Anglers have another reason to bristle over the Lake Erie invasion of zebra mussels and round gobies.
The Eurasian natives have caused mercury concentrations in Erie walleyes to rise 50 percent since they invaded the lake 20 years ago, while levels in other Great Lakes walleyes have declined or remained stable. That's according to a study by the Canadian Ministry of the Environment, which sampled more than 5,800 walleyes and lake trout between the mid-1970s and 2007.
"During the 1980s, Lake Erie walleyes had the lowest mercury levels, compared to the other Canadian Great Lakes," said researcher Sityana Bhavsar, who led the 30-year study recently published in the American Chemical Society's Environmental Science & Technology journal. "Although Erie levels are now similar to, or lower than, the other lakes, what's disturbing is the increasing concentration trend."
According to the study, the average Erie walleye sampled in the past decade contained about 0.18 parts per million of mercury, an increase of 0.03 ppm over the previous decade. That's well within the limits of Pennsylvania's general advisory to consume no more than one-half pound of fish per week when mercury concentration is between 0.13 and 0.25 ppm. However, because of PCBs, another industrial pollutant, Pennsylvania recommends limiting most Erie fish, including walleyes, to one meal per month.
"These statistics are not alarming," said Pennsylvania Fish and Boat Commission executive director John Arway, noting that mercury from past and future industrial emissions is a concern on many waterways.
Bhavsar focused the study on walleyes because they are present in all the Great Lakes, and the University of Toronto is currently conducting a similar study on other species, such as perch. Although he included lake trout in his research, he said there were too few in Erie to provide conclusive data.
Mercury also can impact fish health and reproduction, but that wasn't an area explored by Bhavsar's research. He blames the Lake Erie mercury increase on gobies and zebra mussels, which Erie has in greater numbers than other waters of the Great Lakes system. Both invaders are native to the Black and Caspian seas and are believed to have arrived in Erie in the ballast water of transoceanic ships around 1990.
"They've changed the food web," Bhavsar said, explaining that mussels filter feed on the lake bottom, taking in mercury along with water. Gobies are also bottom-dwellers and forage heavily on zebra mussels. "As mercury goes up the food chain, it magnifies," he said. "By the time it reaches walleyes, they get the full web effect."
Humans are the top predators in the food chain and walleyes are coveted pan fare in the Great Lakes' $7 billion fishing industry. Canada's commercial fishermen harvested about 2 million walleyes in 2007, while recreational anglers in Michigan, New York, Ohio and Pennsylvania harvested a combined 2 1/2 million walleyes that same year. Pennsylvania does not have a commercial walleye fishery, but its recreational industry, including charter captains, is a key part of the Erie economy.
Matt Hrycyk of Chasin Steel charters said he's not surprised by the Canadian findings on walleyes and would expect to learn that perch are similarly affected.
"When you catch perch, they're just loaded with zebra mussels," he said. "Look in shallow water and you'll see the lake's covered with them. The gobies are everywhere, too. It's a shame, but there's nothing to be done about it."
Hrycyk said the study won't influence his behavior.
"I've been eating walleyes for 26 years and I'm not going to stop now," he said.
But while he and others may be meticulous in how they clean and fillet walleyes, there's no way to cut or cook mercury out of a fish's body, Bhavsar said. Unlike some industrial toxins that accumulate in belly fat, mercury builds in muscle tissue, which is the part people eat.
Charter captain Pete Alex, head of the 250-member Lake Erie Sportfishing Association, said he tries to stay on top of contaminant issues so that the two dozen charter captains who belong to his group can address customer concerns.
"That's the No. 1 or 2 question my customers ask -- is it safe to eat Erie walleyes?" he said.
Alex said he has taken walleyes and other species to an Erie lab for testing three times in recent years, and while he had just one walleye analyzed on each occasion, results showed only trace amounts of mercury.
"The levels were well below what's considered safe, compared to standards set both by the U.S. government and Canada," he said.
Alex said he's not concerned about the Canadian findings, and he and his family will continue to eat Erie fish.
While mercury occurs naturally in the environment, it also is discharged by coal-fired power plants, paper mills and other industries. Bhavsar said that while regulation of industrial emissions increased with adoption of the Clean Water Act of 1972, what is now contained in Lake Erie sediment reflects prior decades of accumulation, and will take decades to go away.
"Mercury could be dredged out, but that's not a realistic option," he said. "You really have to wait for it to wash out or for new sediment to accumulate on the bottom of the lake, and that will be a very slow process."
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