To study on the actual state of spawning of commercial fishes in the fishing grounds around Oki Islands, the vertical hauls from 50m level in depth to the sea surface with “Marutoku”-net were operated during the years from 1957 to 1961 with following result:
The periods of occurrence of eggs and larvae were April to. June (mainly April) for sardine and round herring, and April to November (mainly May to July) for anchovy.
The average numbers of eggs per haul during main spawning seasons were 4.8 for sardine (April), 1.6 for round herring (April) and 20.6 (May) -12.7 (June) for anchovy.
Eggs and larvae of sardine occurred mainly in the area on the continental shelves, and their distributions were most strictly limited there but eggs and larvae of anchovy were considerably abundant in the offing, as well.
As for sardine and round herring, the collected number of eggs and larvae decreased year by year during survey period, and in 1961 those of eggs of sardine and round herring were 0.4% and 2% against to those in 1958. The collected number of eggs and larvae did not coincide with the catch of adult fish during the spring fishing season in each year.
Comparing with the results of collections in the adjacent waters to Goto Islands, one of the most important spawning grounds of sardine in Japan, the collected number of eggs of sardine, round herring and anchovy per haul in this area were not little.