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Kubo K.,Hokkaido University | Kubo K.,Japan Institute for Environmental Sciences | Yamaguchi K.,Japan Institute for Environmental Sciences | Mitsuhashi M.,Kushiro Fisheries Research Institute | And 2 more authors.
Marine Pollution Bulletin | Year: 2013

The concentrations of PCB congeners in the blubber and liver of male and female Steller sea lions (Eumetopias jubatus; SSLs) collected from the Shakotan Peninsula and the Nemuro Strait, Hokkaido, Japan in 2008 and 2010 were measured by HRGC-HRMS, in order to express the concentration profiles in SSLs at these regions. #153 predominated in both organs, followed by #138, #99 and #118. In males, #28 and #31 were concentrated particularly in the blubber, while #177 and #199 were accumulated specifically in the liver. The differences in these concentration profiles might be expressed by the differences in the organs and their functions. The concentrations of #99, #118, #138, #153, and #180 in the blubber appeared to correspond significantly with the differences between genders. The details of the surveys on PCB congeners in SSLs could clarify the differences in the residue levels of individual congeners for organs and genders. © 2012 Elsevier Ltd. Source

Kayaba T.,Kushiro Fisheries Research Institute | Wada T.,Fukushima Prefectural Fisheries Experimental Station | Murakami O.,Mariculture Fisheries Research Institute | Sawaguchi S.,Seikai National Fisheries Research Institute | Kawabe R.,Nagasaki University
Fisheries Research | Year: 2015

For conservation and management of fish stock, reliable reproductive parameters, especially information on the spawning period, are greatly needed. Until now, the spawning period of male fish was estimated mainly using the gonadosomatic index (GSI) and microscopic observation of the testes. However, these methods pose the problem of estimation accuracy and handiness for analysis, respectively. To identify biological characteristics that would allow accurate determination of spawning periods, we investigated the seasonal development of testes and sperm ducts in our model fish, the barfin flounder Verasper moseri. GSI (testis weight. ×. 100/body weight) reached a maximum during November-December; however, this peak period occurred approximately two months before the onset of spawning. In contrast, the sperm duct index (SDI) (sperm duct weight. ×. 100/body weight) sharply rose from February to March when spermiation and sperm release actively proceeded. On comparing the SDI of all gonadal development phases, it was found that only the fish that underwent spawning had significantly enlarged sperm ducts due to sperm accumulation. This finding strongly suggested that sperm duct volume is an adequate indicator for accurately identifying spawning period in male fish. Moreover, analysis using SDI takes less effort for sample processing, suggesting to be practical for continuous monitoring of stock assessment. © 2015 Elsevier B.V. Source

Takiya A.,Central Fisheries Research Institute | Fukushi A.,Kushiro Fisheries Research Institute
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

Two groups of Pacific herring Clupea pallasii juveniles, i.e., with and without intermediate culture before release, were released on the same day to clarify the damage to the juveniles during the transportation and release processes. A sudden decrease in triglyceride content, a sudden rise in acid phosphatase activity, and abnormal ring formation in the otoliths were observed in the juveniles after transportation and release. Abnormalities such as variations in swimming depth of the juveniles and abnormal feeding behavior of the juveniles were observed in the early periods after release. The damaged juveniles required approximately 5 days after transportation and more than 10 days after release to achieve recovery. Obvious differences in rates of abnormal ring formation in the otoliths in both groups suggest that the damage was more pronounced in the group without intermediate culture before release than in the group with intermediate culture before release. Source

Sato M.,Tokyo University of Marine Science and Technology | Tokai T.,Tokyo University of Marine Science and Technology | Mori Y.,Japan Fisheries Information Service Center | Nakame Y.,Kushiro Fisheries Research Institute
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2016

A drift net series consisting of several net panels of nine different mesh sizes was used to investigate pelagic fish resources in the waters off Hokkaido, Japan during June-July and September-November. This study aimed to determine the most appropriate mesh size combination of research drift net series with an approximate constant catching intensity over a large range of fish length for research on chub mackerel Scomber japonicus the resources of which are in the process of recovering. Selection curves were estimated for the mesh sizes from the data of the drift net research carried out in the two periods of June-July and September-November. Across all mesh sizes, fish caught in June-July had slightly greater fork length than those in September-November, and they also had a lower condition factor implying a smaller body girth following spawning. The pooled relative catching intensity steeply declined for fish with fork length over 300 mm at the current mesh combination, suggesting a possible underestimation of stocks of large fish. A simulation showed that the addition of two panels with larger mesh sizes (82 and 106 mm) kept a constant intensity for fish below 350 mm fork length. © 2016 The Japanese Society of Fisheries Science. Source

Kusaka A.,Japan National Research Institute of Fisheries Science | Shimizu Y.,Japan National Research Institute of Fisheries Science | Sato T.,Kushiro Fisheries Research Institute | Yoshida J.,Tokyo University of Marine Science and Technology
Journal of Oceanography | Year: 2016

Direct current measurements by a shipboard and bottom-mounted acoustic Doppler current profiler and concurrent hydrographic observations with a CTD were conducted off southeastern Hokkaido, Japan, between January and May 2005 to reveal temporal variations in the current structure and volume transport of the Coastal Oyashio (CO). The CO, which has a baroclinic jet structure with southwestward speeds exceeding 90 cm s−1 and a width of 7–8 km, was associated with a surface-to-bottom density front and was formed on the offshore side of the shelf break. The volume transport of CO (TCO) was estimated by integrating the fluxes of lower-density water that was trapped against the coast along the density front represented by the 26.2 σθ isopycnal line. This transport decreased monotonously from 0.79 Sv (1 Sv = 106 m3 s−1) in January to 0.21 Sv in March and subsequently to 0.12 Sv in May, possibly due to the decay of the East Sakhalin Current Water in the Okhotsk Sea. Accompanied by a decrease in TCO, the location of the jet structure associated with the density front moved toward the coast while the maximum speed of the jet decreased and the tilt of the front became more horizontal. Consequently, more saline offshore Oyashio water flowed into the deep part of the shelf area, and the current structure altered from relatively barotropic in winter to baroclinic in spring. This study is the first to estimate the observed volume transport of the CO from direct current measurements. © 2016 The Oceanographic Society of Japan and Springer Japan Source

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