Early fish colonization and community development in a shallow re-established lake

The establishment of new lakes has gained momentum throughout Europe and North America as a way to remove nutrients, manage extreme rain events, establish recreational areas, and increase biodiversity. We compared freshwater fish colonization and community development of re-established Lake Fil, a 900-ha lake in Denmark, with fish communities in lakes in close proximity as well as those throughout the region. We found that fish migrated quickly into the lake from nearby refugia with fast initial colonization followed by saturation of the species pool. A total of 14 fish species migrated into the lake during the first five years. Over this period, the lake showed increasing similarity not only to the two directly connected lakes, but also to other lakes in the region. This could be seen in terms of species occurrence similarity, catch per unit of effort (CPUE) and biomass per unit of effort (BPUE). The first immigrant was the three-spined stickleback (Gasterosteus aculeatus), followed by roach (Rutilus rutilus) and pike (Esox Lucius), which both came to dominate the fish biomass in the following years. However, the pike population showed no reproduction and perch (Perca fluviatilis) had low immigration and reproduction, pointing to a limited success, overall. One solution might be to stock Lake Fil and other new lakes with predatory fish, which might ensure a more balanced food web structure which positively influence the turbidity of the lake water and provide recreational value for anglers.