原著論文 ORIGINAL PAPER

小規模湧泉におけるイバラトミヨの生息と保全

神宮字 寛^1)*・ 近藤 正¹⁾・ 沢田 明彦²⁾・ 森 誠一³⁾

1) 秋田県立大学短期大学部 〒010-0444 秋田県南秋田郡大潟村南2-2
2) 秋田県仙北平野土地改良事務所
3) 岐阜経済大学

Hiroshi JINGUJI1^1)*, Tadashi KONDO¹⁾, Akihiko SAWATA²⁾, Seiichi Mori³⁾: Habitat conditions and preservation of the Ninespine Stickleback, Pungitius pungitius in small springs. Ecol. Civil. Eng. 2(2), 191-198, 1999.

1) Akita Prefectural College of Agriculture, 2-2, South Ogata Village, South Akita district 010-0444, Japan
2) Land Improvement Engineering Office of Senboku Plain in Akita Prefecture
3) Gifu Keizai University Faculty of Economics

Abstract:This study aims at clarifying the relations of habitat conditions required for Pungitius pungitius to the environmental factors of springs in non-irrigation period and at considering with the way of spring management desirable for conservation of the fish populations. The study was conducted in five springs in Hataya, Senhata Town, Akita Prefecture, from December 1997 to April 1998. In those springs, the population density of P. pungitius decreased from December to March, when the amount of eruption water decreased. Particularly distinct decrease in the population density of fry was observed in the springs where the average water temperature in December showed a larger temperature balance between at the eruption point and at other measuring points in the spring. Even in the spring with a smaller value of the temperature balance throughout the investigation period, the lower population density was also observed where the vegetation coverage of aquatic plants was small. In the springs with small fiuctuations in the water temperature and high coverage of aquatic plants, occurred the higher population density of fry and distinct rise of the total population density during March through April. In order to avoid the affects of farm land consolidation on the fish population, it is desirable to make connect, via ditches, springs being capable of drying up or having large water temperature fluctuation with those having much amount of eruption and less water temperature fluctuation.

Key words: spring eruption, Pungitius pungitius, population density, water tempera ture, conservation

摘要

本研究では,農閑期の湧泉の環境条件とイバラトミヨ Pungitius pungitiusの生息状況の関係を明らかにし,湧泉保全についての考察を行った.調査は,秋田県下畑町畑屋地区の5カ所の湧泉を対象に,イバラトミヨの生息密度数調査および物理的環境調査を1997年12月から 1998年4月に行った.その結果,すべての湧泉において,12月から4月にかけて,湧出量の減少に伴い生息密度が低下した.生息密度が大きく低下したのは,そのうち2カ所であった.生息密度が低下した湧泉では,12月に平均水温が低下し,湧出口水温と大きな差が生じた。また,融雪期にあたる3月に300mm以下の水位での水温低下が大きく,未成魚の生息密度の低下が大きかった. また,調査期間を通じて湧出口水温との差が少ない湧泉においても,水生植物の植被率の低下から,生息密度が低下していた. 一方,湧出量が安定し,水温変動が少なく,水生植物の植被率が高い湧泉では,3月から4月にかけて生息密度の増加がみられ,未成魚の生息密度が高かった.
圃場整備による湧泉環境への影響を回避するためには, 同場整備による地下水位の低下に伴い枯渇する可能性が高い湧泉や水温変化が大きい湧泉を湧出量が多く水温変化が少ない湧泉と水路で連結する改善策が望まれる.

1999年3月12日受付, 1999年10月12日受理
* e-mail: jinguji@agri.akita-pu.ac.jp