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5 | Prevention and control
Once a non-native species is established in the Great Lakes, it is nearly impossible to get rid of it. Therefore, it is extremely important to prevent introductions of new species. Because ballast water is the primary pathway of species introduction, efforts have been focused on preventing the introduction of exotics through ballast water treatment. The most common method of treating ballast water is open-ocean exchange, the act of replacing freshwater ballast with seawater during the voyage. Because saltwater-dwelling species generally cannot survive in freshwater, this water exchange can reduce the likelihood of a new exotic species establishing a population in the Great Lakes. Vessels entering the Great Lakes and St. Lawrence Seaway are required to replace their ballast water with seawater during their voyage. If they do not perform open-ocean ballast exchange, they are not permitted to release ballast in the Great Lakes.
Open-ocean ballast exchange, however, is not the ideal solution as it is sometimes unsafe and not completely effective in preventing introductions. Research is underway on different ballast water treatment options to supplement or replace open-ocean ballast exchange. Some of the research includes:
Controlling the numbers and distribution of existing nonindigenous species in the Great Lakes is still extremely important in the ongoing battle against invasive species. There are a variety of methods of controlling existing populations. Some examples include:
Graphic: Rusty Crayfish from Lake Superior. Courtesy Jeff Gunderson/Minnesota Sea Grant.