Penn State Agriculture Magazine

strangeinvaders page 2

Today, Ruffing is researching the impact of gobies on Lake Erie. A few of the little fish, mottled green-and-brown with flat faces and thick lips, turned up in a state Fish and Boat Commission sampling net in 1995. Now, less than a decade later, scientists say the lake has more pounds of gobies than any other fish.

Their exploding population is having a huge impact on Lake Erie’s native aquatic species, warns Ruffing, who is pursuing a doctorate in ecology under the guidance of ichthyologist Jay Stauffer. Already, she says, many sculpins and darters have virtually disappeared from Lake Erie, upsetting the aquatic food chain. She fears that the gobies threaten sensitive and endangered aquatic life not just in the Great Lakes system, but across the state and perhaps across the country.

Gobies might be the best—or worst—recent example of the havoc that exotic, invasive species can wreak in an environment like Pennsylvania, particularly if natural controls, such as predators, are not present. But invasive species are not new here, and they are as common on land as they are in the water. Invasive pests such as the gypsy moth have been causing damage for decades.

Calculating the ecological and economic impact of invasive species is nearly impossible, but it is immense. Invasive species—organisms that grow and reproduce quickly, spread aggressively, and displace other species—typically take food and habitat away from or prey upon native species. Their populations boom, unchecked by predators because none have evolved in that location with them, resulting in often severe damage to ecosystems and economically valuable plant and animal species. In the worst cases, native species may become extinct because of their inability to compete with or survive predation by invasives.

Researcher Renae Ruffing inspects gobies she is raising in a Penn State laboratory, looking for clues to how their burgeoning population might be controlled. The Asian interloper is having a major impact on Lake Erie's aquatic ecology. Scientists say there are now more pounds of gobies in Lake Erie than any other fish.

In the case of Lake Erie, an $82 billion annual sport fishery may be at risk from the effects of invasives, including gobies. But in almost every case where invasive species are damaging the natural ecology, scientists at Penn State and elsewhere are scrambling to devise ways to control them.

Gobies, which only average 6 inches in length when fully grown, have strong jaws, big heads, and wide mouths relative to their small bodies. The fish swam into perfect habitat when they were inadvertently released into the Great Lakes system from the ballast of some ocean-going vessel from Europe or Asia about a decade ago.

The Great Lakes had previously been invaded by zebra and quagga mussels, and the shallowest one, Erie, offered fertile habitat for both Asian interlopers. The mussel populations exploded. As it turns out, mussels are gobies’ favorite food, so the fish’s numbers have reached staggering proportions.

“Gobies breed prodigiously,” Ruffing points out. “They are nest guarders that chase predators away from their eggs, which gives their fry a much better chance of surviving. They also spawn several times per season. What a nursery for gobies Lake Erie has turned out to be!”

In their native Eurasia, people eat gobies. “There is a commercial fishery for Eurasian gobies,” Ruffing says. “But gobies in the Great Lakes eat both quagga and zebra mussels, and those mussels have been found to be high in heavy metals, presumably because they have filtered toxins from past and present pollution out of the water. It wouldn’t be healthy to eat the gobies in Lake Erie.”

In Eurasian waters, gobies were originally a brackish water fish, notes Ruffing, who says they have adapted “amazingly well” to fresh water. But it is precisely those saltwater roots that make Ruffing and other scientists worry about the devastation gobies could cause in the United States. Researchers are now studying gobies to see whether they could readily adapt to the waters of the Chesapeake Bay. “We hope not,” she says. “They could wipe out the shellfish in the bay.”

Gobies would show up first, Ruffing believes, in lakes close to Erie, such as Edindoro or Pymatuning. “We are concerned that they might get into waters such as French Creek in the Allegheny River system, where most of our native mussel species are either endangered or threatened,” she says.

Some gamefish species feed on gobies—both smallmouth and largemouth bass target them, and bass numbers in Lake Erie seem to be up. Increasingly, however, anglers are using gobies as bait, and Ruffing worries that will contribute to their spread into other waters.

Zebra and quagga mussels are so similar in appearance it is difficult to tell them apart. There are so many in Lake Erie now, their constant water-filtering feeding has made the water clearer than it has ever been.

“ Gobies are very effective baits for bass in Erie,” she observes. “How long will it be until some angler takes a bucket of them bass fishing in French Creek and then dumps them in after he’s done? It may have happened already.”

The goby explosion has occurred at the same time as the apparent collapse of Lake Erie’s highly valued walleye population, and scientists are wondering about a connection. “We have no proof that the two are related,” Ruffing says. “But what if walleyes are broadcasting their eggs in places where there are millions of gobies on the bottom just gobbling them up? That might explain a lot.”

Ruffing says gobies are believed to be in the upper reaches of the Mississippi River as well, steadily working their way downstream and threatening future ecological mayhem in the lower river and delta. Scientists believe that they reached the Mississippi through Lake Michigan and the Chicago Canal.

“There doesn’t seem to be much we can do about them,” she says. “Our most immediate concern is that they will get into French Creek in northwestern Pennsylvania, one of the most ecologically diverse streams in the East. There are many species of mussels and darters in French Creek, and we think that if the gobies were there, the darter populations would be decimated. We don’t know what impact gobies would have on native mussels, but I can’t imagine it would be good.”