As we continue to endure one of the warmest Canadian winters on record, some are basking in the mild temperatures and ice-free car windshields. But for Ontario’s fish species, including lake trout, walleye, and yellow perch, this warmer weather presents a potential threat to their habitats—and their future.
What do fish have against warm weather? “Temperature is a critical factor in determining the physiological processes of fish,” says Adam Weir, fisheries biologist at the Ontario Federation of Anglers and Hunters. “Of all the factors, temperature is arguably the most important one.” Here’s how specific fish species in Ontario are adapting, or not, to milder weather across the province.
Lake trout, sunfish, and largemouth bass
One particularly temperature-dependent fish species is lake trout. “Lake trout are a sensitive cold water species that seek out cool areas of lakes for their higher degree of dissolved oxygen,” says Weir. With warming temperatures, dissolved oxygen becomes harder for the lake trout to find, and without it, Weir says the fish are likely to die. “In general, increased temperatures restrict the availability of suitable lake trout habitat in lakes, making it harder for them to carry out their day-to-day activities,” says Weir.
While higher temperatures may threaten lake trout, these conditions can actually be beneficial for warmer-water species such as sunfish and largemouth bass. “We call these species ‘climate change winners,’” says Weir. “These are species who are projected to benefit from increasing temperatures.”
For sunfish and largemouth bass, Weir explains warming temperatures will likely increase both the amount of available habitat for the fish as well as the quality of the habitat overall. As a result, species like these will see advantages such as expansion and population boosts.
But Weir cautions they’re competing fish, meaning their ability to thrive in warm waters will affect other species that depend, instead, on cooler waters, such as lake trout. What does that mean? Fish ecosystems as a whole will change greatly as temperatures continue rising. More adaptable fish species will expand, while less adaptable fish species will potentially disappear. So too will their important contributions to biodiversity.
Take lake trout, for example. “Lake trout are an integrator species, so they move important nutrients and energy from nearshore areas to deeper waters,” explains Weir. Without these important functions, Weir says the health and functionality of entire aquatic ecosystems are potentially at risk.
Walleye and yellow perch
The effects of climate warming on species such as walleye—a popular sport and food fish in Ontario—and yellow perch aren’t as clearly defined, however. “Walleye require long, extended winters of three to five months where temperatures, on average, reach below 10°C,” says Weir. “Without these conditions, research shows that walleye experience poor ovary development, see a decrease in egg size, a rise in egg mortality, and an overall drop in reproductive success.” At the same time, Weir says other studies show rising temperatures could actually increase walleye habitat in more northern parts of Ontario, potentially resulting in greater populations of the species in these areas.
Similar to walleye, a study from scientific journal, Nature, shows that Lake Erie yellow perch face similar reproductive struggles as a result of shorter and milder winters. That being said, yellow perch could stand to benefit from climate change in an unexpected way: “Juvenile yellow perch have an interesting survival strategy where they find refuge from predation in clouds of river plumes,” says Weir. “An increase in extreme precipitation events due to climate change will mean more prominent river plumes, providing better refuge for larval yellow perch to evade predators.”
All said, Weir explains the outcome of climate warming on species like these is incredibly difficult to confirm. “It’s really hard to put your finger on which of these impacts of climate change will be the bigger factor.”
What climate warming means for anglers
Whether rising temperatures will mean more or less fishing for anglers remains to be seen, says Weir, but it’s safe to say fish populations will change dramatically in the coming months and years. Some species, especially those that depend on cooler temperatures, might disappear in certain areas as they search for more hospitable waters elsewhere. Others, unable to adapt, could disappear completely. Some, however, may thrive in the warming temperatures of Ontario’s lakes and rivers. Whatever the case, Ontario’s aquatic ecosystems will continue to see significant modifications as we continue grappling with climate warming.
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