Coldwater, stenothermic fish seem bound to suffer under the spectre of future warming

Climate change has the potential to impact lacustrine fish populations by affecting both their physiologies and phenologies. Coldwater, stenothermic fishes that spawn in winter may be at the highest risk of being negatively impacted by predicted future climate warming. To investigate this subject, we tested the impact of temperature on the embryonic and larval stages of coldwater, stenothermic salmonid whitefishes (coregonines). Embryos of two coregonine species from Upper Lake Constance (a large, deep perialpine lake bordering Austria, Germany and Switzerland) were incubated at three temperatures approximating historic and potential future water temperatures. After hatching, larvae from all incubation treatments were transferred to two rearing temperature treatments. Hatching times were advanced by higher temperatures, whilst mortality and larval performance responses to higher temperatures were generally negative, suggesting that future climate warming will reduce coregonine recruitment in Upper Lake Constance. The two species tested varied in their specific responses to temperature and in the sensitivity of their responses to temperature. Additionally, we found that incubation temperature affected the performance of coregonine larvae up to two and a half months after hatching. Using our data on hatching times, we infer that future climate change could advance coregonine phenologies in Upper Lake Constance by up to two weeks by the end of the 21st century.