Harbour porpoises historically occurred regularly along the entire Swedish coast, including the northernmost parts of the Gulf of Bothnia, where the species is virtually absent today, suggesting a notable range retraction.

While harbour porpoises appeared less frequently in the Baltic Sea than along the west coast of Sweden, the number of Baltic records indicates that porpoises occurred more frequently than today. The peak occurrence of porpoises during spring and summer suggests that the Gulf of Bothnia historically constituted an important foraging habitat for animals migrating from the southern Baltic.