Tag: round goby

Bird and Fish Poisoning Spreads in Great Lakes

  • Botulism is killing fish and the shorebirds that eat them. The cause is likely due to a disruption in the ecosystem by invasive zebra and quagga mussels. (Photo by Lester Graham)

A deadly toxin is killing fish and birds along the Great Lakes shoreline.
Researchers think type-E botulism works its way up the food chain from
the bottom of the lake through several invasive species. Bob Allen
reports:

Transcript

A deadly toxin is killing fish and birds along the Great Lakes shoreline.
Researchers think type-E botulism works its way up the food chain from
the bottom of the lake through several invasive species. Bob Allen
reports:


These days, Ken Hyde dreads walking the pristine sandy beaches along
the Sleeping Bear Dunes. He’s the biologist in this national lakeshore
along the Michigan coast, and he only has to hike maybe a hundred feet
to find a dead bird twisted head down and half-buried in the sand:


“This is a cormorant. Just in the last two or three weeks we’re
starting to see a lot more of them. So they’re probably starting to
migrate down from the upper parts of the lake.”



Last year botulism killed over 2,500 dead birds along this 35 mile stretch
of shoreline, mostly gulls and diving ducks, including nearly 200 loons
migrating south from Canada.


This year the die-offs started earlier in the summer and struck more
species. The park lost four endangered piping plovers. The National Park
Service brought in a research team from Minnesota to look for answers.
They’ve been diving in the lakeshore now for two years.


What they’ve found is a huge shoal stretching more than a mile off shore.
It’s covered with native green algae and loaded with invasive zebra and
quagga mussels:


The Park’s research boat docks at a small village along Lake Michigan.
Dive team leader Brenda Moraska Lafrancois was surprised when she
first saw the underwater landscape:


“Last year when we first dove this area we went down and it was
shocking how little of the biomass down there was native. I think
we’re looking at a really altered system.”


Here’s what researchers know so far. The mussels filter nutrients from
the water, the clearer water allows more sunlight to reach the bottom, and
that spurs more algae growth. For good measure, the mussels excrete
phosphorus, in effect fertilizing the algae in the near shore zone. When
millions of mussels and big globs of algae begin to decompose, that uses up
most of the oxygen in water near the bottom of the lake, and that’s a
condition just right for a naturally occurring botulism to grow.


So how does the botulism migrate from the bottom to the surface and
poison shorebirds? Enter the round goby. It’s a small invasive fish that
comes from the same Caspian Sea area where zebra mussels originated.


Last year the research team at Sleeping Bear saw gobies in some places.
Now, says Byron Carnes, everywhere they looked when diving on algae
beds there solid sheets of mussels and blankets of gobies, and he
watched them feeding on mussels:


“Part of the zebra quagga mussel that is the juiciest these guys tend
to go right in and do this frenzy feeding where they just come in and
start pounding away at all the broken shells and trying to get out as
much of the good stuff inside the quagga mussel as they possibly
can.”


Mussels don’t have a nervous system, so they aren’t harmed by botulism
toxin. But when gobies get a dose they flop around on the surface for a
day or so while succumbing, and that’s when shorebirds pick up an easy
but potentially deadly meal.


Some diving ducks may also get poisoned by feeding directly on the
mussels. That’s the theory most scientists in the field think explains
what’s happening, but Harvey Bootsma says it’s not active all the time, so
it’s hard to prove each step. He’s with the Great Lakes Water Institute in
Milwaukee:


“I think the problem is it’s usually a sporadic and short-lived event
when this occurs. And unless somebody happens to be fortuitously
collecting the right samples at the right place and the right time it”s
very difficult to pin down the process as it’s occurring.”



While researchers try to pin down the effects of invasive species in one
place, the cycle spins off somewhere else. This fall there are half as
many dead birds along the Sleeping Bear Dunes shore as last year, but
the die-off is now spreading farther north along the Lake Michigan coast,
and there have been similar outbreaks along Lakes Erie and Huron.


So far Harvey Bootsma says there are no good solutions to break the
cycle of algae, mussels and gobies that scientists think is transporting
botulism toxin to shorebirds.


“And it’s just a great example of how huge an impact a new species
can have on an ecosystem. And I think it makes it all the more
imperative that we try to stem the tide of exotic species coming into
the Great Lakes.”


Researchers say it may take decades for the Great Lakes to recover from
the effects, if they ever do.


For the Environment Report, I’m Bob Allen.

