Return Rates of Chum Salmon are Affected by Different Timings of Juvenile Release

Abstract Excerpt:
Recently, there has been a decreasing trend in the return rate of late-run chum salmon juveniles released from hatcheries in southern Hokkaido. According to previous studies, return rates are critically affected by high mortality of juveniles along the coast (Healey 1982; Bax 1983; Fukuwaka and Suzuki 2005), which is related to coastal sea surface temperature (SST) and juvenile weight at release (Mayama and Ishida 2003). In the Hokkaido hatchery program, chum salmon are classified into three populations (early-, middle-, and late-run) depending on run timing. Their offspring are released in the corresponding order, and juveniles of each run population experience different coastal environments.