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The Japanese Pacific stock (JPS) and the northern Japan Sea stock (JSS) of walleye pollock Theragra chalcogramma are mainly distributed in the Pacific Ocean and the Sea of Japan off northern Japan, respectively. This paper summarizes and compares the factors affecting the recruitment variability of these two stocks. Spawning season is from December to March for both stocks. JPS recruitment has a positive relationship with the water temperature in January and February, whereas that of JSS has a negative relationship with the water temperature in January, February, and April. One possible reason for this is that pollock larvae have an optimum growth temperature of approximately 5 °C in the field. Drift of early life stages also appears to be an important influence on the recruitment of both stocks. Because the current generated by the northwest wind carries eggs of JPS into the main larval nursery ground, JPS recruitment is enhanced in years when the northwest wind is predominant in February. On the other hand, early life stages of JSS are transported into the nursery ground by the Tsushima Warm Current. However, this current also carries early life stages into the Sea of Okhotsk and offshore, resulting in poor JSS recruitment in years when this current is strong in March. In contrast to JPS, the recruitment of which is significantly impacted by cannibalism, young pollock have not been found in the stomachs of adult JSS. Warm temperatures in the Sea of Japan seem to induce the separation of young and adult pollock, and the shape of the stock-recruitment relationship also suggests that cannibalism is not important for JSS. Based on this knowledge, and on the hatch date distributions of larvae and juveniles, we propose mechanisms that can explain the recruitment fluctuations for JPS and JSS pollock. [ABSTRACT FROM AUTHOR]

The purpose of the present paper was to examine the genetic population structure of Buccinum tsubai in the Japan Sea. Mitochondrial 16SrRNA gene sequence analysis was performed with specimens from various stations in the Japan Sea. Mitochondrial lineages were clearly patterned geographically in four separate areas: the Hokkaido area, the Yamagata–Toyama area, the Yamato Bank area, and the San’in area. The main distribution depth range of B. tsubai is between 200 m and 1000 m isodepths, and the horizontal distance between the 200 m and 1000 m isodepth lines represents the specific spatial scale of the habitat (SSSH). These four areas were separated either by the complete discontinuity of the SSSH area or by its narrow spatial extension. Genetic distances between the main haplotypes of each area were calculated as Jukes–Cantor distances, the value of which ranged between 0.012 and 0.017. This value seemed to be unrelated to the geographic distance. There was no tendency for clustering according to depth. In future, the morphological characters of the four lineages of B. tsubai should be compared in detail in order to elucidate significant genetic differences among them. [ABSTRACT FROM AUTHOR]

Milky hemolymph syndrome (MHS) has been observed in both reared and wild populations of the snow crab Chionoecetes opilio from the Sea of Japan. The virus presumably associated with MHS and detected with electron microscopy was designated ' Chionoecetes opilio bacilliform virus' ( CoBV), but little is known about its infectivity or pathogenicity in the snow crab. In this study, we performed an infectivity experiment in which snow crabs were injected with a viral inoculum prepared from MHS-affected crabs and then maintained at 2 °C or 2-8 °C. Cumulative mortality increased more rapidly at 2 °C than at 2-8 °C, reaching approximately 80% in both groups at the termination of the experiment. This result demonstrates the temperature-dependent pathogenicity of CoBV in the snow crab. CoBV-infected crabs displayed the clinical and histopathological signs of MHS. Mortality tended to increase as the viral load in the hemolymph increased at both 2 °C and 2-8 °C. The viral load in the hemolymph was significantly higher in dead crabs than in surviving crabs and was also elevated in various other organs. We conclude that CoBV is the causative agent of MHS and that severely affected crabs develop viremia that leads to death. [ABSTRACT FROM AUTHOR]

