(Above: Dr. Isobel Pearsall, project le
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Seals: Taking a bite out of salmon survivalBy Pacific Salmon Foundation,
When seals became federally protected in 1970, their numbers increased exponentially around the Strait of Georgia from 5,000 in 1970 to about 40,000 in 2008. These numbers coincided with a precipitous decline in Chinook and Coho salmon returns to the region, triggering research efforts through the Salish Sea Marine Survival Project to determine how many juvenile salmon seals are eating in the Strait of Georgia. Preliminary results have finally confirmed some long-held suspicions.
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Seal beanies, backpacks and poop
Beanies and backpacks - the hottest new seal accessory
Through the Marine Mammal Research Unit at UBC, Dr. Austen Thomas started efforts with a project in 2014. He used a high-tech seal 'beanie' and backpack that measured exactly how many juvenile salmon were being consumed, and included the collection of seal scats (poop) from sites around the Strait of Georgia. Then UBC doctoral student Ben Nelson, analyzed the scats for salmon DNA and plugged the results into a mathematical model that takes into account how much each seal eats and the total number of seals.
The Salish Sea Marine Survival Project was started to figure out why salmon in the Strait of Georgia mysteriously declined by about 90% twenty years ago and never recovered.
Seals love salmon
Ben Nelson on his way to a seal haul-out site
They discovered that from May to October, about 40 to 60 per cent of total juvenile Coho, and about 30 to 50 per cent of juvenile Chinook, could be lost to seal predation.
What's interesting is that there are significantly more Chum juveniles in the Strait, but the seals are targeting Chinook, Coho and Sockeye. Scientists posit that this is likely because they are larger than Chum when they enter the salt water, so it's more worthwhile for seals to target them.
But according to Thomas, simply removing the seals won't necessarily solve the problem. The key question is why are seals now targeting these juvenile salmon?
Other studies through the Salish Sea Marine Survival Project suggest that juveniles in the Strait could be compromised due to pathogens, poor food supply, or a lack of refuge habitat, which in turn makes them more vulnerable to predation. So if you remove the seals, another predator may simply move in to fill that void. Work in 2018 will help fill in the blanks when scientists begin analyzing the huge amount of data collected through the Project.
One other question that has come out of this is whether the abundance of hatchery fish in the Strait is signaling seals to feed on juvenile salmon rather than other species. A potential solution would be to work with hatcheries to vary number of fish released and timing to see if it makes an impact on seal predation.
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