The basic idea of a catch-and-release fishing tournament is that the fish are let free and can go back into the water to continue to breed and expand the fish stock.

Researchers in Saskatchewan are finding that doesn't always happen — and that a number of fish caught in these tournaments could end up dying.

Over the weekend, Rebecca Eberts, a biologist and research technician at the University of Regina, was part of a research team at Last Mountain Lake in Saskatchewan studying how catch-and-release affects the fish.

When fish have barotrauma they often float belly up because of air filling an air sac. (Cory Herperger/CBC)

The lake is a popular fishing spot for walleye, and the home to Last Mountain Fall Walleye Classic, a catch-and-release fishing tournament that's run nearly 30 years.

One thing Eberts and her team are finding, along with biology professor and fellow researcher Richard Manzon, is that the fish simply get stressed out.

The causes range from temperature stress from being brought up from the cold depths to the warm surface, to becoming exhausted from fighting against the pull of the angler, to having internal organ damage associated with swallowing the hook.

Pressure stress

The one stress that's showing up most prevalently is a condition called barotrauma.

"The first thing you'll notice is it's really bloated," said Eberts of the fish.

Eberts says, if left untreated, a fish with barotrauma isn't likely to survive when let go. (Cory Herperger/CBC)

"So you might think it's a big, heavy fish, but if you actually touch your finger to its belly, it'll be rock hard. It'll feel like air, like a balloon," she said.

The pressure change that happens when a fish is brought up from deep water affects an organ called the swim bladder, which allows some species of fish to move up and down in the water by filling with air.

When the fish are brought up from depths ranging from nine to 15 metres, the swim bladder fills up with air and that makes the fish go belly-up along the surface — making it an easy prey for predators.

Eberts said barotrauma is an issue for fish species around the world.

"It's an issue that people are definitely paying more attention to as far as catch-and-release," she said.

Treatment methods

This is where the research comes in.

Eberts and Manzon are experimenting with three different methods of treating barotrauma.

One of them, calling venting or fizzing, involves puncturing the fish's swim bladder with a hypodermic needle to alleviate the pressure.

The concern is that if done inappropriately, it could create damage to the fish - Richard Manzon , physiologist

"If you talk to an angler, that's probably the technique they've encountered or witnessed before," Eberts said.

Manzon said there is controversy over this technique, especially over how it it is administered.

"It's not an easy technique to implement. The concern is that if done inappropriately, it could create damage to the fish," Manzon said.

Richard Manzon is studying the physiological effects on fish when they are caught. (Cory Herperger/CBC)

Another fairly new technique uses something called a descending device, which is a weighted hook that sends the fish back down to the depth that it was caught at to reverse the barotrauma.

The third technique, which Manzon is studying, involves clipping a weight to the fish's fins to turn it upright, allowing it to reorient itself and recover.

Tournament response

Despite the issues the research points out with catch-and-release tournaments, the tournament organizers are completely on board — and even put money towards sponsoring it.

"We all love the fish," said tournament director Andre Laberge.

"We want to take care of them. We don't want to be cleaning fish all the time. We want to keep them out there so more people can come out and enjoy the fishing," he said.

There were 135 teams of two registered for the 2016 catch and release tournament at Last Mountain Lake in Saskatchewan. (Cory Herperger/CBC)

And with a tournament like this, the livelihood of hundreds of fish is at stake.

Over the tournament, 135 teams of two were attempting to catch as many walleye as possible in an eight-hour period out on the lake. The team that caught the highest weight took home a hefty grand prize of $18,000.

The hope is that anglers at the tournament can learn from some of the techniques the researchers are testing, and be able to administer the techniques themselves.

Right now, some anglers try to alleviate barotrauma on their own when fishing, but not everyone is aware of what to watch for or do.

Layne Maier, an angler participating in the tournament, said he usually just tries to stay out of the deep water to make sure the fish is in good shape when it's brought up.

Avid fishermen Layne Maier says some people treat the fish better than others. (Cory Herperger/CBC)

"We just try and do the best we can. There's always going to be mistakes. Stuff happens; they are fish. But do your best and usually they turn out OK," Maier said.

Without a healthy fish population, events like the catch-and-release tournament can't go on, Laberge said. And the survival of one fish can lead to hundreds of thousands of eggs and more fish in the future.

"Last Mountain Lake is a great fishery. It's been well maintained over the years. Our ancestors started it and our grandparents took care of it and our fathers took care of it. Now it's our responsibility to take care of it," he said.

Preliminary results

In earlier tests, Eberts said her team saw signs of success from the treatments, although they are still working on gathering data to have the statistical evidence.

Over the weekend, Eberts aimed to tag 18 fish with barotrauma to release back into the lake and track over 10 days, after administering some of the techniques.

Another 24 with the condition are being kept in a holding tank near the lake to test the effectiveness of the fin weight technique.

In total, Eberts said up to 675 fish were caught at the tournament, although the amount with barotrauma was not tallied as part of the study.

We suspect that it won't do very well. - Rebecca Eberts , biology research technician

Without treatment, the fish likely won't overcome barotrauma on their own, Eberts said. It would take about 48 hours, and the fish would have to avoid getting eaten in that time.

"We suspect that it won't do very well," Eberts said.

"We've seen pelicans come by and pick up these fish. So, it's better for the fish to get them back down in the water," she said.

The project is part of a research program under Chris Somers, a biology professor and Canada Research Chair in genes and the environment at the University of Regina.

The team's final research results are expected to be published later this winter.