Spawning of White-spotted Charr Salvelinus Leucomaenis and Population Dy Mics of Its Underyearlings in an Artificial Spawning Channel

27 Mar Spawning of White-spotted Charr Salvelinus Leucomaenis and Population Dy Mics of Its Underyearlings in an Artificial Spawning Channel

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Abstract

2005年から2007年にかけて，岐阜県の神通川水系蒲田川の砂防堰堤下流に造成されたイワナ，ヤマメの人工産卵河川において，両種の産卵と当歳魚の生態を調査した．2005年11月に8ヵ所の人工産卵場のうち4ヵ所で，2006年同月に15ヵ所の人工産卵場うち8カ所で多数のイワナの産卵がそれぞれ確認された．両年ともにヤマメの産卵は確認されなかった．2005年のイワナの産着卵数は2,503粒，卵の発眼率は90.0％であった．イワナ当歳魚は4月に産卵床付近で多く観察され，その後経時的に人工産卵河川全体に分散した．この傾向は2006年に強かった．イワナ当歳魚の10月における水表面積1m2当たりの密度と現存量は，2005年級群では0.29個体と2.32g，2006年級群では0.75個体と4.73gであった．10月の尾叉長と体重の平均値は，2005年級群では86.0mmと8.00g，2006年級群では80.2mmと6.31gであった．2005年級群の卵から当歳10月までの生残率は3.2％であった．これらの結果から，人工産卵河川の造成はイワナの増殖に有効であると考えられた．

English Abstract

The effectiveness of construction of an artificial spawning channel to enhance white-spotted charr (Salvelinus leucomaenis) and masu salmon (Oncorhynchus masou masou) was examined in a channel (approximately 270 m long and 1 m wide) constructed below an erosion control dam, in the Gamata River, Jinzu River system, Gifu Prefecture from 2005 to 2007. Eight and 15 artificial spawning grounds were constructed in the channel in 2005 and 2006, respectively. As a result, multiple spawnings of the charr were observed at 4 of 8 grounds in 2005 and 8 of 15 grounds in 2006, respectively. The number of spawned eggs and the percentage of eyed eggs were 2503 and 90.0% in 2005. A lot of underyearling charr were observed in April of both 2006 and 2007. The growth, density, standing stock and survival rate of the underyearlings were studied from July to October in both years. The average fork length and body weight in October were 86.0 mm and 8.00 g for the 2005 year-class and 80.2 mm and 6.31 g for the 2006 year-class, respectively. The density and standing stock in October were 0.29 fish/m2 and 2.32 g/m2 for the 2005 year-class and 0.75 fish/m2 and 4.73 g/m2 for the 2006 year-class, respectively. The survival rate of the 2005 year-class was 3.2% from the spawned eggs to the underyearlings of October. The underyearlings were observed near the spawning redds in April, after that they dispersed throughout the channel. No spawning of masu salmon was observed throughout the channel in both years. The results suggest that the construction of artificial spawning channel is effective for the enhancement of white-spotted charr.