Carl here is a study I found for Texas. I do know that these numbers vary by state, size of tournament and also time of year.
BASS FISHING TOURNAMENT STUDY NETS RECOMMENDATIONS TO REDUCE DELAYED BASS MORTALITY
"I’ve tournament fished for years and never weighed a dead bass" is often heard from tournament anglers when asked about the health of the fish they bring to weigh-in. "The live well in this boat is great" they say, "my bass are always alive and kickin'."
But what do anglers know about the long-term survival of those bass after they are weighed and released?
All too often, a few days after a tournament, the state fishery agency phone rings with calls from concerned, and often angered, marina operators, Park Rangers, or lake residents complaining about dead bass floating to shore around a boat ramp or beach.
The contestants thought their fish were healthy. After all "when we released 'em they took off like scalded cats!" The lethal effects of stress, which are often completely invisible, may have built up to a point that many many of the released bass died days later, after the anglers had gone home.
The past two years, the Oklahoma Department of Wildlife Conservation (ODWC) has been conducting a study of delayed mortality of bass released from tournaments. Their objective was to find out what tournament directors and anglers could do to keep bass healthier.
Tournaments at several Oklahoma lakes were chosen to represent the more than 1500 events held each year. Three Angler's Choice events were among those studied.
Weigh-in procedures suggested by the ODWC were used at each tournament. Dissolved oxygen levels and water temperatures were recorded from every live well as teams came to weigh-in. Boaters were asked how and when they ran their aerators.
After weigh-in, fish were held in large live-nets placed in marina boat stalls. Several control fish that had not undergone tournament stress were collected by electroshocking. These bass were tagged and placed in each net to see if confinement was enough to cause mortality.
Oxygen levels and temperatures were measured in and around the nets to insure good water quality in the holding area.
The nets were checked after three and six days. Dead fish were counted and removed each time. The mortality estimates were reduced to account for any dead control fish. After the sixth day, live fish were given a therapeutic treatment and released.
Results
Only five of 132 control fish died during the two-year test. This indicated that net confinement was not strongly inf) uencing mortality.
Spring tournament mortality in 1 995 was very low, averaging only 6%, or four fish per event. Water temperatures averaged a cool 63ºF and oxygen levels were good, averaging over 5 parts-per-million.
In summer however, although less than three bass were brought in dead to each weigh-in, biologists saw an average of 39% mortality after six days. Water temperatures over 80ºF and low oxygen levels in boat live wells stressed many fish beyond their limits.
Of special concern was the higher mortality among larger bass. Quality-sized bass, those over 16 inches long or about three pounds, apparently stressed more easily and had a significantly higher mortality rate than smaller fish.
To get an idea of what was causing high summer mortality, fish from one tournament were separated according to boat oxygen levels. One group was from low-oxygen live wells (below 5 parts-per-million) and another from high-oxygen live wells (above 5 ppm).
The fish from boats with low oxygen levels had a 51% mortality rate while the fish from the boats with higher oxygen had only a 35% mortality rate.
The key to having a low or high oxygen level appeared to be how the contestant used the live-well aerators. Boaters that ran aerators continuously rather than on a timer had better oxygen levels and 16% lower mortality!
The Second Year
Knowing that summer tournaments were the most stressful on the bass, the study's second year focused on tournaments from July through September. Weigh-ins were conducted using the same procedures as in 1995.
In 1996 however, teams were given specific instructions on how to handle their catch and run live-well aerators. Some were supplied with ice and salt to add to their live wells during the day.
Group #1 added ice and salt and used recirculating aeration. Fresh water was added two or three times during the day to flush out toxic ammonia.
Group #2 pumped fresh water through their live wells all day but did not use ice or salt, All anglers ran live-well aerators continuously.
Fish were held in live-nets as before. Control fish were again collected by electroshocking and added to each net.
Mortality of fish from Group #1 using ice, salt & recirculation averaged only 14%. Group #2 using constant fresh-water flow-through averaged a mortality of 18%. When compared to 39% mortality from 1995 tournaments, this was quite an improvement.
Over half of the dead fish counted in this study were found at the bottoms of the nets. It often took them five to six days to float to the surface. Turtles were often seen circling the nets. It is likely that these scavengers "clean up" many dead bass that sink to the bottom before they float and become visible to the public.
Conclusions
By simply requiring all contestants to run their fresh-water pumps & aerate continuously, the mortality in the 1996 summer tournaments was cut in half. Anglers willing to be a little more diligent and use ice, salt, and continuously recirculating aeration reduced mortality even more.
Anglers should take a stand for conservation of our fishery resources and protect the future of bass fishing. Tournament directors should require more of their contestants and anglers should require more of themselves in making sure fish are kept alive and healthy.
Reducing bass mortaiity is not only good for the resource it’s good public relations for the sport of bass tournament fishing.
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Brendan C.
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