Measuring The Trauma Of Catch-And-Release

Fishing is a popular and lucrative sport around the world, but it can contribute to declining fish stocks. To maintain stable numbers of fishes in aquatic ecosystems, many countries have implemented catch-and-release fishing — a practice where fishes are caught and immediately released — to enable the continuation of recreational fishing.

In this study, a group of biologists set out to study marine shiner perches (Cymatogaster aggregata) by combining high-speed videography and computational fluid dynamics (CFD) to determine the role of hook-induced injuries in the performance and hydrodynamics of suction feeding. In other words, while catch and release is meant to be a conservation-minded practice, does it have unintended negative consequences for fish?

Previous research has reported that the average post-release mortality of some fishes can be as high as 67% after they experience the stresses of catch and release. These stresses occur during fish capture and handling and include factors such as time exposed to air, handling roughness, time from being hooked to being brought out of the water, where the fish was hooked, the experience of the angler, the depth from which the fish was pulled, and fish size. Interestingly, mortality of fishes after being caught by recreational anglers exhibits species-specific variability, with most mortalities occurring between four hours and four days after being caught. In general, successful healing may partially explain why short-term mortality of fishes is generally higher when compared with their long-term mortality.

In this study, the non-injured control group of perches exhibited significantly faster prey velocities than the injured group. CFD simulations identified the reason for this drop in performance: a lower pressure gradient developing during mouth expansion due to holes caused by hooks. Still, this did not completely account for the larger decrease in real performance.

The authors note that the use of barbed hooks likely has even more adverse effects because the barb makes the hook harder to remove, thereby increasing the overall handling time and effective hole diameter. Such injuries might push the fishes to consume different types of prey in nature until they can resume normal feeding behaviors.

The implications of such injuries are severe: a minimum of 29% of fish caught recreationally in Canada during 2010 were ones who employed suction feeding as the main mode of prey capture, while in the U.S. the figure was 53%. Therefore, it is crucial to study the effects of recreational fishing on both the physiological and behavioral traits of affected individuals.

Although more field studies are necessary to determine whether there is a link between impaired feeding and mortality among fishes exposed to catch and release, animal advocates will surely see such injuries caused by recreational fishing as a welfare detriment that needs to be addressed in the short term.