The effects of climate change on the growth and spawning phenology of fishes in aquatic boreal environments
Slongo, Brenden David
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Global climate change is occurring and observed warming patterns have had significant impacts on aquatic environments as trends in water temperature are closely related to trends in air temperature. In ectothermic organisms such as fishes, temperature is relevant to the maturation and deposition of gametes during spawning, and lifetime growth potential. By using historical spawning and size at age datasets spanning 43 years, I estimated more than 100 peak spawning dates for White Sucker (Catostomus commersonii) and Lake Trout (Salvelinus namaycush) and described changes in growth of White Sucker to summarize the observed effects that local climate warming over the past 50 years has had on two economically and culturally important fishes in Northwestern Ontario. I show how spawning events are dependent on annual variation in seasonal thermal conditions, and how long-term increases in average fall surface water temperatures by 1.4oC and decreases to thermal cooling by 87 oCᐧdays in lakes have shifted the peak spawning date of Lake Trout by 5 days over the past 4 decades. Additionally, I show how changes in population density, likely as a result from increased survival and recruitment of juvenile White Suckers have worked to dramatically reduce the body size of White Sucker by over 90% in weight and 50% in length in some populations. Finally, I discovered that declining White Sucker body size appears to be a common pattern across an expansive geographic range. These results fill knowledge gaps in the current literature by providing observational accounts of climatic impacts to inland fish populations for a highly studied culturally significant species, and for a lesser considered, but ecologically important species.