Quirks & Quarks

Hook injuries could hamper fish's ability to feed

New research by a marine biology student at the University of Alberta suggests that hook injuries could be hampering the ability of "catch and release" fish to feed.

Researcher and avid angler Melissa Thompson says her findings have changed how she fishes

This golden perch was caught with a lure equipped with barbless hooks, which can still injure the fish and reduce its ability to feed. (Codman/Wikimedia)

Conservation-minded anglers might not know they may be doing more harm than good when they catch and release their prized fish. 

New research by a marine biology student at the University of Alberta suggests that hook injuries could be hampering the ability of released fish to feed. 

Melissa Thompson has been an avid angler herself since she was two, and did the research while taking a marine biology course through the University of Alberta at the Bamfield Marine Sciences Centre on Vancouver Island.

"What I discovered was when they're hooked correctly in the side of their mouth, it can decrease the suction performance of fish." 

Many fish, like the shiner perch Thompson caught either by barbless hooks or by net to use in her experimental research, feed by sucking water with the prey into their mouth. 

"They open their mouth and they increase the volume in basically the back of their throat," Thompson told Quirks & Quarks host Bob McDonald. "By doing that, it causes all the water in front of the fish to rush into the mouth, and any food or shrimps or tiny fish in front of the fish's mouth gets sucked into the mouth."

Hole in the mouth reduces fish's ability to feed

After an angler removes the hook from a fish's mouth, the suction becomes compromised. Thompson said it's like what happens when you drink out of a bent straw with a hole in it.

"[The fish are] drawing in the water from both in front of the mouth and through the hole through the side. So it just decreases the amount of water that comes from the front of the mouth."

If they have less of a suction, then they're not going to be able to get those really fast prey types like little shrimps or little fish that have a higher chance of escaping.- Melissa Thompson, Former University of Alberta student

The speed at which the injured fish were able to suck in their prey was reduced compared to uninjured fish. Thompson said that affects how precise the fish are when targeting their prey. 

"If they have less of a suction, then they're not going to be able to get those really fast prey types like little shrimps or little fish that have a higher chance of escaping."

She also noticed the fish with holes in their mouth seemed less willing to feed than the uninjured fish. 

All of this has led Thompson to believe the injury a hook leaves behind plays a part in the mortality rates they see for fish caught by catch-and-release. According to established literature, up to a third of fish caught by this method end up dying. 

Overall effects of catch-and-release 

According to a computational fluid analysis model, the hook injury in the fish didn't fully account for the reduced feeding performance, Thompson observed. She believes stress the fish experiences explains the rest.

When an angler is reeling in a fish, it's struggling to survive. The fish comes in exhausted from the fight they put up as they're reeled in. Then when they're taken out of the water so the angler can get a trophy photo and remove the hook, the fish are essentially suffocating until they're back in the water. 

Approximately one third of fish caught by catch and release end up dying. Scientists think this is due to its reduced ability to feed from the hook injury, as well as stress. (Enzol / Pixabay)

"If the fish is above the surface water for 30 seconds, the stress hormones in its blood don't go down for two hours after," said Thompson based on previous scientific literature. "So [catch-and-release] has a very large effect on the stress hormones. And then other research shows that it's less likely to breed." It also makes the fish more likely to abandon their eggs if they have them. And as she discovered in her study, it also affects their ability to feed.

Thompson says despite what she's discovered, she has no intention of putting down her fishing rod, but it has changed how she fishes. 

"I keep the fish in the water. I try not to disturb the fish's mucousy layer on the outside of it. And I just try to be gentle and give them time to breathe — make sure that they're OK."

And if she does hook one and it looks like it's not going to survive, even if it's not that big or she wasn't planning on having it for dinner, if they're within the allowable size limits, she'll keep it and eat it anyway. 

"It's just good practice."


  • An earlier version of this story stated that about a third of all fish caught by catch-and-release die. In fact, the mortality rate of different fish species can vary, but generally up to a third of all the fish caught by this method die after being released. 


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