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Shimada H.,Central Fisheries Research Institute | Sakaguchi K.,Kushiro Fisheries Research Institute | Sakaguchi K.,Central Fishries Research Institute | Mori Y.,Kushiro Fisheries Research Institute | And 3 more authors.
Bulletin of the Plankton Society of Japan | Year: 2012

To evaluate the seasonal/annual changes and regional variations in biomass structure,175 zooplankton samples were collected from the 0-150 m layer and the 0-500 m or the 0-300 mlayer using a modified NORPAC net at four areas around Hokkaido (Doto and the Donan area of the North Pacific, the northern Japan Sea and the southern Okhotsk Sea) every one-three months during February 2008 to December 2011. Seasonal zooplankton biomass peaks were found from April to June every year, with the exception of the southern Okhotsk Sea. Large cold water copepods (.Neocalanus spp., Eucalanus bungii and Metridia spp.) dominated the biomass throughout the areas, composing ca. 40-50% of the total zooplankton biomass in terms of wet weight. The most dominant species varied with area; i.e. E. bungii (Doto and Donan area), N. plumchrus/flemingeri (northern Japan Sea) and M. pacifica/okhotensts (southern Okhotsk Sea). The biomass of large copepods, especially N. plumchrus/flemingerit showed significant year-to-year changes. In the northern Japan Sea (Tsushima Warm Current area), N. plumchrus/flemingeri were abundant during spring 2010, when the current was less warm and high chlorophyll-a values were observed. In the Doto and Donan area of the North Pacific, N. plumchrus/flemingeri were less abundant during spring 2009, when their was less Oyashio water and lower chlorophyll-a concentrations were found Our results suggest that the biomass of large cold-water copepods fluctuates year-to-year, being influenced by the physical/biological environment-especially in spring. © 2012 Plankton Society of Japan.


Sugawara M.,Hokkaido National Fisheries Research Institute | Yamashita N.,Hokkaido National Fisheries Research Institute | Sakaguchi K.,Hokkaido Research Organization HRO | Sato T.,Kushiro Fisheries Research Institute | And 5 more authors.
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2013

To identify factors affecting the somatic growth of the winter-spawning stock of Japanese common squid, the somatic growth of squid caught in the East China Sea, the Pacific Ocean and the Tsushima Strait from 2000 to 2011 was estimated using age determination from statolith microstructure analysis. The relationship between estimated age in days and dorsal mantle length was fitted using a Gompertz growth equation. The residuals of dorsal mantle length from the growth equation differed among year classes, hatch months, and sexes. Although no environmental factors correlated with the annual difference in growth, increased sea water temperature in spring in the Kuroshio-Oyashio transition region corresponded to increased growth with hatch month. Growth was smaller in males than in females during the southward migration, which suggested depressed growth in males due to earlier sexual maturation than in females.


Kawauchi Y.,Hokkaido University | Shida O.,Central Fisheries Research Institute | Okumura H.,Hakodate Fisheries Research Institute | Tojo N.,Aquatic Research Station | And 2 more authors.
Journal of Marine Science and Technology | Year: 2011

We examined the vertical distributions of walleye pollock Theragra chalcogramma juveniles for two size groups (smaller and larger than 30 mm) during the period of transition for feeding (PTF) and after this period in Funka Bay, Hokkaido, Japan. Samplings were conducted in May and June in 2006 and 2007, and water temperature and salinity were measured. The correlation between juvenile sizes and distributed depth was observed using net sampling. From this result, size groups were divided by depth. In addition, the distribution and abundance of juveniles were examined using acoustic data. In the PTF (May), juvenile size increased with increasing depth, and after the PTF (June), most juveniles descended. In the PTF, juveniles smaller than 30 mm in TL dominated above 43 m depth in 2006, while juveniles larger than 30 mm in TL dominated below 18 m depth in 2007. After the PTF, juvenile sizes were larger in 2006 than in 2007. The relationships between juvenile distributions and water masses in the PTF were analyzed, and it was found that surface water of coastal Oyashio water (S-CO) dominated in the layers where small juveniles were distributed, and that Oyashio water (OW).


Nishikawa T.,Toho University | Oohara I.,Japan National Research Institute of Fisheries Science | Saitoh K.,Japan National Research Institute of Fisheries Science | Shigenobu Y.,Japan National Research Institute of Fisheries Science | And 5 more authors.
Zoological Science | Year: 2014

The solitary ascidian Ascidiella aspersa (Müller, 1776) has sometimes been regarded as conspecific with A. scabra (Müller, 1776), although previous detailed morphological comparisons have indicated that the two are distinguishable by internal structures. Resolution of this taxonomic issue is important because A. aspersa has been known as a notoriously invasive ascidian, doing much damage to aquaculture e.g. in Hokkaido, Japan. We collected many specimens from European waters (including the Swedish coast, near the type localities of these two species) and Hokkaido, Japan (as an alien population) and made molecular phylogenetic analyses using the mitochondrial cytochrome c oxidase subunit I (COI) gene, and found that in terms of COI sequences all the analyzed specimens were clustered into two distinct groups, one of which is morphologically referable to A. aspersa and the other to A. scabra. Thus, these two species should be regarded as distinct from each other. © 2014 Zoological Society of Japan.


