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Tsuboi J.-I.,Yamanashi Prefectural Fisheries Technology Center | Iwata T.,Yamanashi University | Morita K.,Hokkaido National Fisheries Research Institute | Endou S.,Prifoods Co. | And 2 more authors.
Freshwater Biology | Year: 2013

Endangered native populations of stream salmonids in Japan face three major threats: (i) negative interactions with introduced hatchery-reared fish, (ii) fragmentation of habitat by impassable dams and (iii) recreational angling. To prevent imminent extinction of many local populations, we evaluated these threats and possible conservation actions for red-spotted masu salmon (Oncorhynchus masou ishikawae) and white-spotted charr (Salvelinus leucomaenis japonicus) in the Fuji River system in central Japan. Red-spotted masu salmon and white-spotted charr occupied only 0.73 and 2.4% of suitable thermal habitats, respectively, with masu salmon typically occupying habitats closer to human population centres. Population viability analysis resulted in a 100-year probability of extinction of 78.1% for masu salmon and 48.1% for charr. However, extinction risk of both species was predicted to be <5% if the carrying capacity increased from 141 to 303 for masu salmon and from 94 to 125 for charr, by allowing fish passage at the lower end of the habitat, and if annual adult survival rate increased by 0.04. Adult survival rate was the principal factor associated with population persistence. To conserve isolated populations of stream-dwelling salmonids, we recommend (i) assessing the distribution of remnant native and non-native fish populations, (ii) that fishing regulations are modified to improve adult survival and population persistence and (iii) that fragmented reaches be reconnected to adjacent habitat, for example by removing or modifying artificial barriers to increase the carrying capacity of the isolated populations. Reconnection of fragmented reaches should, however, be avoided if it results in non-native fish invading isolated populations. © 2013 Blackwell Publishing Ltd.

Nakabo T.,Kyoto University | Tohkairin A.,Kyoto University | Muto N.,Humanity | Watanabe Y.,Saiko Gyogyo Kyodo Kumiai the Lake Saiko Fisheries Cooperative | And 6 more authors.
Ichthyological Research | Year: 2014

Biological characteristics of "Kunimasu" (Oncorhynchus kawamurae), poorly known even before the species was prematurely believed extinct, have now become apparent following the examination of 59 specimens from Lake Saiko, Yamanashi Prefecture, Japan and comparison with 58 examples of "Himemasu" (kokanee of Oncorhynchus nerka in Japan), also from Lake Saiko. Significant (p < 0.01) differences between Kunimasu and Himemasu from Lake Saiko occurred in counts of anal-fin rays, pectoral-fin rays, gill rakers (no overlap found) and pyloric caeca. Secondary sexual characters related to maturity level were also found in Kunimasu, the body being more compressed in pre-spawning and spawning males and females than in immature and maturing individuals. Furthermore, maturing male Kunimasu and Himemasu also differed in body shape. Body coloration of Kunimasu also differed according to level of maturity, the nuptial coloration in both sexes being olive-green when alive and black when fresh. Dark dots, found in ca. 40 % of Kunimasu individuals examined, were less distinct than in Himemasu. The spawning season of Kunimasu extended through winter and early spring in Lake Saiko, with spawning males and females remaining near the bottom, compared with non-spawning individuals which occupied the upper and middle profundal zones in the daytime. © 2014 The Ichthyological Society of Japan.

Tsuboi J.-I.,Yamanashi Prefectural Fisheries Technology Center | Ashizawa A.,Yamanashi Prefectural Fisheries Technology Center | Kumada N.,University of Tsukuba | Arima T.,University of Tsukuba | Abe S.,Japan National Research Institute of Fisheries And Environment of Inland Sea
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

We investigated factors preventing the establishment of stocked ayu Plecoglossus altivelis by sampling with casting nets and measuring microhabitat at several locations. In our analysis, three factors were selected as explanatory variables of the probability of capture of more than one ayu (or not? per casting net: 1) larger diameter of drifted sands, 2) lower frequency of cobbles (size class of 65-256 mm) and boulders (>256 mm), and 3) higher frequency of cobbles and boulders buried by sands or caddisfly cases. These three factors were strongly correlated with the amount of drifted sands. We concluded that the amount of drifted sands is useful as an indicator for management decisions concerning stocking sites.

