Sunday, February 5th, 2023
Sunday, February 5th, 2023

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Virus suspected in deaths of 731 bass

By Dean
Bortz
Editor

La Crosse, Wis. „ Heading into a September tournament that is
supposed to help the DNR assess the losses of culled bass, the
agency will test Shawano Lake for a bass virus ahead of the
tournament Ü so it can avoid a fish kill like the one that occurred
in La Crosse in early August.

The DNR counted 731 dead fish during the FLW Everstart Tour
event that took place Aug. 3-6 on the Mississippi River out of La
Crosse. That total included ñreference fishî the DNR had netted
ahead of the event and housed in a ñbass penî fastened to a
commercial pier. The DNR had 1,085 fish in that pen. Of the 731
fish that died, 625 of were largemouths and 105 were
smallmouths.

Of the 1,085 fish in the pen, 132 were reference, or control,
fish (106 largemouths and 26 smallmouths).

When the fish started to die, DNR officials were surprised that
more largemouths than smallmouths were turning belly up, according
to Patrick Schmalz, DNR fisheries regulation specialist.

ñThe smallmouths were less impacted than the largemouths. You
would expect smallmouth mortality to go way up (if the fish died
because of stress and warm water temperatures),î Schmalz said.

When conservation warden Russ Wilson noticed about 40 dead
largemouths Ü that werenÍt the result of the tournament Ü floating
on the river near a bridge, DNR biologists suspected the fish might
have died from a disease, not from tournament handling.

They took the dead fish to the U.S. Fish and Wildlife Services
laboratory in La Crosse for testing and discovered the fish had
succumbed to the largemouth bass virus. Actually, Schmalz suspects
the fish died from other factors because their immune systems were
ñcompromisedî by the virus.

ñAt first, we didnÍt know what to think Ü other than this (fish
kill) was not expected,î he said. ñThen after a couple of days we
were seeing that the largemouths were dying at a higher rate. We
also heard of largemouths dead in Iowa waters. Then game warden
Russ Wilson was out checking something in the Black River area and
people pointed to dead fish from a bridge. He counted 39 dead bass
in the Black River area, along with a few dead bluegills and a
channel catfish.î

ThatÍs when they ran fish to the the federal lab for some quick
tests. Schmalz said keeping the infected fish in close proximity
(in the pen) to healthy fish allowed the disease to spread more
quickly than it might in a natural setting in the river.

The next ñcullingî tournament will be Sept. 24-25 in Shawano
Lake. That will be the Wisconsin State Bass Federation
Tournament.

DNR crews will head to Shawano Lake a couple days ahead of that
event to catch some bass with electrofishing gear. Those bass will
be killed and taken to a lab for testing. If the testing reveals
the largemouth bass virus, the DNR will not attempt to keep
ñcontrolî fish or angler-caught fish in a pen.

However, Schmalz does not believe the DNR would cancel the
tournament permit, either.

ñAs of right now, I donÍt think youÍd cancel the tournament,î he
said. ñIf we find the virus, we just wonÍt do the mortality
assessment at that tournament (because) confinement (in the pens)
can spread the disease.î

Schmalz acknowledged that confinement of tournament-caught fish
in a livewell could also spread the disease, even if the DNR
doesnÍt put fish in its holding nets. Stressing fish by catching
them and releasing them also could make fish susceptible to the
disease.

ñThis does give us some information to think about when it comes
to tournament rules,î Schmalz said. ñHow should we deal with the
bass virus? Some fish tournament groups have decided not to come to
the Mississippi next year because of the bass virus. They donÍt
want to risk a fish kill from the virus.î

The Legislature required the DNR to allow, and then study, bass
culling during four tournaments this summer. Culling is not allowed
in Wisconsin. Four tournaments were selected for the study, but
that number has since dropped to three when one bass series
canceled.

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