Hitching a Ride into Wisconsin’s Inland Waters: Scientists Often Surprised By the Paths Invasive Aquatic Species Take
By Lee Bergquist, Milwaukee Journal Sentinel
Jun. 17–When a deadly fish virus popped up in a pair of lakes last month, it became the latest in a growing tide of Great Lakes invasive species to litter Wisconsin’s inland waters.
The invaders are blamed for threatening resources valued at billions of dollars because of their potential to clog water with non-native vegetation and deplete local fish populations.
Many inland waterways remain unscathed, but officials worry that the actions of a single careless boater could suddenly introduce a new invasive species anywhere in the state.
Scientists and state officials are attacking the problem with research and relatively small sums of money. But often little is known about where the next invasive species will show up and what it might be.
The aquatic invasive thing, for me, is my biggest professional source of frustration,” said Mike Staggs, director of the state Department of Natural Resources’ Fisheries Management and Habitat Protection Bureau and overseer of Wisconsin’s $2.3 billion fishery.
“There isn’t any question that we have lower fish populations because of invasive species.”
The latest threat is viral hemorrhagic septicemia. Officials had expected it to show up in Lake Michigan or Lake Superior this spring after the virus had killed fish in Lake Huron.
The Great Lakes are responsible for the vast majority of invasive species that move into the state’s inland lakes.
And yet officials were surprised when the first reports of the virus came on May 11 from Lake Winnebago and Little Lake Butte des Morts — and not from the Great Lakes.
Almost two weeks later, it was discovered in a smallmouth bass in Sturgeon Bay in Door County and a brown trout in Lake Michigan near Algoma in Kewaunee County.
The virus is “an extremely serious pathogen” that was first known to kill large numbers of farmed rainbow trout in Europe in the 1930s, said the U.S. Animal and Plant Health Inspection Service.
In 2005, it was discovered in the eastern Great Lakes and St. Lawrence River and has been blamed for killing thousands of fish. No mass die-offs have been reported in Wisconsin, though Lake Erie had large numbers of dead fish.
The Wisconsin DNR is relying on its experience with other invasive species by clamping down on ways the virus could be spread.
The agency approved emergency regulations last month that prohibit anglers and boaters from moving live fish, including minnows, and water from the Lake Winnebago watershed, Lake Michigan, Lake Superior and the Mississippi River, as well as their tributaries up to the first dams impassable to fish. The virus can live in fish, water and even frozen bait.
The DNR’s Staggs says the virus has mutated over time so that it can infect more species of fish and has been found to live increasingly in warmer temperatures.
The virus has the fishing and conservation world abuzz, but it doesn’t appear to have cast a pall over fishing the way chronic wasting disease hurt deer hunting.
Brian Uttech, a fishing guide from Eagle River, is keeping his eye out for evidence of viral hemorrhagic septicemia, which can cause fish to bleed to death.
“The guys I have coffee with every morning, we shoot it around a little bit. But no one is getting crazy about it,” he said.
Sales of fishing licenses through the Memorial Day weekend were up over 2006, DNR figures show.
“The big difference (with the virus) is that it is not a human health risk,” said George Meyer, former secretary of the DNR and now executive director of the Wisconsin Wildlife Federation. Though there is no known human health risk from chronic wasting disease, scientists liken it to the deer version of mad cow disease and authorities advise the public not to consume infected venison.
High cost of treatment
Invasive species began increasing in the late 1970s, as roads improved and second-home ownership grew, enabling the public to unwittingly move invaders great distances, said the DNR’s Carroll Schaal.
The granddaddy of invasive species is the Eurasian water milfoil, which has bedeviled 475 Wisconsin lakes since it first crept into Waukesha County lakes in 1950s from Lake Michigan, the DNR said.
The weed can reduce fish populations and choke out native plants. On some lakes, it has forced property owners to spend thousands of dollars a year to remove it — often with mixed results.
DNR spending for combating aquatic invasive species has climbed from $500,000 in 2004 to $1.5 million in 2006 and is expected to stay at that level for the foreseeable future.
Property owners have ponied up an estimated $1 million a year for the chemical or mechanical removal of weeds in the past five years, the DNR said.
But more and more people are calling for bigger steps to be taken.
Todd Ambs, administrator of the DNR’s Division of Water, said federal legislation or international treaties are needed to prohibit the discharge of ballast water and the invasive species they carry from overseas ships.
For years, such efforts have been mired in politics, but Ambs sees what he describes as “traction” in Congress because of growing concerns about the health of the Great Lakes.
The number of Wisconsin lakes with zebra mussels — a hitchhiker from the Caspian Sea that’s devastated the Great Lakes — has more than doubled since 1999, the DNR said.
By the end of 2006, the DNR said, there were nearly 100 infested lakes. Zebra mussels consume vast quantities of plankton that otherwise are eaten by forage fish, which in turn are eaten by larger fish.
Zebra mussels have been most prevalent in lakes in southeastern Wisconsin, underscoring the link to Lake Michigan.
Other invaders
New invaders are threatening inland waterways as well, often in relative obscurity.
Jake Vander Zanden, an assistant professor for the Center of Limnology at UW-Madison, and a team of researchers last year canvassed about 20 lakes in Vilas County in northern Wisconsin for the Chinese mystery snail. They found about half with populations of the nearly golf ball-sized snail.
A native of Asia that probably is released from aquariums, the snail is already present in the Great Lakes and could carry disease.
In October 2003, the spiny water flea, a zooplankton that lives in the Great Lakes and is a native of northern Europe, was discovered in the Gile Flowage in Iron County.
Nearly 200 lakes have since been tested and no more have been found.
But Vander Zanden said the Gile is perfectly situated between Lake Superior and the bounty of lakes in Vilas County to spread the invader.
“They are incredibly voracious — they are predatory for other native zooplankton,” he said.
And the round goby is now moving up tributaries of Lake Superior and Lake Michigan, including the Milwaukee River.
An aggressive, bottom-dwelling fish and voracious feeder, it is known to push less aggressive fish away from prime spawning areas.
Scientists are trying to identify which lakes and rivers might be most vulnerable to invasive species.
They are learning zebra mussels might not be able to live in northern Wisconsin lakes because they need high levels of calcium to build their shells. Lakes in the north are low in calcium.
Another invasive species is the rusty crayfish, a native of the Ohio River. UW-Madison researchers have been able to substantially reduce its population on Sparkling Lake in Vilas County by trapping them — 80,000 in five years — and by the DNR lowering bag limits of bass, which eat the crayfish.
But with no controls on adjacent Trout Lake, the crustaceans have wiped out weed beds and the population of native invertebrates, snails, pumpkinseeds and bluegills.
“It was a major ecological change,” said Vander Zanden. “What it is doing is altering the lake in a major way.”
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