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Fukuwaka M.-A.,Hokkaido National Fisheries Research Institute | Kaga T.,National Salmon Resources Center | Azumaya T.,Hokkaido National Fisheries Research Institute
ICES Journal of Marine Science

Chum and pink salmon abundances vary on a decadal time-scale. We examined the relationship between large-scale climate indices (CIs), regional climate factors (RFs), and rates of change in regional catches (RCs) of chum and pink salmon in five regions of the North Pacific. Correlation coefficients of RCs with RFs were larger than those of RCs with CIs, although the correlation coefficient of particular variables varied among regions. Climate affected salmon stocks as indicated by significant relationships with various terrestrial and ocean climate factors on a regional scale. These results suggest that no single CI or RF controls salmon abundance in all regions; however, global climate changes could affect regional climate directly and regional salmon abundance indirectly. A warming trend in the North Pacific might affect the long-term change in salmon abundance. The mechanisms controlling regional salmon abundance must be understood better to forecast successfully future conditions for Pacific salmon stocks, because the response of salmon stocks to global climate change varies among regions. © 2011 International Council for the Exploration of the Sea. Source

Kano Y.,Kyushu University | Ohnishi K.,Ohsugidani Nature School | Tomida Y.,National Salmon Resources Center | Ikeda N.,Ohsugidani Nature School | And 5 more authors.
Environmental Biology of Fishes

In the autumn of 2004, a typhoon caused a catastrophic flood of the Miyagawa River in Japan. Based upon snorkeling surveys conducted every autumn from 2005 to 2009, we monitored the post flood fluctuation of the local fish assemblages at nine sites of both the main stream and subsidiary streams of the river. Results revealed that species richness significantly increased from 2005 to 2009. In addition, the fish densities of eight species significantly increased over the same period, whereas the density of one species decreased, and that of eight others remained unchanged. Categorization based on Euclidean distance revealed five main clusters from the nine sites. Among these sites, fish assemblages within subsidiary streams were stable as they remained within the same clusters while those in the main stream were dynamically variable through time as they changed cluster membership. In addition, the Euclidean distance between two arbitrary fish assemblages was positively correlated with environmental distance (the Euclidean distance calculated based on river width, depth, velocity and pebble size), time distance, and spatial distance along the river. In conclusion, the fish assemblages were dynamically and regularly altered and varied in the five years after the flood, except for those in the subsidiary streams, and such variation was related to environmental, temporal and spatial variation. © 2011 Springer Science+Business Media B.V. Source

Onuma T.A.,Kyushu University | Onuma T.A.,Hokkaido University | Ban M.,National Salmon Resources Center | Makino K.,Hokkaido University | And 6 more authors.
General and Comparative Endocrinology

Gene expression for growth hormone (GH)/prolactin (PRL)/somatolactin (SL) family hormones in the pituitaries of homing chum salmon were examined, because gene expression for these hormones during ocean-migrating phases remains unclear. Fish were collected in the winter Gulf of Alaska, the summer Bering Sea and along homing pathway in the Ishikari River-Ishikari Bay water system in Hokkaido, Japan in autumn. The oceanic fish included maturing adults, which had developing gonads and left the Bering Sea for the natal river by the end of summer. The absolute amounts of GH, PRL and SL mRNAs in the pituitaries of the maturing adults in the summer Bering Sea were 5- to 20-fold those in the winter Gulf of Alaska. The amount of GH mRNA in the homing adults at the coastal seawater (SW) areas was smaller than that in the Bering fish, while the amount of PRL mRNA remained at the higher level until fish arrived at the Ishikari River. The gill Na+,K+-ATPase activity in the coastal SW fish and the plasma Na+ levels in the brackish water fish at the estuary were lowered to the levels that were comparable to those in the fresh water (FW) fish. In conclusion, gene expression for GH, PRL and SL was elevated in the pituitaries of chum salmon before initiation of homing behavior from the summer Bering Sea. Gene expression for GH is thereafter lowered coincidently with malfunction of SW adaptability in the breeding season, while gene expression for PRL is maintained high until forthcoming FW adaptation. © 2010. Source

Nagoya H.,National Research Institute of Aquaculture | Nagoya H.,National Salmon Resources Center | Kawamura K.,Mie University | Ohta H.,Kinki University
Fisheries Science

With the aim of improving artificial androgenesis in teleost fishes, we tested two methods for producing androgenetic diploids of amago salmon (Oncorhynchus masou ishikawae), namely, fertilization of gamma-ray irradiated eggs with fused spermatozoa (sperm-fusion method) and the fertilization of irradiated eggs with untreated sperm followed by the blocking of cell division (mitosis-inhibition method). Our results showed that the optimal condition for sperm fusion was to treat the sperm with 50% polyethylene glycol (molecular weight 7500) for 100 s. The efficiency of the two methods of androgenesis was compared in terms of fertilization rate, hatching rate, and larval survival after hatching. The rate of fertilization was lower with the sperm-fusion method than with the mitosis-inhibition method, but the reverse was true for the hatching rate. The survival rate of hatched larvae was the same with the two methods. Androgenesis was confirmed with a recessive albino color marker, and all viable offspring were found to be heterozygous based on analysis of the microsatellite markers. Our results suggest that androgenesis with the sperm-fusion method is a promising approach with potential applications in both aquaculture breeding programs and the preservation of endangered freshwater fishes. © The Japanese Society of Fisheries Science 2010. Source

Fukuwaka M.-A.,Hokkaido National Fisheries Research Institute | Sato S.,National Salmon Resources Center | Yamamura O.,Hokkaido National Fisheries Research Institute | Sakai O.,Hokkaido University | And 5 more authors.
Marine Ecology Progress Series

To provide a key piece of information for understanding the functioning of the Bering Sea pelagic ecosystem, we estimated the biomass of immature chum salmon in the Bering Sea basin in autumn using a return-at-age analysis incorporated with the results of genetic stock identification studies. The estimated biomass was 742 000 t in 2002 and 617 000 t in 2003, which is possibly an underestimate because of the uncertainty of trawl selectivity parameters used in the estimation. Although chum salmon has been the dominant nekton species in the pelagic ecosystem of the Bering Sea basin in recent years, biomass estimates for the species were smaller than one-tenth of the maximum biomass of walleye pollock in the 1980s. Previous studies have highlighted the importance of the huge biomass of mesopelagic planktivores, such as myctophid fishes and gonatid squid, to the ecosystem function of the pelagic Bering Sea. Planktivorous Pacific salmon including chum and pink salmon may also play a significant role as competitors and predators of small planktivores, thus affecting the dynamics of ecosystem function and nekton community structure in the pelagic Bering Sea. © Inter-Research 2010. Source

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