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I. Introduction
Human activities are profoundly affecting the earth's support systems. Population growth has been accompanied by a variety of stresses of natural ecosystems including habitat destruction and modification, chemical contamination, and the unintentional introduction of various nonindigenous invasive species (NIS).
 | | The zebra mussel, whose November 2000 distribution in the U.S. is shown here, is the "poster child" of invasive species in North America. Its distribution in the U.S. (above) and Canada also demonstrates how the Great Lakes system serves as an aquatic gateway to the heartland waters of North America. |
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Some nonindigenous invasive species have had significant adverse effects on human, plant or animal health, local and regional economies, and on the ecosystems they invade. Recent examples of notorious invasive species include fire ants and African honey bees in the southern US, West Nile virus and Asian longhorn beetles in the eastern US and Canada, and, of course, the zebra mussel in the Great Lakes and eastern half of the US and Canada.
Fortunately, many releases of nonindigenous species occur with little or no apparent adverse effect, primarily because the species do not become established (i.e., form a self-sustaining, reproducing population). For example, European flounder reported occasionally in the Great Lakes (most recently in Lake Superior in 1995 and in Lake Erie in 2000) do not seem to be capable of reproducing in freshwater1. Others may become established but remain in small, local populations that do not spread significantly (e.g., Corbicula, the Asian clam, in the Great Lakes).
A general rule of thumb used by many scientists is that about 10% of all introduced nonindigenous species actually become established, and about 10% of those that become established also become invasive and harmful. Some estimates place these numbers closer to 15%. In spite of the small numbers of successful introductions of invasive species that might be expected by applying this "rule of thumb", there are thousands of invasive species in the US and Canada today, all of which have some degree of impact on the ecosystems they have invaded and on societal uses of those ecosystems, with commensurate economic costs and losses. Because of the regularity with which new species are being introduced throughout the world, some scientists are now heard to refer to our age as the 'homogecene'.
The Office of Technology Assessment (U.S. Congress, 1993) calculated almost $100 billion in U.S. economic losses over an 85-year period from just 79 nonindigenous species. Pimentel et al (2000) estimated losses to the United States economy of at least $137 billion per year associated with the effects of nonindigenous species on native ecosystems, agriculture, and natural resources, including the costs for control efforts. As noted by the Union of Concerned Scientists (2001), the accuracy of the Pimentel et al. calculations is difficult to assess, but probably is a minimum. In addition to economic and human health costs, aquatic invasive species (AIS) are anticipated to be the leading cause of biodiversity change in lakes in the coming century (Sala et al., 2000) and of extinctions in North American freshwater ecosystems (Riccardi and Rasmussen 1999).
The Great Lakes are the largest freshwater ecosystem on earth (not counting the polar ice caps). They are the economic, cultural, and recreational lifeblood of millions of North Americans. They are the gateway to the heartland waters of the United States and Canada. Threats to the systems have changed through the times, and so too must responses. Introduction of aquatic nonindigenous species is arguably the most serious economic and ecological threat to the Great Lakes today.
In this document we summarize the status of a variety of issues related to aquatic species invasions and the Great Lakes. We also provide analyses of what we believe are appropriate actions and priorities that are necessary if significant progress is to be made on these issues.
1 Though not an invasive species, European flounder are, nonetheless, very important indicators. Their inability to reproduce in freshwater means that the arrival of each specimen can be dated more accurately than with invasive species, i.e. within its lifespan, and this information can be used to track the effectiveness of various ballast management strategies.
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