marine species threaten Great Lakes
Published June 14, 2004
MINNEAPOLIS Vast populations of foreign fish,
mussels and other creatures have invaded and damaged the
Great Lakes in the last few decades, creating a more difficult
problem than the industrial contamination that fouled
the lakes in the 1960s, the Star Tribune reported in Sunday
The invasion began in the early 1800s, but accelerated
after the St. Lawrence Seaway opened the lakes to oceangoing
ships in 1959. More than 40 per cent of the 179 alien
species have been documented since then, with most arriving
by ship from Europe or Asia, according to research data
analysed by the newspaper.
A new invader is identified in the lakes about every
seven months, faster than scientists can study them.
Henry Regier, a professor emeritus of zoology and environmental
studies at the University of Toronto, describes the Great
Lakes basin as "a sick system." In 50 years
of studying the lakes, he said, he has never seen such
Prof. James Carlton, director of the Maritime Studies
Program at Williams College in Mystic, Conn., said the
lakes have been permanently modified "on one of the
greatest scales in any aquatic environment in the world."
Unlike industrial pollution, much of the new damage is
nearly invisible, hidden in the lakes' murky depths. Yet
biologists who study lakes say the evidence is mounting
that the unintended introductions of species from around
the world could soon dominate the lakes' ecology, the
Star Tribune reported.
On the shores of Lake Erie, the destruction can be seen
in the deaths of birds who have eaten the round goby,
a 10- to 15-centimetre-long European fish with bulging
eyes that has found a new home in the Great Lakes.
Often the meal is a death sentence. More than 50,000
loons and other birds died after eating gobies over the
past five years _ victims of poisoning. Scientists say
the gobies become toxic food by ingesting quagga mussels,
another recent invader from Europe, which accumulate botulinus
toxin from the lake bottom.
So many dead birds have washed ashore during recent fall
migrations that beach patrols hauled them away with ATVs
and flatbed trucks.
A critical link in the Great Links food chain is the
half-centimetre-long Diporeia, a pale orange shrimplike
organism that lives on the bottom of lakes. Loaded with
fat, they long have been a high-energy, abundant food
source for fish in the Great Lakes. But over the past
decade, Diporeia have vanished from more than 44,000 square
kilometres of lake bottom _ an area more than twice the
size of New Jersey. Every lake except Superior has been
Scientists began to document the losses in the early
1990s, in areas where zebra or quagga mussels had invaded.
As the fish food disappeared, so did native fish, especially
the commercially valuable whitefish, which depend on Diporeia
for up to 70 per cent of their diet.
The speed and success of a single species' invasion can
be stunning. Scientists found a few dozen Eurasian ruffe
in the Duluth harbour in 1986. The small, spiny, perch-like
fish from Europe exploded to two million by 1991 and to
more than eight million in 1998 before declining slightly,
according to federal estimates. It now is the most abundant
fish species in the harbour.
One reason that some invasive species are surviving and
proliferating is that harbours and estuaries are cleaner
today. Taxpayers and industries invested billions of dollars
to improve sewage treatment, remove phosphorus and reduce
chemicals, allowing the Great Lakes and their native fish
and wildlife to progress toward recovery during the 1970s
and 1980s. Invaders are undercutting those achievements.
The changes affect not only fish, but also the smallest
plants, invertebrates, snails and mollusks. For example,
20 species of native mussels lived in Lake St. Clair,
part of the waterway between Lake Huron and Lake Erie,
in 1986. Two years later, zebra mussels spread into the
lake. By 1997, all of the native mussels were gone except
in a few shallow areas.
Invaders also pave the way for future intruders. The
newcomers sometimes alter the habitat in ways that help
other alien creatures to thrive. For example, invasive
gobies spread quickly in areas where zebra mussels have
become established because the gobies eat the mussels.
In other places, zebra mussels attach themselves to non-native
Eurasian watermilfoil plants. The mussels gain a place
to live, while the milfoil grows better because the clinging
mussels filter and clear the water.
Commercial ships have been the main carriers of the invaders,
which can ride in the water that empty ships carry as
ballast and then dump as they take on cargo upon reaching
U.S. fish farms also contribute to the problem. Two kinds
of Asian carp imported to clean U.S. fish farm ponds and
tanks escaped into southern waterways in the early 1980s.
They have spread up the Mississippi River and its tributaries
toward Lake Michigan, jeopardizing a $4.5-billion commercial
and recreational Great Lakes fishery.
Invasive species also have entered the lakes through
bait buckets, as anglers intentionally or inadvertently
dumped them into the water. Unwanted aquarium fish have
been released into waterways because their owners thought
it was a humane or convenient way to dispose of them.
About a third of the invasive species in the Great Lakes
basin are aquatic plants, such as Eurasian watermilfoil,
which have been spread by ships, boats, trailers, garden
nurseries and other means. This vegetation can overtake
lakes and interfere with boating, fishing and swimming.
Michigan has 185 infested lakes, Wisconsin has 44, and
Ontario has dozens, especially along a highway of interconnected
lakes, rivers and canals that extends more than 320 kilometres
between lakes Ontario and Huron. The spread of invasive
species in Ontario threatens a $1.4-billion-a-year recreational