Fish find worrisome for Great
By Jen Horsey
A worrisome fish discovered in Lake Ontario again has
raised the spectre of invasive species in Canada as authorities
across the country struggle to keep various imported pests
Toronto conservation officials doing a routine survey
of the fish population at the mouth of the Don River recently
discovered a grass carp.
The large, grey fish with black-edged scales is one
of four invasive Asian carp species authorities fear could
upset the delicate ecology of Canadaís Great Lakes.
"All those things we value most about the Great
Lakes could, and would, change if invasive species continue
to become established," warned Nicholas Mandrak,
a research scientist with the federal Department of Fisheries
None of the four Asian carp-grass, bighead, silver,
and black-are believed to have become entrenched, but
authorities are on alert for a full-blown assault.
"Itís a lot easier to deal with invasive species
by preventing them from being introduced in the first
place because itís much more difficult to control them
after theyíve become established," said Mandrak.
Ballast-water monitoring and an electrical barrier that
repels fish in a canal connecting the Mississippi River
to Lake Michigan are just two initiatives in place to
protect the lakes against invasive species, he said.
Conservation authorities hope this latest grass carp
was on its own-perhaps released into an area waterway
by would-be diners who purchased it at a local market
but opted not to eat it.
The long-term effects of invasive species on the native
environment are impossible to predict, authorities say,
but there already have been some awful surprises.
In the Great Lakes, the zebra mussel is being blamed
for a fatal botulism outbreak that has swept through waterfowl
species. Early research has indicated birds pick up the
toxin when they eat fish that feed on the infected, fingernail-sized
The mussels are believed to have arrived from foreign
waters as stowaways in the ballast water of seafaring
"Undoubtedly there will be additional negative
impacts that we have not foreseen," said Mandrak.
Grass carp have been discovered previously in the Great
Lakes-the first in 1985 in Lake Erie. Commercial fishing
nets have since captured three others in 1989 and 1998
in Lake Huron, but each is believed to have been an isolated
Several bighead carp also have been discovered in the
Canadian waters of the Great Lakes (the black carp and
silver carp have yet to make an appearance).
Even the seemingly innocuous goldfish-another carp variety-is
making a mess of our native water systems.
"We couldnít guess, not realistically, the damage
these species are doing," said Bill Beamish, a University
of Guelph professor. "Itís huge."
The grass carp, for example, has an aggressive habit
of ripping through underwater vegetation and reproducing
quickly-threatening the food and habitat of native wildlife.
And various agencies now spend $25 million-$30 million
each year to control sea lampreys, said Beamish.
The lampreys - known for clinging to other fish and
literally sucking the life out of them - originally arrived
in Canadian waters in the 1960s through the newly-opened
St. Lawrence Seaway.
Canadian waters arenít the only trouble spot.
Across the country, authorities are shredding native
forests in an effort to contain multiple-front invasions
of such pests as the Asian longhorn beetle, the emerald
ash borer, and the brown spruce longhorn beetle.
Of the 441 species listed at risk by the Committee on
the Status of Endangered Wildlife in Canada, about two-thirds
can attribute their decline to invasive species, said