Kasugai K.,Salmon and Freshwater Fisheries Research Institute | Hayano H.,Salmon and Freshwater Fisheries Research Institute | Mano S.,Salmon and Freshwater Fisheries Research Institute | Watanabe T.,Salmon and Freshwater Fisheries Research Institute | And 5 more authors.
Ichthyological Research | Year: 2014

Otolith Sr:Ca ratios of 11 masu salmon (Oncorhynchus masou) in Lake Kussharo and its tributaries, of which outlet river has no barriers to the ocean, were analyzed to estimate their migration histories. The Sr:Ca ratios of all masu salmon generally fluctuated below 2. Masu salmon from Lake Kussharo presumably do not migrate to the ocean. However, more specimens must be analyzed to clarify the migration history of masu salmon in this lake. © 2014 The Ichthyological Society of Japan.


Kawauchi Y.,Hokkaido University | Chimura M.,Hokkaido National Fisheries Research Institute | Mutoh T.,Mariculture Fisheries Research Institute | Watanobe M.,Hakodate Fisheries Research Institute | And 2 more authors.
Fisheries Science | Year: 2014

We examined factors affecting the vertical distribution of juvenile walleye pollock during "the second critical period" (i.e. the transition period of prey size) in and around Funka Bay, Hokkaido, Japan. During the day, small juveniles (<30 mm) were distributed mainly in shallow, warm, and low-salinity water within the bay, whereas larger ones (≥30 mm) occurred in deeper, cold and saline water. During the night, the large juveniles migrated to shallower depths. Outside the bay, small- and large-sized juveniles were distributed in water masses of similar physical properties during the daytime, whereas during the nighttime, most of the juveniles moved to shallower depth, and some juveniles dived to deeper water mass. Dietary analysis revealed that large juveniles fed on large copepods (≥0.5 mm in body width) more than small juveniles did. The composition of zooplankton in our survey area showed that large-sized copepods often occurred in deeper saline water. From these results, there is a possibility that juvenile pollock inside and outside Funka Bay occupied different water masses preferable for each feeding advantage. © 2014 The Japanese Society of Fisheries Science.


Nakada S.,Kyoto University | Ishikawa Y.,Japan Agency for Marine - Earth Science and Technology | Awaji T.,Kyoto University | In T.,Japan Agency for Marine - Earth Science and Technology | And 5 more authors.
Journal of Geophysical Research: Oceans | Year: 2013

Heat and water mass transports tagged by water type in a bay were investigated using daily outputs from a high-resolution land-sea coupled model. The modeled circulation and water property distribution were similar to those reported by observations. In this paper, the heat angle is introduced to accurately define the roles of the lateral heat flux (LF) into the bay and the net surface heat flux on temperature changes in the bay water. As a result, ocean phenomena in the bay can be categorized by using the heat angle in an intensive LF regime on short-period timescales and a gradual LF regime on intraseasonal timescales. Our close examination revealed that the velocity fields can be classified into three flow patterns: a twin vortex accompanied by positive LF, a clockwise flow with negative LF, and an anticlockwise flow with both LFs. These patterns occur in both intensive and gradual LF regimes. Intensive wind-driven LF forced by atmospheric disturbances was often observed from summer to autumn in 2008, accompanying the intrusion of southern subtropical Tsugaru warm water that was colder than the deep bay water (LF < 0) and subarctic Oyashio water that was warmer than the surface bay water (LF > 0), but both were hardly found in 2009. This thermal contrast affects the interannual difference in the stratification inherent in the bay. Our integrated analysis method is useful for prompt and robust understanding of the thermal and dynamic states in a bay based on ocean simulation data. Key Points We analyzed outputs from a high-resolution land-sea coupled model in Funka Bay. We show integrated analysis of heat and water mass transports from the Pacific. Our approach can categorize phenomena into three patterns tagged by water type. ©2013. American Geophysical Union. All Rights Reserved.


