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PubMed | University of Windsor, Salmon and Freshwater Fisheries Research Institute and Nihon University
Type: Journal Article | Journal: Theriogenology | Year: 2016

In most teleost fish species, sperm competition is a key factor in determining male reproductive success, leading to selection on males to increase their reproductive investment in gonads and ejaculate competitiveness. In this study, reproductive investment patterns were assayed by examining the relative investment in gonads and sperm quality metrics (in river water and in the presence of ovarian fluid) of masu salmon, Oncorhynchus masou, representing two fixed male alternative reproductive tactics (ARTs; small sneaking parr males and large dominant anadromous males). Although anadromous males were significantly larger in body size compared to parr males, the latter invested significantly more in relative gonad mass than the former. Sperm velocity and motility were significantly higher, and longevity was significantly lower in parr males than in anadromous males in river water. However, no difference in any of these sperm quality metrics was detected between the ARTs in the presence of ovarian fluid. Sperm velocity and motility were not affected by the presence of ovarian fluid compared to river water for parr males, but both traits increased significantly for anadromous males in ovarian fluid relative to river water, whereas longevity significantly increased in the presence of ovarian fluid compared to river water for both ARTs. We interpret these findings in light of potential cryptic female choice mechanisms and the sneak-guard model of sperm competition that is based on differences in sperm competition risk and alternative investment possibilities among ARTs.


Kasugai K.,Salmon and Freshwater Fisheries Research Institute | Torao M.,Salmon and Freshwater Fisheries Research Institute | Nagata M.,Salmon and Freshwater Fisheries Research Institute | Irvine J.R.,Canadian Department of Fisheries and Oceans
Fisheries Science | Year: 2013

The relationship between release date and migration speed was examined for hatchery chum salmon Oncorhynchus keta fry exiting the Nishibetsu River in eastern Hokkaido, northern Japan so that future releases might be scheduled so that fry arrive at the ocean during periods favoring high survival. Separate marked groups of chum salmon released in early April, mid-April, and early May in 2008, late March and mid-April in 2009, and mid-April in 2010 were recaptured with a rotary screw trap 12 km above the river mouth. Chum salmon in later release groups tended to migrate downstream faster than fish in earlier release groups. Those released after mid-April arrived in the lower river on average 9 days after release, while those released before mid-April arrived on average 26-28 days after release. Most marked fish arrived in the lower river during late April to mid-May. These results suggest that chum salmon are adapted to adjust their migratory speed so as to arrive at the ocean during a relatively discrete period, presumably during a time of high productivity favoring good survival. © 2013 The Japanese Society of Fisheries Science.


Kawai H.,Hokkaido University | Nagayama S.,Hokkaido University | Nagayama S.,Japan Aqua Restoration Research Center | Urabe H.,Salmon and Freshwater Fisheries Research Institute | And 2 more authors.
Environmental Biology of Fishes | Year: 2014

Recent studies have demonstrated that the energetic profitability (net energy intake potential; NEI potential) of a habitat, which is calculated as the gross energy gain from foraging minus the energy expenditure from swimming at a focal point, may be a useful tool for predicting the salmonid biomass. The effectiveness of the NEI potential should be tested in various systems. Even if the NEI potential is validated, its predictive accuracy and transferability could be limited if the cover habitat, which is known to be an important factor for determining salmonid abundance, is not considered. We tested whether the NEI potential is effective for predicting the salmonid biomass even in a stream with abundant cover and whether combining the NEI potential and cover effects can improve the predictability of fish biomass using a generalized linear model. Our results demonstrated that the NEI potential could generally predict the fish biomass (percent deviance explained = 79.9 %), and the model that incorporated both the NEI potential and the cover ratio improved the predictive accuracy (percent deviance explained = 88.5 %). These results suggest that energetic profitability can be an effective indicator for assessing habitat quality and is relatively transferable to other systems. Furthermore, when cover effects are considered, the habitat quality is more accurately represented; thus, combining the energetic profitability and the cover effects might improve the transferability of the assessment across habitats. © 2014 Springer Science+Business Media Dordrecht.


Ohashi R.,Hokkaido University | Yamaguchi A.,Hokkaido University | Matsuno K.,Hokkaido University | Saito R.,Hokkaido University | And 4 more authors.
Deep-Sea Research Part II: Topical Studies in Oceanography | Year: 2013

