What to do About Introduced Species?By Robert Bock
reprinted from American Currents, Spring 1997
Maryland longears. West Virginia guppies. Florida cichlids. Colorado River angelfish. Michigan sea lampreys. And everywhere-- bluegills. We human beings have an incredible propensity for moving other species around. According to the Office of Technology Assessment's 1993 report, Harmful Non-Indigenous Species in the United States, at least 4,500 species of foreign organisms have established free-living populations in the United States. These include not only plants and plant parasites, but also insects and other invertebrates, birds, mammals, and at least 126 species of fishes, 47 of which are known to have established stable breeding populations.
Presumably, the list does not include species native to one part of the U.S. and established in another. If you're new to NANFA, you may not realize that fish native to this continent can often do as much damage once they're transplanted to another drainage system as any species from a foreign country could. Sometimes people introduce species deliberately. Rainbow trout, striped bass, and large and smallmouth bass have been introduced far outside their original ranges to establish both recreational and commercial fisheries. The Great Lakes salmon fishery is based on the coho salmon, a species native to the West Coast. Other times, new species arrive by accident. An unintentional stowaway, a European perch called the ruffe, was taken on in the ballast tanks of ships headed to the U. S., and escaped when the ships discharged their ballast water in the Great Lakes. (Dan Logan speculates that an Asian shrimp he and the other Northwest NANFA members discovered in Oregon was introduced to the U.S. this way.) Similarly, fish raised for the aquarium trade and sport fishing may escape in the hatchery outflow.
At still other times, new species become established through various combinations of kindheartedness and indifference, when people release pets they no longer wish to keep. Goldfish, an Asian native, now live in ponds, lakes, streams, and rivers throughout the U.S. In the Winter 1996 issue of this publication, the Riffles column contained an item about freshwater angelfish that were thriving in a weedy stretch of the Colorado River.
The warm waters of Florida, Texas, and other parts of the Southwest have become a haven for free-living populations of oscars, Jack Dempseys, jewelfish, firemouths, convicts, midas cichlids, tilapia, swordtails, mollies, platies, croaking gourami, walking catfish, and at least three species of suckermouth (loricarid) cats. And a few years ago, when I visited the thermal springs in Berkely Springs, West Virginia, I was surprised to find veil-tall guppies thriving and reproducing in the warm water!
These introductions can be disastrous. Roughly $10 million is spent each year on research and control of the parasitic sea lamprey, which migrated from Lake Ontario to the other Great Lakes when the Welland Canal was constructed. We notice the effects of introductions when they exact a heavy financial toll. But if an introduction doesn't affect us economically, we probably aren't going to pay much attention to it. Few people will care if stocking rainbow trout in a midwestern stream reduces the populations of native darters and sculpins that hardly anyone knew were there in the first place.
And the damage such introductions do may not become apparent for many years. When I was a kid, my family and I would visit my uncle in the Catskills and I would fish in the lake nearby. Occasionally, I'd pull in a golden shiner among the yellow perch and pumpkinseed sunfish that were unlucky enough to try to eat the worm at the end of my bobber. The shiners were introduced into the lake by fisherman who dumped the contents of their bait buckets into the water when they were through fishing. When I visited the lake again about 25 years later, the native perch and pumpkinseeds appeared to have been severely out competed by the shiners. I pulled in about 50 shiners that morning and only a few pumpkinseeds and perch.
And who knows what effect such an introduction will have on the local species in 25 more years? I fear that in many cases, the damage we do may not become apparent until long after we're gone. Who can say whether smallmouth bass stocked in a northeastern river today won't lead to local extinctions 50, 100, or even 1,000 years later?
Sometimes introductions have consequences no one could have predicted. For example, the seemingly innocent stocking of one fish in Arkansas seriously jeopardized an endangered species in Utah. In 1968, the Arkansas Game and Fish Commission introduced the Asian grass carp into Arkansas lakes. The fish soon spread to the Mississippi River and became established. The grass carp carried with it from Asia a parasitic tapeworm that eventually spread to red shiners, a popular bait fish. Anglers or bait dealers introduced the infested shiners into the Colorado River, and by 1984 the shiners had found their way to the Virgin River in Utah. Here the tapeworm infected the woundfin, a native minnow already endangered because of dams and water diversions. Not as resistant to the tapeworm as were the red shiners, perhaps weakened due to competition with the shiners for food and space, the woundfin suffered a rapid decline from which it has barely recovered.
