abstract

Original Paper
Title Unique hydrographic structure of intermediate water offshore the Enshu-nada in the Kuroshio region south of Japan
Authers Kosei KOMATSU* and Kiyoshi KAWASAKI*
Keywords intermediate water, Enshu-nada, Kuroshio
Citation Bull. Fish. Res. Agen. No.5, 1-22, 2002
Abstract
Hydrographic structure was observed with focus on the intermediate water (density range of 26.6 - 27.5 σθ) along subtracks of the satellite TOPEX/POSEIDON across the Kuroshio south of Japan in late summer in 1999 and 2001. In the coastal region northern side of the Kuroshio current-axis in the Enshu-nada where supply of nutrient from deeper layers is relatively rich, the hydrographic structure was remarkably different from one observed in the neighboring region. The structure might be attributed to stronger effects of vertical diffusion or vertical mixing in this region, where isopycnal profiles of salinity were lower in the upper layer (<25.9σθ) and higher in the intermediate layer (>25.9σθ), compared with profiles obtained in the neighboring region. This unique structure occurred in both cruises, although the Kuroshio took a straight pattern during the cruise in 1999 and meandered during the cruise in 2001. These results indicated the possibility of the structure to exist almost steadily due to some effects of topography.

Accepted on June 19, 2002
Contribution No.A 22 from the Fisheries Research Agency
* National Research Institute of Fisheries Science, Fukuura 2-12-4, Kanazawa, Yokohama 236-8648, Japan


Title Spatio-temporal variation of sea surface temperature observed by ferryboat in Izu-Ogasawara ridge Ⅰ. Interannual variation
Authers Kosei KOMATSU*, Akira TOMOSADA*, and Kiyoshi KAWASAKI*
Keywords sea surface temperature, ferryboat, interannual variation, Izu-Ogasawara ridge
Citation Bull. Fish. Res. Agen. No.5, 23-37, 2002
Abstract
Sea surface temperature (SST) was observed continuously from 1983 through 1997 by the ferryboat Ogasawara-maru, which made round trips every 5-7 days across the Kuroshio between Tokyo (35.6°N) and Chichijima (27.0°N) south of Japan. Focused on the temporal variation longer than one year, the section line can be divided into four regions based on the difference in characteristics of the variation: the coastal region (34.5°N-), the Kuroshio region (33-34.5°N), the intermediate region (28.5-33°N), and the southern region (27-28.5°N). The trend of SST was not clear in the above first and the third region, on the other hand, increase of temperature was found about 0.03℃/year in the second and the fourth region. Compared with variation of the Kuroshio current axis, the mode with a period of two years had high coherency in the first and the second region and the phase of this mode was late for a half of year from that of the Kuroshio. In the southern regions, the coherency versus the Kuroshio was very low.

Received on June 19, 2002
Contribution No.A 23 from the Fisheries Research Agency
* National Research Institute of Fisheries Science, Fukuura 2-12-4, Kanazawa, Yokohama 236-8648, Japan


Title Spatio-temporal variation of sea surface temperature observed by ferryboat in Izu-Ogasawara ridge Ⅱ. Variation shorter than one year
Authers Kosei KOMATSU*, Akira TOMOSADA*, and Kiyoshi KAWASAKI*
Keywords sea surface temperature, ferryboat, Kuroshio, meso-scale eddy, Izu-Ogasawara ridge
Citation Bull. Fish. Res. Agen. No.5, 38-54, 2002
Abstract
Meridional structure of sea surface temperature (SST) in the Izu-Ogasawara ridge was analyzed focused on temporal variation with time scale shorter than one year. The SST data were obtained continuously from 1983 to 1997 by the ferryboat Ogasawaramaru, which made round trips across the Kuroshio between Tokyo (35.6°N) and Chichijima (27.0°N) south of Japan. From the time-latitude map of SST with 5day×0.05゜mesh, it was found out that the variation of SST deviated from seasonal cycle had modes with similar period as that of the Kuroshio axis. In addition, the SST variation in the southern region from 31゜N had advanced phase compared with that in the Kuroshio region which was synchronized by the variation of the Kuroshio. This meridional time-lag could be attributed to some temporal deviation in effect of mesoscale eddies on the SST in the target area by time-latitude analysis of satellite altimetry data, which showed a possibility to forecast the position of the Kuroshio axis of two years later with some accuracy.