The diversity of cyanobacteria and diazotrophs in the Japan Sea was investigated by analyzing sequences of cyanobacterial 16S rRNA genes and nitrogen fixation genes ( nifH) from seawater sampled at depths ranging from the surface to 100 m at two stations. Of the 107 cyanobacterial 16S rRNA gene sequences obtained, 97 and three sequences were assigned to Synechococcus sub-cluster 5.1 and Prochlorococcus HL (II), respectively. Unlike other oceanic regions, at our two sampling stations the composition ratio of the sequences assignable to Synechococcus sub-cluster 5.3 was relatively high (8 %). No sequences of diazotrophic cyanobacteria were found in the cyanobacterial 16S rRNA genes. In the nifH clone library (36 sequences), ten sequences were identified as a UCYN-A group of diazotrophic cyanobacteria; the other 26 sequences (72 %) were assigned to proteobacteria. These results suggest that heterotrophic bacteria, including UCYN-A, dominate the diazotrophic community in the Japan Sea. Our study reveals the dominance of Synechococcus in cyanobacterial community and (photo)heterotrophic diazotrophs in the diazotrophic community in the Japan Sea, suggesting its unique characteristics. [ABSTRACT FROM AUTHOR]

Milky hemolymph syndrome (MHS) is a previously undescribed disease in snow crab Chionoecetes opilio. Outbreaks of this disease occurred in reared and wild populations from the Sea of Japan when the water temperature was 2-3°C. The common symptom of the disease was a distinct milky or opaque coloration of the hemolymph. Some severely affected crabs also showed yellow or ivory discoloration on the ventral shell and uncalcification of the arthrodial membranes of walking legs. Histopathological changes consisted of widespread cellular degeneration characterized by enlarged nuclei with marginal hyperchromatosis and basophilic intranuclear inclusions in the interstitial connective tissues of various organs. Electron microscopy analyses of degenerated cells revealed a nonoccluded, enveloped bacilliform virus within the nuclei. The virus morphologically resembles white spot syndrome virus (WSSV) or unassigned intranuclear bacilliform viruses (IBVs) reported from other crustaceans. However, we could not detect WSSV from diseased tissues by PCR using WSSV-specific primers, and the tissues targeted by the virus differed from those targeted by IBVs. This is the first report of a virus from the genus Chionoecetes. Thus, we have tentatively designated the virus presumably associated with MHS as Chionoecetes opilio bacilliform virus ( CoBV) until its relationship with other crustacean viruses can be clarified. [ABSTRACT FROM AUTHOR]

Effects of sampling errors on abundance estimates from virtual population analysis (VPA) were quantified with the bootstrap method for stock of walleye pollock in the the Sea of Japan. In the bootstrap method, individual fish measurements were resampled. A total of 1000 bootstrap samples were produced for each year from 1991 to 2001. The coefficients of variation (CV) of catch at age in 2001 ranged 6.1–33.1%. The CV of an abundance estimate in 2001 ranged 9.0–35.7%. Abundance estimates of the oldest age and the latest year, which had larger CVs than the other estimates, were sensitive to sampling errors. Effects of sampling errors became smaller when the catch at age had been accumulated over a few years. Although VPA includes various types of errors, only the sampling errors have room for improvement in reality. Quantifying the effect of sampling error on VPA estimates is essential for sound and efficient stock management, and is emphasized in this study. [ABSTRACT FROM AUTHOR]

SUMMARY:The productive structure and productivity of a Sargassum macrocarpum C. Agardh population were studied from June 1993 to July 1994 in Fukawa Bay facing the Sea of Japan, Yamaguchi Prefecture. S. macrocarpum formed a dense population at a depth of 8 m in the study area. Using the stratified clip technique, monthly changes in the productive structure from 1993 to 1994 were clarified. The dry weight of leaves and main branches increased with the elongation of branches. Thalli in the middle to high stratum began to bear receptacles from March 1994 and the dry weight of receptacles was approximately one-third of the standing crop in June. The loss of leaves increased from April to June 1994, and the loss of main branches and receptacles from June to July 1994. Productivity of branches and receptacles reached maxima of 4.67 g dry wt/m2 per day from February to March and 5.33 g dry wt/m2 per day from April to May, respectively. Productivity of the leaves, however, was almost constant at approximately 2 g dry wt/m2 per day from July 1993 to March 1994. Therefore, maximum productivity of the S. macrocarpum population of 7.17 g dry wt/m2 per day occurred from February to March. Annual net production of newly sprouting branches in June 1993 was 1600.1 g dry wt/m2 per year based on the summation method, which was calculated from the monthly changes in the productive structure. [ABSTRACT FROM AUTHOR]