These fish have been introduced, either intentionally or accidentally, into the Great
Lakes. Also called "exotic" or "nonindigenous" species, these
newcomers can cause trouble by changing the ecological balance of the lakes and,
sometimes, crowding out native species. Some non-native species are ecologically harmless
and or even beneficial, but others cause great harm.
For example, the sea lamprey (shown in the illustration) is a predator that attaches
itself to a fish, rasps a hole with its large sucking disk, and sucks blood and body
tissues until it becomes satiated or the victim dies. Sea lampreys have caused great
damage to the lake trout, whitefish, and burbot populations in the Great Lakes. Before the
lamprey invasion of Lake Superior (prior to 1952), the lake trout harvest averaged about
4.5 million pounds; by 1960, it was less than 500,000 pounds.
See also Lake Michigan, Lake Superior, Lake
Huron, Lake Erie, or the complete listing.