Lakes fish food in decline
The Associated Press
CHICAGO (AP) -- A quarter-inch crustacean that makes up
the bulk of the diet for some Great Lakes fish is disappearing
from some areas, and researchers blame the invasion of
non-native zebra mussels.
The spineless scud, also called diporeia, is a shrimplike
bottom dweller that makes up 25 to 75 percent of the whitefish
diet, according to the National Oceanic and Atmospheric
Administration. It also feeds sculpin, smelt and chub,
which in turn feed trout and salmon.
Tom Nalepa, research biologist with the Great Lakes Environmental
Research Lab, said Lake Michigan scud declined 68 percent
from 1994 to 2000. They still are found along the Wisconsin
shore but have vanished from Chicago, Gary, Ind., and
the Michigan shore.
Nalepa wrote about the decline in "The State of
the Great Lakes 2003," a report released last week
as a joint project of the U.S. Environmental Protection
Agency and Environment Canada. The report also notes a
scud decline in Lake Ontario.
"The decline is so dramatic that we're worried about
what it will do to the food web and the upper-level fisheries,"
Researchers believe zebra mussels, transported to the
lakes in ship ballast water in the 1980s, are starving
scuds by straining the algae they eat out of the water.
But Nalepa said scientists also are looking into the possibility
"It just doesn't make sense that an animal that
is not infected is dying off completely," he said.
Biologists have noticed changing feeding habits and thinner
whitefish with the decline. Zebra mussels found in whitefish
stomachs indicate a switch to the less nutritious mollusks,
which are harder to digest.