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Virus Killing Great Lakes Giants

  • Fishing guide Rich Clarke of Clayton, NY, is famous for muskie hunts. He's worried so many adult muskies are falling victim to VHS. (Photo courtesy of Rich Clarke)

Fall is when avid anglers flock to the Great Lakes for one of the most
challenging freshwater catches: the muskellunge, or muskie. Some call it
“the fish of 10,000 casts.” This year’s muskie season is clouded by bad news
of a new fish disease and invasive species crowding muskie habitat. David
Sommerstein reports scientists are watching this top-of-the-food-chain
species carefully:

Transcript

Fall is when avid anglers flock to the Great Lakes for one of the most
challenging freshwater catches: the muskellunge, or muskie. Some call it
“the fish of 10,000 casts.” This year’s muskie season is clouded by bad news
of a new fish disease and invasive species crowding muskie habitat. David
Sommerstein reports scientists are watching this top-of-the-food-chain
species carefully:




It’s a cool afternoon as fishing guide Rich Clarke fillets the day’s catch:


“Went out, caught some northerns, a few bass, some jack perch. Had a
pretty good morning.”


Clarke’s specialty is hunting for muskies, 60 pound fish with a lot of fight:


“I mean, the rod screams, they yank, yank, and yank. It doesn’t come all that
often, but when it comes, it’s one of the most exciting things you’ll see when
you fish in fresh water.”


Clarke worries that magical hit might become even more rare. Since 2005,
several hundred of those prized muskies were found belly-up dead, victims
of viral hemorrhagic septicimia, or VHS.


(Sound of hose)


Clarke washes down his fillet table. He mutters VHS is just another non-
native organism threatening the muskie. There are already more than 180
invasive species in the Great Lakes-St. Lawrence River system:


“Everything from the goby to the , y’know, and weed species and all
sorts of stuff, spiny water fleas, you name it, all sorts of stuff that are not native to this
waterway that we have to deal with, and it changes the whole ecology.”


A new invasive species is found every six to nine months. Scientists can
barely keep up in understanding the impact on the native environment.




In a nearby bay of the St. Lawrence River in northern New York State,
Roger Klindt, John Farrell, and a crew drag a huge net through the water:


“We’ve got two people pulling it slowly through the vegetation just trying
to basically corral fish.”


This is called seining, getting a sample of all the fish that live here. Klindt
and Farrell have been doing this in the same marshy shallows for more than
20 years. And Farrell says what they’ve found this year is disturbing:


“Muskellunge numbers in the index are at their lowest levels on record since
we’ve been collecting data.”


Down from almost 50 in the spring spawning run of 2003 to just 4 this year.
Farrell’s a researcher with the State University of New York Environmental
Science and Forestry. He says this could be the result of VHS killing so
many adult muskies in their reproductive prime.




Yet another invasive species is also troubling, the round goby. It’s an ugly
little fish from Eastern Europe that breeds like crazy. Farrell and Klindt
count minnows flipping and fluttering in the seining net:


“15 black gins, 8 blunt nose, 5 spot tail.”


“I didn’t actually count things, I was just picking gobies.”


Farrell says they’ve found more round gobies in these marshes than ever
before:


“Which is a bit of a surprise to us.”


Now the muskie young have to compete with round gobies for food:


“How these species are going to respond to the presence of gobies is
unknown at this time, but they have high predation rates, they’re very
prolific, becoming extremely abundant, so the food web in this system is
shifting.”


This is what frustrates people who study invasive species. Once researchers
train their focus on one, like the fish disease VHS, another emerges to
confound the equation. Roger Klindt is with New York’s Department of
Environmental Conservation:


“Change happens, y’know, nothing stays the same forever. But when we
have invasive species and exotic species come in, the change is often so
rapid that native species can’t adapt to it.”


That talk makes anglers nervous. Peter Emerson’s been fishing around here
for years. In fact, he participated in a catch and release program that brought
muskie populations back to health in the 1980s:


“There was a real bonanza, til this virus showed up. I’m hopeful they don’t
go extinct.”


Biologists expect adult muskies that survived VHS will develop resistance to
the disease. But they fear the next generation won’t inherit the immunity,
causing more die-offs of one of America’s most prized freshwater fish.


For The Environment Report, I’m David Sommerstein.

