GLIN==> Illinois-Indiana Sea Grant News: The Troubled Youth of Lake Michigan Yellow Perch

[Irene Miles <miles@uiuc.edu>]

June 22, 2004

The Troubled Youth of Lake Michigan Yellow Perch

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,
Illinois Department of Natural Resources, Lake Michigan Fisheries Program
administrator. 

“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 sportfish. 

Zebra mussels, introduced into Lake Michigan in the late 1980s, may be
the cause of depleted Diporeia sp. populations, the young yellow
perch’s food source. Diporeia, 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 it 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 sea-like
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 towards 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.

Originally, perch evolved 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 to be less concerned about maintaining
significant populations along Michigan. Accomplishing this would require
well-integrated multi-state 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.

--30--

Irene Miles
Illinois-Indiana Sea Grant
376 NSRC
1101 W. Peabody Dr.
Urbana, Il 61801
(217) 333-8055
FAX (217) 333-8046