Population Growth and Dynamics of Smelt (Osmerus eperlanus) in Lake Mjøsa, Southeast Norway

The article is a literature study supplemented with self-collected data on fish density, age and growth of smolt (Osmerus eperlanus) in Lake Mjøsa over the last 40–50 years. Smolt is an important prey fish for piscivorus brown trout, and the development of the trout population is described by catch reports. The smelt population in Lake Mjøsa declined in the period 1980 to 1990 but increased sharply in 2018 and 2023. Recruitment to the smelt population is positively correlated with air temperature in May and July. Increased smelt population is a possible reason why the large trout population also appears to have increased, while smelt has shown reduced individual growth in recent years. The trout population does not appear to have a decisive effect on the smelt population but may have contributed to increased mortality in smelt in the material from 2006 to 2022 as compared to 1980. The effect of trout stocking, made for the last time in 2021, is uncertain, but future catch reporting will provide a better answer to this.