Tagging project aims to solve salmon mystery
Acoustic sensors on wild species to provide data on their migration
A high-tech salmon tagging project may help resolve one of the vexing unanswered questions of the Cohen Commission report on the decline of the Fraser River sockeye.
Justice Bruce Cohen made no judgment on the effects of net-pen salmon farms on wild salmon — it was one of four potential smoking guns identified in the proceedings — but he did hear a mountain of testimony alleging harm and some evidence to the contrary. Among the recommendations of the report was a Sept. 30, 2020, deadline for resolving the question of harm to wild salmon by fish farms in the Discovery Islands.
A multi-year study financed by the Pacific Salmon Commission aims to do just that.
“There is real mystery about where and when salmon die,” said Tony Farrell, a professor of biology at the University of British Columbia. “A female sockeye produces 3,000 eggs, but you only need two survivors to sustain the population, so that means 99.6 per cent of the eggs die at some stage of the salmon’s life, most of them as juvenile fish and later in life.”
New programmable tags used in the study are small enough to implant in fish only 10 centimetres long, which will provide rich information about what happens to young fish in fresh water and later when they reach saltwater and migrate to the open ocean.
“We are asking the question, what is the mortality rate for fish as they go past fish farms moving from the Strait of Georgia and out to the Hec- ate Strait?” Farrell said. “There are people who believe that wild salmon going past the fish farms are suffering undue mortality and this is one way to get at that.”
The project will also shed light on the directions that juvenile salmon take on their way to the ocean, where and when they succumb to disease or predation.
“This year’s work with Chilko chinook and sockeye will tell us what routes these fish take, whether that is the back channels where the fish farms are or straight up Discovery Passage west of Quadra Island,” said Dave Welch, president of Kintama Research Services, which is doing the tagging and sen- sor deployment. “(Discovery Passage through to Johnstone Strait) is the main channel through and it looks like most of the smolts are taking that way, where there are no fish farms.”
About 100 chinook salmon from the Chehalis River Hatchery were tagged and released earlier this month. Another 300 sockeye will be tagged and released later this year in the Chilko River. They will be the smallest fish ever to carry acoustic transmitters.
The fish that survive will pass arrays of acoustic receivers strung under the water in the Fraser River and salt waters between the mainland and Vancouver Island from the Strait of Juan de Fuca to the north end of Johnstone Strait.
This year’s goal is to prove the effectiveness of the tiny programmable tags. Upgrades to sensor arrays will provide a more precise picture of the geography of juvenile salmon mortality, possibly providing an answer to Justice Cohen’s question about the impact of fish farms on wild salmon.
Tags on half of the salmon in the study will run until the end of summer, while the other half will turn themselves off to conserve battery power and then turn back on as the first set of tags shut down, allowing researchers to monitor fish movements and survival until winter.
“The V5 tag gives us the flexibility to adjust the strength of the signal and turn the tag on and off over limited periods. By doing tricks like that we are able to capture data over a much longer period of time,” said Brian Riddell, president of the Pacific Salmon Commission.
The B.C. Salmon Farmers Association is contributing $150,000 over three years to the project.
“Salmon farmers know a tremendous amount about the fish they raise,” said Jeremy Dunn, executive director of the salmon farmers association. “What is apparent is that more knowledge is needed on wild Pacific salmon and understanding their migration timing and routes is important information.”