The fish may also be unable to swim upright and submerge. The fish will float at the surface for several hours until the swim bladder depressurizes. This condition by itself may not be lethal, but the fish expends a lot of energy trying to submerge, and it may be struck by a boat or killed by a predator.
Not all floating fish die, but enough do to be a concern.
What anglers and even fisheries biologists don't know is the best way to treat hyperbuoyancy in order to increase survival of fish after they are released.
Texas Parks and Wildlife Department Inland Fisheries biologists intend to find out.
"It's important to understand that if you catch a fish from 30, 40, 50 feet deep and immediately release it, it usually goes right back down with no problem," says Randy Myers, Inland Fisheries district biologist from San Antonio. "Even after it goes through the struggle of being caught, the fish may have enough energy to swim back down to a depth where neutral buoyancy is regained. But if that same fish is kept in a livewell for several hours with an over-inflated bladder, it becomes exhausted from struggling to stay upright and floats on the surface."
Budweiser ShareLunker program manager David Campbell has probably dealt with more big bass suffering from hyperbuoyancy than anyone else, and he feels that fish can develop hyperbuoyancy for several reasons. "I strongly believe that exhaustion happens when the fish is trying to adjust to its environment, whether that is caused by being pulled from deep water, the stress of being caught, lack of oxygenated water or being in a crowded livewell," he says. "When a fish has room to swim but starts swimming nose down, has to fight to stay down or swims right-side up but never stays more than a few inches below the surface, it has preliminary hyperbuoyancy symptoms and needs relief-and the sooner the better for survival."
Three techniques have been developed to deal with hyperbuoyancy. Two involve puncturing the air bladder to vent gas and reduce the pressure, a procedure commonly called fizzing because when done properly while holding the fish underwater, a stream of bubbles is released.
Fizzing can be done by inserting a hypodermic (hollow) needle into the air bladder through the fish's side or mouth.
The third technique is deep release, sometimes called caging. Using this method, fish are lowered to the approximate depth where they were caught in a weighted cage (a small plastic laundry basket works well) that is open on the bottom. The cage is then lifted free of the fish, which will be repressurized and neutrally buoyant. Deep release can be done immediately or several hours after a fish was caught.
Dr. Hal Schramm, a fisheries biologist at Mississippi State University, helped develop deep release with Gene Gilliland, senior fisheries biologist with the Oklahoma Department of Wildlife Conservation. "No scientifically valid evaluations have been conducted on this technique, but the FLW Tour uses this for hyperbuoyant fish in their walleye tournaments, and they claim it works great," Dr. Schramm says.
Dr. Schramm notes that valid scientific evidence does exist that deflating bass swim bladders with a hypodermic needle inserted through the side of the fish does not adversely affect them. David Campbell says his experience with ShareLunkers supports that. "Before we started puncturing the air bladder, all the fish that had hyperbuoyancy symptoms died," he says. "Since then we have punctured the air bladder on close to a hundred of these big fish, and most survived."
"There is also evidence that swim bladder over-inflation in largemouth bass causes several physiological problems in addition to impairing their ability to return to depth," Dr. Schramm says. "This suggests that the best time to relieve swim bladder over-inflation is as soon as possible after the fish is caught-after you have determined that the fish is unable to submerge. No one, to my knowledge, has tested the effects of depressurization immediately upon capture versus after several hours."
Enter Randy Myers and his team of TPWD fisheries biologists.
"In spring and early summer of 2009 we plan to conduct studies to answer two questions," Myers says. "One, which technique-side fizzing, mouth fizzing or deep release-increases survival the most? And two, will fish survive better if they are treated immediately after being caught rather than after having floated in a livewell for several hours?"
The study is particularly important to Texas, which has some deep reservoirs. "What alerted us to the problem was Lake Amistad," Myers explains. "Often the majority of fish have hyperbuoyancy throughout the year, probably because the fish live deep."
Fish do not have to be caught from extreme depths to be affected, Myers notes. "One study found that hyperbuoyancy signs could be seen when fish were caught from as shallow as 11.5 feet," he says. "My experience is that fish caught from more than 20 feet deep will show some signs."