Research reveals migrating Great Lakes salmon carry contaminants upstream

Dec 06, 2012 by Carol C. Bradley
Research reveals migrating Great Lakes salmon carry contaminants upstream
Gary Lamberti.

(Phys.org)—Be careful what you eat, says University of Notre Dame stream ecologist Gary Lamberti.

If you're catching and eating from a Lake Michigan tributary with a strong run, the stream fish—brook trout, brown trout, panfish—may be contaminated by pollutants carried in by the salmon.

Research by Lamberti, professor and chair of biology, and his laboratory has revealed that salmon, as they travel upstream to spawn and die, carry into streams and tributaries. The research was recently published in the journal .

It's a problem inadvertently created by people with good intentions, he notes.

"Most people don't realize that salmon are a non-native species in the Great Lakes," he says. "They were introduced to control alewives—another non-."

Although salmon fed on and contained the alewives—and have become important to sport fishing—there were unintended consequences. That's because of a lengthy history of industrial of the Great Lakes.

"All the Great Lakes have some level of pollution," says Lamberti, "especially near cities—Chicago, Detroit, Cleveland. There are far fewer pollutants now than over the past century, but many are persistent. There are hot spots, and Lake Michigan has a lot of them—, mercury, like PCBs."

PCBs (polychlorinated biphenyls) come from fluids in older electrical transformers. Also present is DDE (dichlorodiphenyldichloroethylene), a breakdown product of the banned insecticide DDT, and PBDEs (polybrominated diphenyl ethers). PBDEs, notes Lamberti, are used in furniture, mattresses and children's clothing. "They wash out when you do the laundry."

Research reveals migrating Great Lakes salmon carry contaminants upstream
Brook trout with salmon eggs pumped from its stomach.

Even intentionally introduced species such as the can result in unintended consequences for the ecosystem and the environment.

Salmon acquire pollutants through the lake food chain. When they are young, they feed on invertebrates—worms and insect larvae. As they grow larger, salmon consume more and more fish, such as alewives—which have also picked up pollutants through invertebrates they eat, which have picked up pollutants from algae and bacteria.

Salmon are a fatty fish, and these polluting chemicals are particularly "sticky," Lamberti says. "They are lipophilic—they absorb into fat tissue."

The consequence is that the salmon magnify the pollutants as they move up the food chain. "Salmon are longer lived, eat more, and the pollutants are then bio-concentrated."

The concern is that salmon are naturalized to many tributaries of the Great Lakes. "And it's a one-way street for them," Lamberti says. "They spawn, die in the stream where they spawn, and then leave their contaminant load in the stream. Stream fish eat salmon eggs, and may also eat carcass tissue as they decompose."

Fish in streams and tributaries with large salmon runs—fish that never go out into the lake, he notes—show contaminant levels very similar to that of Great Lakes salmon.

"Let's keep in mind," he adds, "there are FDA advisories for pregnant women and children on the risks of eating large Great Lakes fish, because of the danger of chemical contaminants.

"But there are no warnings for stream fish—that's the specter. If you're eating fish from a stream with a lot of salmon, you might as well be eating the salmon. I would err on the side of caution when eating any fish from a salmon river. Either that or harvest fish only upstream of where salmon spawn."

For comparison purposes, Lamberti's research analyzed the tissue of fish upstream from where salmon spawn and die.

"The upstream section of the same river was not contaminated. Below the salmon, the river had measurable levels of contaminants. There's no other way for the contaminants to get there but the salmon. Water doesn't flow uphill."

The conclusion?

Although salmon are an economic benefit to the Great Lakes and perform important ecological functions (such as controlling the population of alewives), we need to consider the impact of salmon on streams where they spawn.

"If we want to remove a dam on a river—and that will allow salmon to move upstream—we need to realize that the salmon will carry pollutants with them and disperse them into the food web," Lamberti says.

"In sensitive areas with a lot of native fish, we might want to prevent salmon from moving upstream. And in the Great Lakes, maybe we should consider restoring the native populations of lake trout and whitefish rather than encouraging more salmon."

Explore further: Leave that iguana in the jungle, expert tells Costa Rica

More information: pubs.acs.org/doi/abs/10.1021/es301864k

add to favorites email to friend print save as pdf

Related Stories

Scientists wonder where salmon are

Jul 07, 2005

Biologists and fish and wildlife experts in Washington State say only about 100,000 sockeye salmon have returned to spawn and they want to know why.

Maine salmon may be facing extinction

Jan 31, 2006

Maine salmon might be facing extinction despite a $20 million, five-year rescue effort and inclusion on the federal government's list of endangered species.

Norway may halt salmon fishing season

Apr 18, 2008

Norwegian wildlife management officials said stocks of wild salmon have dropped so low they may have to halt the salmon fishing season.

Recommended for you

Team defines new biodiversity metric

Aug 29, 2014

To understand how the repeated climatic shifts over the last 120,000 years may have influenced today's patterns of genetic diversity, a team of researchers led by City College of New York biologist Dr. Ana ...

Changes in farming and climate hurting British moths

Aug 29, 2014

Britain's moths are feeling the pinch – threatened on one side by climate change and on the other by habitat loss and harmful farming methods. A new study gives the most comprehensive picture yet of trends ...

User comments : 0