Ecology Lesson: A Great Lake is not the Pacific Ocean

Coho Salmon Breeding Male (By A. Hoen and Co. [Public domain], via Wikimedia Commons)
Great reporting by the Milwaukee Journal Sentinel’s Dan Egan on the historical background of an issue I mentioned in an essay for the April 2014 issue of Milwaukee Magazine: the demise of invasive alewives and stocked Pacific salmon in Lakes Huron and possibly Michigan leading to the return of native lake trout, and, as Egan reports, other native species of fish. It’s a story of what happens when scientists (and other people) tinker too much with the natural world, in this case to create a superheated, apparently short-lived fishing industry.

In the first two installments of the series, Egan introduces two Michigan fishery biologists and their plan for the stocking of Coho and Chinook salmon, native to the Pacific Northwest, into Lakes Michigan and Huron. The stocked salmon were placed not primarily to consume alewives but to create a fishing industry. As Egan tells it:

And just like a rancher trying to raise every ounce of beef from a pasture, biologists boosted annual hatchery plantings on Lakes Michigan and Huron in the 1970s and 1980s.

Their plan worked but too well. The Pacific salmon readily adapted to the inland seas and began to breed on their own. Unfortunately, invasive mussels then reduced the food of the invasive alewives, thereby reducing the number of alewives, and thereby quickly reducing the numbers of the alewife-dependent, humanly-placed salmon, whose population expanded beyond the power of people to control.

Lake trout, however, are not as dependent on one food source, for as native fish they have evolved to eat a varied Great Lakes diet. Now a lack of alewives and salmon in Lake Huron (and increasingly Lake Michigan) is giving lake trout an opportunity to regain their population.

While Lakes Michigan and Huron are indeed quite large, even putting their areas and volumes together does not come close to replicating the size and ecosystem of the Pacific Ocean. In hindsight, the idea of placing an ocean fish into the Great Lakes to revive and propel a Great Lakes fishery was an act of scientific hubris, a bold if unwise attempt to create a new sportfishing market as well as rectify the folly of allowing ocean-going tankers into the Lakes, and thus an opening for invasive species. Ironically, it is the non-intentional stocking of invasive mussels which seems to be removing the alewives and the intentionally invasive salmon.

Egan reports that contemporary fish biologists don’t criticize their fellow fisheries specialists for, in essence, trying to play God with the Great Lakes or, at least, most don’t:

Few biologists today fault Tanner and Tody for so audaciously reconstituting the Great Lakes — Michigan’s new research vessel for Lake Huron will bear Tanner’s name.

But the lesson many of today’s biologists have taken from what happened on Lake Huron is one of humility.

It’s a good lesson for all of us.

Postscript: And finally Dan Egan brings us up-to-date on what is happening with fish in Lake Michigan. Note the conflict between the state and federal plans: fishing as money-maker vs. restoring the native ecosystem– a now familiar contrast in priorities.

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