Related Links

Ten Threats: Natives Bite Back

  • A big female Lake Erie water snake and a territorial male goby. Snake researcher Dr. Rich King caught the snake out of the lake with the goby in its mouth... the snake was swimming toward shore to enjoy its meal. (Photo by Rebecca Williams)

These ten threats to the Great Lakes are complicated. Researchers are finding new ways that nature reacts to them. For example, alien invasive species often compete for food and crowd out the native species. Once a foreign species takes control in an area, there’s not much anyone can do to get rid of them. But occasionally, a native species will bite back. The Great Lakes Radio Consortium’s Rebecca Williams has that story:

Transcript

Invasive species have been a real problem for native species in the Great Lakes, but some native species are turning tails on the invaders. The Great Lakes Radio Consortium’s Lester Graham is our guide in exploring the series Ten Threats to the Great Lakes:


These ten threats to the Great Lakes are complicated. Researchers are finding new ways that nature reacts to them. For example, alien invasive species often compete for food and crowd out the native species. Once a foreign species takes control in an area, there’s not much anyone can do to get rid of them. But occasionally, a native species will bite back. The GLRC’s Rebecca Williams has that story:


(waves)


These islands in Lake Erie seem like floating Gardens of Eden. They’re
popular with tourists. These islands also really appeal to a rare
snake.


“So there’s a dozen or so of them heading out into the water.”


Meet the Lake Erie water snake. It can grow up to four feet long. Snake expert
Rich King and I are watching a bunch of them swimming away, gray heads
peeking up like periscopes.


These snakes like the lake. They like hanging out in huge piles on docks
and boats, and Rich King’s discovered the snakes love to eat round gobies.


Gobies are invasive fish that are thought to have hitched a ride in the
ballast water of ocean-going ships from foreign ports. The gobies eat the
eggs of native fish such as smallmouth bass, and compete with other fish for
food and nest sites. As gobies have taken over the lake bottom, the native
fish the snakes used to eat are getting harder to find.


“What we’re seeing is that the gobies are apparently a very abundant food
source for the water snakes. Compared to the 1980’s and early 90’s when the
snakes were feeding exclusively on native fish or mudpuppies – the snakes
are now consuming over ninety percent of their prey items are round gobies.”


(Sound of walking over rocks and zebra mussels)


Today, Rich King and his students from Northern Illinois University are
prowling the beaches for snakes. They carry their catches in faded
pillowcases tied to their belt loops. This is the annual snake survey,
Nerodio. That’s Nerodia, the snake’s scientific name, and rodeo, as in
cowboy roundup.


The snake biologists don’t just look under rocks. They dive into the lake
for snakes. They sneak up on piles of snakes and then grab the whole
writhing mass.


The snakes bite. The researchers’ arms are covered in snakebites. The bites aren’t life threatening, but they’re really, really bloody. And then it comes to the job at hand. The biologists are going to force the snakes’ stomach contents out. They call it “barfing the snakes.”


“Some snakes are easier to puke versus others. The water snakes, for
example, they sometimes voluntarily just, bleagh, just puke it out when you
pick them up.”


PhD student Kristin Stanford promises me it’ll be a good show, and we’re in
luck: just down the road, Rich King makes his first prize catch of the day.


“I got a snake with a goby in it. See the bulge: that’s the head end of
the goby. I’m virtually sure it’s a goby. (laughs) So you just very gently work it
forward, and drop it into our ziplock bag. That’s a round
goby.”


King says the snakes are growing faster and getting fatter on their goby
diet. Bigger snakes are less vulnerable to predators, and bigger females
can have more babies.


The researchers are pretty happy about that. That’s because the water snakes
are listed as threatened under the Endangered Species Act. This is the
only place in the world these snakes are found. For years, people were
shooting snakes and bashing them with rocks. Their numbers were getting
dangerously low.


The snake biologists say they understand that a lot of people hate and fear
snakes, but they say now that the snakes are eating gobies, they’re
starting to get a little more popular, especially with fishermen.


(Sound of fisherman casting a spinning rod)


Mark Green fishes for smallmouth bass. Green says it seems like when he
sees more snakes, he has better luck.


“If they’re eating the gobies, that is a good thing. I mean, I’m sure they have their
place… just not at my place.” (laughs)


Green didn’t realize until today that the snakes like to hang out under the
metal rim of the pier, right by his feet. He cringes, but his curiosity
gets the better of him, and he peeks inside one of the pillowcases bulging
with snakes.


