原著論文　ORIGINAL PAPER

佐渡島の河川のドジョウ密度を決定する要因とその保全策への応用

田中 亘^１）＊ ･ 鹿野 雄一^２） ･ 山下 奉海^１） ･ 斉藤 慶^３） ･ 河口 洋一^４） ･ 島谷 幸宏^１）

１) 九州大学大学院都市環境システム工学専攻　〒819-0395　福岡市西区元岡744
２）九州大学大学院工学研究院環境都市部門　〒819-0395　福岡市西区元岡744
３）新潟大学大学院自然科学研究科　〒950-2181　新潟市西区五十嵐二の町8050
４）徳島大学大学院ソシオテクノサイエンス研究部　〒770-8506　徳島市南常三島2-1

Wataru TANAKA^１）＊, Yuichi KANO^２）, Tomomi YAMASITA^１） , Kei SAITOU^３）, Yoichi KAWAGUCHI^４）, Yukihiro SHIMATANI^１） : Determinants of the Misgurnus anguillicaudatus population and its application to conservation planning in Sado Island, Japan. Ecol. Civil Eng. 14(1), 1-9, 2011.

1) Department of Civil Engineering, Faculty of Engineering, Kyushu University, 774 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
2) Department of Urban and Environmental Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
3) Graduate School of Science and Technology, Niigata University, 8050 Igarashi 2-cho, Nishi-ku, Niigata 950-2181, Japan
4) Ecosystem Design Institute of Technology and Science, University of Tokushima, 2-1 Minami-josanjima, Tokushima 770-8506, Japan

Abstract: This paper aims to propose concrete measures for the conservation of the mud loach (Misgurnus anguillicaudatus) in Sado Island of Japan, associated with the reintroduction of Japanese crested ibis (Nipponia nippon) that has a predilection to feed on the loach. The field survey was conducted at 80 sites on 7 rivers in the island in August 2007 and March 2008, in which the loach density and the micro-scale environmental factors (water depth [WD], degree of aquatic vegetation [AV], degree of riparian forest [RF], current velocity [CV], mud river bed [MB], concreted river bed [CB], and river bed pebble size [PS]) of the habitats were surveyed. Additionally, the macro-scale factors(paddy fields area [FA] and reservoirs area [RA] within a specific buffer circle) were also obtained using GIS software. The analysis using GLM and AIC showed that the AV (positive), MV (positive), CB (negative) and RA (positive), and AV (positive), MV (positive) and PA (positive) effect the loach density in August and March, respectively, indicating that the loach preferred the less artificial habitat surrounded by the paddy fields. The potential maps of the loach density were drawn by adapting the models on the rivers in the island: The loach density was especially high in the Kuninaka Plain that situated at central region of the island in both August and March, indicating the region was priority area for the conservation of the loach. In conclusion, removal of concrete revetment in the habitats and improvement of creek networks between rivers and landscape elements (paddy field and reservoirs) in the Kuminaka Plain would be the effective conservation measurements for the loach.

Key words: conservation planning, GIS, AIC, model selection, Misgurnus anguillicaudatus

摘要

本研究は, ドジョウの保全を目的に,河川のドジョウ生息量に対する景観スケール･局所スケールの環境要因の影響を, GLM により明らかにした. また, 得られたモデルよりドジョウの潜在的な生息量を地図上に予測し, ポテンシャルマップを作成した. その結果, 以下の知見が得られた.
1) 8月の河川のドジョウの生息量に対して, 水中植生, 泥床, コンクリート床, 周囲のため池面積が強い影響を及ぼすこと, 3月の河川のドジョウの生息量に対して, 周囲の水田面積が強い影響を及ぼすことが示された.
2) 佐渡島中央部に位置する国仲平野の河川で高いドジョウ生息量があると推測され, 同地域がドジョウの保全対象地域としてふさわしいことが明らかになった.
3) この結果から, 佐渡島のドジョウの保全には, 国仲平野において, 河川とため池･水田とのネットワークの改善, 水際の植生の再生, コンクリート床の撤去が有効な対策であると考えられた.

2009年9月16日受付, 2011年1月31日受理
* e-mail: river29@civil.kyusyu-u.ac.jp