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 mm), identified as wild based on comparison with the expected minimum size of hatchery fish (> 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.

日本鲑鱼的可持续保护管理需要有关野生鱼类的生态信息。本研究调查了新泻县无种群河流中的产卵时间和野生鱼苗的发生情况。在 10 月中旬至 12 月中旬期间，在河床中观察到了大多数红点，这些河床的溪水温度不定但寒冷的温度高于 5.4 °C。鲑鱼鱼苗（< 41 毫米），根据与孵化场鱼的预期最小尺寸（> 41.2 毫米）的比较确定为野生，一般在 3 月初至 5 月初当海面温度 (SST)为 7.4-17.5 °C。这一时期与根据调查河流累积水温预测的出现时间基本相符。广义线性模型预测，发生的概率会随着海温的增加而降低，即使海温为 15 °C 时也为 42.5%。新泻县的孵化鱼将于 3 月下旬放养。我们的研究结果表明，受对马暖流影响，分布南端的野生鲑鱼苗在海温较高时入海，主要是在 3 月至 4 月，甚至在结束后 2 个月的 5 月孵化场放养。