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Background

Fisheries-induced life history changes in terms of for example reduced age at first spawning have been observed in many demersal fish species. However, such changes have not been observed in pelagic species, although they too are under constant fishing pressure. Does this mean that the theory is wrong, or is there something else going on with pelagic species?

Norwegian spring-spawning herring is one of the largest pelagic fish stocks in the world. At the same time, it is most likely the best documented pelagic stocks with time series data on catches back to 1899, on population dynamics back to 1904 and biological data on individual starting from 1935. A number of changes in life history traits in accordance with the expectations of life history theory have been observed in this population. At the same time, stock assessment is overestimating population size year after year. Based on massive amount of data on Norwegian spring-spawning herring collected over the years, life history theory and statistical modeling, this project will examine how these observed patterns are connected, and how much of the changes are caused by evolution. The results of this project can help with population estimates and sustainable management of this commercially and ecologically important population, while they are also going to increase our understanding of human-induced evolutionary changes in natural populations.