Comparative morphology related to reproductive strategy in two chum salmon (<I>Oncorhynchus keta</I>) populations in the Yurappu River

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Differences in age composition, body size and morphology in adult chum salmon (<I>Oncorhynchus keta</I>) collected from mid October 2005 to early January 2006 in lower and upperreaches in the Yurappu River were investigated. Although no difference in age composition was evident between upper and lowerreach populations, latter was characterized by significantly larger male body size than the former, there being no such difference in female body size. Stepwise discriminant function and allometric analyses revealed that the lower-reach males had greater body depth and smaller head proportions, including snout and upper-jaw lengths, than their upper-reach counterparts, lower-reach females having a larger caudal peduncle and smaller head proportions than those in the upperreach. These morphological differences between populations may reflect plasticity and a tradeoff between escapement risk and breeding competition in the reproductive strategy of chum salmon.
日本魚類学会の論文