Nonnative Species Are Big Fish in U.S. Ponds

America’s native fish diversity is in steep decline.

A century ago, the country’s fish populations were far more regionalized. There were rainbow trout on the West Coast, striped bass on the East Coast and distinctive lists of fish species for each state.

Today, though, America’s fish populations are “homogenized”--blended into one group of increasingly common fish. Like pigeons and rats, three fish--largemouth bass, black crappie and the common carp--are now found in each of the lower 48 states, according to a new study that is among the first to quantify just how large the problem has become.

“Many species are being replaced by common, weedy species that are very successful,” said Frank J. Rahel, a professor and fisheries biologist at the University of Wyoming who conducted the survey, published in the journal Science.

Once exotic species become established, they are almost impossible to remove, biologists said. And removals are expensive. The eradication of the nonnative white bass from Lake Kaweah in Tulare County cost taxpayers $7.5 million. And state officials are still paying the political cost of poisoning Lake Davis near Portola in a failed effort to kill off northern pike.

The same trend affects mammals, birds and insects. Biologists warn that continuation of the trend will lead to a loss of the country’s regional uniqueness.

“What if you went to Hawaii and all you saw were starlings, sparrows and pigeons?” asked Michael J. Mac, who directs the fisheries program of the U.S. Geological Survey’s Biological Resources Division.

The main cause of this blending is not extinction, as biologists had long expected, but widespread introductions of nonnative species, Rahel said.

In his analysis, Rahel compared states to see how many fish they had in common historically and how many they have in common now. On average, he found, pairs of states now share 15 species more than they did before European settlement. Arizona and Montana, for example, historically had no species of fish in common. Today, they share 33 species.

The spread of hardy, exotic species is propelled by habitat changes, such as dam building and marsh draining, that harm the more vulnerable natives, experts said.

“It’s a one-two punch,” said Peter B. Moyle, a professor of fish biology and expert on native California fishes at UC Davis. “You change the habitat, then you send in the exotics, and the poor native fish don’t stand a chance.”

The displaced fish come from several sources. Some are exotic aquarium escapees, such as swordtails, guppies and even piranhas. Many are poured from bait buckets, like the red shiner minnows that course through L.A. Basin streams. (Biologists say unwanted aquarium fish should either be given away or euthanized, and bait fish should be returned to the bait shop or killed.)

The migration of fish, reports Rahel, mimics the migration of Americans: They move east to west. As early settlers spread west, they became disenchanted with local fish. Minnows were too small and suckers were too bony.

So the Easterners brought their favorite eating fish along. Those menu choices, brown trout from Europe and largemouth bass from the East, still swim through today’s Western ponds and lakes.

Of Nevada’s 85 species of fish, 24 hail from the East. In Kentucky, however, only one of 212 species--the rainbow trout--is a native Westerner. Most Western fish do not tolerate the warmer waters of the East; the rainbow trout does. Eastern fish are thriving in Western dam impoundments and reservoirs--waters warmer than natural mountain streams and lakes.

Late 19th century fish and wildlife officials were happy to oblige the demands of new residents and stocked many Western lakes with pike and walleye, voracious predators of other fish.

In 1882 alone, fisheries officials distributed more than a quarter million of the now dreaded carp for establishment across the country. Some workers went to extreme lengths to introduce brook trout into remote mountain streams that held cutthroat trout.

What we see today, said Rahel is “a legacy of fisheries management of the past 120 to 150 years.”

The legacy is clear. Of 17 widely introduced species, 12 are game fish.

In California, two thirds of the state’s 116 native fish require special protection, said Moyle. Chinook salmon face nonnative predators such as striped bass as they swim downstream through the Central Valley.

The Sacramento perch must compete for spawning sites with transplanted bluegill and green sunfish, and “aggressive Easterners always win,” Moyle said.

“Far too many anglers believe themselves to be amateur biologists. They just don’t know what they’re doing,” said Norville Prosser, a vice president of the American Sportfishing Assn., a group that supports the stocking of game fish if it is “scientifically based” and works to protect fish habitat.

The recent illegal introduction of lake trout into Yellowstone Lake, he said, is endangering the premier cutthroat trout fishery there. Efforts to remove the lake trout have not had much effect.

Despite the relentless spread of exotics, some biologists see cause for hope. New laws addressing the problem have recently gone into effect, said the USGS’s Mac.

In California, there is a $50,000 fine and imprisonment penalty of up to one year for importing nonnative aquatic species--plants or animals--into state waters, said Chuck Knutson, a senior biologist with the California Department of Fish and Game.

New interventions may also help. Moyle has shown that altering water flow near dams increases the number of native tule perch, Sacramento pikeminnow and rainbow trout downstream.

Although we will probably have to live with many of the exotics that are established, Moyle said it is imperative to prevent new species from taking their first footholds here and causing even more disruption in the future.

As soon as unwanted species are introduced, they should be immediately eradicated, he said.

“One of the things we have to think about in California,” he said, “is developing SWAT teams for exotic species.”

For more information on this issue, go to: https://nas.er.usgs.gov/ To anonymously report the illegal transplantation of aquatic species to the Department of Fish and Game, call (888) DFG-CALTIP.

Usha Lee McFarling can be reached at usha.mcfarling@latimes.com

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Taking Over

Fish populations in rivers, streams and lakes across America today are remarkably similar because of the widespread introduction of fish beyond their native ranges. In pre-Colonial times, many regions had their own specific species. Today, a few species are found throughout the continental United States.

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SUCCESSFUL INVADERS

These fish are now found in more than 40 states, though none is native to such a widespread area.

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STATES WHERE SPECIES IS:

NATIVE INTRODUCED

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FISH NATIVE RANGE Common carp 0 48 Eurasia Goldfish 0 42 Eurasia Rainbow trout 6 41 Western U.S. Smallmouth bass 23 45 Eastern U.S. Black crappie 28 48 Eastern U.S. Yellow perch 26 46 Eastern U.S. Fathead minnow 25 44 Eastern U.S. Walleye 25 44 Eastern U.S. Largemouth bass 29 48 Eastern U.S. White crappie 27 45 Eastern U.S. Bluegill 31 47 Eastern U.S. Green sunfish 30 45 Eastern U.S.

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The map shows states with high populations of introduced fish species. Alaska and Hawaii were not part of the study.

Sources: Frank J. Rahel, University of Wyoming; Freshwater Gamefish of North America