Clipping fin on hatchery salmon could reduce swimming ability: study
By Judith Lavoie, Postmedia News July 11, 2011
VICTORIA — The long-established practice of clipping the small back fin on hatchery salmon may be affecting their swimming ability and the survival rate of the fish, suggests a new study co-authored by University of Victoria biologist Tom Reimchen.
"The practical issue emerging from our study is, what is the result of the increased loss of their swimming ability and their reduced competitive performance and do they come back at a lower rate than fish with an adipose fin," Reimchen said in an interview.
The adipose fins are removed from hatchery fish so, when they are caught, they can be identified. The information is sent to Fisheries and Oceans Canada to help in stock assessment and gauging trends in salmon abundance and survival.
Hatcheries initially tried marking by cutting the lobes of the dorsal and caudal fins and rapidly discovered that fish could not swim symmetrically without those fins. However the adipose fin was thought to be vestigial — meaning it had no practical use.
But that always puzzled Reimchen. "Many years ago I started to reflect on why fish would retain a structure for 60 million years unless it had some use," he said.
Reimchen also noticed that, when the fin was cut the fish would jerk.
"It was clearly unhappy, which suggested to me there had to be nerves running through that fin," he said.
Reimchen previously found that, when the small fin is removed, the fish needs to use more energy to keep up speed and position, something likely to put the fish at a disadvantage in the ocean, where salmon face numerous survival challenges, ranging from climate change to predation.
The new study, by Reimchen and fellow authors from St. Francis Xavier University in Nova Scotia, is being published in Proceedings of the Royal Society.
They studied brown trout — members of the salmon family — and found that the adipose fin is a sensory organ laced with a network of nerves similar to those found in the brain.
"This strongly suggests that the fin acts as a mechano-sensory organ that relays positional information to the fish," Reimchen said. That means the fin would play an important role if the fish was trying to navigate through turbulent waters.
"There could be a better way of (marking) that doesn't compromise their swimming ability," Reimchen said.
"Our results suggest that we should be rethinking the removal of a vital sensory device, especially when these fish are already subjected to considerable demographic and environmental stresses."
In Canada hatchery coho are usually marked by a cut fin and sometimes also with a coded nose wire tag; in the U.S, chinook and coho are marked. Canada and the U.S. mark about 45 million juvenile salmon annually.
Department of Fisheries and Oceans spokesman Tom Robbins said the department has not yet had time to review the study.
At Goldstream Hatchery only a portion of the young coho are marked, said president John Mace.
Some of the marked coho make it back to Goldstream each year, Mace said.
"We've restored the Goldstream runs from almost extinction," he said. "Whether more would return (without clipping) I don't know."
