Great Lakes fish in the balance; biologists have little control

By Jeff Gillies, jeffgillies@gmail.com
Great Lakes Echo
Sept. 4, 2009

Editors note: This is the final story in a three-part series about the challenges of managing non-native fish in the Great Lakes.

Managing invasive alewives in the Great Lakes is like walking a tightrope.

Too many stymie native lake trout reproduction. Too few cripple the profitable salmon fishery.

And some biologists say it is an impossible task.

“You can’t manage on that fine of a line,” said Mark Ebener, fish assessment biologist with the Chippewa Ottawa Resource Authority. “It’s an impossible tightrope to walk.”

But the state agencies that manage Lake Michigan are giving it a shot.

“In Lake Michigan we are definitely trying to strike this balance,” said Jim Dexter, Lake Michigan basin coordinator for the Michigan Department of Natural Resources.

The managers have recently stocked fewer salmon to ease the pressure on alewives. At the same time, they aim to boost lake trout stocks in shallow, rocky sections in the middle of Lake Michigan. Lake trout laid eggs on those mid-lake reefs before the species collapsed in the 1940s and 1950s.

It’s too soon to tell if the plan will work, but early signs are positive, Dexter said. Anglers are catching salmon, and lake trout aren’t so plagued by alewife-driven ailments.

One of those ailments is a vitamin deficiency. Lake trout that eat too many alewives have babies that die early. Lake trout vitamin levels are up in Lake Michigan because they’re eating another invasive fish — the round goby, Dexter said.

Even if managers strike a middle ground between salmon and lake trout, they can’t take much credit for the success, he said. The Lake Michigan ecosystem is too big for people to make large-scale changes.

“Mother Nature really holds all the keys,” he said. “We just try to work with it as best we can and try to just nudge things as we can.”

The best evidence for their lack of control is in Lake Huron over the past five years. The alewife population collapsed there in 2004, and the salmon fishery went with it.

“It wasn’t like management planned that,” said Charles Madenjian, a fish biologist with the U.S. Geological Survey’s Great Lakes Science Center. “It just happened.”

Now native fish like lake trout and walleye thrive in Lake Huron. Alewife critics like Ebener say that’s because the invader’s die-off cleared the way.

“It’s no accident in Lake Huron that when alewife collapsed, lots of good things happened with reproduction of native fishes,” Ebener said.

If clever fish management didn’t kill the alewives in Lake Huron, what did?

Biologists have a few suspects. Two are zebra and quagga mussels, Eurasian species that snuck into the Great Lakes inside of ocean-going ships.

The mussels sit on the lake bottom and suck tiny plants and animals out of the water. The nutrients in those plants and animals used to make their way up the food chain to alewives. But mussel colonies locked them up at the bottom of the lake, and the alewives went hungry.

Those that didn’t starve were eaten up by a massive influx of naturally born salmon. Lake Huron managers plant annually around 3 million hatchery-raised salmon. The year before alewives collapsed, another 12 to 13 million wild-born salmon inundated Lake Huron from tributary streams and rivers, Madenjian said.

“That’s probably more salmon than the lake had ever experienced in the past,” he said. “And it looks like they were able to do a real big cleanup job of the alewives.”

If Lake Michigan managers wanted to give native species a boost, they could engineer an alewife collapse by ramping up salmon stocking, he said. That could polish off the alewives and leave the salmon to find something else to eat or die off.

While that could be a boon to the lake trout population, it could be a bust for state fishing revenues.

The salmon collapse in Lake Huron has cost the lake half of its charter fishing industry, said Dan Thomas, president of the Great Lakes Sport Fishing Council.

“Licenses are in decline for fishing in Lake Huron,” he said. “If you don’t have a fishery, you don’t sell fishing licenses.”

So Lake Michigan managers will continue trying to walk the line between too many and too few alewives, Dexter said. But while that plan may be working now, there’s no guarantee for the future.

“When you’re on a tightrope you can fall off either side really quick,” he said.