Invading Species

Australia imported cats to deal with rat overpopulation. When the rat population declined, the Australians were left with more cats than they could handle. In North America, nonnative lamprey eels invaded the Great Lakes with the opening up of the Erie and Welland canals. They attach their suction cup mouths to sea trout and whitefish. Using their sharp teeth, lampreys rasp away a fish’s skin and suck its blood. When the fish dies, the lampreys move on to a new host.

Exotic species are also transported in the bilge water of incoming vessels. Oceangoing vessels adjust their hydrodynamic characteristics by changing their centers of buoyancy. In the old days, mariners used rocks, which created few problems when thrown overboard. Today, vessels change the water level in their ballast tanks. When water is pumped on board, it comes complete with a waterborne population. These organisms are discharged into the environment when the ballast tanks are emptied in other waters. A case in point is the zebra mussel, which migrated from its native Black and Caspian seas to Europe via man-made canals. After living in Western and Central European freshwater for almost 20 years, the mussels wound up in a ballast tank and came to the U.S. First discovered in Lake St. Clair in June 1988, they quickly spread to Lake Erie, Lake Ontario and the St. Lawrence River. Since then, they’ve migrated all over the Great Lakes, into a growing number of US and Canadian canals. They are still spreading.

Exotic species often have no natural preditors in their new home. They can grow to large numbers until they dominate and exhaust a habitat’s available nutrients or become predators and devour the native species. Large populations can also foul up human projects. Without predators, zebra mussels coat vessel bottoms, decreasing headway and fuel economy. By clogging intake ports at power plants, they restrict or stop the water flow required to cool and precipitate the used steam back into liquid.

Likewise, exotic plant species may grow to such proportions that they cover the water’s surface and prevent light from penetrating, decreasing photosynthesis and oxygen and killing native species.

What can you do to mitigate the problem?

If the fishing bait you use is indigenous to the area you’re fishing, there’s nothing wrong with tossing your unused bait overboard. However, if you get your bait from the local bait shop, you have no idea where it came from. Tossing it overboard could have serious repercussions. Don’t toss bait overboard unless you know it came from the area.

If you trailer your boat, canoe, kayak, personal watercraft or other vessel from one body of water to another, remove plants and animals from your boat trailer and equipment before leaving the water access area. Don’t forget to drain your live wells, bilge water and transom wells before leaving, and empty your bait bucket on land. After thoroughly washing your boat, let it dry three days before launching it in another body of water.

Learn what invasive organisms look like, and report any sightings to your local authorities.

Invasive species Canada
British Columbia


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