The Invasive Largemouth Bass

Largemouth bass. Photo © Ken Schultz

By Ken Schultz

Surely you have read articles and seen documentaries about invasive species and the effect that they’ve had on native flora and fauna throughout the world. Back in 2005, a sidebar to a  National Geographic article on invasives listed the 100 least wanted invasive species worldwide, according to a global invasive species database maintained by the World Conservation Union.

They were not listed in order of the degree of threat they imposed. Among the seven species listed in the fish group was Micropterus salmoides. Yep, the darling of the North American freshwater sportfishing community and the single-most popular predatory fish species in the U.S.: the largemouth bass.

Which, by the way, was endemic to parts of the North American continent, yet is now found 

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in every state except Alaska (having been introduced to many of them). It has also been exported to Central and South America, Europe (including Spain and Italy), a handful of countries in Africa, and to China and Japan in Asia.

Japan has been undertaking an effort to eradicate bass, which must be kept and killed by anyone catching them in some, if not all, lakes. This is because largemouths have caused harm to native fish, a result that often occurs when species that have evolved to fill a specific biological niche are transplanted to other environments where the local species are unable, or poorly able, to cope with the invaders.

Think kudzu, milfoil, hydrilla, spartina grass, zebra mussels, lamprey eels, and carp, for close-to-home examples.

How often have you heard American anglers speak disparagingly of carp, which are not native to North America, but which are pervasive throughout the continent? Carp came to North America from Europe, by way of Asia, where they are native. According to a report on exotic fish by the Sport Fishing Institute, carp “were apparently brought to the United States from Europe in 1831 and 1832 by a private citizen.” The New York Department of Environmental Conservation reported that carp were first introduced into New York in 1831.

As many have written, the introduction of the common carp (also on the 100 least wanted list) to North American waters was a monumental mistake. Ironically, at the same time that carp were being distributed across the United States, so were brown trout, which were imported from Germany and also make the 100 least-wanted list.

While some exotic introductions are ecologically harmless, many are very harmful and have caused the extinction of native species. Freed from the predators, pathogens, and competitors that have kept their numbers in check in their native environs, species introduced into new habitats often overrun their new home and crowd out native species. In the presence of enough food and a favorable environment, their numbers explode. Once established, exotics rarely can be eliminated.

So, alas, the largemouth is no longer wanted in Japan by those who wish to see the native species of that country prosper, even though there’s a sizable interest in fishing for bass among Japanese freshwater anglers. 

Perhaps Japanese environmentalists are thinking about what happened in Africa, which not only has largemouth bass, but also Nile perch (also on the 100 least wanted list), a species native to that continent but not to some of its biggest waters. Lake Victoria, which is the second largest freshwater lake in the world, borders three African countries, many of whose people depended on that lake for subsistence and commercially fished for sale to the aquarium trade and food markets. The deliberate introduction of Nile perch into Lake Victoria is believed to have caused the apparent extinction of hundreds of small native tropical species in that enormous lake, and is now viewed as one of the most destructive exotic introductions of all time.

Perhaps at this point you’re thinking about the fuss that has been stirred up in the past few years by the discovery in Maryland (and now other states) of the snakehead, a high adaptive and fiercely predatory invasive Asian fish that can tolerate low levels of oxygen and which is unlikely to be eradicated. Some folks in the U.S. are very worried about snakeheads, which, incidentally, are native to India and China. Some have suggested that there might be a turf war between predator largemouth bass and predator snakeheads - a Survivor series in the making.

But just last month, Virginia biologists opined in a blog that snakeheads in the Potomac River, which is bordered by Virginia and Maryland, have “not had any noticeable impact on the largemouth fishery.” Instead of killing them, they encouraged people to enjoy fishing for them.
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The Potomac is a fertile place and evidently has enough food to accommodate the snakehead aliens. This may not be true in other places where they’ve spread.