Fish guts show changes on the Lake Huron menu

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Remnants of a bird found in fish stomach. Image: Katie Kierczynski, Department of Fisheries and Wildlife, Michigan State University

By Michaela Kratofil

When your favorite food disappears from the menu, what do you eat next?

That’s the question Katie Kierczynski, a Michigan State University fisheries and wildlife graduate student, worked to answer by studying gamefish diets in Lake Huron.

Alewives were once an important food source for top predators and popular gamefish such as salmon and lake trout. But Great Lakes populations of the small fish started to decline in the early 1980s, and finally crashed during the 2000s, said Brian Roth, lead professor on Kierczynski’s project.

Graduate student Katie Kierczynski analyzing fish stomach content data. Image: Brian Roth, Department of Fisheries and Wildlife, Michigan State University

The crash was likely caused by the state putting too many fish into these lakes, Roth said. Because so many gamefish were stocked into lakes Huron and Michigan to support the state’s multibillion-dollar fishing industry, alewife populations were outstripped, Roth said.

“We had this shocking revelation like, ‘Oh, we can’t depend on alewife populations to feed predators anymore,’” Roth said.

Undergraduate technicians Nick Yeager (near) and Sharon Carpenter (far) analyzing smaller contents from fish guts in the lab. Image: Katie Kierczynski, Department of Fisheries and Wildlife, Michigan State University

Kierczynski researches how the collapse of alewives affects fish that used to depend on them to survive and are important to Great Lakes anglers and commercial fisheries. The best way to do that is to look inside the stomachs of those fish for what they’re eating, she said.

“We analyzed over 3,000 stomachs from 2017 to 2018,” Kierczynski said.

Where did she get all those guts? Mostly from state and local agencies, but also from many fishermen who voluntarily donated their catches’ stomachs for her research. Sometimes Kierczynski and her team would go to fishing tournaments to collect stomachs directly from anglers, she said. Other than that, volunteers brought fish stomachs to a designated drop off site. Anglers’ donations were very helpful in providing samples from places and times where agency workers and Kierczynski couldn’t be, Roth said.

Coke label found in fish stomach. Image: Jordan Andrus, undergraduate technician in Roth’s lab at the Department of Fisheries and Wildlife, Michigan State University

Kierczynski and her army of undergraduate students dissected each fish stomach and identified all the fish or bugs that they could, she said. Sometimes they found more interesting contents, such as a Coke label and bird leg. She compared results from her fish guts with those from an earlier study where stomachs were analyzed from 2009 to 2011.

Although these stomachs came from a variety of fish, Kierczynski studies the main top predators in Lake Huron: lake trout, chinook salmon and walleye.

She found that lake trout and walleye ate more alewives during 2009 to 2011 than they did in 2017-2018. Instead, they ate many more round gobies, an invasive species, during 2017-2018. Yet chinook salmon had a different appetite, having a higher proportion of alewives in their stomachs throughout both sets of years.

Changes in what these fish are eating have important management implications for Lake Huron and the Great Lakes, both Roth and Kierczynski said.

Stomach contents from a lake trout. Image: Katie Kierczynski, Department of Fisheries and Wildlife, Michigan State University

Management agencies like the Michigan Department of Natural Resources use computer models to predict how a given amount of fish stocked into lakes will affect the rest of the ecosystem, such as their prey, Roth said. But he said to do this effectively, agencies need to know the diets of predator fish. Thanks to studies like Kierczynski’s, state agencies can start to smarten up about stocking fish, Roth said.

Great Lakes Echo previously covered Kierczynski’s work here when she was getting started with her research.

4 thoughts on “Fish guts show changes on the Lake Huron menu

  1. I think alewife crash might largely be due to return of walleye to high density. The two fish have double-negative feedback – they eat each other’s young. So if there are allot of alewife (and there were), it depresses walleye, but when you get a few more walleye it works the other way. I do not mean to say that salmonids did not eat many alewife though.
    In case folks don’t know, Lake trout with too much alewife in their diet have trouble reproducing (due to thiamine deficiency) , so loss of alewife has helped them (some predation of young may have been part of it too).


  3. It seems that this is another case of the state introducing non-native species, Atlantic Salmon, etc. into our environment and upsetting an ecosystem for a short term profit.

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