During the past several weeks, news stories have appeared from Minnesota to Michigan about the recent discovery of a feared fish killing virus in Lake Superior. Given the large amount of publicity in recent years, most anglers have heard the term VHS, whose more difficult full name is viral hemorrhagic septi- cemia. That’s the virus that’s just been found for the first time in Lake Superior.

VHS is a disease that causes fish to hemor- rhage, or bleed to death. It is believed to have arrived, like so many other exotic diseases and noxious water plants, in the ballast water of ships arriving in the Great Lakes from Europe. It was discovered in the Detroit area in 2002 and there have been large fish kills in Lake Huron, Lake Erie and Lake Ontario. VHS has also been found in Lake Michigan.

VHS is so feared not because it is harmful to humans, but because it is indiscriminate in the fish species it kills. Previous fish kills have included walleye, bass, muskies, northern pike, crappies, bluegill and perch; pretty much the gamut of fish that Minnesota anglers and tourism visitors seek. It should be noted that the fish recently found infected in the Duluth-Superior Harbor, from Superior and St. Louis Bays in Minnesota and Wisconsin and in Michigan waters of Lake Superior, were all alive when tested.

The disease spreads both by natural and humanaided means. The natural migration of fish throughout the Great Lakes system has led fisheries biologists to believe that it was just a matter of time before VHS would make its way throughout the entire chain of Great Lakes.

The release of water from fishing boat live wells, bilge water from larger pleasure and fishing craft and release of the previously mentioned ballast water from merchant ships, are the most obvious human vectors. Fishing rigs whose exterior surfaces have not been thoroughly cleaned or washed down – and ideally dried for at least 12 hours – can also spread the disease from one body of water to another. This is just like other exotic species, such as zebra mussels and Eurasian water milfoil, now in numerous Minnesota waters.

To avoid the potential for spreading VHS to inland waters, the Minnesota DNR three years ago stopped using walleye eggs from the St. Louis River, which drains into Lake Superior, long before the discovery of VHS in the big lake. The fish hatchery at the French River, which also drains into Lake Superior, is no longer used as a temporary stopover for trout raised in southern Minnesota hatcheries and bound for inland lake stocking.

It has been speculated that the effects of VHS in Lake Superior could be different from those in the eastern Great Lakes and that the large die-offs in Lakes Huron, Erie and Ontario might not occur here. Lake Superior is the deepest and coldest of the Great Lakes and it’s possible that the danger will be mitigated by its size, temperature and perhaps less stress on its fish from environmental or seasonal climatic variations.

But what about the spread to Minnesota’s inland lakes? Several inland lakes in Wisconsin and Michigan harbor VHS and have had fish kills, so it’s clear that the virus is adaptable to just about any aquatic environment. Here is perhaps where the greatest danger to Minnesota fish and fishing lies, in a transfer of the disease from Lake Superior to inland lakes.

If for no other reason than limited space, an inland lake environment makes exposure of its fish populations to the virus more likely. Stress factors like temperature extremes, or oxygen depletion, are also more likely in inland lakes, particularly shallower lakes. If the usual principles of disease and mortality hold true, stressed fish will be more likely to

succumb to a disease like VHS.

The rules that states like Minnesota and Wisconsin have in place are sound. They include boat and trailer cleaning, prohibiting transport of live fish or use of baitfish from infected waters in other bodies of water and encouraging cleaning, draining and drying of fishing boat live wells and bilges. But these are only as effective as angler compliance and commitment.

In fish hatcheries, where potential for spreading VHS also exists, fisheries managers are adopting preventive practices like disinfecting holding tanks and hardware and treating eggs with anti-viral agents or virus-killing ultraviolet light. Where there is even a minimal chance of spreading VHS to un-infected waters, biologists should consider “wasting” hatchery fish rather than risking the spread of VHS.

The optimistic view, one taken by some in fisheries management, is that fish species eventually develop resistance or im- munity to diseases. Worstcase predictions may not come true; or, fish species will recover, with an ability to cope with the threat. That’s everyone’s hope. But no one wants to travel that path to learn just how well, or how soon, Minnesota’s fish populations can adapt or recover from a disease this deadly. Prevention is far more palatable medicine than cure.