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GVSU researcher finds salmon link to contamination in brook trout
A link between chemical contamination levels in brook trout in streams and salmon in Lake Michigan has been described by a researcher at Grand Valley State University’s Annis Water Resources Institute in Michigan. The research might have implications regarding decisions to remove dams that now prevent Lake Michigan salmon from reaching new upstream spawning areas.
David Janetski, a postdoctoral researcher, said he has found a link between spawning Chinook and coho salmon and elevated levels of pollutants in fish found in tributaries to Lake Michigan. Those pollutants include PCBs; DDE, a chemical byproduct of DDT; and PBDE, a flame-retardant chemical classified as toxic by the EPA.
Some of these chemical pollutants accumulate over time in Pacific salmon that have been planted in Lake Michigan since the 1960s, so the Michigan Department of Community Health has published an advisory for many years that offers cautionary advice to those who frequently eat fish caught in the Great Lakes.
Janetski’s research indicates these chemicals may be transferred to smaller fish, including native brook trout, when they eat the eggs Lake Michigan salmon lay in streams during spawning season. His research indicates that those chemical levels found in fish living in Lake Michigan tributaries where the stocked salmon now spawn are, on average, 30 times higher than in fish living in streams the salmon cannot reach.
Janetski told the Business Journal his research team found evidence that there is “a lot of direct consumption” of salmon eggs by other types of fish that live in salmon spawning areas. Brook trout, in particular, “just gorge on salmon eggs. We found brook trout with stomachs just chock full of eggs.”
However, he noted that some of the chemical contamination levels in trout in streams without salmon were barely detectable. Thus, he said, a 30-fold increase from “barely detectable” doesn’t necessarily mean there is a dangerous level of contamination in the trout eating salmon eggs.
Janetski said his team sampled whatever type of resident stream fish they could find, which was mainly brook trout, sculpin and dace. Sculpin and dace are small, not considered sport fish and generally not considered edible, but brook trout are a highly prized game fish and eaten by many people.
“If background levels in these streams are at a certain amount and salmon come in and raise that 30 times, I think that’s important in terms of understanding the dispersal and distribution of pollutants in the Great Lakes basin,” Janetski said. “We’ve found that salmon runs can be very important (to pollutant distribution) in certain situations.”
The research project is a joint collaboration between AWRI and the University of Notre Dame, where Janetski just finished his doctorate in aquatic ecology.
He said some resident fish were studied in salmon-spawning streams that enter Lake Superior, but no contamination was found, mainly because there is far less chemical contamination in Lake Superior salmon.
Janetski noted that the Pacific salmon planted in the Great Lakes have succeeded in controlling the alewife population and are an extremely valuable species for commercial and recreational fishermen alike. He said his research doesn’t mean salmon should not be stocked in the Great Lakes any more, and he was not willing to offer his opinion on whether or not those brook trout from salmon-spawning streams are safe to eat. However, he said that if people are concerned about the spread of chemical contamination in Lake Michigan, it’s worth noting that salmon can be a factor.
“I’m not saying salmon are bad,” he said. “There are different aspects to those introductions (of Pacific salmon into the Great Lakes) that we are trying to understand. They could be important down the road.”
Removal of dams on streams that feed into Lake Michigan “is a thing that always comes to mind, to me. If a dam is removed and salmon move upstream, I think whoever is in charge needs to be aware of the potential impact.”
In fact, there is a major dam removal project underway near Traverse City. Last fall the Michigan DEQ issued permits for drawdown of the impoundment ponds behind the Brown Bridge and Sabin dams on the Boardman River in Grand Traverse County, in preparation for removal of those dams. The Boardman Dam also will be removed. It is a long-term project estimated to cost from $5 million to $8 million, intended to return the river to a more natural state as a free-flowing, cold-water river.
The Boardman, which empties into Grand Traverse Bay, is one of the top 10 trout streams in Michigan and a state-designated “natural river,” according to the organization supporting the project, www.theboardman.org