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北海道南部の4河川において,天然のイワナSalvelinus leucomaenisを用いて,キャッチアンドリリース後の成長,生残,釣られやすさを調べた。釣獲直後の死亡率は6.7%であり,過去の研究結果に近い値であった。一方,キャッチアンドリリースが行われた個体において,成長率や生残率の低下は認められなかった。また,釣られやすさは釣獲経験のある個体と無い個体で同程度であった。よってキャッチアンドリリースを行うことは資源量および釣獲量の増大に有効であることが示唆された。
We examined the effects of catch-and-release angling on the growth, survival and catchability of white-spotted charr Salvelinus leucomaenis in four wild streams in northern Japan. Investigations were made twice at each stream. We angled fish with live bait and caught fish using electrofishing as controls. Angled and control fish were measured for fork length, marked individually and released. Fifty days later, we angled and caught by electrofishing again. A total of 282 angled fish and 376 control fish had fork lengths of 80.5 to 282.5 mm. Hooking mortality within a few minutes was 6.7%, which agreed well with previous data by studies of catch-and-release mortality. There was no significant difference in standardized growth rate between angled fish and control fish. The recapture rates of angled and control fish were 77.9 and 74.2% respectively, suggesting that the survival rate of angled fish is not lower than that of control fish. No significant difference in catchability was found between angled fish and control fish. The results show no evidence that catch-and-release angling affects growth, survival and catchability. We conclude that catch-and-release angling is effective to sustain white-spotted charr populations.
