Barotrauma in Tournament-Caught Largemouth Bass At Amistad Reservoir and Comparison of Treatment Methods

Barotrauma

•Primary Cause•Removing fish from the high-depth, high-pressure zone to the surface results in a substantial increase in the volume of air within a fish, which in turn, affects fish buoyancy

•External symptoms•swollen belly due to over-inflated air bladder•floating upside down•can not re-submerge•bulging eyes•everted stomach

Air Bladder Function

•Compensate for pressure-depth relationship in water•pressure doubles for every 33 feet of depth•neutral buoyancy (conserve energy) •more air at deep depths and less at shallow depths

•Air exchange •circulatory system• rete mirabile•very slow •1 hour per 6 inches in depth

air bladder

rete mirabile

•Fish released immediately after capture

-usually no barotrauma •Fish retained in live wells for later release

-high probability of barotrauma

•Barotrauma is highly specific to tournament-held fish

Barotrauma in Black Bass

•What depth of capture results in barotrauma?

•Strong correlation between depth of capture and barotrauma

•However, capture depth is not a 100% accurate indicator of barotrauma

Although a fish air bladder is acclimated to a certain depth, fish regularly move up and down the water column to feed and in response to changing environmental conditions

Capture Depth and Barotrauma

Depth

Barotrauma Treatments

•Few agencies provide recommendations

•5 of 49 agencies•3 against and 2 promote venting

•Limited scientific study•Barotrauma impact on survival•Comparison of treatment methods

Tournament-weighed black bass

2004 2005 2006 2007 20080

10000

20000

30000

40000

50000•Tournament mortality puts considerable number of fish at risk

•30,000 fish/year at Amistad

•Lowering tournament mortality helps maintain high quality fisheries

Barotrauma

How prevalent is Barotrauma at Amistad?

What percent of Amistad tournament anglers apply barotrauma treament to their fish?

How much does barotrauma affect survival of tournament-released bass?

Which of the treatment methods is best for increasing survival of affected fish?

Does timing of treatment influence survival of affected fish?

Does amount of experience in applying fizzing affect fish survival?

•Develop scientifically-based best management practices for treatment of tournament-retained black bass afflicted with barotrauma

Study Goal and Questions

Study Methods

•Five Amistad tournaments in 2009•Assessed 3,625 actual tournament fish for barotrauma•Interviewed 900 anglers/teams•Determined 3-day post release survival of 433 fish•Fish were differentially marked by clipping fins•Stocked into large holding pens •Fish were held for 3-days•Fish were removed, identified according fin clips, and counted to calculate survival

8’ x 10’ x 37’ deep

Methods•Barotrauma treatment experiments

•Spring 2009 and 2010•464 fish >14 inches collected by electrofishing •Each fish was individually tagged for later identification•Fish were stocked into cages and equally pressurized by lowering cages to 35’•After fish attained neutral buoyancy at 35’ cages were raised to induce barotrauma

Methods

•Immediate release, no treatment, treatments•Treatment 1 or 5 hours after onset of barotrauma•Minimally trained and hands-on fizzers•Fizzing event data collected (blood, time, etc)•Fish stocked in large holding pens •3-d survival

Incidence (%)

Event Mo Temp Fish Treat

Bass Champs

1 55 68 24

Bass Champs

2 58 34 17

BASS-Elite 3 60 46 6

FLW-Stren 5 80 35 7

Permian SIT

9 83 42 9

Results: Incidence of barotrauma and treatment

•On average, 45% of tournament-weighed fish at Amistad experience barotrauma

•45% of 30,000 fish/year is roughly 13,500 fish having barotrauma

Survival (%)

3-day

Event Mo TempBT-neg

BT-pos

Bass Champs

1 55 98 93

Bass Champs

2 58 100 91*

BASS-Elite

3 60 100 93

FLW-Stren 5 80 80 83

Permian SIT

9 83 66 43*

*Chi-square

Results: Barotrauma impact on survival

•For 2 of the 5 tournaments, barotrauma fish had statistically significant lower survival than non-barotrauma fish

•On average, survival was 89% for fish not having barotrauma and 81% for fish having barotrauma

•Barotrauma does indeed negatively affect survival, 8% difference overall

Survival (%): 3 day

Treatment2009

trial

2010

trialCombined

Controls 100 100 100

BT-Immediate release

100 100 100

BT-no treatment

97 97 97

BT-side fizz 97 97 97

BT-deep release

97 92 94

BT-mouth fizz 89 78 83*

Results: Comparison of treatment methods

*Chi-square

•Side-fizzed and deep-released fish experienced statistically similar survival (94-97%) compared to barotrauma fish not receiving treatment (97%)

•Mouth-fizzed fish experienced significantly lower survival (83%) than untreated barotrauma-fish (97%), suggesting that mouth fizzing lowered survival

Survival (%): 3 day

Treatment 1 h 5 h

Deep release 94 94

Side fizz 100 94

Mouth fizz 81 86

*Chi-square

Results: Timing of treatment

•Timing of treatment was unrelated to survival regardless of treatment method. Fish survival was statistically similar for fish treated 1 hour versus 5 hours after barotrauma onset.

Survival (%): 3 day

Treatment Minimal Hands-on

Side fizz 100 94

Mouth fizz 81 86

*Chi-square

Results: Fizzer experience

•For both fizzing methods, fish survival was statistically similar for minimally-trained and hands-on trained fizzers

•Level of training received by fizzers was unrelated to survival

Survival (%)

Fizz type Blood No blood

Side 90 98

Mouth 43 89*

Results: Bleeding

*Chi-square

•Fish that were bleeding from the needle insertion site had lower survival than those that did not bleed, especially for mouth-fizzed fish.

Results Summary

•45% of Amistad tournament fish had barotrauma, represents 13,500 fish/year

•6-24% of anglers/teams treated their fish during the tournament

•Barotrauma lowers survival of tournament fish, however by only 8%

•Side-fizzing and deep-release did not increase or decrease survival •Mouth-fizzing decreased survival by 14%

•Timing of treatment did not affect survival

•Level of fizzer experience did not affect survival

Why did mouth-fizzing cause lower survival?

swim bladder

vertebral columnrete mirabile

fizzing needle

•Trauma to the rete mirabile•Close proximity of anterior kidney and vertebral column•Bleeding -anterior kidney

Anterior kidney

swim bladder

Recommendations

•Although treatment did not increase survival, we recommend that fish be treated.

•Tournament anglers, organizations, and TPWD receive criticism when fish are floating at release sites. These fish appear dead to the untrained eye.

•Use side fizzing or deep-release as these did not lower survival. Mouth fizzing lowered survival.

•Although overall survival did not differ statistically speaking for timing of treatment, we recommend treatment be applied ASAP after onset of barotrauma.

•Side-fizzed fish treated within 1 hour had 100% survival.

•Only minimal training is necessary to successfully perform side fizzing•Fizzing instructions such as the ones we developed are likely sufficient for most anglers.

Differences exacerbatedDeep water

Partners

Cooperators

Inland Fisheries staff