To complicate matters even more, human beings have also gained the ability to create new "species" where none existed before. Last spring, I was trying to catch some pumpkinseed sunfish for my 65 gallon aquarium. In recent years, this native species has become hard to find in my part of Maryland. After hooking and releasing a dozen of the introduced bluegills, I reeled in what I thought was the most colorful pumpkinseed I'd ever seen. On close inspection, however, this fish had a much larger mouth than a pumpkinseed, and a pale orange trim around the edges of the fins. I've tentatively identified it as a cross between a pumpkinseed and a green sunfish. How it got there, I have no idea, as there aren't any green sunfish around for miles.
Hybrids like this one, though, are often stocked, as it's assumed they won't reproduce. But in a recent posting on the NANFA E-mail list, Garold W. Sneegas reported that a small percentage of bluegill x green sunfish hybrids that were stocked in a Kansas pond had indeed reproduced. Such hybrids often grow larger and are more tenacious than either parent species--stiff competition for the native fish that are forced to share their environment with them. And we can only expect the competition from man-made hybrids to get worse, as genetic engineers tamper with the genes of existing species to create fish ever more suited to sportfishing.
To be sure, the Genie's already out of the bottle and there's no chance of returning things to the way they were before Europeans came to this continent. Once a species becomes established, it's difficult to eradicate. And as much as I hate to admit it, to a certain extent we depend on exotics. Sportfishing is a multi-billion dollar industry. If we could eliminate all introduced species tomorrow, people who make a living on everything from worm farms, to bait shops, to lure manufacturing, to angling magazines would be thrown out of work. But as the number of native fish enthusiasts grow, we'll be in more and more of a position to influence things, by lobbying State legislatures and natural resource departments and letting them know when their plans to introduce new species are a bad idea. Perhaps we can even be influential in the creation and maintenance of "sanctuary districts"--streams, lakes, and ponds where exotics would be prohibited and natives could flourish.
But until the time comes when NANFA becomes a big, powerful organization, there's still a lot we can do. First, there's the matter of personal responsibility. In big, bold, capital letters, so you never, ever forget: DON'T RELEASE ANY FISH INTO A DRAINAGE SYSTEM WHERE IT DIDN'T ORIGINATE. Even if the fish doesn't find another of its kind to reproduce with, it could still spread diseases or parasites. Similarly, if you're going to keep fish from a number of different places together in the same tank, you shouldn't release them back into the wild. If you can't keep them or find a good home for them, it's better to euthanize them.
You should also be careful not to transport water from one system to another. Your flooded waders or seemingly empty bait bucket might contain unseen parasites or larvae that could have a damaging effect in new waters.
As NANFA members, we can also encourage the removal of non-natives from the environment. Peter J. Unmack regularly leads trips to the Nevada desert to remove largemouth bass and other introduced species from desert springs, where they pose a serious threat to the native spring fish.
We can also encourage the collection of introduced species that make interesting aquarium fish. I'll start: In this issue, we're publishing information on where to collect the longear sunfish from the C&O Canal in Montgomery County, Maryland. I haven't been able to identify the particular longear subspecies I found while angling there last year. Even though it's not as colorful as the one in Robert Rice's Tropical Fish Hobbyist article on the subject, it's still a nice little aquarium fish. We've published a map and other practical information, so if you're ever in the area, you can try your luck. Most aquarists dream of collecting in the Amazon or in Africa. In fact, they don't have to travel so far.
Cichlids and other exotics are established in Florida and many other places in the South. Again, NANFA members can help by encouraging people to get these exotics out of the environment, either to collect them for home use, or for distribution to pet shops. I'm also asking our Southern members to get together and pool their knowledge, to write an article like "Amazon collecting in Florida," or "Cichlid collection in the South." (I'd write it myself, but I'm unfamiliar with the locale.) I envision the article as a practical, how-to guide, complete with maps and such useful information as where to write for permits. The best place to submit it would be Tropica1 Fish Hobbyist. We could reach a lot of tropical keepers who've never collected before, and get them out into the ponds and streams. At the end of the article, you could mention NANFA and natives, and get them used to the idea that there are interesting natives, as well. If you pulled this off, you'd get a by line, a check, and a chance to publicize NANFA and perhaps net us a few more members. If you'd like some editing help before you send the article off, Chris Scharpf and I would be glad to help.
For more information, check out the Nonindigenous Aquatic Species (NAS) Information Resources web page at http://nas.er.usgs.gov/
Used with permission. Article copyright retained by author.