事例研究 CASE　STUDY

実験河川におけるエレクトリックショッカーによる６魚種の捕獲効率

佐川　志朗^1)*・ 萱場　祐一²⁾・ 皆川　朋子²⁾・ 河口　洋一³⁾

1)株式会社ドーコン環境保全部　〒004-0051　札幌市厚別区厚別中央１条５丁目４番１号
2) 独立行政法人土木研究所自然共生研究センター　〒501-6021　岐阜県各務原市川島笠田町官有地無番地
3) 九州大学工学部地球環境工学科　〒812-8581　福岡市東区箱崎6-10-1

Shiro SAGAWA^1)*, Yuichi KAYABA²⁾, Tomoko MINAGAWA²⁾ and Yoichi KAWAGUCHI³⁾: Catchability of six fish species by electrofishing in an experimental stream. Ecol. Civil. Eng. 8(2), 193-199, 2006.

1) Docon Co., Ltd., Environmental Assessment Dept., 1-5-4-1, Atsubetsuchuuou, Atsubetsu-ku, Sapporo, Hokkaido, 004-0051, Japan
2) Aqua Restoration Research Center, Public Works Research Institute, Mubanchi, Kanyuuchi, Kawashima-kasada-cho, Kagamigahara, Gifu, 501-6021, Japan
3) Department of Earth Resources and Civil Engineering, School of engineering, Kyusyu University, 6-10-1, Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan

Abstract:We examined electrofishing catchability of six most abundant fish species in experimental stream A in the Aqua Restoration Research Center in Gifu, Japan. The electrofishing catchability can be defined as the total catch obtained by electrofishing divided by the sum of catches obtained by electrofishing and by chasing into D-shaped nets. The six species were classified into high catchability species (more than 80% of the catch) (Plecoglossus altivelis altivelis, Misgurnus anguillicaudatus, and Cobitis sp.) and low catchability species (less than 80% of the catch) (Zacco platypus, Gnathopogon elongatus elongatus, and Rhinogobius sp.). Two age groups were confirmed in each of the low catchability species by estimation of the fish size (total length mm). Each peak of the first and the second age groups were positioned less and more than 40 mm, respectively. The catchability of the first age group of Z. platypus as a swimming fish was significantly lower than the second age group of the species. The catchability range of Rhinogobius sp., a benthic fish, was lower (24%-67%) than that of Z. platypus and G. elongatus elongatus values. Furthermore, the catchability of the second age group of Rhinogobius sp. was lower than that of Z. platypus. These results suggest that electrofishing alone is not a suitable capture method because its capture rates for small swimming fish < 40 mm and for all sizes of benthic fishes are low. Therefore, electrofishing should be used along with the D-shape nets and the small swimming fishes and benthic fishes should be chased into the nets. Additionally, we recommend that further studies are required to determine not only the catchability for each of these species but also to study damages by electrofishing to fish under various voltage, pulse, and environmental conditions.

Key words: benthic fish, catchability, electrofishing, Rhinogobius sp., swimming fish, Zacco platypus

摘要

本研究は，水面幅約３mの直線河道を呈する実験河川において，24調査区における努力量を統一させた魚類捕獲調査を行い，エレクトリックショッカーの捕獲効率を算出し，各種に対するショッカーの効用および効果的な魚類捕獲の方法について考察することを目的とした．
　調査の結果，底生魚および遊泳魚ともに捕獲効率が高い種および低い種が存在し，前者としては，アユ，ドジョウおよびシマドジョウ属が，後者としては，オイカワ，タモロコおよびヨシノボリ属が該当した．オイカワおよびタモロコの捕獲効率が低かった原因としては，第１年級群である40mm以下の小型個体の発見率が小さかったことが示唆された．また，ヨシノボリ属については，微生息場所である河床間隙中で感電した個体が発見できなかったために，第１，第２年級群を含めた全サイズ区分にわたって捕獲効率が低かったことが考えられた．
　ヨシノボリ属やコイ科魚類の稚仔魚が分布する河川でショッカーを用いて捕獲を行う際には，たも網を用いて感電個体をすくい捕るのと併せて，あらかじめ通電する箇所の下流に目の細かいさで網を設置しておき，すくい捕りのすぐ後に，足で石を退かせながら水をさで網に押し入れるような捕獲方法を併用することが望ましい．
　今後は，本邦産魚類の各種に対して，様々な水質条件，ショッカー設定下での捕獲効率を明らかにするとともに，各魚類の成長段階ごとにショッカーの影響程度を把握し，効果的で魚類個体群への影響を最小限とする魚類捕獲手法の検討を行う必要がある．

2005年4月4日受付，2005年10月6日受理
* e-mail: ss1121@docon.co.jp