GREEN: “When they get ahold of you, do they let go pretty quick, or do they…”


STANFORD: “Typically, but every now and then you get what
I call a “chewer,” and they’ll just sit there and errr-errr-errrng.”


The people and snakes are starting to arrive at an uneasy truce, and the
snakes seem to be well on their way to recovery from all the feasting on
gobies.


The researchers are hoping to learn just how big a bite the snakes can take
out of the goby population, and if, in the long run, it’s good or bad for
water snakes to depend on a foreign fish.


For the GLRC, I’m Rebecca Williams.

Related Links

Type E Botulism Spreading

  • Type E Botulism is taking its toll on loons and other waterfowl in the Great Lakes region. (Photo courtesy of the National Park Service)

A relatively new disease that kills birds and fish continues to spread in the Great Lakes basin. Scientists want to understand how Type E botulism is transmitted before it becomes an epidemic. The Great Lakes Radio Consortium’s David Sommerstein reports:

Transcript

A relatively new disease that kills birds and fish continues to spread in the Great Lakes basin. Scientists want to understand how Type E Botulism is transmitted before it becomes an epidemic. The Great Lakes Radio Consortium’s David Sommerstein reports:


Type E Botulism has killed thousands of loons, mergansers, and other birds on Lakes Ontario and Erie since 1998. So when biologist Tom Langen heard two dead seagulls on the St. Lawrence River had it, he investigated. He took a 350-mile boat ride along the length of the river. He collected all the dead birds and fish he could find for testing.


Langen says the toxin is related to invasive species like the round goby and zebra mussels and passed up the food chain.


“The link seems to be somehow associated between mussels, the fish which feed on the mussels, and then the birds and fish that feed on the round gobies or feed on the mussels.”


Langen says stopping the spread of Type E Botulism is also important for people. Humans can get the disease if they eat birds or fish that are contaminated.


For the GLRC, I’m David Sommerstein.

Related Links

Empty Ballast Tanks Still Carrying Critters

  • A scientist collects samples of ballast sediment. (Photo courtesy of NOAA)

A new study finds that ocean-going ships that enter the Great Lakes often carry biological pollution in their ballasts, even when they declare their ballasts are empty. The Great Lakes Radio Consortium’s Lester Graham reports:

Transcript

A new study finds that ocean-going ships that enter the Great Lakes often carry biological pollution in their ballasts, even when they declare their ballasts are empty. The Great Lakes Radio Consortium’s Lester Graham reports:


The study by the University of Michigan and the National Oceanic and Atmospheric Administration looked at ships coming into the Great Lakes from the ocean. Nearly 80-percent of them declared “no ballast on board” and avoided inspections by the Coast Guard.


But several of those ships were tested by the researchers. They found that although the ballast water was pumped out, there were thousands of organisms left behind in the sediment in the bottom of the ships’ ballast. Then, when the ships unloaded at their first stop, they took on Great Lakes ballast water which stirred up the sediment.


And that made it possible for the biological contaminants to be pumped out at the next Great Lakes port.


The authors of the study warn that more restrictions must be placed on how the ships handle ballast water, or the Great Lakes will continue to be invaded by more invasive species such as the zebra mussel, round goby, and 180 other foreign aquatic species that have harmed the Lakes’ ecosystems.


For the GLRC, this is Lester Graham.

Related Links

Coast Guard to Fine Ships for Ballast Violations

Later this summer, the U.S. Coast Guard will be able to fine cargo ships that don’t comply with ballast water reporting regulations. The Great Lakes Radio Consortium’s Lester Graham reports on this new effort to stop invasive species from being introduced into the Great Lakes:

Transcript

Later this summer, the U.S. Coast Guard will be able to fine cargo ships that don’t
comply with ballast water reporting regulations. The Great Lakes Radio Consortium’s
Lester Graham reports on this new effort to stop invasive species from being introduced
into the Great Lakes:


Ocean-going vessels have transported aquatic nuisances to the Great Lakes such as the
zebra mussel and the round goby in the ships’ ballast water. Those ships are now
supposed to take measures to prevent bringing in more problems. Beginning in mid-
August, the Coast Guard will have the authority to fine ships up to 27,500 dollars if they
don’t submit a report on the measures taken. Bivan Patnaik is with the Coast Guard’s
Environmental Standards Division…


“The movement of non-indigenous species from one area to another is a very important
environmental issue and we’re all working as hard and as fast as we possibly can.”


Critics say the government has not worked hard and fast enough. Patnaik says the Coast
Guard’s new penalties and other efforts to better manage ballast water are steps in the
right direction.


