Whirling Dan­ger

A nasty dis­ease is dev­as­tat­ing sal­mon stocks around the world. Now it is here in Canada and there’s lit­tle any­one can do

Canadian Wildlife - - BIGGER PICTURE - By Alanna Mitchell Il­lus­tra­tion by Wenting Li

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


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