The Chronicle Herald (Provincial)
Extreme heat waves are putting lakes and rivers in hot water
In British Columbia and Yukon, salmon numbers have declined by as much as 90 per cent and have led the federal government to shut down 60 per cent of the commercial and First Nations communal salmon fishery.
Extreme heat waves have blanketed the Pacific Northwest, Siberia, Greece, the Middle East, Southeast Asia and other regions this summer, with temperatures approaching and exceeding
As temperatures near outdoor survival thresholds, individuals who do not have easy access to air conditioning or cooling stations, or are unable to flee, may succumb to heat waves.
These climate extremes are becoming more frequent. But as tragic as they are to human health, they are only part of a larger climate catastrophe story — the wide-scale damage to the ecosystems that people depend upon, including agriculture, fisheries and freshwater.
Most wildlife cannot seek refuge from extreme heat. An estimated one billion marine animals may have perished during the heatwave this past June in the Pacific Northwest alone.
Many people may perceive lakes and rivers to be refuges from unprecedented heat, but freshwater systems are no less sensitive. Heat waves have killed thousands of fish in Alaska as temperatures exceeded the lethal limit for coldwater fishes.
This year’s hot and dry summer could collapse the salmon fishery in the Sacramento River in California. In British Columbia and Yukon, salmon numbers have declined by as much as 90 per cent and have led the federal government to shut down 60 per cent of the commercial and First Nations communal salmon fishery.
Coldwater fish, such as trout and salmon, are being squeezed out of their cool, well-oxygenated, deep-water habitat. As water contains less oxygen at higher water temperatures, this forces the fish to move into nearshore regions. While these shallower waters may be better oxygenated, they are even warmer and may exceed thermal tolerances of coldwater species.
By the same token, invasive fishes such as smallmouth bass are thriving in warmer temperatures and displacing native Canadian fishes like walleye and lake trout.
The combination of a warming climate, drought and human activities, including irrigation for agriculture, can have drastic consequences for both the quality and quantity of our freshwater supply — ultimately leading to shortages of potable water.
By the end of the century, evaporation is projected to increase by 16 per cent globally. Lakes closer to the equator, which are already experiencing the highest evaporation rates, are expected to experience the greatest increase.