Analys av åldersstrukturen hos sik (Coregonus lavaretus) i sjöar utan gädda (Esox lucius)

Development of morphs within European whitefish (Coregonus lavaretus), might be considered as a beginning of a sympatric speciation process. Unpublished data suggests that presence of the keystone piscivore northern pike (Esox lucius) is the main driver of sympatric divergence in European whitefish (Coregonus lavaretus). Using introduced whitefish populations as controlled experiments, it is possible to determine when different characters diverge in the speciation process. In this study, I analysed age and growth within European whitefish populations of different age to assess if these characters change over time in absence of pike. With using otoliths from whitefish populations of different age, I was possible to determine individual age, and by measuring the length of the fish, growth was calculated. Whitefish populations in lakes without northern pike had rapid growth to maturity and decreased growth afterward, furthermore regression analysis showed no correlations between age and growth measurements, and time since introduction. This suggests that there are no divergences in monomorphic whitefish populations. Compared with outcome from studies of polymorphic populations of whitefish, characters have been observed to differ between morphs, but age and growth of whitefish did not change with the age of populations in lakes with pike, as in lakes without pike. This suggests that other factors influences the changes in whitefish or that it may occur outside the investigated time span.