A review of the population dynamics of coregonids in European alpine lakes
The population dynamics of coregonids in European alpine lakes have been studied intensively during recent decades. Many of these studies have focussed on the impacts of anthropogenic eutrophication and subsequent re-oligotrophication. These changes in productivity represent the single most important perturbation of coregonid habitats since the mid-twentieth century. While the problem of eutrophication has been successfully addressed in many European alpine lakes, new forms of anthropogenic challenge such as climate change and the colonization of lakes by non-native aquatic species continue to impact on coregonid populations and demand research. The picture that emerges from a compilation of primary research papers suggests that abiotic and biotic factors are most influential on year-class strength during the larval phase, exerting more moderate effects during the embryonic and reproductive phases, and only a weak influence during the growth phase. In contrast, individual biomass is mainly determined during the growth phase, but moderate effects on growth may also occur during the larval and reproductive phases. Changes in lake productivity influence the various life-history phases of coregonids in both positive and negative ways, for example by improving feeding conditions and via deterioration of spawning habitat quality. Climate change, on the other hand, seems to influence mainly the embryonic and larval phases, with the available studies suggesting that higher temperatures and earlier onset of stratification in spring tend to boost year-class strength. These effects, however, appear insufficient to balance the marked effects of re-oligotrophication, which has caused and continues to cause a marked depression of growth in many European alpine lakes. The bumper fish harvests obtained during the peak of anthropogenic eutrophication are thus a thing of the past.