lake trout

R/V Laurentian NOAA / Creative Commons

You’ve probably heard about the big bad invasive silver or bighead carp, also known as Asian carp.

But there’s another invasive fish that’s roughly a third the size of the carp that’s already done a lot of damage to Great Lakes fisheries. Alewives have been a particular menace in Lakes Michigan and Huron. The invasive fish cause all kinds of problems for native lake trout.

Alewives scarf down lake trout eggs and very young fish. But even once lake trout grow big enough to turn the tables and eat the alewives, the invasive fish still cause problems.

NOAA

A fish that was almost wiped out in the Great Lakes is making a comeback in Lake Huron.

Lake trout are suddenly doing what biologists have been trying to get them to do for more than 40 years: They’re making babies.

Lake trout used to be a mainstay of Great Lakes commercial fishing in the first half of the twentieth century. The Lakes would produce 15 million pounds of the fish every year.

Then the sea lamprey came in and sucked the life out of the lake trout populations.

A surprising comeback for Lake Huron's native fish

Apr 11, 2013
Photo courtesy of Michigan Sea Grant

For years now, we’ve heard bad news about the Great Lakes. Most of it has to do with invasive species getting into the lakes and wrecking the food web.

One writer called it a slow-moving underwater wildfire.

So it might surprise you to hear that native fish are doing very well in one of the lakes. The changes are so dramatic scientists are a bit puzzled and can’t explain what’s happening.

Lester Graham / Michigan Radio

To understand why salmon are so important to the Great Lakes and the Michigan economy, you first have to understand some history.

It used to be the lake trout was the fish to catch.  It was big.  It was tasty.  But, by the late 1950s, that fish and others had been severely over-fished.  And, an eel-like, blood-sucking parasite called the sea lamprey further reduced lake trout numbers.

Those weren’t even the worst problems for lake trout.  A fish called the alewife invaded the Great Lakes through manmade canals.  Lake trout starting feeding on alewives.  But  alewives caused a thiamine deficiency in lake trout.  A lack of vitamin B-1.

Mark Gaden is with the Great Lakes Fishery Commission

“The thiamine deficiency that the alewives cause is one of the top reasons why natural reproduction has been very slow to occur over the decades in the Great Lakes of these species.”

Catching a lake trout became rare.

Photo courtesy of Michigan Sea Grant

For twenty years now the federal government has been trying to restore wild lake trout in Lake Michigan. Lake trout are native to the Great Lakes and were once the big game fish in all the lakes. The species is doing well in Lakes Superior and Huron these days. But recovery efforts in Lake Michigan have been almost a total failure.

Lake trout don’t have a big fan club. Anglers would prefer to land a salmon. And retail markets for lake trout are weak.

Photo courtesy of Michigan Sea Grant

New research finds that fish in the Great Lakes are contaminated with a chemical used in aircraft hydraulic fluids.

Researcher Amila DeSilva works for Environment Canada, which is like the EPA in the U.S.

She says there have been studies on a number of perflourinated chemicals. They’re used to make textiles, upholstery, paper, and many other things. Studies have shown these types of chemicals can have toxic effects in humans. But not much is known about a chemical called perfluoroethylcyclohexanesulfonate - or PFECHS for short.

DeSilva says no one has really studied whether it's toxic.

She wanted to see if PFECHS was in the environment, so she and her colleagues sampled water and fish in the Great Lakes, specifically lake trout and walleye:

“We were really, really surprised to find it in fish. Because, just based on the structure and our chemical intuition we thought, ‘okay, it would be more likely to be in water than in fish’ so when we found it in fish, when you find anything in fish, it’s a whole other ballgame because humans consume fish.”

DeSilva says other perflourinated acids are endocrine disruptors. That means they create hormone imbalances in humans, and they have other toxic effects. She says once these chemicals are released into the environment they don’t degrade, they just build up. That’s why use of some chemicals in this class is highly restricted in the U.S. and Canada.