On the southeastern Bering Sea shelf, mesozooplankton plays an important role in material transfer between primary producers and fisheries resources. The biomass of mesozooplankton in this region is known to vary annually, but little is known about annual changes in community structure and species composition. In the present study, regional and long-term changes in abundance, biomass and community structure of copepods and chaetognaths on the shelf were evaluated based on NORPAC net samples collected during summers of 1994-2009. During the study period, regime shifts occurred from high interannual variability regime (1994-1999) to low interannual variability regime with high temperature (2000-2005), then to a low interannual variability regime with low temperature (2007-2009). A total of 24 calanoid copepod species belonging to 21 genera were identified from samples. Copepod abundance ranged from 150 to 834,486inds.m-2, was greatest on the Middle shelf, and was higher in cold years, than in warm years. Copepod biomass ranged from 0.013 to 150gDMm-2, and was also higher in cold years than in warm years. Based on the results of cluster analysis, the copepod community was divided into six groups (A-F). The regional and interannual distributions of each group were distinct. Interannual changes in abundance of the dominant copepod on the Outer shelf and Middle shelf were highly significant (p<0.0001), and their abundances were negatively correlated with temperature and salinity. Interannual changes in copepod community that occurred between cold and warm years are thought to have been caused by differences in the magnitude and timing of the spring phytoplankton bloom between the two regimes. Abundance and biomass of the chaetognath Parasagitta elegans ranged from 30 to 15,180inds.m-2 and from 11 to 1559mgDMm-2, respectively. Chaetognath abundance was significantly correlated with the abundance of the dominant copepods (p<0.0001). Differences in cold and warm years may also affect recruitment of walleye pollock. We conclude that on the southeastern Bering Sea shelf, the magnitude and timing of primary production, which is related to climate change, may significantly affect how it is transferred through the food web. © 2013 Elsevier Ltd.


PubMed | Salmon and Freshwater Fisheries Research Institute, Tokyo University of Agriculture and Technology, Chitose Archaeological Operations Center, Hokkaido University and 2 more.
Type: | Journal: Scientific reports | Year: 2015

Human activities have had the strongest impacts on natural ecosystems since the last glacial period, including the alteration of interspecific relationships such as food webs. In this paper, we present a historical record of major alterations of trophic structure by revealing millennium-scale dietary shifts of brown bears (Ursus arctos) on the Hokkaido islands, Japan, using carbon, nitrogen, and sulfur stable isotope analysis. Dietary analysis of brown bears revealed that salmon consumption by bears in the eastern region of Hokkaido significantly decreased from 19% to 8%. In addition, consumption of terrestrial animals decreased from 56% to 5% in western region, and 64% to 8% in eastern region. These dietary shifts are likely to have occurred in the last approximately 100-200 years, which coincides with the beginning of modernisation in this region. Our results suggest that human activities have caused an alteration in the trophic structure of brown bears in the Hokkaido islands. This alteration includes a major decline in the marine-terrestrial linkage in eastern region, and a loss of indirect-interactions between bears and wolves, because the interactions potentially enhanced deer predation by brown bears.


Miyakoshi Y.,Salmon and Freshwater Fisheries Research Institute | Saitoh S.-I.,Hokkaido University
Fisheries Science | Year: 2011

Little is known about the survival rate of wild masu salmon Oncorhynchus masou. To examine the effects of smolt length and migration timing on the recovery rate of wild masu salmon, we reanalyzed past tagging and recovery data (1993-1994). The tagging study was conducted in the Shokanbetsu River, northern Japan; 863 wild masu salmon smolts were captured, tagged, and released in a downstream site, and a total of 19 fish were recovered in coastal fisheries and in the natal river the following year. The data were analyzed by a logistic regression analysis with recapture as a response variable and tagging date and smolt length as explanatory variables; the tagging date had a significant effect on the recapture rate, whereas the effect of smolt size was not significant. Despite the small number of recaptures, this study indicates that migration timing is a factor affecting the marine survival of wild masu salmon smolts, although this conclusion has been repeatedly documented for other species of Pacific salmon Oncorhynchus spp. © 2011 The Japanese Society of Fisheries Science.


Miyakoshi Y.,Salmon and Freshwater Fisheries Research Institute | Nagata M.,Salmon and Freshwater Fisheries Research Institute | Kitada S.,Tokyo University of Marine Science and Technology | Kaeriyama M.,Hokkaido University
Reviews in Fisheries Science | Year: 2013

The hatchery program for chum salmon in Hokkaido, northern Japan, constitutes one of the largest salmon hatchery programs in the world. The hatchery program has been conducted for over 120 years, and returns of chum salmon rapidly increased during the last quarter of the 20th century. Since the 1990s, chum salmon returns to Hokkaido have remained at a historically high level, although different fluctuation trends have been observed among regions within Hokkaido. Although such intensive hatchery programs have been conducted for more than 25 generations, there has been no evidence indicating any decline of genetic diversity. The hatchery program for chum salmon in Hokkaido is successful in increasing commercial catches and will likely be the main management tool in future. However, information on naturally spawning chum salmon in Hokkaido remains scarce. Assessment of naturally spawning populations recently commenced, and it has been revealed that naturally spawning chum salmon populations remain in many rivers in Hokkaido. For future management, monitoring chum salmon of both hatchery and natural origin is important, and a novel strategy that accounts for the enhancement of commercial stocks and the coexistence of hatchery programs and wild populations should be established in Japan. © 2013 Copyright Taylor and Francis Group, LLC.


