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Sano M.,Wakkanai Fisheries Research Institute | Bando T.,Soya Fishery Cooperative | Mihara Y.,Central Fisheries Research Institute
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2011

Seasonal changes in sexual maturity of the Pacific giant octopus Enteroctopus dofleini from the Soya/La Perouse Strait were examined in order to determine a biological index for stock assessment. In addition, the body weight and organ weight of more than 100 specimens were measured at monthly intervals from October 2003 to December 2004. Comparisons of body and gonad weight in females revealed the existence of two groups in the period between autumn and spring. The group with the relatively heavier gonads consisted of mature females containing spermatozoa. A similar relationship was observed in male octopuses between autumn and winter. The group with the heavier gonads consisted of mature males with spermatophores. Based on the assumption that the spawning season was in early summer, the stage of maturity could be used as a biological index for assessing the spawning biomass of Pacific giant octopus in this area. Source


Sano M.,Wakkanai Fisheries Research Institute | Bando T.,Soya Fishery Cooperative
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2015

The seasonal migration of North Pacific giant octopus Enteroctopus dofleini in the Soya/La Peá rouse Strait was investigated using GPS location information of octopus catches by drift fishery boats. Body weight and stage of maturity of the collected octopuses were recorded. Immature octopuses were found at depths of 40 to 60 m in summer and 10 to 30 m in autumn to spring. Although mature octopuses were observed at the same depths as juveniles in most months, in June and July, mature males and females migrated to deeper areas immediately before death and spawning, respectively. Based on bottom water temperatures in areas where the octopus was distributed, it appears that this species migrates to deeper areas to avoid water temperatures above 18°C. Source


Yamaguchi H.,Central Fisheries Research Institute | Goto Y.,Wakkanai Fisheries Research Institute | Hoshino N.,Central Fisheries Research Institute | Miyashita K.,Hokkaido University
Fisheries Science | Year: 2014

We examined growth of northern shrimp Pandalus eous in the Sea of Japan, off western Hokkaido, to improve estimations of catch-at-age for stock assessment. Multiple length frequency analysis based on length frequency data collected by a scientific research vessel was conducted to examine length-at-age in the shrimp population. Multi-normal distributions estimated using maximum likelihood indicated a good fit to length distributions. AIC values and regression analyses revealed annual growth variation and a decreasing trend in the length at several age classes in the shrimp population. We revised the method for estimating catch-at-age from the age-conversion table (ACT), which is a simple method for age determination, to age-length keys (ALK) calculated from the results of multiple length frequency analysis. Abundant year classes caught successively year after year could be more easily identified from the catch-at-age data computed using ALK than by using ACT. Our results suggested not only that the mean size of commercial landings fluctuated based on changes in age composition but also that a decrease in the length-at-age in the population influenced the consistent size decrease of commercial landings. © 2014 The Japanese Society of Fisheries Science. Source


Funamoto T.,Hokkaido National Fisheries Research Institute | Yamamura O.,Hokkaido National Fisheries Research Institute | Shida O.,Central Fisheries Research Institute | Itaya K.,Wakkanai Fisheries Research Institute | And 3 more authors.
Fisheries Science | Year: 2014

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. © 2014 The Japanese Society of Fisheries Science. Source


Fukamachi Y.,Hokkaido University | Ohshima K.I.,Hokkaido University | Ebuchi N.,Hokkaido University | Bando T.,Soya Fishery Cooperative Society | And 2 more authors.
Journal of Oceanography | Year: 2010

Time-series data of the vertical structure of the Soya Warm Current (SWC) were obtained by a bottom-mounted acoustic Doppler current profiler (ADCP) in the middle of the Soya Strait from September 2006 to July 2008. The site of the ADCP measurement was within the coverage of the ocean-radar measurement around the strait. The volume transport of the SWC through the strait is estimated on the basis of both the vertical structure observed by the ADCP and the horizontal structure observed by the radars for the first time. The annual transport estimates are 0.62-0.67 Sv (1 Sv = 106 m3s-1). They are somewhat smaller than the difference between the previous estimates of the inflow and outflow through other straits in the Sea of Japan, and smaller than those obtained in the region downstream of the strait during 2004-05 (0.94-1.04 Sv). The difference in the two periods may be attributed to interannual variability of the SWC and/or the different measurement locations. © 2010 Springer Science+Business Media B.V. Source

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