46 Nebraskaland • January-February 2021
Unifi ed Method, jumped out at him. He
traveled to China in 2015 with another
biologist and a commercial fi sherman
to learn more about it.
There, fl oodplain lakes along the
Yangtze River covering thousands of
acres are used as aquaculture facilities.
Each year, during the course of a few
months, fi shermen start at one end
of the lake and drive fi sh to the other.
"They get out there in these wooden
boats and tiny, funky outboard motors
and make a lot of noise and try and
chase them out," Chapman said. As
they move fi sh from an area, they set
a series of block nets, suspended from
a "forest of bamboo" poles driven into
the lakebed to keep fi sh from returning.
When a cell is cleared of fi sh, they play
"leapfrog" with the nets, moving them
down the lake. At the other end of the
lake, they net fi sh each day and deliver
them to the market live, satisfying
the demand but not overwhelming
it. Fishermen are disappointed if by
year's end they don't capture at least
85 percent of the fi sh in a lake.
Back in the states, Chapman and
others tweaked the method to speed
up the process. "We don't really
want to spend 3
1
⁄2 months catching
a little bit of the fi sh every day," he
said. Rather than simply rely on the
sound of boat motors, they added
sound from underwater speakers and
electrofi shing boats.
Electrofi shing, a method used to
sample game fi sh by stunning them
with a light charge of electricity and
netting them when they fl oat to the
surface, doesn't work well with silver
and bighead carp. Those species sense
the charge and swim from it. Knowing
that, biologists have modifi ed the
electrodes to create a wide fi eld and
reduce the charge when driving fi sh.
"We don't want to stun anything, not
even the native fi sh or the carp, we just
want to tickle them," Chapman said.
The fi rst test of the method came
in 2016 on a 5-mile long, 500-acre
sandpit lake southwest of Chicago
along Illinois River, where biologists
are fi ghting to keep silver and bighead
carp from fi nding their way into Lake
Michigan. Before the test, acoustic
transmitters were implanted in carp
and receivers placed throughout the
lake to measure the eff ectiveness.
When the speakers were turned on,
Disturbed by an electrofi shing boat manned by Kevin Eastman, a Hanson Lake homeowner and Tony Havranek, a biologist
with WSB Engineering in Minnesota, a silver carp jumps out of the water.
