イワナにおける半天然魚の放流効果の検証

摘要

Hatchery-reared salmonids, including char, used for stocking depleted streams for resource management and enhancement have a lower relative fitness to environmental conditions and have a lower survival rate than “native“salmonids after stocking.However, it is difficult to stop the stocking and change to other effective method for resource management and enhancement because fish stocking is a traditional practice and a virtual obligation by Fishery Act.In order to develop more effective stocking approaches, we produced “semi-native“(hybrids between native males and hatchery-reared females)char and evaluated the differences of characteristics and survival after stocking.The eyed egg to fry survival of semi-native char was lower than hatchery-reared char in the hatchery because semi-native char hardly ate feed at the early stage of feeding.However, the survival rate of semi-native char was approximately 2.5 times higher than that of the hatchery-reared char in the mountain streams. Furthermore, there was significant difference in the movement between these two strains in turbid water condition.The results suggest that hybridizations in salmonids are a viable approach to improve the harvest augmentation for recreational fishing in barrier-isolated rivers.