Saturday, January 28th, 2023
Saturday, January 28th, 2023

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MN: Testing: Are silver carp in St. Croix?

St. Paul – The arrival of silver carp may no longer be a matter
of if, or even when.

They may be here already.

While live fish hadn’t been found as of Tuesday morning, water
samples taken from the St. Croix River earlier this summer suggest
the fish – or at least their DNA – are here.

During environmental DNA testing on the St. Croix, 22 of 50 samples
taken in a 4.3-mile stretch of river between St. Croix Falls, Wis.,
and Franconia tested positive for silver carp, the jumping variety
that poses a threat to boaters and the food chain alike.

Testing in the Mississippi River at 50 spots between Lock and Dam 1
and Pike Island didn’t turn up any positive samples for Asian carp,
though officials say that doesn’t mean they aren’t there.

The positive samples in the St. Croix are “discouraging news,” said
DNR Commissioner Tom Landwehr.

eDNA testing doesn’t provide concrete evidence of live fish.
Rather, it proves the presence of silver carp DNA, which is shed
through excrement and mucus and floats on the water’s
surface.

Officials say there could be other explanations for the positive
tests – a dead carp tossed on the river bank, for example – but
that seems unlikely, given the high number of positive tests.

DNR staffers earlier this week began searching for live fish by
using electrofishing equipment and nets. The agency also will
contract with commercial fishermen to set nets in the St. Croix;
that likely will begin later this month.

So far, silver carp haven’t been caught in the St. Croix. And just
two bighead carp – one of the four Asian carp species – have been
caught: one in 1996 and one in April of this year.

“The fish may be closer than we thought they were,” said Paul
Labovitz, superintendent of the National Park Service’s Mississippi
National River and Recreation Area.

One of the main concerns with silver carp is their ability to
disrupt the aquatic ecosystem. They are capable of eating as much
as 20 percent of their body weight each day. The fish are filter
feeders and out-compete native fish for plankton, which is a key
foundation of the food chain.

In recent years, Asian carp have dominated the Illinois River, and
biologists have noted a decline in the body conditions of some fish
species.

“They could chop you off at the bottom of the system and topple the
top in ways we don’t want to see,” said Byron Karns, a National
Park Service aquatic biologist.

An Asian Carp Task Force, which includes state and federal
officials and has been in place since January, will begin planning
a second round of eDNA testing in the Mississippi and St. Croix
rivers. The initial testing cost $17,000. Two non-profit groups –
the Mississippi River Fund and the St. Croix River National Scenic
Riverway Fund of the St. Croix Valley Foundation – covered
it.

Barriers

Pending results of the current sampling, DNR officials say they
will proceed with development of a bubble or sonic barrier at the
mouth of the St. Croix River at Prescott, Wis. The materials for
that barrier would cost an estimated $7 million, and officials say
it wouldn’t be completely effective at stopping carp.

“Our task is to stop or slow down these fish as far south as
possible while we continue to develop technologies and techniques
to slow down their spread,” Labovitz said.

Officials also say they’ll seek emergency closure of the lock at
St. Anthony Falls, though doing so requires an act of
Congress.

“It’s not something that I think is going to be a slam dunk,”
Landwehr said.

Dayton involved

Landwehr met last Friday with Gov. Mark Dayton, who wants the
state’s Congressional delegation and state and federal agency heads
to get together within the next two to three weeks.

The goal: To “get everybody on the same page with the need to
address this issue and get some commitment of resources for a full
frontal assault on Asian carp in particular and invasive species in
general,” Landwehr said.

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