For the Great Lakes Radio Consortium, this is Lester Graham.

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Invasives Altering Great Lakes Food Web

For decades, aquatic invaders have been plaguing the Great Lakes. They’ve changed the way the ecosystems work and affected the balance of life in the lakes. Most of them didn’t just wander in. They hitchhiked a ride into the Lakes in the ballast water of ships from across the Atlantic. The Great Lakes Radio Consortium’s Carolyn Gramling reports… now the combination of these invasive species is causing changes that concern scientists:

Transcript

For decades, aquatic invaders have been plaguing the Great Lakes. They’ve changed the way the
ecosystems work and affected the balance of life in the lakes. Most of them didn’t just wander in.
They’ve hitchhiked a ride into the Lakes in the ballast water of ships from across the Atlantic. The
Great Lakes Radio Consortium’s Carolyn Gramling reports…now the combination of these invasive
species is causing changes that concern scientists:

Zebra mussels were one of those species that hitched a ride in the ballast of a ship. They first
appeared in the Lakes in the mid-1980s. Zebras and their cousins the quagga mussels compete for
food needed by aquatic animals native to the lakes.

Researchers say now these mussels are part of another problem. They’re changing the food web.

The food web is made up of organisms that feed on each other. Usually it’s a chain of small, even
microscopic species that are food for ever larger species. Zebra mussels are near the bottom. For
their food, they filter large volumes of water containing contaminant-laden algae and sediment. In
the process they ingest PCBs and other toxins.

Gene Kim is a researcher in the Ohio State University’s Aquatic Ecology Laboratory. He says that
zebra mussels and a non-native fish called the round goby have helped to form a new food chain
within Lake Erie – a chain that can connect harmful chemicals buried in lake mud to humans.

“A lot of the exotic species, these alien species, have incorporated themselves into the Lake Erie
food web, and there’s a lot of ramifications, in terms of, will they change the cycling of historical
contaminants that right now are in the sediments, but they could be redirected back into sport fish
and eventually, humans.”

Zebra mussels have few natural predators in North America, and they reproduce rapidly. As a
result, they’ve been wiping out native mussels and clogging up water intake pipes in the lake. So
the arrival of the round goby, which likes to eat zebra mussels, would seem to be good news.
Instead, it has proven to be a double-edged sword.

Roy Stein is a professor in Ohio State’s Aquatic Ecology Laboratory. He says the PCBs and other
contaminants, once held captive in the sediment at the bottom of Lake Erie are taken up by zebra
mussels, and then the zebras are eaten by the round goby.

“And then, interestingly enough, round gobies are important prey for smallmouth bass that people
eat, and all of a sudden we have the opportunity for those PCBs that were stored in the sediments
to come up through the food chain and influence humans.”

So, Stein says, those contaminants that were trapped in the sediment now have a pathway up the
food chain.

Gene Kim’s research is confirming the link between smallmouth bass and round gobies. He says
it’s clear round gobies like to eat zebra mussels. But it’s less clear whether bass prefer to eat gobies
over other prey fish. So, Kim devised a laboratory behavior study that let the smallmouth bass
choose between several types of prey, including gobies, emerald shiners, and crayfish.

“The interesting thing is that they actually target these emerald shiners more often than round
gobies, but emerald shiners have superior escape abilities.”

Round gobies, Kim says, just don’t swim away as fast – and so get eaten the most. He adds that
when compared with the stomach contents of Lake Erie bass, this laboratory result is borne out –
more gobies were consumed than any other prey.

Roy Stein says that this puts the system in a kind of double jeopardy.

“The combination of PCBs plus being a slow prey causes perhaps more PCBs to move up through
the food web than otherwise might be the case.”

PCBs have been linked to cancer and birth defects in humans – and they’re not the only
contaminants in the lake.

Other research indicates this new food chain might be helping other pollutants in the sediment find
their way to humans. For example, another Ohio State study finds methylmercury is also getting
into the food web through invasive species. Methylmercury in fish can cause neurological problems
for expectant mothers and other health problems.

Doug Haffner is the Canada Research Chair for Great Lakes Environmental Health and a professor
of Biological Sciences at the University of Windsor. He agrees a zebra mussel – round goby –
smallmouth bass food chain has created a route that exposes humans to harmful chemicals in lake
sediment.

