Adaptation of Atlantic Herring to the Baltic Sea from marine origins was a relatively recent and rapid process that has driven genetic differentiation between the populations. One of the strongest loci is analyzed with this data.

Rapid and recent ecological adaptation of Atlantic herring to the brackish water environment of the Baltic has produced a clear pattern of genetic differentiation in loci that may increase fitness in the new environment. Previous studies of herring have identified these loci and these additional populations extend the power of those analyses.