends on oyster larvae population in Matsushima Bay, especially those from mother oysters which have an early and large production at spawning. This report deals on the relationship between the appearance of oyster larvae and mother oyster population, and also the relationship between spawning perods and the spawning environment at Matsushima Bay from 1953 to 1970. The following are the results of the survey.
1. A close relationship between the quantity of larvae and that of mother oysters appeared to exist in Matsushima Bay. Therefore mother oysters should be protected in order to stabilize and enlarge the seed oyster population.
2. It was observed that oyster spawnings from spring tide to neap tide was twice as large as those from neap tide to spring tide.
3. It was found that the first highest peak of spawning commenced in the middle of July, the second in late July to early August and the third in early August to middle August. Meanwhile spawnings occurred two to three times every two weeks after the first spawning.
4. The first spawning was found to occur when the water temperature and gravity reached 23.3°C and σ15=20.48, the second spawning 25.1°C and σ15=21.20 and the third spawning 25.7°C and σ15=22.59. However, the quantity of spawning increased from the first to the third.
5. The largest appearance of larvae was found when water temperature and gravity reached 27-28°C and σ15=20.00-23.00.
6. It was obvious that the first spawning was originated from the natural oysters, the second from two years old cultured oysters and the third from one year old cultured oysters. Generally, larvae from later spawnings are more apt to damage because the water temperature falls. Therfore the best way to collect larvae is to procure the first or the second spawning.
7. The author described the characteristics of oyster larvae, supplied from Matsushima Bay to Sendai Bay. Also, techniques of predicting seed collection so as to promote a larger production of the seed has been discussed.
