Another sign of zebra mussels' proliferation - TwinCities.com

Not long ago, a dive buddy phoned Rich Rezanka with troubling news.

He had been scuba diving in Lake Ore-Be-Gone on the Iron Range and spotted what he thought might be zebra mussels.

Any sighting of the invasive mussel is troubling, but this one even more so. Zebes, as we're now calling them, hadn't been spotted inland this far north, and Lake Ore-Be-Gone, formally known as the Gilbert Pit, is a former mine pit with clear, alkaline water -- not the type of water generally hospitable to zebes. And it's not connected to any other infested water.

Rezanka, an invasive species specialist with the Minnesota Department of Natural Resources, and another DNR diver checked out the lake last month.

"We were underwater for 20 minutes before we found anything, but sure enough, there they were," Rezanka said. "It wasn't like they were carpeting the bottom, but they were there."

And so on Aug. 28, the "Gilbert Pit (Lake Ore-Be-Gone)" was added to the list of waters infested with one of the most feared invaders. Zebra mussels can proliferate rapidly, crowding out native mussels and filtering so much plankton that they fundamentally alter the chemistry of a lake and threaten to upset the entire food chain.

One more thing: The lake has no cabins. No boat lifts, no private docks. If zebra mussels were there, it wasn't a case of a lakefront property owner transporting a boat lift without cleaning and drying it first, a scenario that was traced to two infestations last

year.

No, this would have to be the scenario all boaters and recreational day users fear: One of the masses unwittingly brought the invaders. Perhaps someone failed to heed state laws requiring a boat's live well to be drained after boating in Lake Superior or some other infested water. Perhaps even a diver didn't properly dry his wet suit and offered a mussel larva a ride, a scenario I had not considered but one that Rezanka said is possible.

Bottom line: In the parlance of aquatic invasive species biologists, the infestation of Lake Ore-Be-Gone was "overland transport."

It's unclear how often this happens, but the DNR is trying to figure that out.

"One of the things we want to see is, 'Are we having an impact with our awareness campaigns and enforcement and new laws?' " said Ann Pierce, the DNR's acting invasive species program supervisor. "We're looking through our data now, looking for those infestations that are clearly the result of overland transport, because those are the ones we're really trying to reduce, ideally, to zero."

The official list of infested waters on the DNR's website fills more than three pages. But many of those waters are connected; some are nothing more than a widening of a river that carries a separate name on a map. In reality, the number of distinct waters is closer to two dozen.

Often, when a "new" infestation is declared, it's merely confirmation of the zebes spreading throughout a watershed, something that probably was bound to happen naturally.

In 2010 and 2011, there were about eight new infestations. How many were overland transport?

"Probably three each year," Pierce said, cautioning that her analysis of those two years isn't final. The plan is to examine data since the state first started collecting it in 1989 with the infestation of Lake Superior.

"The hope is that the number of infestations from overland transport is reduced every year," Pierce said. "If you really want to show this as a trend, you need to be analyzing as many years as you can."

Still, she acknowledges, these are small numbers, and calling anything a trend with such a small sample is tricky.

The only other measuring stick the DNR has now is compliance with laws, as sampled by roadside checks and boat launch inspections. This appears to be improving; this year's boating season started with about a 20 percent violation rate, and officials now report closer to 16 percent.

But we don't know whether an increase in compliance --or all the tickets boaters are being issued -- is having a difference in the rate we're spreading zebes.

One last thing: The zebes Rezanka found -- all of which were near a boat launch on Lake Ore-Be-Gone -- were all from the same year class, and old, in zebe-years at least.

"We didn't extensively survey the whole pit, but we didn't see any 1- to 2-year-olds or young of the year," he said. "Based on their size, they've been there for several years."

That complicates data for Pierce. The lake will be declared infested in 2012, but the infestation probably took place several years earlier.

The good news is that it's possible that the lake's alkalinity won't support zebra mussels or that there simply aren't enough of them for a breeding population. In either case, zebes could soon be gone from Lake Ore-Be-Gone.

The bad news is this means zebes were in the Gilbert area for years before anyone noticed or checked their equipment with extra care. Which means they could be in other lakes.

"I'm sure they are," Rezanka said.

Dave Orrick can be reached at 651-228-5512. Follow him at twitter.com/OutdoorsNow.

Source: http://www.twincities.com/sports/ci_21493625/another-sign-zebra-mussels-proliferation?source=rss

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