Accepted on July 18, 2002
Contribution No.A 24 from the Fisheries Research Agency
* National Research Institute of Fisheries Science, Fukuura 2-12-4, Kanazawa, Yokohama 236-8648, Japan


Title Relation between characteristic of fixed shore net fishing village and formation condition for sightseeing fixed shore net
Authers Tsutomu MATSUURA*
Keywords fixed shore net, formation condition for sightseeing fixed shore net, tourist home, school
Citation Bull. Fish. Res. Agen. No.5, 55-67, 2002
Abstract
The number of commune which has sightseeing fixed shore net in commune is approximately 47 in Japan. Most of fixed shore net manager have started sightseeing fixed shore net since about 1990 in Japan. The license number of fixed shore net which are managed by all households in fishing village is approximately 135 at 2000 in Japan.
 The village managed fixed shore net by all households have trended to promote positively sightseeing fixed shore net. These villages are admired to have excellent function of interchange promotion between urban people and fishing village inhabitant.
 The sightseeing fixed shore net which can invite more visitors are mostly operated by fixed shore net managed by all households of the village. Formation condition of sightseeing fixed shore net in village with tourist home is marking up the confidence between fishery cooperative and visited school. On the other hand, formation condition of sightseeing fixed shore net in the village with no tourist home is making up promotion system between fishery cooperative and village sightseeing development association.
 Fishing village children have few opportunity of experience to see fishing activity on the Ocean. So, some manager of fixed shore net including no sightseeing fixed shore net have invited the pupil of local elementary and junior high school in order to promote understanding of fishing industry, extension of fish feeding, raising of attachment spirit to native town and provision of fishing successor.

Received on July 19, 2002
Contribution No.A 25 from Fisheries Research Agency
*1 National Research Institute of Fisheries Science, Fukuura 2-12-4, Kanazawa, Yokohama 236-8648, Japan



Doctoral thesis
Title Study on the age, growth, and muturation process of Pacific saury Cololabis saira (Brevoort) in the North Pacific
Authers Satoshi SUYAMA*
Keywords Pacific saury, age, growth, maturation process, North Pacific
Citation Bull. Fish. Res. Agen. No.5, 68-113, 2002
Abstract
The Pacific saury Cololabis saira (Brevoort) is widely distributed in the sub-arctic and sub-tropical North Pacific Ocean and is one of the most important commercial fish species in Japan. However, biological information on this fish has been scarce, especially theories about age and growth, lifespan, and reproduction process are not yet established. This study aims to reveal the life history of this species in the western North Pacific.
Estimation of the age and growth of Pacific saury based on the daily otolith growth increments: Growth of Pacific saury was studied based on counting daily growth increments with a scanning electron microscope (SEM). The Pacific saury caught from the western North Pacific were divided into three groups; the small-size group (knob length: 200-240mm), medium-size group (knob length: 240-280mm) and large-size group (knob length: >280mm), and showed increments of 256±26.0(S.D.), 405±76.1 and 566±48.2, respectively. Based on daily growth increment formation, we determined that tha ages of the 3 groups were about 8, 13, and 19 months. Small- and large-size fish were considered to have hatched from autumn to winter and medium-size fish from spring to summer. The oldest specimen of Pacific saury examined in this study was about 23 months of age; thus, the lifespan of Pacific saury in this area seems to be at least 1.5 years. No difference in growth rate between fish from the central and western North Pacific were observed in the present study.
Formation period of otolith hyaline zones of Pacific saury in the western North Pacific : The formation period of hyaline zones in the otoliths of the Pacific saury (n=1,106) collected from the western North Pacific during February 1991 to December 1992 were examined. Five types of otoliths were observed: type Ⅰ(no hyaline zone), type Ⅱ(incomplete hyaline zones) and another type. Approximately 80% of the small- and medium-sized fish (<280mm) exhibited typeⅠ otoliths, and 15.8% and 65.4% of the large-sized fish (>280mm) showed typeⅡ and typeⅢ otoliths, respectively. Most typeⅣ otoliths were observed in larger fish(>314mm). The first hyaline zone in the otoliths of small- and medium-sized fish was estimated to form during winter.
Maturity, spawning and ovarian cycle of Pacific saury : The reproductive biology of Pacific saury were studied by using histological observation of gonads, collected during 1991 to 1992 from the western North Pacific (n=606). Pacific saury were multiple spanner with asynchronous oocytes developments. The smallest matured fish was 253 mm and most large-size fish(>280 mm in knob length) were considered to have spawned. Atretic oocytes of yolked and / or late stage cortical alveoli oocytes were observed in the gonad of postspawning fish. Since, perinucleolus and early stage cortical alveoli oocytes would remain in the gonad of post-spawning fish and their fat condition recovered the same level of immature fish. These atretic oocytes would disappear until the next spawning season. Pacific saury survive after the first spawning. The large-size fish were estimated to be more than one and half years in the former study, which means they become mature fish within 1.5 years after hatching.

Received on July 26, 2002
Contribution No.A 28 from the Fisheries Research Agency
* Hachinohe Branch, Tohoku Regional Fisheries Research Laboratory, 25-259, Shimomekurakubo, Same-cho, Hachinohe, Aomori 031-0841, Japan