Chicago Sun-Times - - OUTDOORS - DALE BOW­MAN dbow­man@sun­ @Bow­manout­side

Some­times you have to gut it out in col­lege. Take study­ing the con­tents of 3,000 stomachs of trout and salmon from Lake Michi­gan.

“I roped in a dozen un­der­grads to help,” Austin Hap­pel said. “They each wrote up a lit­tle re­port. It was a fun teach­ing ex­pe­ri­ence at the Uni­ver­sity of Illi­nois.” Sounds like work­ing the agate desk in the sports de­part­ment at the Chicago Sun-Times.

Half of the stomachs were an­a­lyzed by the stu­dents at Illi­nois, where Hap­pel, a re­search bi­ol­o­gist at the Shedd Aquar­ium, started on the project while work­ing on his doc­tor­ate. The other half were done by Ben Leon­hardt as part of his mas­ters at Pur­due Uni­ver­sity.

The stomachs were part of a wide-rang­ing study on the chang­ing di­ets of salmon and trout on Lake Michi­gan. The study de­liv­ers some things an­glers al­ready know and some in­ter­est­ing tid­bits.

Leon­hardt, now with the U.S. Fish and Wildlife Ser­vice, was lead author on “Diet com­plex­ity of Lake Michi­gan Sal­monines: 2015-2016” on one part of the study. The ar­ti­cle is on­line from the Jour­nal of Great Lakes Re­search and in its Au­gust print edi­tion. The Illi­nois-In­di­ana Sea Grant, the Great Lakes Fish­ery Trust and the Great Lakes Restora­tion Ini­tia­tive funded the study. Sci­en­tists teamed with the USFWS and the Depart­ments of Nat­u­ral Re­sources from sur­round­ing states.

More will be com­ing from the study, which came at diet in three ways: an­a­lyz­ing stom­ach con­tents for im­me­di­ate diet in 2015 and ’16, look­ing at fatty acids to see what they ate over weeks and, fi­nally, an­a­lyz­ing sta­ble iso­tope ra­tios to study months of diet.

“It was a huge ef­fort to ac­com­plish some­thing like this, so we needed help from just about every­body around the lake,” Leon­hardt said in the IISG over­view. “The an­glers were the most im­por­tant con­trib­u­tor.”

Supplying the fish for the study were Lake Michi­gan an­glers and the Lit­tle Tra­verse Bay Bands of Odawa In­di­ans.

Coho salmon and Chi­nook were stocked into Lake Michi­gan be­gin­ning in the 1960s, as part of an au­da­cious plan by Michi­gan’s Howard Tan­ner to con­trol alewives and start a sport fish­ery.

For more than half a cen­tury, alewives were the pri­mary food for salmon and trout. But that’s evolv­ing (well, not so much for Chi­nook, for which alewives make up more than 90 per­cent of their diet) as alewives de­clined while in­va­sive round go­b­ies, ze­bra mus­sels and quagga mus­sels ar­rived.

One of the key find­ings is that “due to their re­liance on alewife, it is likely that Chi­nook salmon will be more neg­a­tively im­pacted than other salmo­nine species if alewife abun­dance con­tin­ues to de­cline in Lake Michi­gan.”

Lake trout, brown trout, coho and rain­bow trout (steel­head) adapted in var­i­ous ways to the de­cline of alewives.

One thing the study showed was that vari­a­tions came even among species chang­ing their diet. Along the Michi­gan side, brown trout and lake trout ate more round go­b­ies than alewives, but on the west side, it was the other way around. Hap­pel said their the­ory is that the rock­ier west shore gives go­b­ies more places to hide while “on the east­ern side, it is more sandy and it is like a snack in an open field.’’

“Larger in­di­vid­u­als eat more go­b­ies than other browns and lak­ers,” Hap­pel said. “As they get larger, they change swim­ming habits. Larger lak­ers are closer to the bot­tom, more ex­posed to the round go­b­ies on the bot­tom.”

Na­tive species, such as bloater chub and sculpin, even in years when their pop­u­la­tions are up, did not im­pact di­ets as much at the in­va­sive go­b­ies and alewives. Hap­pel spec­u­lated that the flash of alewives may be one of their ap­peals. There’s good rea­son an­glers use flash­ing lures and at­trac­tors while pur­su­ing salmon and trout.

An­other odd­ity was that in the spring, only in the south­east por­tion of Lake Michi­gan, coho were full of my­sis, a tiny crus­tacean known as opos­sum shrimp.

The ab­stract noted that rain­bow trout added ter­res­trial in­ver­te­brates.

“That was un­ex­pected for me com­ing into this project,” Hap­pel said. “They were of­ten full of stink bugs or la­dy­bugs or ants. The best ex­pla­na­tion I could come up with is the scum lines. All of [the] fish came from an­glers, so maybe an­glers were tar­get­ing around the scum line. I think they are find­ing them at the scum line, and they are very abun­dant. You also find tiny alewives around scum lines.”

That ob­ser­va­tion might mean some­thing for fish­ing.

Lake Michi­gan keeps evolv­ing, and so do smart an­glers.

The IISG has a good lay­man’s over­view at iisea­­gan-chi­nook-salmon­stick-with-de­clin­ing-alewife-as-their-main­meal/. ✶


Chi­nook are one of the pri­mary draws for an­glers on Lake Michi­gan.


Andy Mikos (right) pleads for a Chi­nook at dawn on a late-sum­mer out­ing in a file photo.


Alewives are a main source of food for Chi­nook.

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