The biological aspects of the Japanese sardine found in Hiuchi–Nada, the Central Seto Inland Sea, were studied in terms of catch fluctuation, egg production, maturation, and growth. Since the end of the 1980s, sardine population around Japan began to decline drastically. However. the sardine catch in Hiuchi–Nada has increased in the 1990s. The peak of catch in the center of the Seto Inland Sea was apparently later than the catch in the entrance of the Seto Inland Sea by tracing the pattern of sardine fishing in the Seto Inland Sea. The fishing of 0– year–old and adult sardines was started in Hiuchi–Nada, in 1995, and 1996. On the bas is of egg production, it was noted that the number of adult sardines that migrated to Hiuchi–Nada had increased in 1993. The characteristic of length frequency distributions of adult sardine in Hiuchi–Nada was similar to that of the fishes in Tosa Bay, which is one of the main spawning grounds on the Pacific coast of Japan. Therefore, adult sardine in Hiuchi–Nada probably migrated from the Pacific coast. Though anchovy catch had been more dominant than the other pelagic catch in Hiuchi–Nada, former was poor when sardine migrated to Hiuchi–Nada. The sardine migrations to Hiuchi–Nada were not continued by the decline of the population along the Pacific coast.

Annual yields of firefly squid (Watasenia scintillans) in Toyama Bay, Japan Sea, widely fluctuated from 473 to 3,895 tons with the average of 1,655 tons from 1982 to 2001. Hence there has been a strong desire for reliable forecasts of annual yield among fisherman. To find out keys for yield forecasts, we examined yearly, 5–day period and daily fluctuations of catch by areas, relation between daily catch and sea temperature, and body size changes of squid during 1982 to 2001. When defining a fishing season as the period from the first date to the last date with over one–ton daily catch, the maximum duration of fishing season in Toyama Bay was from early March to middle July. The potential and optimum sea temperature for squid fishing seemed 9 to 15°C and 11 to 13°C, respectively. The western part, Shinminato, and the eastern part, Namerikawa and Uozu, of Toyama Bay showed distinctively different patterns in annual and daily catches. These differences in catch pattern were considered partly due to bottom topography. When looking at the average of years with rich yields, there were 7 days lags from Shinminato to Uozu in daily catch correlation, suggesting the eastward movement of squid. Body size of squid generally increased through a fishing season. However, the detailed examination of changes in mean body size in comparison with a known growth rate of squid indicated an occurrence of several recruitments during a season every year. This was also supported by an occurrence of several peaks in daily catches for each year and area. Understandings on recruitment mechanisms would be essential for a development of reliable yield forecast.

The drastic growth of the toxic dinoflagellate Gymnodinium catenatum (a causative organism of paralytic shellfish poisoning) was observed in Inokushi and Ogamae Bays in winter. To elucidate the characteristics of the growth and effects of hydrographical conditions on the growth, we carried out the field observations of monitoring of G. catenatum cells, water temperature, salinity and current velocity in Inokushi and Ogamae Bays from 26 January to 20 April in 2004. The cell density of G. catenatum increased gradually from late in January and reached the maximum (8,858 cell L^-1) late in March in the inmost part of Inokushi Bay. After late in March, the cell density decreased rapidly. The growth phases of G. catenatum were divided into four phases; early phase, stationary phase, exponential phase, senescent phase. The hydrographic condition was changed late in March in Inokushi Bay. From January to late in March, the inverse estuarine circulation occurred and warm water masses intruded into the upper layer of Inokushi Bay. After late in March, the estuarine circulation was induced by precipitation and basin water masses flowed out through the surface layer. The growth of G. catenatum was effected by the hydrographic conditions. The cell density increased when the inverse estuarine circulation was occurred and increased remarkably when the water temperature increased. However, the cell density decreased rapidly when the estuarine circulation occurred and allowed cells to flow out of the bay.