In this paper we explore the subsistence economy of the Mesolithic pioneers on the island of Gotland in the Baltic basin, in order to evaluate the importance of freshwater fish to the Early Holocene human population. By analysing faunal remains, the distribution of ¹⁴C dates and the location of the settlement sites, we argue that earlier assumptions concerning the importance of marine mammals to the early human populations should be reconsidered. We suggest that the pioneering settlers of Gotland relied on fish to a significant extent. Radiocarbon dates taken from human bones are skewed by a freshwater reservoir effect, which can be used as an indirect indication of the significance of freshwater fish. The numerous, overgrowing lakes on the island, with their extensive biomass production and large amounts of freshwater fish, provided an important subsistence base. Even if the faunal assemblages that have survived are dominated by seal bones, the hunting season for seals was limited and the hunters mostly targeted young seals. Thus, the importance of seal have previously been overestimated and it appears that the human use of marine resources on Gotland was more limited and related to raw material needs rather than dietary necessity or specialization. Although presented as a case study; the results highlight the need to identify a freshwater fish diet among ancient foragers on a larger scale, as implications thereof can fundamentally change how foraging societies are perceived.