No.104 研究課題 / Project
多摩川水系のムカシトンボの分布と生態Distribution and life-history of Epiophlebia superstes in the Tama River system| 一般研究 General Research |
No.104 |
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| 代表研究者 Principal Investigator |
大森 武昭 takeaki ohmori |
| 所属（採択当時） Affiliation |
元、江東区立南砂中学校教諭 Former teacher, Koto Ward Minamisuna Junior High School |
| 研究内容要約 Research Summary |
多摩川水系のムカシトンボの幼虫の分布状態を見ると奥多摩湖に流入する丹波川水系と小菅川水系では生息水域も狭く、生息密度も小さい。ただ、小菅川水系は丹波川水系より生息地、個体数とも多い。 日原川水系もほぼ同じような分布状態を示す。分布地点が多く、分布密度の高い水系としては秋川水系がある。特に南秋川水系では、ほとんどの沢で確認され、生息密度も高かった。五日市町十里木で秋川に流入している養沢川、五日市町戸倉で秋川に流入している盆掘川にも広く分布しており、生息密度も高かった。 奥多摩湖に流入している河川の中では峰谷川とその支流では広く分布し、個体数も多い。ここ十年ほどで減少の著しい地域は奥多摩町がら石神前までの多摩川に流入する小河川で、特に前回生息確認されていながら、今回幼虫の確認ができなかっ た地点は大丹波川、真名井川を初め９カ所にのぼる。 同じように減少が著しい地域に高尾山周辺がある。案内川の支流中沢川、入沢川、榎窪沢では１０年前の調査では多数の成虫が確認され、また幼虫も入沢川では多数確認されていた。しかし、今回の調査では成虫も３年間で数頭確認されただけで幼虫も激減しているこどが明らかになった。 陣馬山の東面を水源とする北浅川水系は南浅川水系の一つ案内川とともに生息密度の高い地域であった。八王子市羽上案下附近の沢には多数の幼虫が確認できた。 また、南浅川水系の小下沢、日影沢、蛇滝沢にも個体数は多くないが幼虫の生息が確認されている。 According to research on the distribution of Epiophlebia superstes in the Tama River system, its habitat zone is narrow and population density is low in the Taba River and Kosuge River systems, which flow into Lake Okutama . In the two systems, the habitat area is wider and population density is higher in the Kosuge River system than in the Taba River system. Similar distribution patterns have also been observed in the Nippara River system. The species is widely distributed with high population density in the AkigawaRiver system. In the Minami Akigawa River system, especially, the species has been observed in virtually all ravines, with high population density. Also, it is widely distributed with high population density around the Yozawa River, which flows into the Akigawa River at Jurigi District in Itsukaichi Town (Akiruno City of today), and around the Bombori River, which flows into the Akigawa River at Tokura District in Itsukaichi Town (Akiruno City of today). Among rivers that flow into Lake Okutama , the species is widely distributed with high population around the Minedani River and its tributaries. However, the population has dramatically decreased over the past 10 years around rivers that flow into the Tama River between Okutama Town and the Ishigamimae District. In nine rivers, including the Otaba River and the Manai River , larvae were not recently observed even though they were seen in the last study. A similar phenomenon has been observed around Mt. Takao A large number of adults were observed 10 years ago around tributaries of the Annai River ?the Nakazawa and Irisawa rivers?and Enokubo Ravine. In the Irisawa River , larvae were also found. In this investigation, however, only a few adults were observed over 3 years. It was also revealed that the larvae population is decreasing dramatically. The population density of the species was also high in the Kita Asagawa River system originating from the east side of Mt. Jimba , as well as around the Annai River of the Minami Asagawa River system. Several larvae were observed around ravines in the Kamiange District of Hachioji City. It has been confirmed that a few larvae inhabit the ravines of Minami Asagawa River system: Koge Ravine, Hikage Ravine and Jataki Ravine. |
| 共同研究者 Collaborators |
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