Permalink : http://hdl.handle.net/2115/84947

JaLCDOI : 10.14943/lowtemsci.80.445

KEYWORDS : 年齢;成長;生息密度;尾瀬ヶ原;イワナ;age;growth;population density;Ozegahara;white-spotted char

本研究では，尾瀬ヶ原に生息するイワナSalvelinus leucomaenisの年齢，体長組成および生息密度など基礎的な情報を得るため，8つの支流および本流において捕獲調査を行った．その結果，イワナ229尾を捕獲し，それら個体の平均体サイズはオスで15.42 ± 5.57cm，メスで14.21 ± 4.05cmであった．鱗から年齢を査定したところ，0歳から6歳の範囲であり，オスの平均は2.67 ± 1.33歳，メスの平均は2.20 ± 1.03歳であった．体サイズを雌雄間および年齢間で比較を行ったところ，年齢間では差が認められたものの，雌雄間で違いは見られなかった．また，8支流における魚類密度を求めたところ，平均0.035尾m-2（範囲：0.006-0.097尾m-2）であり, 他の河川と比べて低い密度であった．また，各支流における雌雄比は平均で0.58（オス/（オス＋メス））であり，比較的支流の上流域および小規模の支流では下流域に比べて雄の割合が高い傾向が見られた．今後，各支流における付着藻類量，水生昆虫量，さらには落下昆虫量といった河川生態系全体から尾瀬ヶ原に生息するイワナの生態解明が望まれる．
In this study, capture surveys were conducted in eight tributaries and the main stream flowing though Ozegahara to obtain basic information of White spotted char Salvelinus leucomaenis on the size frequency, age and population density. As a result, 229 char were captured and the average body size was 15.42 ± 5.57 cm for males and 14.21 ± 4.05 cm for females. Age was assessed from scales and ranged from 0 to 6 years, with males averaging 2.67 ± 1.33 years and females 2.20 ± 1.03 years. Comparisons of body size showed no differences between males and females, although differences were observed between ages. Fish densities in the eight tributaries averaged 0.035 fish m-2 (range: 0.006-0.097 fish m-2), which was low compared to other rivers. The mean sex ratio in each tributary was 0.58 (male / (male + female)), and the proportion of males tended to be higher in the upper reaches and smaller tributaries than in the lower reaches. Further elucidation of the ecology of char inhabiting Ozegahara is desirable, taking into account the amount of attached algae, aquatic insects, and falling insects in each tributary and the entire river ecosystem.