Isada krill (Euphausia pacifica) is a target species of krill fishery in the North Pacific as well as an important component as a prey organism in marine ecosystem. Objective information of their distribution has been anticipated for the current and future ecosystem-based fisheries management. We thus aimed to quantitatively analyze the distribution characteristics (structures and environments) of isada krill near southern Kuril Islands in the North Pacific Ocean. In 2005, acoustic data at two different frequencies (38 and 120 kHz) and specimens from MOCNESS trawls were obtained as well as temperature and salinity at multiple sampling stations. Using the difference of backscattering at each frequency, backscatterance due to krill was extracted from echograms and numbers of krill in an individual water column over the transect was calculated. Temperature and salinity data were interpolated over transect using Kriging, and compared with the calculated krill numbers at specific locations. In exploratory analyses with vertical profiles along transect, different features of krill distribution and marine environment between north and south of 4°C isotherm, located at 43.27°N, were observed. Also, temperature and salinity where krill were concentrated were significantly different between the north and south of this observed isotherm (p<0.05). Using semivariograms, structural differences of krill distribution between the north and south became obvious. In northern area of the 4°C isotherm, the krill distribution was more disperse and extended to the north-south direction than it was in the southern area where aggregations with variable densities were observed. Specimens in the northern area were mostly of furcilia stages. On the other hand, in the southern area, mainly found were adults. It is likely that life stages of the krill determine their habitat in a given oceanic structure in the area.

We examined age and growth by thoroughly observing otolith sections of tonguefish, Cynoglossus abbreviatus, caught by small trawl nets in the central Seto Inland Sea, Japan, from November 1998 to March 2000. Seasonal change in the proportion of opaque zone at the otolith margin showed that an opaque zone was formed each year from April to June. The Von Bertalanffy growth equations were estimated as follows: TL_t=265.2 (1-e^{-0.91(t+0.325)}) for males and TL_t=328.1 (1-e^{-0.96(t+0.023)}) for females, where TL_t is the total length (mm) at t (year). These equations were significantly different between male and female. Age composition of fisheries landings ranged from 0+ to 6+ and 5+ for male and female, respectively, and showed a large proportion of the landings were immature fish under 2+.

To examine seasonal changes in age composition and growth of Spanish mackerel Scomberomorus niphonius landed in Ehime Prefecture from Iyo-nada, Seto Inland Sea, the fork length of 11,058 fish was measured at the Kaminada Fish Market from 2000 to 2006. Monthly compositions of the fork length were then obtained, which were decomposed into size (age) groups by fitting the normal distribution curves. Based on otoliths examinations from 1,399 samples, age specific mean fork lengths and their standard deviations were estimated and used as the initial inputs for the normal curves. Age composition in spring (March–June) mostly consisted of 2-year-old fish and some 1 and 3-year-old fish, while that in autumn (August–December) mostly of 1-year-old fish with 0-year-old fish occurring in November and December. Monthly growth rate of the fork length was high from summer to autumn and low from winter to spring.

Long-term fluctuations in water quality properties such as water temperature, salinity, density, pH, dissolved oxygen, NH₄-N, PO4-P and transparency in Tokyo Bay were examined using a data set observed by Chiba Prefectural Fisheries Research Center (CPFRC) for fifty-eight years during 1948–2005. As a result, it was shown that the changes of the properties were related to each other. Water temperature was gradually increasing for a long term especially in autumn and winter. This increase caused to prolong the existence of hypoxic water to late autumn. Also, difference in density between bottom water to surface water as indicator of the stratification strength was related to the horizontal coverage of hypoxic water. When the stratification was weak, the annual occurrence of red tides was small. Eutrophication factors such as hypoxic water, annual occurrence of red tides, NH₄-N, PO₄-P and transparency were most remarkable in the 1960s. NH₄-N in 2004 has decreased to the same level of the first half of the 1960s. PO₄-P was higher in bottom water than in surface water because of the dissolution from reductive mud under hypoxia. It has decreased in the late 1990s, especially in March. Transparency increased to the same level as in the 1960s but hypoxic bottom water and annual occurrence of red tides have not always decreased. Eutrophication in Tokyo Bay has caused a large decrease in catch of the bivalves, flatfish and others. In addition, the recent rise of water temperature in autumn and winter has shortened the culture period of laver Porphyra yezoensis. Moreover, fall of PO₄-P in March has damaged the laver culture because nowadays no enough PO₄-P for the growth of laver remains in the water after diatom blooming.