A rare type of botulism is killing
fish and birds in Lake Erie. Biologists suspect that exotic
species are to blame.
New York Times
TURKEY POINT, Ontario
When a botulism outbreak hit
this provincial park on Lake Erie in early September,
it closed the beach.
Thousands of dead fish, their
white bellies glinting in the sun, washed up on the sandy
shore. Hundreds of cormorants, gulls and terns fed on
the dead sheepshead, burbot and perch and quickly keeled
It was one of about two dozen
sudden, random outbreaks this summer and fall on the shores
of Lake Erie.
Over the past four years dozens
of similar outbreaks have occurred, all involving type
E botulism, a rare strain of the potent nerve toxin. Experts
say they still do not know what to make of the outbreaks.
More than 8,000 common loons
have been killed by the botulism, and the species is already
in peril from overdevelopment. "This is just another hit,"
said Grace McLaughlin, a wildlife disease specialist at
the National Wildlife Health Center in Madison, Wis. "It's
The botulism causing the fish
and bird kills is a rare type of the bacteria clostridium
botulinum. Type C botulism, which also kills birds, is
common throughout the country, notably in the Salton Sea
in California; it occurs when drought dries up lakes,
exposing invertebrates that harbor the toxin, which are
eaten by ducks and geese. Types A and B botulism are the
kind generally found in poorly canned foods.
"I've seen botulism my whole
career, but it's always been C," said Dr. Ward Stone,
director of the New York State Department of Environmental
Conservation's pathology laboratory in Delmar. "When we
found E, I was very surprised."
Type E is unusual because
it concentrates in fish, affecting a wider spectrum of
wildlife than type C. It has been found in very small
amounts in the Great Lakes for decades, but never for
this long or in such large quantities. Something has happened
recently to increase the abundance greatly, and biologists
are trying to figure out what.
The prime suspects are three
interlopers: the round goby, a small bottom-feeding fish;
hard-shelled zebra mussels; and quagga mussels. All three
species hitchhiked to the Great Lakes from the Black and
Caspian Seas in the ballast water of international freighters
the mussels in the past decade or so, the goby
in just the past four years. The outbreak of botulism
coincides with their widespread colonization of the lake.
Zebra and quagga mussels are
thumbnail-size filter feeders that live on the bottom
and filter phytoplankton, a one-celled alga, from the
water. Paradoxically, they have made Lake Erie's water
very clear, and that may be a cause of the botulism.
Clear water allows sunlight
to penetrate to greater depths, hastening the growth of
aquatic plants. Botulism flourishes in the sort of oxygen-deprived
environment provided by decaying plant matter.
Scientists theorize that mussels
may also be biological magnifiers, concentrating the toxin
as they filter water to get nutrients or excreting the
toxin into the mud around them. When the mussels are eaten
by gobies, a species of bottom-feeding scavenger, the
botulism is concentrated further. Crippled by the toxin,
the gobies thrash about in the water and attract predatory
fish, mud puppies (a kind of salamander), mergansers,
loons and other birds.
Dead or dying fish on the
lakeshore are an ideal environment for botulism. They
attract scavengers such as gulls and terns that die when
they eat the contaminated fish. Maggots from eggs laid
on the fish become contaminated and pass the toxin to
birds that eat them. Mergansers and loons ingest the toxin
by eating live fish.
Another contributor to the
botulism outbreak may be warming temperatures in the relatively
shallow lake, whose average depth is 60 feet. Last year
was one of the rare winters when Lake Erie did not freeze
Botulism, an extremely potent
and fast-acting toxin, blocks the transmission of impulses
from nerves to muscles. (Type A botulism is the active
ingredient in Botox, the drug that is injected in fashionable
foreheads to paralyze the frown lines of aging.) Birds
that ingest botulism lose their ability to fly and even
hold their heads up and often die by drowning. Fish can
no longer swim.
Humans are not considered
to be at great risk, but officials have warned anglers
not to eat fish that are found floating or that do not
fight on the end of the line. Thorough cooking kills botulism,
but it may survive in some smoked fish. In July, 14 Alaskan
Eskimo villagers became seriously ill from type E botulism
when they ate the tail of a beluga whale that had washed
up on a Pacific beach.
Botulism is not the only problem
associated with the exotic species, which have taken over
Lake Erie with astonishing speed. Zebra mussels showed
up in 1987 and in a few years covered hard surfaces throughout
the Great Lakes, from sewer pipes to rocks. Quaggas showed
up a decade ago, and they now outnumber zebra mussels
10 to 1 because they also fasten to muddy and sandy bottoms.
Gobies now make up more than
90 percent of all living material at the bottom of Lake
Erie. About 5 inches to 7 inches long, they not only outcompete
other fish for food, but also eat rivals' eggs and fry,
even using decoys to draw fish away from their young so
other gobies can gobble them up. Biologists worry that
game fish like perch and bass will be decimated.
The quagga mussel is also
a suspect in the "dead zone," a 60-by-20-mile plume of
oxygen-depleted water in the center of the lake.
Every freshwater lake, healthy
or unhealthy, has such a zone. In the summer, warm water
traps cold water on the bottom; because the cold water
is buried away from the atmosphere, its oxygen is eventually
consumed and nothing can live there.
But in Lake Erie, the dead
zone has been growing over the last few years. Some scientists
blame the proliferation of quaggas, which produce phosphorus-rich
waste, a fertilizer for algae. When the algae decompose,
they creates a "detrital rain" that falls to the lake
bottom and sucks oxygen from the water.
The growing size of the zone
may also be a natural fluctuation, or it may be that substantially
lower lake levels and climatic warming are making the