On the Ocean age of Masu Salmon Oncorhynchus masou in a Natural Population, Shiretoko Peninsula, Japan

A study on masu salmon (Oncorhynchus masou) in the Orumappu River, Shiretoko Peninsula, Japan, challenges conventional age assessment methods. Researchers tagged 667 wild smolts and recaptured 11 adults, all of which spent one winter at sea but showed inconsistencies in scale annuli—four lacked clear winter rings, while one exhibited two or three closely spaced resting zones. This suggests that relying solely on scale analysis may underestimate the ocean age of adult masu salmon, complicating population studies and conservation efforts.

Morita, K., & Sahashi, G. (2018). On the Ocean age of Masu Salmon Oncorhynchus masou in a Natural Population, Shiretoko Peninsula, Japan. Journal of Ichthyology, 58(4), 594–599. https://doi.org/10.1134/s0032945218040136