東京灣におけるシャコの分布と小型底*網漁場との關係

The Distribution of the Japanese Mantis Shrimp Oratosquilla oratoria and its Relationship to Fishing Grounds in Tokyo Bay

From May 1985 to February 1987, sampling surveys with small beam trawlers at 20 stations were carried out every season in Tokyo Bay. With these results and logbook data from several fishermen, the distribution of the Japanese mantis shrimp Oratosquilla oratorio and its relationship to fishing grounds were investigated. The distribution of the mantis shrimp covered a wide area of the bay from autumn to winter, but from spring to summer, it was concentrated towards the southern part. From the results of the mark-recapture experiment, this southern concentration is considered to be caused by the movement of the mantis shrimp. The distribution of fishing grounds was concentrated towards the southern part of the bay from summer to autumn and it expands to a wider area from winter to spring. In Tokyo Bay, larval mantis shrimp seem to settle in a wide area throughout the bay. As individuals settled in the northern (inner) area of the bay are not fished to any areat extent until the following summer, they are secure to be recruited to the stock unless natural death occurs. I year-old and over individuals are the target for small beam trawlers and are caught rather intensively in summer and winter.