1Kuroshio Research Division, National Research Institute of Fisheries Science, Fisheries Research Agency, Kochi, 780-8010, 2Kochi Prefectural Government, Kochi, 780-8570, Japan
Growth and migration of the greasyback shrimp Metapenaeus ensis were studied in Tosa Bay (33°N, 133°E). Specimens were caught in 1998 by small beam trawlers in Tosa Bay (offshore water), and by push net in the estuary of Urado Bay, the adjacent semi-enclosed water of Tosa Bay. The push net specimens were 9-29 mm in CL from May to July and 3-20 mm in CL from July to October. These results indicated that the zero-year class alternated with the one-year class in July. The small beam trawler specimens were 30-45 mm in CL in females and 25-35 mm in CL in males in April, and became smaller than 35 mm in CL in females and 30 mm in CL in males in July. In addition, it appeared that the one-year class alternated with the two-year class between May and July. Therefore, growth and migration of the greasyback shrimp in Tosa Bay were estimated to be as follows. The zero-year class settles in the estuary of Urado Bay in summer. The next year, they reach the one-year class and migrate from the estuary to Tosa Bay in summer. The year thereafter, they reach the two-year class and disappear until summer.