“For a chemical to be of concern to us, it has to be biologically available, it has to be able to enter a
human being or a fish or whatever it might be. Some chemicals may be out there but not available;
we can measure them, but they’re not really a risk to the ecosystem per se. But processes can
change, which make them available.”

Martin Berg is a professor of Aquatic Ecology at Loyola University Chicago. He says the non-
native species have had a similar impact on PCB transfer from Lake Michigan sediment.

“You can think of it almost like a conduit, like a pipe. Now we have a direct link, as you move up
the food web, to organisms that are going to be directly consumed by humans.”

And the problem spreads as the non-native species expand their range. Researcher Gene Kim says
that the implications are far-reaching.

“Not only are we just talking about a Great Lakes phenomenon – zebra mussels have already
escaped into the Mississippi drainage, and right now round gobies – we’re spending a lot of money
to prevent round gobies from entering that same drainage.”

Scientists’ concerns about toxins in the Lakes are not limited to how invasive species are changing
the food web. Researchers say that other changes caused by people can help harmful chemicals
trapped in sediments to return to the ecosystem. Ultimately, they say, each of these issues is part
of a much larger concern: the overall health of the environment.

For the Great Lakes Radio Consortium, I’m Carolyn Gramling.

Related Links

Tubenose Goby Extends Its Reach

An exotic fish species called the tubenose goby made its way into the St. Clair River after it was flushed from a ship’s ballast water 11 years ago. The tubenose hasn’t spread as fast as its cousin, the round goby, but researchers were recently surprised to find the tubenose spreading further into Lake Erie. The Great Lakes Radio Consortium’s Karen Schaefer reports:

Transcript

An exotic fish species called the tubenose goby made its way into the St. Clair River after it was flushed from a ship’s ballast water 11 years ago. The tubenose hasn’t spread as fast as its cousin, the round goby, but researchers were recently surprised to find the tubenose spreading further into Lake Erie. The Great Lakes Radio Consortium’s Karen Schaefer reports:


The invader was captured this July. The tubenose is related to the round goby, whose population explosion across the Great Lakes has scientists concerned. Round gobies eat contaminant-laden zebra mussels, and then pass those toxins on to sport fish favored by humans. But Jeff Ruetter, director of Stone Lab, says the tubenose goby actually first appeared in the Great Lakes two years before its cousin and so far, isn’t widespread.


“And the concern will be with its competition with other species in the ecosystem. Is it going to force them out?”


Ruetter says the appearance of the new invader underscores the need for tighter controls on exotic species. For the Great Lakes Radio Consortium, I’m Karen Schaefer.

Native Lake Species Fighting Back

  • Alewives washed up on Lake Michigan shores after the invaders' populations exploded, then crashed. Researchers have a difficult time predicting how invasive species will affect the balance of nature in the Great Lakes.

Ever since the Great Lakes were opened to shipping, exotic species of aquatic animals have invaded the lakes. Nearly always it’s been bad news for the region’s native fish and wildlife. The Great Lakes Radio Consortium’s Lester Graham reports on the latest effects of the invaders:

Transcript

Ever since the Great Lakes were opened to shipping, exotic species of aquatic animals have invaded the lakes. Nearly always it’s been bad news for the region’s native fish and wildlife. The Great Lakes Radio Consortium’s Lester Graham reports on the latest effects of the invaders.


Some of the exotic species that have caused major problems in the Great
Lakes have been around since the 1940’s and ’50s. For example, the sea lamprey found its way into the lakes through manmade channels. It’s a parasite that attacks lake trout and other large game fish. It devastated the lake trout fisheries. Only recently have efforts gotten the lamprey under control. It’s still out there, but it’s not decimating the lake trout population as it once was.


More recently, a big concern has been the zebra mussel. It hitchhiked its way to the Great Lakes in the ballast water of cargo ships. In the last couple of decades the zebra mussel has caused major changes in all the lakes except for Superior where it seems limited to the shallow and warmer bays.


David Jude is a researcher with the University of Michigan’s Center for
Great Lakes and Aquatic Sciences. He says the huge numbers of zebra mussels siphon through lake water like a giant network of filters. There are so many of them that water in the lakes is actually clearer.


“I think people tend to hear about the water clarity increases. ‘Ah, the water’s clearer,’ you know, ‘That’s great!’ But it’s not great, because there’s a lot of things going on in the water column.”


