Spawning and distribution of Euphausia pacifica were investigated bimonthly using Norpac and large cylindrical-conical nets along the coastal areas off northeastern Japan [Southeastern Hokkaido (44-43°N), Sanriku (38-41°N) and Joban (36-38°N) from March 1997 to February 1998. Copulated females, egg and calyptopis stage were abundant off Sanriku in spring and off southeastern Hokkaido in mid fall, but rare throughout the survey areas in late fall. They mainly occurred near the marginal area of Oyashio Current (T₁₀₀=5°C) throughout the year, Furcilia and immature stages tended to expand their distribution into warmer southern areas compared to younger stages (eggs and calyptopis stage) in each season. Copulated females, eggs, calyptopis, furcilia and immature stages were few or absent throughout the year except in mid fall off southeastern Hokkaido, where cold waters of the Oyashio (T₁₀₀<2°C) dominated. Small adults (≤15mm) occured in all survey areas including the areas off southeastern Hokkaido throughout the year, Large adults (>15mm), which are considered to be individuals that have overwintered, however, were few from August to December off Sanriku and Joban where the warmer waters of the transitional area (10°C≤T₁₀₀≤15°C) dominated. It is suggested that the geographical change in the distribution and spawning activity depend mainly on the seasonal changes of the water masses associated with the Oyashio Current.

To reveal the occurrence pattern of white-spotted conger larvae (Conger myriaster) and its relationship to oceanographic conditions, we recorded daily changes in landings at a fish market and water temperature in southern Tohoku area from 1993 to 2002. Fishing season of larvae was from February to June, with its duration and peak fluctuating among years, corresponding to year-to-year variations in water temperature. Catch per unit effort (CPUE) of whitespotted conger larvae were approximately 0 at water temperatures <10 and ≤18°C in every year. Maximum and high values of CPUE occurred at 10–15°C. Leptocephalus larvae before metamorphosis occupied a greater proportion of the developmental stage compositions of samples collected before early April 2001 and 2002, whereas they scarcely appeared when the water temperatures were above 15°C after mid-April. It was concluded that the white-spotted conger larvae mainly immigrated into the southern Tohoku area at 10–15°C.

Statolith increment analysis was applied to 400 specimens of the Japanese common squid, Todarodes pacificus, in order to estimate ages and population structure. Samples were collected during June–November 2001 in the Japan Sea and the Okhotsk Sea off northern Hokkaido. Three groups having different hatching dates were detected. Squids that hatched in autumn–winter (Sep.–Feb., mainly late Nov.–middle Dec.) and in winter–spring (Dec.–Jun., mainly middle Feb.) occurred in the Japan Sea off northern Hokkaido during June–September and October–November, respectively. Squids that hatched in spring (Feb.–May, mainly early Apr.) occurred in the Okhotsk Sea off northern Hokkaido during October–November. During June–September, the squids that hatched in autumn–winter migrate northward to the Japan Sea off northern Hokkaido, and then they migrate southward from the area to the spawning ground. After that during October–November, the squids that hatched in winter–spring recruit and form the main population in the area. Based on the current results, two catch-peaks in the Japan Sea off northern Hokkaido and one catch-peak in the Okhotsk Sea off northern Hokkaido resulted from catching the three groups of the squid in the areas.

An ecosystem model was constructed to evaluate the influence of estuarine circulation process on the biological production in the northern Hiroshima Bay, Japan. In summer season, of the estimated total input DIP (dissolved inorganic phosphate), decomposition of detritus, river discharge of the Ohta river and vertical advection and diffusion from the lower layer, amounted 44%, 12% and 44%, respectively. While, 80% DIP was estimated to be supplied by decomposition process in the lower layer. Total amount of DIP utilized by primary production in the area amounted 8.7-folds of that from the riverine input. Sensitivity analyses revealed that the biological production in northern Hiroshima Bay is most responsible to the variation of the nutrient concentration in the lower layer of neighboring southern area. In the viewpoint of environmental management of northern Hiroshima Bay, it is important to evaluate the influence of the estuarine circulation quantitatively in addition to the influence by land.