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論文投稿 Comparison of fish fauna in a river that received pyroclastic flow from the volcanic eruption of Mt. Ontake in 2014 with that in neighboring rivers

作成年度 2016 年度
論文名 Comparison of fish fauna in a river that received pyroclastic flow from the volcanic eruption of Mt. Ontake in 2014 with that in neighboring rivers
論文名(和訳)
論文副題
発表会 Limnology in Tokai Region of Japan (陸の水)2016年論文集
誌名 Rikunomizu(Limnology in Tokai Region of Japan )
巻・号・回 10 74
発表年月日 2016/10/01
所属研究室/機関名 著者名(英名)
国立研究開発法人土木研究所水環境研究グループ自然共生研究センター小野田幸生
国立研究開発法人土木研究所水環境研究グループ河川生態チーム萱場祐一
抄録
AbstractImpacts of the 2014 eruption of Mt. Ontake on fish distribution were preliminarily evaluated by undertaking fish censuses in five streams near the mountain in 2015. The Nigorigawa River, which received pyroclastic flow, was used as an impact site. Another two rivers (the Shinokurosawa River neighboring the Nigorigawa and the Ohtakigawa River, which has confluence with the Nigorigawa) were used for evaluating whether the impacts extended beyond the Nigorigawa River. The other two rivers (the Shirakawa and Kurokawa), which received no pyroclastic flow from Mt. Ontake, were used as control sites. Fish censuses were conducted from September to November in 2015 by snorkeling for 5 to 50 minutes, according to observed fish density, the exception being the upstream site of the Ohtakigawa where collection was conducted for 5 minutes using a brail net. Approximately 1800 individual belonging to six taxa (Japanese charr, Salvelinus leucomaenis; red spotted masu trout, Oncorhynchus masou ishikawae; Japanese dace, Tribolodon hakonensis; Japanese fat minnow, Rhynchocypris logowskii steindachneri; juvenile cyprinidae; common freshwater goby, Rhinogobius sp.) were observed. Although no fishes were observed at the Nigorigawa site or in the Ohtakigawa River downstream of its confluence with the Nigorigawa, the same absence of fishes had been reported before the eruption occurred. Additionally, the other censused sites, including those in the neighboring streams, contained some fishes, suggesting that the impacts of the eruption (if any) were locally limited. The fact that the Nigorigawa had previously experience disturbance following a landslide suggests that mountain streams that have undergone disturbance once may tend to experience successive disturbances due to geomorphic changes such as valley deepening. Accordingly, even neighboring mountain streams may have contrasting disturbance regimes that influence the recovery of fish fauna from stream disturbances. Further studies involving large-scale and long-term surveys are necessary to accumulate data on the relationships between the presence/absence of fish and water environments associated with disturbance.Key words: fish fauna, mountain stream, disturbance regime, refugia, spatial heterogeneityIntroductionVolcanic eruptions are among the largest and most broad-scale disturbances, and assessing the associated destruction and recovery of ecosystems can provide opportunities for elucidating the important processes that determine the distribution of organisms. Accordingly, the effects and impacts of volcanic eruptions on ecosystems and organisms should be examined. In previous studies, the effects and impacts of such eruptions have been almost exclusively assessed in terrestrial ecosystems (Griggs, 1915; Yoshii, 1932; Yoshioka, 1966; Tagawa, 1989; reviewed in Tsuji and Kosugi, 1991; Nakashizuka et al., 1993; Hasegawa and Abe, 2006), with few surveys in aquatic ecosystems, particularly in Japan (but see Kimura et al., 1978; in addition to Newcomb and Flagg, 1983; Brusven and Horning, 1984; Martin et al., 1984). However, volcanic eruptions can also have impacts on aquatic organisms by causing changes in water quality, such as decreases in pH and increases in turbidity, due to inflows of tephra into streams and rivers (Stewart et al., 2006). For example, low pH and high turbidity can impact fish species in a number of ways, including perturbation of responses, such as avoidance behavior; reduced feeding and growth; immunological depression; and decreases in migration and reproductive success (for pH: Ishio, 1963; Ikuta, 1999; for turbidity: Japan Fisheries Resource Conservation Association, 1994; Waters, 1995). Of these reactions, the change in avoidance behavior is initially caused by moderate changes in pH and turbidity, and this may potentially change fish distribution (see Waters, 1995; Ikuta, 1999). Thus, impacts associated with volcanic eruptions can be examined by assessing changes in fish distribution (before-after design). In cases without data collection before eruptions, however, a viable alternative is to compare fish distribution among both impacted and non-impacted streams (control-impact design). In this study, we preliminarily evaluated impacts of the 2014 volcanic eruption of Mt. Ontake (located at the border between Nagano and Gifu Prefectures in central Japan, erupted at 27 September 2014, see Oikawa et al., 2014; Iguchi and Nakamichi, 2015) by comparing fish distribution among streams in the vicinity of the volcano.
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