Ten Threats: The Beloved Invader

  • Because alewives are the main source of food for some sport fish, some people forget that they're an invasive species. (Photo courtesy of NOAA Fishery Service)

As we look at the “Ten Threats to the Great Lakes,” we’re spending some time examining the effects of the alien invasive species that have changed the Lakes. One of the first invasive species to arrive in the Great Lakes was the alewife; it’s native to the Atlantic Ocean. It has become the most beloved of all the invasives. That’s because it’s food for the most popular sport fish in the Great Lakes. But in the beginning, the sport fish was introduced to get rid of the alewives. Peter Payette reports:

Transcript

Today we’re continuing our series on Ten Threats to the Great Lakes. The Great Lakes Radio Consortium’s Lester Graham is our series guide:


As we look at the “Ten Threats to the Great Lakes,” we’re spending some time examining the effects of the alien invasive species that have changed the Lakes. One of the first invasive species to arrive in the Great Lakes was the alewife; it’s native to the Atlantic Ocean. It has become the most beloved of all the invasives. That’s because it’s food for the most popular sport fish in the Great Lakes. But in the beginning, the sport fish was introduced to get rid of the alewives. Peter Payette reports:


When autumn arrives in Northern Michigan, salmon fishermen line the rivers. The fish, native to the Pacific Ocean, swim upstream to spawn and then die. That’s why Tim Gloshen says they’re not interested in his bait.


“But if you irritate ’em enough and keep putting it in front of them, they’ll snap at it sometimes and you got to be ready when they hit it and set your hook.”


Anglers caught eight million pounds of salmon in Lake Michigan last year. Most of the fish are caught out in the lake.


“I got buddies that are catching couple hundred a year out there. They’re out there twice a week at least, all summer long, you know.”


Tim and his buddies and everyone else who fishes for salmon in the Great Lakes are at the top of the food chain. The money they spend on food, lodging, tackle, and boats figures heavily into decisions about how to manage the Lakes.


But it wasn’t always so.


Pacific salmon were stocked here about forty years ago to control the invading alewives. The native lake trout had just about been wiped out by overfishing and the sea lamprey. With no big predators left, the alewife population exploded.


At one point, it was estimated that for every ten pounds of fish in Lake Michigan, eight were alewives. Occasional die-offs would cause large numbers of alewives to wash up on beaches all over the Great Lakes. Historian Michael Chiarappa says all this was happening as America was feeling the urge to get back in touch with nature.


“And that’s when you get this rise in greater interest in sport fishing, recreational fishing, hunting. Teddy Roosevelt sort of epitomized the spirit of the strenuous life; get back out there and engage nature. It’s good for the soul, it’s good for the body, it’s good for the mind.”


So the salmon was brought in to control the alewife population and transform the Great Lakes into a sport fishing paradise. And it worked. But alewives remained the best food source for the ravenous salmon.


So now a healthy alewife population is seen as a good thing by the states that benefit economically from the recreational fishing. Mark Holey, with the U.S. Fish and Wildlife Service says this has caused people to forget alewives are an invasive species.


“If alewives were knocking on the door today, there may be a much different discussion about it. It may be more like the Asian carp.”


How the alewife would compare to Asian carp is unknown, because the Asian carp has been found in the Mississippi River, but not yet in the Great Lakes. What is known is that when alewives are abundant, native fish don’t do well. For example, Holey says biologists used to think PCBs caused many young lake trout to die. Now they know early mortality is mostly due to thiamin deficiency.
Thiamine is a vitamin lacking in lake trout that eat too many alewives.


“From the studies that we’ve been involved with, anywhere, right now, anywhere between thirty to fifty percent of the females that we take eggs from show some… their eggs show some signs of thiamine deficiency. Which means survival of those eggs are impaired.”


In some cases, none of the eggs will survive. So a worse case estimate would be half of the wild lake trout in the Great Lakes can’t reproduce because of alewives. This is why advocates for native fish species have been happy to see the alewife populations decline in recent years. They almost disappeared from Lake Huron.


Mark Ebener is a fisheries biologist for the Chippewa Ottawa Resource Authority. He says the government agencies that stock salmon and lake trout should stock more than ever to keep pressure on the alewife. Ebener thinks with alewife numbers down, there’s an opportunity to reestablish the native herring as the main prey fish in the Lakes, especially in Lake Huron.


“Saginaw Bay used to have a huge population of lake herring that’s essentially gone. They used to have a tremendous commercial fishery for it, and people used to come from miles around to buy herring there, and everybody in the lower end of the state used to have herring come fall and the springtime when the fishers were fishing, but they’re gone.”