Natsuike M.,Hokkaido University | Kanamori M.,Hokkaido University | Kanamori M.,Hakodate Fisheries Research Institute | Baba K.,Fisheries Research Institute | And 3 more authors.
Harmful Algae | Year: 2014

The 2011 Great East Japan Earthquake and the subsequent huge tsunami greatly affected both human activity and the coastal marine ecosystem along the Pacific coast of Japan. The tsunami also reached Funka Bay in northern Japan and caused serious damage to the scallop cultures there, and this tsunami was believed to have affected the coastal environments in the bay. Therefore, we investigated the changes in the spatial abundance and distribution of the toxic dinoflagellates Alexandrium tamarense cysts before the tsunami (August 2010) and after the tsunami (May 2011, August 2011, May 2012 and August 2012) in the bay. Further, monthly sampling was conducted after the tsunami to identify seasonal changes of Alexandrium catenella/tamarense cysts and vegetative cells. Significant increases were observed in the populations of A. catenella/tamarense cysts, comparing the abundances before the tsunami (in August 2010; 70±61cystsg-1 wet sediment) to those just after it (in May 2011; 108±84cystsg-1 wet sediment), and both A. tamarense bloom (a maximum density was 1.3×103cellsL-1) and PSP (Paralytic Shellfish Poisoning) toxin contamination of scallops (9.4 mouse unitg-1 was recorded) occurred in the bay. Seasonal sampling also revealed that the encystment of A. tamarense and the supply of the cysts to bottom sediments did not occur in the bay from September to April. These results strongly suggested that the mixing of the bottom sediments by the tsunami caused the accumulation of the toxic A. tamarense cysts in the surface of bottom sediment through the process of redeposition in Funka Bay. Moreover, this cyst deposition may have contributed to the toxic bloom formation as a seed population in the spring of 2011. © 2014 Elsevier B.V.


Liu Y.,Hokkaido University | Saitoh S.-I.,Hokkaido University | Ihara Y.,University of Tokyo | Nakada S.,Kobe University | And 5 more authors.
ICES Journal of Marine Science | Year: 2015

The Japanese scallop (Patinopecten (Mizuhopecten) yessoensis) is an important commercial species in Funka Bay, Japan, where it is farmed using the hanging culture method. Our study was based on 6 years (from 2006 to 2011) of monthly in situ observations of scallop growth at Yakumo station. To produce a basic spatial distribution dataset, we developed an interpolation solution for the shortage of Chl- A concentration data available from the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite. Additionally,we integrated four-dimensional variational (4D-VAR) assimilation water temperature data from ocean general circulation models (OGCMs), with four vertical levels (6, 10, 14, and 18 m) from the sea surface. Statistical models, including generalized additive models (GAMs) and generalized linear models, were applied to in situ observation data, satellite data, and 4D-VARdata to identify the influence of environment factors (interpolated Chl-a, temperature, and depth) on the growth of scallops, and to develop a three-dimensional growth prediction model for the Japanese scallops in Funka Bay. We considered three methods to simulate the growth process of scallops (accumulation, summation, and product), and used them to select the most suitable model. All the interpolated Chl- A concentrations and 4D-VAR temperature data were verified by shipboard data. The results revealed that GAM, using an accumulation method that was based on a combination of integrated temperature, integrated log Chl-a, depth, and number of days, was best able to predict the vertical and spatial growth of the Japanese scallop. The predictions were verified by in situ observations from different depths (R2 = 0.83- 0.94). From the distribution of three-dimensional predicted scallop growth maps at each depth, it was suggested that the growth of the Japanese scallop was most favourable at 6 m and least favourable at 18 m, although variations occurred in each aquaculture region in different years. These variations were probably due to the ocean environment and climate variation. © 2015 International Council for the Exploration of the Sea. All rights reserved.


Kanamori M.,Hakodate Fisheries Research Institute | Kanamori M.,Hokkaido University | Baba K.,Hokkaido Research Organization | Natsuike M.,Tokyo Institute of Technology | Goshima S.,Hokkaido University
Journal of the Marine Biological Association of the United Kingdom | Year: 2016

The European sea squirt, Ascidiella aspersa was first found as an alien species in 2008 from Funka Bay, Hokkaido, northern Japan, causing serious damage to the scallop aquaculture industry. We investigated A. aspersa on cultured scallops and larval occurrence from July 2010 to June 2014 to clarify life history traits and population dynamics, and consider the relation between the life history of A. aspersa and the process of scallop aquaculture. Larvae of A. aspersa were found from June to December, and recruitment on cultured scallops occurred mainly between July and October. The ascidians grew well and their weights increased until February. We found that 60–80% of A. aspersa that had settled in summer had eggs or sperm in autumn, and 90–100% of A. aspersa matured early the following summer. Maturity size in September was 17–20 mm as male, 22–24 mm as female. Scallops in Funka Bay are hung in the spring and harvested from winter to the next spring. Ascidiella aspersa settle as larvae in early summer, and grow well until winter, resulting in overgrowth on scallops in the harvest season. The linking of the process of scallop aquaculture and the life history of A. aspersa explains why this invasive ascidian has caused serious damage to the aquaculture industry in the bay. In comparison to the earlier descriptions of the native population, A. aspersa in Funka Bay has longer reproductive and growth periods, earlier initiation of reproduction, and possibly smaller maturity size. Copyright © Marine Biological Association of the United Kingdom 2016

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