The science behind catch and release

I recently had the privilege to attend a lecture on the science of catch and release by Dr. Steven J. Cooke, who is an associate professor and Canada Research Chair of Environmental Science and Biology at Carleton University (Ottawa, Ontario), in the field of fish ecology and conservation physiology.  

Cooke and his students have produced an astronomical number of studies (more than 400 published papers) on fish and fishing, covering a lot of topics of interest to those who fish, especially in open water.

Cooke noted that catch and release took off in the 1970s, especially among trout fisherman. I didn’t realize the scale of catch and release. We know that it varies depending on fish species, type of gear used, and type of angler.

For fish like muskies, release rates can approach 95 percent, although whether that would still be true if there were no size limits isn’t clear. Estimates of how many fish are caught and released around the world are around 30 billion fish annually, or upward of 60 percent of all captured fish.   

We all hope that a released fish will recover and rejoin other healthy ones and be there for someone else to catch. My son and I released a lot of slot walleyes this past year on Lake Winnibigoshish, and it was fun to watch them swim into the depths until you get that last glimpse of the white-tipped tail propelling them downward.  

I have this feeling – dumb, I know – that the walleye is torn between taking advantage of the potential to escape and wanting to come back up and smack you in the nose. Although I grew up well before the catch-and-release ethic took hold – and it still gives me a twinge to set loose such fine table fare – I feel a strong sense of good about it when it works. Or, I think it works.

I thought catch and release was pretty much just common sense, and had little science, per se, behind it. I was wrong. Fisheries biologists do more than just ask us to release fish. They are trying to figure out if it actually helps fish populations. 

In the biggest surprise to me, Cooke talked about the practice of taking a fish to be released, holding it by the tail, and moving it forward and backward through the water to revive it, after it lost an epic battle with you. I’d say 100 percent of the fishermen in the audience nodded knowingly, pleased that the fish doctor wasn’t telling us something we didn’t already know. I think he led us on, because he then said that was a bad thing to do for the fish.

That startled me, as just the week before we had “revived” a slot walleye on Winnie by doing just that. Cooke pointed out that fish don’t swim backward and by pulling them backward you cause water to flow over the gills in an unnatural way that might actually be counterproductive. Fish need to be moved forward to get the maximum effect. Not easy to do while you’re leaning over the boat in rough water with a tired-out walleye in hand. In fact, I’m not sure now how to revive a tired-out walleye, but I guess I won’t pull it backward.

Most people know that some fraction of released fish will not make it, owing to injuries sustained from the hook, exhaustion, or susceptibility to disease or predators. We’ve all seen some dead fish that were hooking mortalities. How do fisheries biologists figure out whether fish survive? Typically, fisheries biologists take captured fish, by whatever method, and put them in artificial enclosures, and see how long they survive. Some mortality occurs up to several days after release. 

What the studies in captivity don’t show, which Cooke thinks is important, is how these fish would do in their native environment. Fish that are eaten by other fish can be very vulnerable after release. I would guess that only a very large northern pike or muskie would take a 5-pound walleye that was experiencing disorientation and distress from being caught and released. But who knows, maybe they do. Just because they swim off doesn’t mean that the stress or injuries are not eventually going to be fatal.  

Cooke spent time talking about what types of tackle cause the greatest injuries to fish. Circle hooks can result in a 50-percent reduction in hooking mortality, whereas J-shaped hooks get father down into the mouth and often cause more damage. It is especially true if live bait is used, and angler experience also matters. Inexperienced anglers tend to let a fish take a bait too far into its throat before setting the hook. I admit that some pretty small perch have not fared well during my sleepy times because of all the time I gave them.

I suspect most people, including me, thought barbless hooks are better for fish than barbed ones, but, according to Cooke, the research is not supportive of this. Getting hooked with a barbless hook can still make a wound fatal, although barbless hooks are easier to remove. I would think that a barbed hook could make a non-fatal hooking fatal during hook removal, but I’m not sure there’s research on that. Cooke stressed the importance of cutting off hooks that were deeply embedded.

Does cutting and leaving the hook in place help a released fish survive? Yes, most of the time. Sometimes the hooks dissolve (others do not rust) or become not too big a problem, but it can be fatal. Cooke said that there is basically no way to remove a deeply set hook without endangering the survival of the fish. Research shows that hooking mortality increases in higher-temperature, summer waters. Not surprisingly, there is very little research on the effects of catch and release during the ice-fishing season. There’s a research niche for an enterprising fisheries biologist.  

Best practice is to minimize air exposure and handling. If you’re taking a photograph, make your fish’s time out of water brief. If not, a fish’s gills can collapse, it can become dehydrated or experience cardiac difficulty, lose equilibrium, and have impaired swimming ability. If a fish is upside-down when put back in water, it is six times more likely to experience major issues.  

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