This opportunity to bring herring back might not last much longer. The warm weather this past summer will probably help alewives rebound next year.


For the GLRC, I’m Peter Payette.

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Commercial Fishers Angling for Trout Fishing Rights

  • Steve Dahl is one of about 25 commercial fishers on the North Shore of Lake Superior. Dahl makes a modest living selling herring, but he'd like to be able to fish for lake trout too. When he's fishing for herring, Dahl pulls his gill net up and passes it across his boat, plucking herring from the mesh. (Photo by Stephanie Hemphill)

Some fish populations in the Great Lakes have recovered dramatically from the devastating pollution of the last century. But the very health of the fishery presents a new set of challenges for people. Who gets to catch the fish? Most states favor sport anglers, but some commercial fishing operations are asking for a bigger share. The Great Lakes Radio Consortium’s Stephanie Hemphill reports:

Transcript

Some fish populations in the Great Lakes have recovered dramatically from the
devastating pollution of the last century. But the very health of the fishery presents a
new set of challenges for people. Who gets to catch the fish? Most states favor sport
anglers, but some commercial fishing operations are asking for a bigger share. The Great
Lakes Radio Consortium’s Stephanie Hemphill reports:


(sound: engine zooms, slows)


Steve Dahl guides his aluminum boat to his gill net, anchored below the waves of Lake
Superior. He fishes out of Knife River, a small town just up the shore from Duluth
Minnesota. A few feet at a time, the net offers up its catch – slender silver herring
caught by the gills.


“The mesh actually has a little bit of flex to it. That’s why I can squeeze them out. One
that’s too big or fat, you have to back it out, so you don’t harm the flesh.”


The openings in the net are just right to catch herring. Too small for lake trout. Dahl
isn’t allowed to catch lake trout anyway. He says they mostly just bounce off the net.


When the net is empty, about 40 herring – each of them about a pound – are lying in a tub
at the bottom of the boat.


Dahl is working hard for these fish. It’s pretty cold, and the wind is gusting.


(ambient sound)


Dahl says sometimes the current is so strong, he can’t pull the net up out of the water.
Sometimes there are no fish in the net. In the
summer, they move around and they’re hard to find. And of course, he can’t fish when
the lake is frozen.


But he loves this life.


“I get to be outside all the time, my own boss. It’s great fun.”


Steve Dahl sells his catch to the restaurants and fish houses that dot the North Shore of
Lake Superior. He makes his living this way. He says he doesn’t make a lot of money,
but it’s a good life.


Dahl says the money would be better if he were allowed to fish for lake trout. He figures
he’d be able to make several thousand dollars more a year if he could catch even just a
few hundred lake trout.


“That’s all we’re asking for is to be able to supply the local restaurants through the peak
tourist season.”


Lake trout were almost wiped out by over-fishing and by the parasitic sea lamprey in the
1960’s and 70’s. The lamprey are under control now, and decades of stocking lake trout
have brought the population back up. People who fish for sport have been catching more
and more lake trout. Last year, they caught about 15,000 of the fish on the Minnesota
side of Lake Superior. But so far the state of Minnesota won’t allow commercial fishers
to go after them. Neither will Michigan, although Wisconsin and Ontario do.


Don Schreiner manages the Lake Superior fishery for Minnesota. He says restoring the
lake trout population is taking a long time. That’s why they don’t want to open it up to
commercial fishing just yet.


“Right now we’re pretty cautious, we’ve just started kinda pulling back on stocking and it
seems a little premature to start thinking about opening the door for commercial
fisheries.”


Next year, Minnesota plans to create a new ten-year plan for the fish in its Lake Superior
waters. Don Schreiner says during the planning process, everyone will be able to have
their say. But sport anglers far outnumber the two dozen or so commercial fishermen on
the North Shore. So they’ll need to find allies in their claim on the lake trout.


Paul Bergman is likely to speak up in favor of commercial fishing for lake trout. He
owns the Vanilla Bean Bakery & Café in Two Harbors, Minnesota. He buys herring from
Steve Dahl. He says half his customers order fish, and they love it when it’s locally
caught.


“People really do come up here for the native fish on the North Shore, so we’re getting so
many more repeat customers now from the cities. More and more are asking for the fish.”


Bergman puts a sign in the window when he has fresh herring, and he says it pulls people
in. He’d like to be able to do the same with lake trout.


For the Great Lakes Radio Consortium, I’m Stephanie Hemphill.

