A nasty disease is devastating salmon stocks around the world. Now it is here in Canada and there’s little anyone can do
The scourge had already run through much of Europe and the United States, parts of Africa, Asia, and even New Zealand by the time it struck Canada. On August 23, 2016, came the dreadful confirmation that whirling disease had been found in this country. And not just anywhere, but in Johnson Lake, the headwaters of the mighty Bow River and the heart of Banff National Park, crown jewel of Canada’s park system.
It’s awful for the salmonids — fish in the salmon family — particularly rainbow trout. When they are infected young enough, their tails turn black, their skulls and spines look like they’ve been crushed in a vise, and they spin around in spirals as if in a mad dash to catch their own tails. And then most of them perish. The disease has no known effect on human health.
Whirling disease is caused by the parasite Myxobolus cerebralis, which first injects itself into the guts of tubifex worms, living within them for as long as three months. Finally, the parasite ripens up into spores. At that point, it bursts forth from the worm into the water on a mission to find fish. Armed with self-propelling spears to puncture the fish’s skin and hooks to hang on for dear life, the parasite heads straight for the young fish’s nervous system once it has gained entry, and then for the cartilage.
But although in most cases the young fish dies, the parasite does not. As the fish’s body rots, the parasite lies in wait in lake or river sediment, patiently on the lookout for another tubifex worm. When it finds one, the cycle starts all over again.
If this gives you the impression that the parasite is relentless, you’re right. Despite years of research and heroic experiments, American scientists have been unable to eradicate it, forced to watch as the parasite has insinuated itself into watersheds across the United States. Sport fisheries have been devastated in some states, to the tune of 90 per cent trout loss in parts of Montana and Colorado.
The parasite has also infected hatcheries and fish farms. In fact, there is some evidence that the very first case, found in Germany in 1893, came from hatchlings imported to Europe from the United States. Some American hatcheries have simply been forced to close down when the infection coursed out of control.
That rapaciousness has characterized its assault on Canada. Within a single year, the infection has marched across Alberta. From Johnson Lake to the Bow and Elbow river systems, then the Oldman watershed and all the way to Waterton National Park in the province’s south. Then the Red Deer River system. One by one, Canada’s iconic western waters have succumbed: Spray River, Cascade Creek, Carrot Creek, Jumpingpond Creek, Crowsnest River, Stoney Nakoda First Nation.
Park rangers in Banff have tried to get ahead of the parasite by killing every last fish in Johnson Lake. Officials in Alberta and with the Canadian Food Inspection Agency have warned that while the parasite does a superb job of spreading itself, humans can also play a role if they transport infected live or dead fish or their guts, or move infected worms, equipment or water. They are pleading with anglers and boaters to clean, drain and dry off any gear that touches water. Mud, they warn, is one of the truly excellent carriers of the parasite.
Conscious that the disease is an attack not only on the fish but also on the cherished pastime of angling, Alberta has set up an action plan that involves much more testing, education and protocols for trying to limit the spread. But the main strategy is to catalogue where the disease goes and then wait it out. While trout in Montana and Colorado were decimated through the 1990s, the effects now seem to be abating, for reasons that defy understanding.
In this era, the Anthropocene, when human-caused activities are affecting so many of the planet’s species, one of biologists’ duties is to look at disruptions through the lens of climate change. Is it a factor in whirling disease’s rampage across North America? Unclear. But it is clear that the parasites revel in the warmer waters that result from less snowpack in the mountains and higher air temperatures, both happening under climate change.
And whether or not climate change is the direct culprit, the sad truth is that this outbreak is a textbook example of the sort of thing that is bound to happen more and more as the climate gets wonkier. Strap in, folks. The ride is getting bumpy.a
DESPITE YEARS OF RESEARCH AND HEROIC EXPERIMENTS, SCIENTISTS HAVE BEEN UNABLE TO ERADICATE WHIRLING DISEASE. THE EFFECT HAS BEEN DEVASTATING