Cormorants’ effect on perch scrutinized

Correspondent

Green Bay, Wis. For more than a decade, anglers have blamed
double-crested cormorants for the sharp decline in yellow perch
numbers on Green Bay.

In the coming months, they’ll find out whether there’s any truth
to their suspicions.

When the U.S. Fish and Wildlife Service recently adopted rules
to allow certain state and federal agencies to kill cormorants when
the birds are harming public resources, fishermen breathed a
collective, “About time.”

But it’s not that easy, says DNR Great Lakes specialist Bill
Horns.

“I know a lot of people want us to get out there and start
blasting these birds, but we need to know for sure,” he said. “It’s
controversial.”

Money from the Fox River Natural Resources Damage Assessment
settlement will help fund a proposed two- or three-year project to
find out exactly what cormorants are eating from lower Green Bay
waters.

“If cormorants are eating a lot of yellow perch, this should be
the summer to find out,” Horns said. “There’s a big potential
year-class of perch that will be growing into the size that
cormorants like.”

Sarah Meadows, a UW-Madison student, began working as a limited
term DNR employee in April. She’ll be earning a master’s degree
under the supervision of UW-Madison wildlife ecology professor
Scott Craven. Craven said it’s obvious some cormorants will have to
be killed to see what they’ve been eating, but he said researchers
will be looking at other methods, too.

The plan is to have Meadows check cormorants from the time the
birds arrive in spring to the time they leave in fall. She’ll look
at regurgitated food samples from nesting colonies on Cat Island
and regurgitated prey from feeding flocks spooked to flight by her
boat in open water. Along the way, she may also be able to check
the impact of a growing flock of white pelicans on lower Green
Bay.

Craven’s research in the early 1980s into the eating habits of
cormorants nesting on the Apostle Islands found that nine-spine
sticklebacks and other forage fish were the main food item at the
time, and intermittent unpublished data collected on birds nesting
on Green Bay from 1983-97 by UW-Green Bay’s Tom Erdman and former
DNR fisheries biologist Brian Belonger found that alewives were the
main food items.

Other theories often mentioned for the decline in yellow perch
include impacts from invasive species such as zebra mussels and
white perch, lower water levels, rapid fluctuation in spring water
temperatures, spawning habitat destruction by carp, and improved
water clarity resulting in greater predation by large game fish.
Still, the double-crested cormorant has been the most visible
target.

The birds are named for the two small tufts or crests of
feathers that appear for a short period on either side of the head
of adult birds during breeding plumage. The birds are found
throughout North America. Those in the Great Lakes population
migrate south, along the Atlantic Coast and the Mississippi River
drainage, to overwinter in the Southeast and Gulf of Mexico.

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