There’s something fishy going on in Ontario, and it appears climate change is to blame. Invasions of the competitive, predatory smallmouth bass are putting the native Canadian walleye at risk.

York University scientists say competition for food resources and the bass’s taste for young walleye are contributing to shrinking walleye fish populations.

As climate change has been warming the waters of northern Ontario lakes, smallmouth bass have been spreading north since the 1980s. The bass prefer warmer water and the colder northern lakes used to be a deterrent. But with a warming climate, that’s been changing. 

To arrive at their conclusions, Sapna Sharma of York’s Department of Biology and Thomas Van Zuiden, data manager and statistical analyst in the Sharma Lab, relied on their lab’s small computing cluster. 

They weighed reams of climate data from the Intergovernmental Panel on Climate Change (IPCC) against freshwater surveys taken between 2008 -2012 from hundreds of Ontario lakes. What Sharma and Van Zuiden discovered doesn’t bode well for the popular recreational and commercial fish.

“Our dataset spanned 722 lakes and over 200 predictor variables, as we had information on 130 fish species, lake morphology, water chemistry, and monthly climate (temperature and precipitation) from the IPCC,” recalls Sharma. “The general circulation data that we used from the IPCC were huge files – in total several terabytes. Just downloading and extracting the data took several months and all our lab computers.”  

To see what would become of the walleye in the future as climate change extends, the team of scientists ran their datasets through univariate regression and multivariate models. Close inspection of Ontario lake data revealed that smallmouth bass prefer different environmental conditions than walleye.

The future is looking dim for walleye in Ontario lakes under climate change because of both habitat loss and competition from invading smallmouth bass. ~Sapna Sharma

However, when walleye and smallmouth bass are in the same lakes, the scientists found there are three times fewer walleye. The change in population dynamics has far-reaching implications for the lake inhabitants and human societies that rely on them, the scientists note.

“Walleye play an important role in lake-ecosystem dynamics as top predators, and they are also popular angling targets for commercial and recreational fisheries,” said Van Zuiden. “Climate change poses a serious threat to their survival in Ontario lakes, and our study shows that invasion of smallmouth bass is exacerbating the problem.”

Under future scenarios of climate change, the researchers predict that the co-occurrence of the two fish species may increase as much as 332 percent by the year 2070, increasing the vulnerability of walleye populations across the Canadian province.

Without baiting a hook, computational biologists and climate scientists have identified a threat to the economic well-being of a staple regional industry — fisheries in the Great Lakes.

“As climate change continues to facilitate smallmouth bass invasions into new lakes, Canada’s native fisheries that lean on walleye and lake trout are at greater risk of collapse,” Sharma recognizes. “The future is looking dim for walleye in Ontario lakes under climate change because of both habitat loss and competition from invading smallmouth bass.”

Sharma and Van Zuiden join thousands of scientists around the world who are learning what climate change spells for the future of biodiversity and the human civilizations who rely on a diverse ecosystem in order to flourish.

Their study is a prime illustration of the importance of including multiple environmental stressors and biological realism in statistical models when attempting to understand changes in biodiversity.