LAUSR

Sustainable conservation management of chum salmon in Japan requires ecological information on wild fish. This study investigated the spawning timing in a nonstocked river and the occurrence of wild fry in a surf zone in Niigata Prefecture. Most redds were observed from mid-October to mid-December on riverbeds having stream water of variable but cold temperatures above 5.4 °C. Chum salmon fry (  41.2 mm), were collected at the surf zone generally from early March to early May when the sea surface temperature (SST) was 7.4−17.5 °C. This period largely matched the predicted time of emergence based on the surveyed river cumulative water temperature. A generalized linear model predicted that the probability of occurrence would decrease as SST increased, being 42.5% even when SST was 15 °C. Hatchery fish are stocked by late March in Niigata Prefecture. Our results reveal that wild chum salmon fry at the southern limits of their distribution, which is affected by the Tsushima Warm Current, enter the sea when SST is relatively high, mainly from March to April, and even in May, 2 months after the end of hatchery stocking.