Below is an adapted excerpt from Beyond the Sea: The Hidden Life in Lakes, Streams, and Wetlands by David Strayer. Copyright 2024. Published with permission of Johns Hopkins University Press.
Biological invasions sometimes are seen as an inevitable result of modern life, but like other human impacts on inland waters, we can control them if we choose to do so. The North American Great Lakes have been heavily invaded by nonnative species: almost 200 nonnative species have been established in the Great Lakes basin, chiefly since the mid-twentieth century. Although most of these species have had small impacts, a few dozen problematic species have had strong ecological and economic effects.
No control has been attempted for most of the established invaders, which are not thought to have troublesome impacts. Other invaders that have had serious harmful effects (common carp and the problematic wetland plant phragmites, for example) have not yet been brought under control, despite repeated efforts. Nevertheless, experience from the Great Lakes shows that biological invasions can be managed or prevented.
Photo courtesy of Johns Hopkins University Press
Probably the most intensive control effort of an established invader was targeted at the sea lamprey. This parasitic fish came into the upper Great Lakes through the Welland Canal. It badly damaged valuable fish populations, nearly eliminating lake trout from Lake Huron and Lake Michigan within a few years of its arrival. Trout landings in these lakes fell from an average of 9.8 million pounds per year (4.4 million kilograms per year) between 1930 and 1945 to just 126,000 pounds per year (57,000 kilograms per year) from 1952 to 1961.
Such catastrophic impacts spurred scientists to undertake intensive studies of lamprey biology in the hope that they might find vulnerabilities that could be exploited for control. The insights gained from these studies led to a multifaceted, broad-scale control program that combined barriers and traps on tributary streams with applications of pesticides that were lethal to lampreys but caused relatively little harm to other species. Control measures must be applied every year, are costly, and have some undesirable effects on species other than lampreys, but they have been effective in controlling the invader: sea lamprey populations have fallen by more than 90%, which has allowed valued fish populations to recover.
Purple loosestrife is another species successfully targeted for control. This plant had overrun many wetlands in the northern United States and Canada, crowding out other wetland plants and damaging wildlife habitat. Attempts to control this species through herbicides, water management, mowing, and burning were not very successful, so a biological control program was developed in the 1980s. This program found several species of beetles from purple loosestrife’s native range in Europe that ate a lot of loosestrife but did not bother native plants.
Following releases of these beetles in the 1990s, loosestrife populations declined in many (but not all) wetlands in the Great Lakes region. The control programs for lamprey and loosestrife show that it is sometimes possible to control troublesome invaders, if you have the right combination of detailed biological research, luck, and tolerance to costs and nontarget effects.
However, it is often less expensive and more effective to prevent invasions than it is to later try to control them. By 1990, it was clear that untreated ballast water was bringing many invaders into the Great Lakes, including some of the most damaging species (zebra and quagga mussels, round gobies). By the late 1990s, the states and provinces around the Great Lakes had agreed to require ships entering the Great Lakes to treat their ballast water.
Since then, ballast-water invasions into the Great Lakes have nearly stopped. These measures probably have already prevented dozens of new invasions, avoiding the need to later mount targeted control campaigns against any that turned out to be harmful. The ballast water controls did not require shutting down trade into the Great Lakes or imposing impractical burdens on the shipping industry.
We know how invasive species are moving into inland waters—ballast water, the pet and horticulture trade, contaminated boats and recreational gear, canals, and so on—and we have remedies that could be applied to each pathway that would slow the movement of invaders and prevent future problems. We just don’t always have the political will to apply these remedies.
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Featured image: The sea lamprey (two of which are attached to an unfortunate lake trout), a troublesome invader of the Great Lakes whose populations have been reduced through targeted control efforts. (Photo courtesy of Great Lakes Fishery Commission/Wikimedia Commons via Johns Hopkins University Press)
