USGS news: Changing tides: Lake Michigan could best support lake trout and steelhead

August 16, 2017

Invasive mussels and less nutrients from tributaries have altered the Lake Michigan ecosystem, making it more conducive to the stocking of lake trout and steelhead than Chinook salmon, according to a recent U.S. Geological Survey and Michigan State University study.

Reduced stocking of Chinook salmon, however, would still support a substantial population of this highly desirable recreational salmon species, which is a large contributor to the Great Lakes multi-billion-dollar recreational fishery.

"Findings from our study can help managers determine the most viable ways to enhance valuable recreational fisheries in Lake Michigan, especially when the open waters of the lake are declining in productivity," said Yu-Chun Kao, an MSU post-doctoral scientist and the lead author of the report.

Managers have reduced Lake Michigan stocking levels of Chinook salmon at least three times over the past decades in response to declining prey fish and the natural reproduction of Chinook salmon. For the new study, scientists investigated the lake's current and future abilities to support different fish stocking efforts. They found that recent decreases in critical lake nutrients, partly due to increases in invasive species such as quagga mussels , reduce the amount of Chinook salmon that the lake can support.

"Our model showed that stocking Chinook salmon can still help maintain their populations in Lake Michigan," said Mark Rogers, a USGS Tennessee Cooperative Fishery Research Unit scientist and co-author on the study. "When stocking was completely eliminated in the model, the long-term amount of salmon was predicted to decrease considerably. The key is to determine how much stocking is most effective. It's a balancing act."

The study also found that lake trout and steelhead may fare better because these two species can switch from eating alewife, which are in decline, to bottom-dwelling round goby, another newly established invasive prey fish that feeds on quagga mussels.

The scientists modeled Lake Michigan's food web dynamics under 288 scenarios that accounted for various levels of stocking and nutrients, as well as the effects of invasive mussels. These scenarios were developed based on responses to a survey from fishery managers, water-quality managers and researchers.

"Interestingly, reducing stocking by 50 percent in the model resulted in long-term Chinook population numbers that were similar to the numbers when stocking was not reduced," said David "Bo" Bunnell, a USGS co-author on the study.

Lake Michigan's open-water food web has changed significantly since the 1970s, becoming less productive as a result of decreased nutrients such as phosphorus, a process called oligotrophication. Nutrients help sustain phytoplankton and zooplankton, the tiny aquatic plants and animals at the base of the food web that support other aquatic life, including prey fishes. In Lake Michigan, oligotrophication occurred partly as a result of invasive mussels, which filter phytoplankton from the water column.

Declines in prey fishes such as alewife were likely due, in part, to decreases in plankton. Because the Chinook salmon diet consists of over 90 percent alewife, the new study predicts a smaller Chinook salmon population if nutrients remain low and invasive mussels remain abundant.
For more information about USGS ecosystems research in the Great Lakes, please visit the USGS Great Lakes Science Center website .

USGS provides science for a changing world. Visit, and follow us on Twitter @USGS and our other social media channels.

Subscribe to our news releases via e-mail, RSS or Twitter.

US Geological Survey

Related Salmon Articles from Brightsurf:

Alaska's salmon are getting smaller, affecting people and ecosystems
The size of salmon returning to rivers in Alaska has declined dramatically over the past 60 years because they are spending fewer years at sea, scientists report.

Chinook salmon declines related to changes in freshwater conditions
A new University of Alaska-led study provides the first evidence that declines in many of Alaska's chinook salmon populations can be attributed in part to climate-driven changes in their freshwater habitats.

Size matters in the sex life of salmon
For Atlantic salmon, size matters when it comes to love.

What does drought mean for endangered California salmon?
Droughts threatens California's endangered salmon population -- but pools that serve as drought refuges could make the difference between life and death for these vulnerable fish.

Salmon provide nutrients to Alaskan streambanks
Nutrient cycling of stream ecosystems dependent on portion of salmons' lifecycle.

Melting glaciers will challenge some salmon populations and benefit others
A new Simon Fraser University-led study looking at the effects that glacier retreat will have on western North American Pacific salmon predicts that while some salmon populations may struggle, others may benefit.

Bigger doesn't mean better for hatchery-released salmon
A recent study in the Ecological Society of America's journal Ecosphere examines hatchery practices in regards to how Chinook salmon hatcheries in the PNW are affecting wild populations over the past decades.

Salmon get a major athletic boost via a single enzyme
A single enzyme anchored to the walls of salmons' blood vessels helps reduce how hard their hearts have to work during exercise by up to 27%.

Salmon are shrinking and it shows in their genes
Male salmon are maturing earlier and becoming smaller, and it shows in their genes.

Young salmon may leap to 'oust the louse'
A study by Simon Fraser University aquatic ecologists Emma Atkinson and John Reynolds reveals that young salmon may jump out of water to remove sea lice.

Read More: Salmon News and Salmon Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to