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Tracking Long-Term Zebra Mussel Changes

Zebra mussels have been colonizing North American lakes and rivers since 1991. Scientists have looked at many of the ways mussels affect those ecosystems. But a new study underway shows how those effects are moving up the food web…and are having two very different results. The Great Lakes Radio Consortium’s Mark Brodie reports:

Transcript

Zebra mussels have been colonizing North American lakes and rivers since 1991. Scientists have looked at many of the ways mussels affect those ecosystems. But a new study underway shows how those effects are moving up the food web…and are having two very different results. The Great Lakes Radio Consortium’s Mark Brodie reports:


Between 50 and 5-hundred billion zebra mussels now live in New York’s Hudson River. That’s a lot of hungry mouths to feed on the river’s zooplankton and phytoplankton. The problem is the mussels are not the only ones that like to dine on the microscopic plants and animals. A new report suggests the mussels are stealing food from some of the river’s fish.


That’s forcing those fish to look elsewhere for their meals. Sandra Nierzwicki-Bauer is the director of the Darrin Freshwater Institute, and a biology professor at Rensselaer Polytechnic Institute in Troy, New York. She says the zebra mussels can dramatically alter an ecosystem.


“They’re very rapid filter feeders, and as such, they’re able to remove tremendous amounts of phytoplankton, algae, bacteria in the water column. As such, the phytoplankton serves as food sources for other organisms so you really are impacting the entire food web.”


Nierzwicki-Bauer says those impacts go all the way up to fish. David Strayer is a freshwater ecologist at the Institute of Ecosystem Studies, and a lead author of the report on the Hudson River. He says his team studied fish populations in the Hudson both before and since zebra mussels colonized there.


“In open water fish species, we saw a decline in abundance, we saw declines in growth rates, and we saw that the populations of those fish tended to shift downriver compared to the period before the zebra mussel invasion.”


That means some of the most common and popular fish in the Hudson are no longer where they used to be…among them American shad, herring, and white perch. That’s because the zebra mussels are eating those fish’s food…forcing the fish to go elsewhere.


But Strayer says while some fish have had to move away from the mussels…some species have welcomed their new neighbors.


“In the same period of time, we saw populations of fish that live in the weed beds…we saw those populations increase, we saw growth rates of those fish increase, and we saw the populations of those weed bed fish shift upriver into the area where the zebra mussels lived.”


These forage fish have more to eat because the plants at the river’s bottom are growing more. That’s because the zebra mussels clear up the water, which allows more sunlight to reach the plants. Strayer says the zebra mussels have changed almost everything about the Hudson’s ecology.


But he says some of those changes have been difficult to predict, and the changes may not apply to all bodies of water where the mussels have colonized. This is one of the first studies using long term data that looks at the zebra mussels’ affect on fish populations…but there is some evidence that other bodies of water are dealing with similar situations. There have been reports that zebra mussels may be affecting smelt and chub in Lake Michigan…these smaller fish are food for larger species, such as trout and salmon. But while the results are comparable, David Strayer says the changes in the Hudson River are more pronounced than changes elsewhere.


“This isn’t because we have more zebra mussels in the Hudson than in the other places, but it’s because there are differences in the structure of the ecosystem between the Hudson River and the Great Lakes and other places that have been invaded. So, you have to be a little cautious extrapolating from one body of water to the next.”


That sentiment is shared by Andy Kahnly. He’s a fishery scientist with the Hudson River fishery unit of the New York State Department of Environmental Conservation. He also worked on the new study. Kahnly warns for now, the results only apply to young fish…and not adults. That’s because fish can live up to 30 years, and the data don’t go that far back.


“Quite often, changes in early lifestages will take some time to translate into changes in fish populations and then to changes in fish communities. So it takes a lot of data, a lot of years of data to see a change.”


Kahnly says that means anglers in the Hudson might begin to notice some changes over the next few years… and he says the study did find a dramatic decrease in many of the species that people catch.


“If these changes in production of young persist into the future, then definitely there will be a decrease in the abundance of the adults which people are fishing for.”


But that depends on what you’re fishing for. The Institute of Ecosystem Studies’ David Strayer says your perspective might change depending on that you’re trying to catch.


“If you’re concerned about shad populations, if you’re a shad fisherman, then you might be concerned with the zebra mussel invasion and think it’s a bad thing. If you like the weed beds, if you’re a duck hunter or a large mouth bass fisherman this might be regarded as a positive thing.”


Strayer says the study shows zebra mussels are capable of having a tremendous impact on an ecosystem. He says it also shows the importance of being careful to prevent the introduction of invasive species…like zebra mussels…into an ecosystem.


For the Great Lakes Radio Consortium, I’m Mark Brodie.

New Invasive Species Found

A new exotic species is invading the Great Lakes. The Great Lakes Radio Consortium’s Lester Graham reports that this new invader has been causing problems for anglers: