Seal cull not yet warranted despite large salmon diet say researchers

Harbour seals off B.C.’s South Coast may consume up to 60 percent of the Strait of Georgia’s young chinook and coho salmon every year, according to UBC research.

Harbour seal population in the Strait of Georgia has gone from 5,000 in the 1970s to 40,000 today

UBC research shows young chinook and coho salmon make up two to five per cent of the diets of harbour seals in the Strait of Georgia. (Linda Kenny)

Harbour seals off B.C.'s South Coast may consume up to 60 per cent of the Strait of Georgia's young chinook and coho salmon every year, according to UBC research.

Growing concerns about B.C.'s salmon numbers has focused on orca populations and rising water temperatures in the past, but this study suggests the dramatic increase in the harbour seal population in recent decades may play a role as well.

Still, the connection between low salmon stocks and a large harbour seal population is not clear enough to warrant a seal cull, scientists warn.

"We don't think [our results] would be grounds for a cull right now. There are just too many unknowns," said Ben Nelson, a PhD candidate at UBC's Marine Mammal Research Unit.

"We still really don't know if some other predator species might step up to fill that void."

Salmon are an important food source for many B.C. predators, including orcas and bears.

But understanding the specific connection between salmon and seal populations will require some complicated math.

"The next step is to use some mathematical models to combine information on the seal population and the salmon population historically... to figure out, could those changes in harbour seals explain the changes in salmon mortality over the years," said Nelson.

Collecting data

Juvenile chinook salmon make their way from the rivers where they hatched to the open ocean before returning inland as adults. (University of Oregon)

Nelson collected seal feces in the Strait of Georgia for several years and, using DNA analysis, determined that juvenile chinook and coho salmon make up two to five per cent of a harbour seal's diet.

That may not seem like a big deal, but Nelson points out juvenile salmon are small, and it would take many of them to make up even a small portion of a seal's dinner.

The harbour seal population in the Strait of Georgia has exploded from about 5,000 in the 1970s to about 40,000 today, according to Nelson.


To listen to the full audio, click the link labelled: Harbour seals eat a lot of young salmon research shows.

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