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4. Control and Eradication
Control and eradication of AIS poses a dilemma to managers in North America. In general, eradication of an established aquatic invader is very difficult at best, and more often impossible unless the established population is localized, and can be isolated before it spreads.
However, there have been some recent success stories worthy of note, when conditions allowed action to be taken rapidly:
- Australia eradicated an invading mollusc, the Black-striped mussel Mytilopsis sallei, from its coastal waters through quarantine and chemical treatment of the entire affected harbor (Ferguson 2000). They were able to do so because: 1) the harbor had a narrow opening to the ocean that could be blocked off; and 2) the Australian federal government had the complete and sole authority to make the decision.
- Recently, managers in southern California have been using a biocide treatment to attempt eradication of Caulerpa taxifolia, an invasive nuisance species of green algae discovered in a coastal lagoon (Withgott 2002). Mortality in the original patch is estimated to be about 97%, but additional patches have been found in the same lagoon and treatment is on-going. There is an unconfirmed report that another patch has been found at a location far removed from the original infestation, and there may be problems with the chemical treatment reaching and destroying the entire organism.
The experience in the Great Lakes with the sea lamprey illustrates both the difficulty with eradication and the potential benefits of attempting control. After almost 50 years, the sea lamprey has resisted eradication and its numbers are controlled only via chemical and other treatments at great expense and effort. The sea lamprey's unique biology and devastating effect on Great Lakes fisheries made control a worthwhile approach and research made it possible. Barriers have been successfully employed to curtail sea lamprey entry into Lake Winnebago, Lake Simcoe, and numerous tributaries. The only other NIS that fishery managers have sought to control is the alewife - by stocking trout and salmon to supplement the population reduction of native predators caused by sea lamprey.
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