Anglers’ catch-and-release method stops fish feeding properly, study finds

Findings will be alarming for those who consider their hobby not only harmless to fish, but also a way to conserve at-risk species

Mouth injuries caused by hooks can hinder the ability of fish to eat properly, according to a new study.

The findings will be alarming for anglers who consider their hobby not only harmless to fish, but also a way to conserve at-risk species.

Catch-and-release methods are common in recreational fishing, and often those involved will use barbless hooks in an effort to reduce the harm caused to their targets.

However, new research from a team of California-based scientists has added to a growing body of evidence that even practices assumed to be humane can have unintended consequences.

When a fish is hooked through its mouth, and the hook is subsequently removed, it leaves a wound that can disrupt the suction feeding system used by many popular target species like trout and carp.

The principle, according to Professor Tim Higham from the University of California, Riverside, is quite simple.

"The suction feeding system is somewhat similar to how we drink liquid through a straw," he said.

"If you poke a hole in the side of your straw it's not going to work properly."

The debate about whether or not angling causes fish any harm has raged for years, generally with animal cruelty campaigners on one side and hobbyists on the other.

As for the science, this had been far from clear. Neurobiologists have often argued that fish do not have the capacity to feel pain as we imagine it, but some experiments have suggested the opposite.

But the new study undertaken by Professor Higham and his colleagues, and published in The Journal of Experimental Biology, does not attempt to answer this question. Instead it is simply a question of mechanics.

Suction feeding relies on negative pressure being created in the animal’s mouth, which sucks in prey, and the scientists wondered if this would change after being pierced by a hook.

To investigate they studied the effect of different fishing methods on 20 shiner perch caught near the Bamfield Marine Sciences Centre in Canada.

Ten of these fish were caught using nets, and 10 were caught using a hook and line.

After catching the fish, the scientists immediately transported them to the laboratory. Once there, they gave the fish food and used cameras placed in tanks to monitor their feeding performance.

All the fish seemed equally keen to eat the food they were given, but the ones that had been caught with hooks seemed to have difficulty doing it.

"As we predicted, the fish with the mouth injuries exhibited a reduction in the speed at which they were able to draw prey into their mouths," said Professor Higham.

"This was the case even though we used barbless hooks, which are less damaging than barbed hooks."

The fish were returned safely to the water following the experiments.

"This study emphasises that catch-and-release is not as simple as removing the hook and all being well, but rather is a complex process that should be studied in more detail,” said Professor Higham.

He emphasised that from these experiments alone it is not possible to gauge to what extent angling affects the feeding performance of these fish in the wild. However, while they are waiting for their mouths to heal, he said it is likely their ability to feed would be affected.