Things such as, algae converting the sun’s energy into more phytoplankton.
Small fish and tiny invertebrate animals called zooplankton eat the phytoplankton and then they become food for fish. But, the zebra mussels filter out a lot of the phytoplankton, stealing food from the native zooplankton.


David Jude says a couple of other invaders are also causing havoc at the base of the food chain in the Great Lakes. Instead of eating just the green phytoplankton, zooplankton invaders from the Black and Caspian Seas also eat their North American cousins.


“These are predators. And they feed on the zooplankton, our native zooplankton that is out there already. So, not only do we have the impact of zebra mussels removing algae which is a food for these zooplankton, now we’ve got two predators that have been introduced and both of those will eat zooplankton which would have been food for fish to eat.”


Besides the zooplankton floating around in the water column, a major food source for fish is in the sediment at the bottom of the lakes, and it’s disappearing. James Kitchell is with the University of Wisconsin – Madison. He says many different kinds of fish depend on a little creature called diaporeia, which have become scarce in many areas.


“It appears to correlate in general with an increases in zebra mussels. So, there’s the prospect that diaporeia is literally starving to death as a consequence of zebra mussels eating the available food, but when you look at the diaporeia, they appear to be healthy. They’re not skinny and look to be starving. So that doesn’t explain it.”


It’s a big concern because a lot of fish that anglers like, such as yellow perch, depend on diaporeia for food.


Besides the zebra mussels and the two zooplankton predators, a fourth invader is causing problems. Populations of the round goby, an ugly, aggressive feeding little fish from Eastern Europe, have exploded in the Great Lakes. The round goby scours the bottom, eating the eggs and larvae of native fish. The University of Michigan’s David Jude says as big of a problem as the invasive fish has been over the last several years. The round goby’s future might soon be curtailed a bit.


“We did SCUBA dives in Lake Erie, for example, we’d turn over rocks. Round gobys would tear out from under the rocks and we’d have small mouth bass following us around and they would ignore the round gobys. They didn’t know how to catch a round goby. But, because there’s so many round gobys now, they had to learn how to eat them or die. So, the predators are definitely learning how to eat round gobys.”


Other native fish are beginning to eat the exotics. The silver chub, which once nearly disappeared from the Great Lakes, is making a bit of a comeback feasting on zebra mussels. With each invader, the lakes ecosystems go through upheaval, and then find a new balance. But make no mistake. It’s a different balance. Nicholas Mandrak is a researcher at Youngstown State University. He says exotic species invading the Great Lakes will mean continued changes, and for people who fish the lakes, not many of the changes will be good.


“You’re not going to be able to catch as many species that you’re used to catching. You know, the native species are going to decline. The walleye are going to decline. So, I think the bottom line is the recreational and commercial fisheries are going to change in a manner that is negative to most people.”


Researchers, though, have learned to be careful about predicting how invasive species will affect the lakes. They’re often surprised by the intricacies of the food web and the ecosystems that support it. Throwing an exotic invader into the mix makes it that much more unpredictable, and it will likely get worse. Mandrak says they’ve been studying how global warming might affect the lakes. One scenario suggests 30 to 40 new exotic species from the South will make their way through manmade canals as temperatures rise. For the biologists, it’s a worrisome concept. For the Great Lakes Radio Consortium, this is Lester Graham.

NATIVE LAKE SPECIES FIGHTING BACK (Short Version)

It appears that fish native to the Great Lakes are beginning to prey on some of the alien species that have invaded the lakes. The Great Lakes Radio Consortium’s Lester Graham reports:

Transcript

It appears that fish native to the Great Lakes are beginning to prey on some of the alien species that have invaded the lakes. The Great Lakes Radio Consortium’s Lester Graham reports.


Aquatic Species from Europe and elsewhere have hitchhiked to the Great Lakes in the ballasts of cargo ships for many years. A lot of them have upset the natural ecosystems of the lakes. Lately, though, some native fish are taking advantage of the invaders. Nicholas Mandrak is a researcher at Youngstown State University. He says a Great Lakes minnow that was once thought to have died out has recently re-emerged.


“And they’re eating zebra mussels. So, it looks like the increase
in silver chub is related to zebra mussels, so we finally found a native
fish that is benefiting from the zebra mussel.”


Other researchers say small mouth bass are beginning to prey on another invasive species, the round goby, which eats the eggs and larvae of fish native to the Great Lakes. The researchers say the benefits don’t outweigh the negative affects on native species. But it evens the score a little. For the Great Lakes Radio Consortium, this is Lester Graham.