Since 1966, Pacific-native salmon have been present as stocked fish in Lake Michigan. Soon after, they were added to other Great Lakes. The big fish are now a common feature of the lakes and the basis of what is today a $7 billion annual recreational fishery in Lake Huron.
The fish were brought in to take care of an invasive problem: alewives, small fish similar to herring that are native to the Atlantic Ocean, which first entered the Great Lakes via canals in the late 1800s. The prey fish had huge numbers by 1960 and so exceeded the load level of the Great Lakes that there were mass die-offs, with the small fish littering lake beaches.
For quite a while, coho and Chinook salmon seemed like a great solution. They ate the alewives and thrived, and the small fish's mass die-offs ended.
But the alewives also caused problems as they ate the youthful stages of several types of Great Lake native fish, including yellow perch and lake trout.
Now, a new computer-modeling study led by the University of Michigan has found that the Chinook salmon fishery in Lake Huron will probably never again be at a high pitch and a focus of the lake because the lake cannot support the alewife at this point.
With findings like that, the study authors suggest that Lake Huron natural-resource managers should zero in on restoring native fish species like lake trout, lake whitefish, walleye and lake herring. As time goes on, Lake Michigan's alewife population will likely collapse in a way similar to the situation in Lake Huron, which will cause a crash of its Chinook salmon fishery too.
"These results serve as a reality check for those who continue to pressure the resource managers to stock Chinook salmon in Lake Huron," noted Sara Adlerstein-Gonzalez, study co-author and a fishery scientist at U-M. "The findings are also good news for native fish species and for the restoration of the entire Lake Huron ecosystem. Maybe we should celebrate the improvements in the native fish populations and try to adapt to this new situation."
The alewife population in Lake Huron fell through in 2003, followed soon after by a definite decline in Chinook salmon. While Michigan and the nearby province of Ontario halted Chinook salmon-stocking in the southern end of Lake Huron in 2014, they have continued stocking the northern end.
Already in Lake Michigan, alewife and salmon populations are on the decline, and Chinook stocking is taking place at much reduced levels.
The new computer-modeled study used food webs to look at factors backing the 2003 collapse of alewives in Lake Huron and results and implications for future populations of fish there. Causes of the alewife collapse included the spread of non-native quagga mussels and declining phosphorus (an essential nutrient) from rivers and streams.
The findings were recently published in the journal Ecosystems.
Follow Catherine Arnold on Twitter at @TreesWhales.
