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

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AR: Gas Bubble Trauma likely cause of fish kills

LITTLE ROCK – According to recent tests, two large fish kills
below Ozark Dam on the Arkansas River were likely caused by
increases in atmospheric oxygen and nitrogen in the water after
spillway gates were opened.

About 83,000 freshwater drum and 800 yellow bass died Dec. 29
after 10 spillway gates were open for 10 hours. About 500 drum died
Jan. 28 shortly after seven gates were open for two hours.

Bob Limbird, an AGFC district fisheries supervisor; Frank Leone,
an AGFC fisheries management biologist; Kelly Winningham, an AGFC
fish pathologist, and Andy Goodwin of the University of Arkansas at
Pine Bluff conducted experiments Feb. 15 at Dardanelle Dam and Feb.
17 at Ozark Dam and filed the report. They had the cooperation of
the U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service,
UAPB and Arkansas Tech University.

They tested the water below Ozark Dam for temperature, oxygen,
oxygen saturation and total gas saturation with spillway gates
closed. About 50 minutes after 10 gates were opened, drum and white
bass began struggling.

“We collected 21 freshwater drum and four white bass,” the
report states. “All fish were floating upside down at the water’s
surface but were still alive. All fish were stiff and had hard
sides. Internal examination revealed the fish had distended and
full air bladders.”

Tests taken after the gates were closed showed the water
temperature unchanged, a drop in dissolved oxygen and a rise in
total gas saturation.

A similar test below Dardanelle Dam revealed similar

According to the report, “The results of our test give us a high
level of confidence regarding the cause of death as related to the
Dec. 29 and Jan. 28 fish kills observed below the Ozark Dam on the
Arkansas River. It is our opinion that these kills were the result
of increased atmospheric oxygen and nitrogen gases being added to
the water following the opening of the spillway gates of Ozark

The AGFC Fisheries Division decided to conduct the tests because
Winningham and Goodwin believed Gas Bubble Trauma may have caused
the Jan. 28 kill. The fish had full air bladders, which made it
impossible for them to dive and orient their bodies.

“Freshwater drum are highly susceptible to gas supersaturation
and gas bubble trauma,” states the report. “In addition, a very
deep hole (48 feet deep) exists below gate 5 (Ozark Dam) and may
act to congregate freshwater drum during the winter months. These
facts may help explain why freshwater drum were the most affected
species during the kill events.”


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