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


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

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

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

“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.

Related Links