Catch and release not always a benefit to fish

Globally, 60 percent of fish caught by recreational anglers are released and many of those anglers use manual release techniques they believe will help the fish survive.

However, according to a recent study, many of those fish will live just a short period of time. The delayed mortality rate can be as high as 35 percent and, as this study determines, catch and release is deadly for female fish.

Overall, manual release techniques have little to no impact on survival, the study concluded.

The study, published online June 2, 2015, in the Transactions of the American Fisheries Society, concludes that the techniques of releasing fish promoted by conservation and angling groups simply does not result in a mortality benefit for fish, at least for the tens of thousands of sockeye salmon caught and released by anglers every year in British Columbia’s Fraser River system.

(In 2011, recreational anglers released 62,642 sockeye salmon out of 145,291 caught in the Fraser River system, a 43 percent release rate.)

“This was the first study to examine the extent to which different recovery techniques help fish to recover from catch-and-release fishing events,” said co-author Dr. Steven Cooke, Associate Professor of Environmental Science and Biology at Carlton University in Ottawa. “Given that so many anglers spend time recovering fish after capture, we expected recovery would be uniformly beneficial, but that was not the case.”

He added that the benefits of using recovery techniques depends on the condition of the fish at release, with the “greatest benefits for the fish that were in the roughest shape.”

Delayed mortality of fish released from anglers is due to injury or the “inability of the fish to regain physiological homeostasis,” the report says. It begins with the “burst swimming” the fish goes through while being fought by the angler.

In technical terms, the report says, burst swimming events are “fueled by anaerobic metabolism of glycogen resulting in the accumulation of metabolites (e.g., lactate and protons) in white muscle and plasma, which will ultimately alter the acid-base status and cause ion-osmoregulatory imbalance.”

And then there is the exposure to air when the fish is landed, the hook is removed and, in some cases, the fish is photographed prior to release.

The recovery technique most recommended by angling groups is to cradle the fish in the water, holding its head upstream, allowing the fish’s gills to work and to take in oxygen. That oxygen uptake must exceed the normal metabolic rate of oxygen intake, according to the report.

The researchers did two field experiments. In the first experiment on Harrison Rapids sockeye salmon, salmon were seined from the river, put through stressful forced exercise to imitate burst swimming, then released immediately, exposed to air and released or released after using the manual recovery technique.

The second field experiment used actual anglers to catch and release the fish from the Fraser River, releasing them immediately, after exposure to air and after using the manual recovery technique.

In the first experiment, 25 of 140 (17.9 percent) salmon survived to reach their natal spawning areas. Of these fish, there was no significant effect of ventilation assistance, the report says.

Survival did not differ significantly between the group that received assisted ventilation (4.3 percent) and the group that did not (9.8 percent). Some 42.9 percent of fish survived that were released immediately following capture. Female fish did not survive to reach their natal spawning areas unless they were released immediately after capture (in this case 36 percent survived, while 52.9 percent of males survived under this scenario).

Survival was better for the angling experiment, with short term survival (72 hours) achieving 73.3 percent at an upstream receiver station under all three scenarios (immediate release, after exposure to air, after using the manual recovery technique).

The results of the field studies led the researchers to conclude that there is no evidence of any benefit to migration success by using the manual recovery technique. However, the most exhausted fish could still benefit from the technique.

“More vigorous fish may not benefit from recovery, whereas more impaired fish may reap the potential benefits of increasing the oxygen available for uptake during excess post exercise oxygen consumption,” the report says.

That is a clue for anglers as to when to use the recovery technique. If the fish is unable to maintain equilibrium and drifts downstream for an extended period, it would benefit from the technique.

On the other hand, if a fish is exhausted but able to maintain equilibrium, “holding that animal in the river current may simply represent an unnecessary and additional handling stressor.”

“The best strategy is to treat fish in a manner such that they do not become totally exhausted and are able to swim away under their own volition upon release,” Cooke said. “We suggest that efforts to help revive fish should be limited to those individuals that are truly exhausted and unable to maintain equilibrium or have the vigor to swim away.

“For those fish that are in good condition, retaining them to ‘help them recover’ may in fact reduce their survival,” he said.

The report, “Influence of Postcapture Ventilation Assistance on Migration Success of Adult Sockeye Salmon following Capture and Release,” can be found at http://www.tandfonline.com/doi/full/10.1080/00028487.2015.1031282.