One of the world's leading authorities on the fish-killing VHS virus says he expects some fish in and around Lake Superior to perish now that the disease has moved in, especially muskies, but he said lake trout and salmon have proven resistant to the virus.
Jim Winton, a microbiologist and section chief for the U.S. Geological Survey's Western Fisheries Research Center in Seattle, was responding to the startling news released recently that Cornell University researchers have discovered small levels of VHS in tissue in a small number of Lake Superior fish.
It is the first time the disease, which is harmless to people, has been confirmed in Lake Superior.
The fish tested came from two Wisconsin bays in the Duluth-Superior harbor and two bays near Whitefish Bay in Michigan.
VHS first was found in the Great Lakes in 2005 and caused massive fish die-offs in some areas.
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The News Tribune interviewed Winton by phone.
What's the significance of finding VHS in Lake Superior?
"You don't want to be a defeatist and say it was inevitable, but I don't think anyone was surprised. ... The real story here is less about VHS and more about the risk to our native species from this influx of exotic species. There are so many stressors on native species now, and we know there will be more [invading species] coming ... along with climate change and [human-caused changes like development and pollution]. The issue is how do we move to stop that invasion of species? Some people may have overreacted to the ultimate threat of VHS. But we aren't reacting enough to stop" invasive species from coming in.
What does the presence of VHS mean for fish in Lake Superior?
"It's bad. But it's not the end of the world. No disease exterminates 100 percent of its host species, so it isn't going to eliminate fish. ... But there are some species that are more vulnerable, such as yellow perch and walleye. Muskellunge are unbelievably susceptible. ... But salmonids (trout and salmon) have proven very resistant."
Will VHS reduce fish populations in Lake Superior?
"I'm not a fisheries biologist, but from what I know about Lake Superior fish densities, I would say probably not. Where fish are farther apart, the [virus] can't spread as well. And lake trout probably are less susceptible. ... The exception might be in your [harbors, bays and estuaries], where fish like perch and muskie could see population reductions. ... On the lower St. Lawrence River [in New York] they have seen a 47 percent reduction in muskie population" since VHS was confirmed there.
How come we haven't seen fish die-offs yet?
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"Probably because it's relatively new to the lake ... and then again, you may never see windrows of fish dead on the shores of Lake Superior because of VHS. This virus is behaving a little differently in each lake and in each species and, again, I'm no expert on Lake Superior, but it may be that the species makeup and ecology of Lake Superior won't be conducive to large die-offs like we had in 2005 and 2006 in Ontario and Erie. ... We also think that [the virus] has more impact when other stressors are happening, such as rapid changes in water temperature."
How long has VHS probably been in Lake Superior?
"Probably not very long, maybe a couple of years. ... If the virus had been in the Great Lakes for some time we would have seen more [mutations] by now, and the strains we're finding are nearly identical. It might have made a move into the lakes at one point in the past that didn't take ... but this latest round hasn't been going on very long. And with the fish kills like we saw in 2005 and 2006, if those had happened before, someone would have noticed and tested. The [testing procedures] haven't changed that much in 20 years."
Will cold water stop VHS?
"No, actually warm water does. We saw in Bud Lake in Michigan where we had a VHS outbreak and a fish kill and then, the next year, we found no VHS presence at all. ... We now think it's because the water got very warm and the virus can't tolerate temperatures above [73 degrees Fahrenheit]. So warmer lakes might have more protection. This [VHS] is actually a fairly cold-water [virus] species'' that favors temperatures from the upper 30s to the 50s Fahrenheit.
So climate change will be good to stop VHS?
"Yes, the fish will be frustrated [because they can't reproduce in warmer water] but they won't be sick.''
Do fish build up immunity to VHS?
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"Yes, and that may be why we haven't seen another major round of die-offs. The fish that made it through have some immunity now, for at least some period of time, maybe several years. ... The young fish that weren't there for the first round are the most susceptible now. ... The immunity isn't passed down'' but must be developed by exposure.
Can we stop VHS from spreading to other lakes?
"Possibly. There are so many vectors for movement. ... But the things people already are doing to kill other invasive species like zebra mussels, like disinfecting and drying their boats, also work to kill VHS. ... It hates chlorine and doesn't stand up well to dryness or hot water. ... One thing I would look at is stopping the sale of wild-caught bait [from lakes and ponds]. The states need to move to certified, VHS-free bait from rearing facilities that can be monitored and controlled. ... We really can't be scooping up emerald shiners [from a lake] that are then moved around to hundreds or thousands of lakes and expect to contain VHS."
