Online

Stewart, Taylor R.

Biology

2022

Ph. D.

Changes in winter conditions, such as increased temperatures and decreased ice coverage, have been observed worldwide. The responses of many lake fish populations to changing winters are projected to be inadequate to counter the speed and magnitude of climate change. Such environmental changes have been hypothesized to explain the low recruitment observed in freshwater whitefishes (Salmonidae Coregoninae). My research focused on measuring the impact changing winter conditions may have on coregonine reproductive phenology and developmental and morphological traits to better predict changes in coregonine populations as a result of climate change. I used experimental incubation methods and modeling to explore how climate-induced changes in water temperature and ice coverage may impact coregonine adults during spawning and early-life stages within and among species. First, I experimentally evaluated the response of embryonic development to increasing water temperature for cisco (Coregonus artedi) from lakes Superior and Ontario, and vendace (C. albula) and European whitefish (C. lavaretus) from Lake Southern Konnevesi, Finland. Embryo survival, incubation duration, and length-at-hatch were inversely related to temperature whereas yolk-sac volume increased with temperature within study groups. However, responses varied in magnitude among study groups suggesting differential levels of developmental plasticity. Next, I quantified how cisco embryos from lakes Superior and Ontario responded to simulated changes in incubation light conditions representing 0-10 (high light), 40-60 (medium light), and 90-100% (low light) ice coverage. Embryo survival was highest under medium light, and light intensity had no effect on incubation duration. Increasing light intensity decreased length-at-hatch in Lake Superior but had no effect in Lake Ontario. Yolk-sac volume was positively correlated with increasing light in Lake Superior and negatively correlated in Lake Ontario. Contrasting responses between lakes suggest populations' response to light is flexible. Furthermore, I analyzed different embryo incubation temperatures on post-hatching survival, growth, and critical thermal maximum of larval cisco from lakes Superior and Ontario. Larval survival and critical thermal maximum were negatively related to temperature, and larval growth was positively related to temperature. The magnitude of change was greater in Lake Superior than Lake Ontario for all traits examined, suggesting Lake Superior larvae may possess a more limited ability to acclimate to and cope with environmental change. Lastly, I used simulation modeling to investigate changes in reproductive phenology under climatic-warming scenarios for coregonine populations across the Laurentian Great Lakes and Europe. Models predicted that climate-induced increases in water temperatures may cause delayed spawning, shorter embryo incubation lengths, and earlier larval hatching. I quantified how climate change could affect coregonine populations, including changes in embryo development traits, reduced physiological condition of larvae, and shifts in reproductive phenology. Climate-induced responses of coregonines to changing environmental conditions are likely to vary within and among species and with the magnitude of climate warming. Management strategies that maximize phenotypic variability could improve the ability of coregonines to cope with environmental change.