Ann Arbor — Lake Huron’s glory days as a salmon fishery are likely gone forever, according to a study whose lead researcher says Lake Michigan is following a similar pattern.
Lake Huron’s population of the alewife, the herring-like fish that are the Chinook salmon’s main food source, collapsed in 2003, according to researchers. Heavy stocking of Chinook in Lake Huron contributed to increased predation of alewives; the sharp Chinook decline started soon after.
In Lake Michigan, populations of alewives and salmon are both declining.
The study, published Monday in Ecosystems, used a food-web modeling approach to determine factors on the decline of salmon in Lake Huron. It determined that heavy stocking of salmon led to increased predation of alewives. The increase in non-native mussels also competed with small fish — such as alewives and rainbow smelt, another salmon food — for nutrients.
“We are seeing all the same warning signs in lakes Michigan and Ontario,” said Yu-Chun Kao in a release. Kao conducted the work for his doctoral dissertation at UM under study co-author Sara Adlerstein-Gonzalez. “We’re seeing decreasing nutrient loads, a decrease in soft-bodied, bottom-dwelling invertebrates due to the mussels, a decrease in rainbow smelt and, as a result, Chinook salmon feeding almost solely on alewives.”
Kao is working to follow this research with a study that focuses on Lake Michigan. He is now a post-doctoral researcher at Michigan State University who works at the U.S. Geological Survey in Ann Arbor.
Additional modeling work will be needed to determine if the pressure on the alewives population is as high in Lake Michigan as it was in Lake Huron, said study co-author Ed Rutherford, a fisheries biologist for the National Oceanic and Atmospheric Administration. No single factor contributed to the decline, he said.
“It took a sort of perfect storm,” he said.
While there is a fear that there will be an alewives collapse in Lake Michigan, it is possible that the population could rebound, he said.
“Some are worried it’s happening right before our eyes,” Rutherford said, referring to the Lake Michigan alewives population. “Alewives tend to have reproductive events in years that are warm. I think it’s a little to early to tell if they are going to collapse and not rebound.”
Rutherford said alewives are notorious for having wide swings in population size.
A September report from the Michigan DNR said that the Lake Michigan salmon population is down 75 percent from its peak in 2012, due partly to reduced stocking rates and declines in reproduction from a lack of prey.
“DNR biologists believe the only way to keep Lake Michigan from following Lake Huron is to manage the fisheries by balancing
predator (salmon) and prey (alewife) so neither collapse,” that report said.
Rutherford said it can be tough to find a balance.
“What we know a little bit sooner is what’s going with the fish population,” he said. “The ability for management to respond very quickly is harder to do.”
Pacific salmon were introduced into the Great Lakes in the 1960s to control non-native alewives. But the alewife and rainbow smelt populations crashed in the early 2000s for reasons that included the invasion of foreign mussels that disrupted aquatic food chains.
Researchers say Lake Huron resource managers should focus their efforts on restoring native fish such as lake trout, walleye, whitefish and lake herring.
Staff Writer Candice Williams contributed.
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Lake Huron salmon unlikely to rebound, study says
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