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Naturalists seek to help troubled youth of Lake Michigan: yellow perch     Send a link to a friend

[JUNE 26, 2004]  URBANA -- Not long after they hatch, yellow perch larvae from the west side of Lake Michigan leave home. They are swept away by the great lake's massive currents, possibly traveling clear across to the Michigan coast. There, in terms of food sources for perch, it is the poor side of town. This information is critical to understanding the perils of the perch, assessing the species status and managing it for the future, according to John Janssen, a University of Wisconsin-Milwaukee biologist.

Lake Michigan perch have had poor recruitment since the late 1980s. "The decline of yellow perch abundance is due primarily to poor recruitment of newly hatched perch into the fingerling life stage," said Tom Trudeau, Lake Michigan Fisheries Program administrator for the Illinois Department of Natural Resources.

"If this trend continues, the yellow perch populations in the lake could become critically low," said Janssen. "This has biological implications for the entire lake food web." Changes that have already taken place in the food web, combined with the lake currents, may be taking their toll on the popular sport fish.

Zebra mussels, introduced into Lake Michigan in the late 1980s, may be the cause of depleted Diporeia populations, the young yellow perch's food source. Diporeia sp., an amphipod, feeds on phytoplankton that has settled on the muddy bottom. Zebra mussels siphon water just above them, so the mussels are able to feed on phytoplankton before the amphipods can.

According to Janssen and fellow researchers, the west side of Lake Michigan is rockier than the east side and provides the preferred habitat of yellow perch for feeding and spawning. There, food is abundant. But, Janssen has documented that tiny yellow perch larvae that hatch on the rocky west side of the lake are swept into the sealike currents of Lake Michigan and travel for 40 or more days, adrift in the water column -- away from the food source they will need when they grow larger, and toward Michigan, where this soft-bottomed region has become a veritable desert in terms of Diporeia.

"We were able to measure the movement of the larvae directly by towing out our nets while riding on research ships on other missions. Two weeks after hatching, the larvae had traveled 20 miles," said Janssen.


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Scientists believe that, originally, perch developed in smaller water bodies, where the current effect is less dramatic on the tiny larvae. Janssen compares the flows in the Great Lakes to oceans, where marine fish larvae frequently drift far from coral reefs and other feeding grounds. "Getting a good year-class of perch for the west side of Lake Michigan may require unusual current patterns to return the young fish to the west side," said Janssen.

Janssen's research provides insights that can play a role in monitoring and managing this species. First, if perch prefer rocky habitat, assessing young-of-the-year perch through the use of trawls on soft bottoms is probably ineffective. This sampling method is commonly used in Lake Michigan.

"The perch's preference for rocks also suggests that it may be a good idea to manage the yellow perch in terms of sources and sinks," said Janssen. "We might aim for robust populations off the rocky coasts of Illinois and Wisconsin but be less concerned about maintaining significant populations along Michigan. Accomplishing this would require well-integrated multistate coordination and cooperation."

"Janssen's work has improved our understanding of the early life history of yellow perch," said Trudeau. "The significance of perch larval drift in determining annual recruitment success will be better understood as we learn more about larval perch diet, as well as how fingerlings return to areas where they began as newly hatched perch."

This project was funded by Illinois-Indiana Sea Grant and coordinated with the Lake Michigan Yellow Perch Task Force.

[Illinois-Indiana Sea Grant news release]

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