Kumada N.,University of Tsukuba | Arima T.,University of Tsukuba | Tsuboi J.-I.,Yamanashi Prefectural Fisheries Technology Center | Ashizawa A.,Yamanashi Prefectural Fisheries Technology Center | Fujioka M.,University of Tsukuba
Fisheries Research | Year: 2013

In Japanese rivers, there is a serious conflict between the great cormorant (Phalacrocorax carbo hanedae) and fisheries. The basis of this conflict is that the cormorants feed on ayu (Plecoglossus altivelis), a commercially important fish that is stocked primarily for recreational fishing. To understand how cormorants alter their foraging habitats in relation to the stocked fish and fishing activities, we examined the relationship between cormorant abundance and ayu biomass during the cormorant breeding season (from April to July) using two approaches that differ in spatial scale. First, we compared cormorant numbers in different river sections that were defined based on ayu stocking. The cormorant numbers in the sections stocked with ayu increased during the ayu release period, whereas the cormorant numbers in other sections showed no clear seasonal patterns. Second, we tested whether cormorant numbers were correlated with the biomass of ayu caught with cast nets. Positive correlations were observed between the biomass of ayu and the number of cormorants that were within 900. m, 1. km, or 2. km of fish sampling points; however, such correlations were not observed within 100-800. m of the sampling points. The biomass of ayu caught with cast nets increased steadily from April to June despite predation by cormorants; however, this biomass decreased sharply in July when the fishing season opened. This study indicates that although cormorants altered their feeding areas in accordance with the mass stocking of ayu in a Japanese river, sufficient numbers of ayu were still maintained for anglers. © 2012 Elsevier B.V.

Miura M.,Yamanashi Prefectural Fisheries Technology Center | Tsuboi J.-I.,Yamanashi Prefectural Fisheries Technology Center | Okazaki T.,Yamanashi Prefectural Fisheries Technology Center | Oohama H.,Yamanashi Prefectural Fisheries Technology Center | Ashizawa A.,Yamanashi Prefectural Fisheries Technology Center
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

Multiple characteristics of two breeds of hatchery-reared ayu Plecoglossus altivelis (YD, Yamanashi Dam breed; YS, Yamanashi Sea breed) as a fishing resource were assessed in a natural river. The breeds were reared under identical conditions from egg fertilization to stocking. From June to October 2009, recapture experiments were conducted for fin-clipped and stocked ayu using casting nets and "tomo-zuri" fishing, i.e., using a live decoy, in the studied river. The results indicated that YD was more vulnerable to fishing than YS, especially early in the fishing season. However, as YD matured earlier, it had a shorter fishing season than YS. Conversely, YS exhibited symptoms of bacterial cold water disease (BCWD) less frequently than did YD, showing that YS better tolerated BCWD. This finding was consistent with the results of experimental infection. We concluded that the characteristic traits of the two breeds of hatchery-reared ayu differed after stocking in a natural river, although both breeds were raised under identical hatchery conditions.

Oohama H.,Yamanashi Prefectural Fisheries Technology Center | Okazaki T.,Yamanashi Prefectural Fisheries Technology Center | Aoyagi T.,Yamanashi Prefectural Fisheries Technology Center | Kaji K.,Yamanashi Prefectural Fisheries Technology Center
Nippon Suisan Gakkaishi (Japanese Edition) | Year: 2012

We captured smallmouth bass Micropterus dolomieu from Lake Motosu by gillnets and spearfishing. From 1997 to 2004, 68 smallmouth bass were caught by gillnets and 18 by spearfishing. Catch per unit effort (CPUE) ofsmallmouth bass by gillnets gradually decreased from 0.36 in 1997 to 0 in 2002. The CPUE by gillnets and underwater observation rate were high in the southeast zone before 1998 and significantly higher in the northwest zone after 1999. The annual estimated capture rate of smallmouth bass by gillnets was consistently more than 50- Smallmouth bass were illegally released into Lake Motosu for fishing; however, they were unable to establish in the water body. Smallmouth bass might have been eradicated since they did not reproduce, their extermination began quickly, habitat information was fed back to gillnet operation, and the capture rate using gillnets was high.

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