Nagata M.,Salmon and Freshwater Fisheries Research Institute | Miyakoshi Y.,Salmon and Freshwater Fisheries Research Institute | Urabe H.,Salmon and Freshwater Fisheries Research Institute | Fujiwara M.,Salmon and Freshwater Fisheries Research Institute | And 5 more authors.
Environmental Biology of Fishes | Year: 2012

The chum and pink salmon catches in Hokkaido, Japan have increased dramatically since the 1970s and the 1990s, respectively. In contrast, masu salmon catches have been steadily decreasing. Despite intensive hatchery development in Hokkaido, naturally spawning salmon populations persist based on results from a recent river survey. This paper focuses on the challenges of maintaining hatchery salmon populations while protecting natural chum, pink and masu salmon populations in Hokkaido. Two important initiatives related to meeting this ambitious goal are managing hatcheries in a way that minimizes negative interactions between natural and hatchery salmon populations, and initiating new efforts at restoring and rehabilitating degraded freshwater habitats. In addition, in order to maintain a balance of demand and supply in the domestic market through the exportation of extra salmon, Hokkaido has decided to enter full assessment to gain Marine Stewardship Council (MSC) certification of the Hokkaido chum salmon trap net fishery. This would involve a fundamental shift in fisheries management as practiced in Japan, specifically elevating the importance of managing the fishery in a way that conserves natural salmon populations. A key component of a new salmon management strategy is the establishment of a zone management framework based on the designation of stream units to spatially separate natural salmon from hatchery salmon to minimize negative effects of hatchery fish and to utilize effectively hatchery salmon for commercial fisheries. This effort is allied with similar initiatives in other Pacific Rim countries that are focusing on management reform to restore natural ecosystem function and maintain the coexistence of wild and hatchery salmon. © Springer Science+Business Media B.V. 2011.


Taniyama N.,Hokkaido University | Kaneko N.,Hokkaido University | Inatani Y.,Hokkaido University | Miyakoshi Y.,Salmon and Freshwater Fisheries Research Institute | Shimizu M.,Hokkaido University
General and Comparative Endocrinology | Year: 2016

Insulin-like growth factor (IGF)-I, IGF-binding protein (IGFBP)-1 and RNA/DNA ratio are endocrine and biochemical parameters used as growth indices in fish, however, they are subjected to environmental modulation. Chum salmon (Oncorhynchus keta) migrate from freshwater (FW) to seawater (SW) at fry/juvenile stage weighing around 1 g and suffer growth-dependent mortality during the early phase of their marine life. In order to reveal environmental modulation of the IGF/IGFBP system and establish a reliable growth index for juvenile chum salmon, we examined effects of SW transfer and fasting on IGF-I, IGFBP-1 and RNA/DNA ratio, and correlated them to individual growth rate. Among serum IGF-I, liver and muscle igf-1, igfbp-1a, igfbp-1b and RNA/DNA ratio examined, muscle RNA/DNA ratio and muscle igfbp-1a responded to SW transfer. Serum IGF-I, liver igf-1 and liver RNA/DNA ratio were sensitive to nutritional change by being reduced in 1 week in both FW and SW while muscle igf-1 was reduced 2 weeks after fasting. In contrast, igfbp-1a in both tissues was increased by 2 weeks of fasting and igfbp-1b in the liver of SW fish was increased in 1 week. These results suggest that the sensitivity of igf-1 and igfbp-1s to fasting differs between tissues and subtypes, respectively. When chum salmon juveniles in SW were marked and subjected to feeding or fasting, serum IGF-I showed the highest correlation with individual growth rate. Liver igfbp-1a and -1b, and muscle igf-1 exhibited moderate correlation coefficients with growth rate. These results show that serum IGF-I is superior to the other parameters as a growth index in juvenile chum salmon in term of its stability to salinity change, high sensitivity to fasting and strong relationship with growth rate. On the one hand, when collecting blood from chum salmon fry/juveniles is not practical, measuring liver igfbp-1a and -1b, or/and muscle igf-1 is an alternative. © 2016 Elsevier Inc.


Urabe H.,Salmon and Freshwater Fisheries Research Institute | Nakajima M.,Salmon and Freshwater Fisheries Research Institute | Torao M.,Salmon and Freshwater Fisheries Research Institute | Aoyama T.,Salmon and Freshwater Fisheries Research Institute
Transactions of the American Fisheries Society | Year: 2010

We examined the effectiveness of energetic potential (net energy intake [NEI]) estimated from bioenergetics models as an index of habitat quality for stream salmonids in seven streams within four watersheds in Hokkaido, northern Japan. In addition, we confirmed the utility of the NEI as an index of habitat quality by comparing it with several other habitat variables, including pool volume, pool area ratio, and prey density, that are often used as indices of habitat quality for stream salmonids. The mean NEI at each study reach was closely related to salmonid abundance, although the physical environment and drifting prey density differed considerably among study sites. In contrast, the relationships between habitat variables and fish abundance were weaker (drift density) or nonsignificant (pool volume and area). These results suggest that the NEI is more widely applicable as an index of habitat quality for drift-feeding fish, although its validity should be tested in additional systems. © by the American Fisheries Society 2010.

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