North Pacific Anadromous Fish Commission

Technical Report 17

Table of Contents

Does Long-distance Downstream Migration Influence the Survival of Chum Salmon? Comparison of Adult Returns between the Upper and Lower Reaches Release Sites

Authors: 
Kiyoshi Kasugai, Mitsuru Torao, and Mitsuhiro Nagata

Abstract Excerpt:
Mass mortalities are presumed to occur immediately after entry into the ocean in the early life stages of chum salmon, Oncorhynchus keta (Wertheimer and Thrower 2007). However, high levels of mortality in chum salmon fry have been observed in rivers (Kasugai et al. 2013, 2014; Morita et al. 2015). In the Nishibetsu River, located in eastern Hokkaido, northern Japan, chum salmon fry migrate downstream over a distance of approximately 100 km from the hatcheries in the upper reaches to the river mouth. Chum salmon fry released into the upper reaches in mid-April arrived at the lower reaches approximately two weeks later (Kasugai et al. 2013). The condition factors of fry caught in the lower reaches were lower than those of fry caught in the upper reaches (Kasugai unpublished data). In addition, glycogen, triglyceride and nutrient conditions of fry caught in the lower reaches were remarkably lower than those at the release sites (Mizuno and Misaka unpublished data). Thus, it was suggested that the condition of released fry becomes poor during downstream migration in the Nishibetsu River.

*This is the first paragraph of an extended abstract. Download the full abstract below.

DOI:
https://doi.org/10.23849/npafctr17/42.43.

Citation

Kasugai, K., M. Torao, and M. Nagata.  2021.  Does long-distance downstream migration influence the survival of chum salmon? Comparison of adult returns between the upper and lower reaches release sites.  N. Pac. Anadr. Fish Comm. Tech. Rep. 17: 42–43.  https://doi.org/10.23849/npafctr17/42.43.