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Common hatchery practice of clipping fins could harm salmon, says UVic researcher

Technique meant to mark fish, but forces them to spend more energy to maintain position and speed.

Photo courtesy of Wikimedia Commons.

VANCOUVER -- The common practice of clipping the small back fin of salmon to discern hatchery-raised fish from wild may not be as harmless as experts once believed.

In an environment where every step counts for salmon survival, a study from the University of Victoria suggests hatcheries may need to find another way to mark their fish.

Biologist Tom Reimchen said that as far back as the 1970s, he noticed that salmon fry would flinch when their adipose fin was cut, indicating that clipping the fin hurt.

Experts long believed the tiny fin between the dorsal and tail was like cutting a finger nail.

Instead, Reimchen and co-author John Buckland-Nicks, of St. Francis Xavier University in Nova Scotia, revealed in a recently published study in Proceedings of the Royal Society that the adipose fin is a sensory organ especially important when the fish is swimming in turbulent water.

Reimchen, an evolutionary biologist, said Monday that clipping the fin might be compared to losing a hand for a human -- damaging but not necessarily deadly.

"You can still survive without it, but if you're in any type of competitive interactions or where you're under the gun from maybe not enough food or long swimming distances like salmon have been, then you would expect that its affects are going to be noticeable.''

They found the adipose acts like a complex feeling device, allowing the fish to detect water flow and then compensate.

"It's clearly much more complex than fisheries biologists thought before.''

When the tiny fin is removed, he said the fish need to use much more energy to maintain position and speed in the water.

"If you can imagine a school of 100,000 salmon swimming out, the ones with the adipose clipped will be expending more energy to go that same speed,'' he said.

While he and Buckland-Nicks are convinced clipping the fin has an impact, they aren't sure what percentage of fish may be lost because of the practice.

A previous study by Reimchen showed that fish without the adipose had to move their tail about 15 per cent more to compensate for water thrusts.

The idea came to him when he was watching salmon in the stream hardly moving while their adipose fin flapped quickly back and forth. He said the salmon without the fin moved much more, appearing to compensate for the loss.

No one from the federal Department of Fisheries and Oceans was unavailable for comment.

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