Migration route, growth, and natal-river selectivity of masu salmon Oncorhynchus masou released in the Yoneshiro River
2015
Sato, M. (Akita Prefectural Institute of Fisheries, Oga, Akita (Japan)) | Shibuya, K.
To investigate the migration route, growth, and natal-river selectivity of masu salmon Oncorhynchus masou, a total of 323,620 smolts were released in the Yoneshiro River between 1996 and 2010 (except 2007). A total of 501 fish were recaptured by November of the second year after release. Based on recapture data, we estimated that masu salmon migrated to the Okhotsk Sea for the summer and to the eastern area of the Tsugaru Strait for overwintering. Subsequently, the salmon ran up the river by the summer of the second year after release. The mean fork length of recaptured fish steadily increased between April of the first year after release and June of the second year after release. The mean growth rate in the sea was 0.09 +- 0.03 cm/day. Increases in mean fork length were not observed after July of the second year after release. These results indicate that masu salmon grow during the ocean stage. Of the 36 fish recaptured in the rivers, four individuals were recaptured in rivers other than the Yoneshiro, suggesting that these fish had not imprinted on the natal river.
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