Study seeks to solve mystery of where salmon go when they are out to sea

It's a bit of a mystery where salmon go when they're far off the coast.

But, with the help of Indigenous knowledge and tracking devices, scientists hope to change that.

The Department of Fisheries and Oceans has launched a study to better understand Atlantic salmon migration in the waters off Eastern Canada, particularly in areas where there is oil and gas activity.

"We don't know a lot about the migration patterns of Atlantic salmon as they're leaving Eastern Canada," said Martha Robertson, a research scientist with DFO.

"In order to know what the potential factors are that could impact the survival of salmon, we need to know when they're in a certain place and how long they're there for."

Robertson is leading a team of researchers in the study. It will include tracking 1,000 salmon smolts, young salmon that are ready to migrate out to sea, and 300 kelts, salmon that spawned the year before. 

A Department of Natural Resources fund is providing $11.8 million for the project. The money comes from levies on lease-holding oil and gas companies.

Indigenous knowledge

The study, which launched this spring, is focusing on rivers across Eastern Canada, especially those important to Indigenous communities. 

Robertson said salmon are important culturally and for food. She said Indigenous partners are key in this study.

"We're relying on Indigenous knowledge to know where to catch the fish, and the timing of when the fish would be leaving the rivers."

Levi Denny, the Indigenous partnership and research co-ordinator with the project, also works with the Unama'ki Institute of Natural Resources in Eskasoni, N.S. The Unama'ki Institute is one of several community partners receiving funding for the project. 

Denny was busy tagging salmon in Cape Breton this spring. 

"In Cape Breton we tagged 12 salmon with the satellite tags to find out where the salmon go and when they come back to spawn and whether they go back to the same rivers," he said.

"Normally salmon do, but, in Cape Breton specifically, we have noticed the returning population hasn't been as great as the year before."

Tagging methods

Acoustic telemetry is being used to track the smolts. A transmitter inserted into the fish while they are under anesthesia emits a signal that can be picked up by a receiver in the ocean.

But some of the older salmon are being tracked using satellite tags. That involves a type of harness that's placed under the salmon's dorsal fin. Once the satellite tag is finished tracking the salmon, they are programmed to pop off and float to the surface.

Unlike tagging and tracking sharks by satellite, the salmon can't be tracked until the satellite tag is retrieved. Salmon swim too deep in the ocean to be tracked continuously. 

In order to get the offshore data, some tags will track the first few days of being attached to the salmon and then be shut off to conserve batteries. Then in a few weeks, when it's presumed the fish are at sea, the trackers will be turned back on. 

Dalhousie University is getting $2.4 million for acoustic telemetry work in the project and the Atlantic Salmon Federation is getting $2.5 million for field work involving satellite telemetry.

Researchers and community partners will track fish for three years of the study to ensure they get a good sample size, that includes factors such as water temperature changes and possible changes to migration patterns.

The study will involve more than 50 community partners and possibly some international research.

"There are salmon that go to west Greenland from Canada and we are actually going to Greenland capturing the salmon and placing satellite tags on those fish," said Robertson. 

"Then we can monitor the migration pattern from west Greenland back to their home river in North America."

Robertson had hoped to start that portion of the project sooner but it wasn't possible with the current travel restrictions.