Naturalists seek to help troubled youth of
Lake Michigan: yellow perch
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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,"
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."
was funded by Illinois-Indiana Sea Grant and coordinated with the
Lake Michigan Yellow Perch Task Force.
Sea Grant news release]