Recent trend in Chum Salmon stock decline and its potential mechanisms in Hokkaido, Japan
https://doi.org/10.36038/0234-2774-2021-22-4-16-26
Abstract
The analyses revealed that the return rate of chum salmon is positively correlated with coastal sea surface temperatures (SSTs) at ocean entry timing. This suggests that the SST during the ocean entry timing of chum salmon juveniles would be a major driver in controlling the broodyear abundance, and that the decline of the stock level would be caused by the «cold-spring» phase around the Pacific coastal area in Hokkaido, but 2015 brood year was exceptional. I analyzed the relationships between age at maturity of brood years and the ratio of 4 (5)-yearold fish to 3 (4)-year-old fish abundance, i. e., sibling relationships, to identify the factors affecting precision of the forecast. The analyses revealed that the age at maturity had decreased, and it resulted in the recent decline in precision of pre-season forecast. Additionally, recent decline of the age at maturity suggests that survival rate of fish with slower growth rate might be decreasing. These results suggest that the decline of chum salmon stock levels in Hokkaido would have been mainly caused by cold ocean conditions at the Pacific coast during spring. But, the low survival rate of the 2015 brood year, which matched favorable ocean conditions in the coastal area, was not explained by the general survival mechanism above, suggesting that survival rate in the Okhotsk Sea and/or farther area might be decreasing, recently.
About the Author
Hirokazu Urabe
Salmon and Freshwater Fisheries Research Institute, Hokkaido Research Organization
Japan
Japan
3–373 Kitakashiwagi, Eniwa, Hokkaido
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Review
For citations:
Urabe H. Recent trend in Chum Salmon stock decline and its potential mechanisms in Hokkaido, Japan. Problems of Fisheries. 2021;22(4):16-26. (In Russ.) https://doi.org/10.36038/0234-2774-2021-22-4-16-26
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