Thermal regime of coastal waters and possible mechanisms of formation for strong year-classes of West Kamchatka pink salmon

Dynamics of downstream migration is considered for juvenile pink salmon at West Kamchatka in 1975–2023. Lengthening of the migration period is noted for recent years with high parental stocks. These changes happened on the background of four-decade increasing of the sea surface temperature in waters at the western coast of Kamchatka (till 2016), on average from 3.0 to 6.5 ºC, and its further decreasing back to 3–4 ºC from 2017 to 2023. So, the warming trend in coastal waters at western Kamchatka is significantly weaker than that at eastern Kamchatka, that does not confirm a hypothesis on formation of super-strong year-classes of West Kamchatka pink salmon in recent years due to warmer environments for early marine feeding of the juveniles in the coastal zone. Presumably, these extreme year-classes were formed as a result of prolonged downstream migration of fry produced by rather numerous spawners in conditions of increased abundance of small-sized plankton transported to the coast of western Kamchatka from the deep-water areas of the Okhotsk Sea and the North-West Pacific.