Science

Salmon are being 'squeezed' from 40 YEARS of changes in the rivers and freshwater seas they swim in 


Salmon populations are being ‘squeezed’ after 40 YEARS of changes in the rivers and freshwater seas they swim in, including climate change and seals preying on them

  • Five different species of Pacific salmon and trout are declining because of 40 years of changes in their marine and freshwater environments
  • The species being affected are seeing declines in numbers in the Keogh River, near Port Hardy on Vancouver Island
  • A fluctuating climate, increase in seals, competing salmon, warmer water temperatures and an increase in watershed logging are playing a role 
  • Steelhead and coastal cutthroat trout populations declined by 80% and 70% between 1976 and 2015










The population of Pacific salmon and trout are declining rapidly not only because climate change is getting worse, but also because of 40 years of changes in their marine and freshwater environments, a new study has found. 

Five different species of Pacific salmon (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden and Coastal Cutthroat Trout) are all seeing drastic declines in numbers in the Keogh River, near Port Hardy on Vancouver Island. 

Coastal Cutthroat Trout (pictured) are seeing drastic declines in numbers

Steelhead trout (pictured) populations declined by 80 percent between 1976 and 2015

Five different species of Pacific salmon and trout are declining because of 40 years of changes in their marine and freshwater environments

Five different species of Pacific salmon (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden and Coastal Cutthroat Trout) are all seeing drastic declines

Five different species of Pacific salmon (Steelhead, Coho Salmon, Pink Salmon, Dolly Varden and Coastal Cutthroat Trout) are all seeing drastic declines

The declines in numbers are happening in the Keogh River, near Port Hardy on Vancouver Island

The declines in numbers are happening in the Keogh River, near Port Hardy on Vancouver Island

Researchers at Simon Fraser University’s Salmon Watershed Lab found that stressors in the environments in which the fish swim and live, such as a fluctuating climate, an increase in seals and other competing salmon species are taking their toll. 

Warmer water temperatures and an increase in watershed logging, are also playing a role in the decline in the populations of the five salmon species, as well as steelhead and coastal cutthroat trout.

Steelhead and coastal cutthroat trout populations declined by 80 percent and 70 percent between 1976 and 2015, the researchers found

Steelhead and coastal cutthroat trout populations declined by 80 percent and 70 percent between 1976 and 2015, the researchers found

Steelhead and coastal cutthroat trout populations declined by 80 percent and 70 percent between 1976 and 2015, the researchers found.

‘It’s not just the ocean that is driving declines,’ the study’s lead author, Kyle Wilson, said in a statement

Particularly concerning is the survival rate of lower juvenile salmon, which are impacted by watershed logging

Particularly concerning is the survival rate of lower juvenile salmon, which are impacted by watershed logging

‘The combination of marine and freshwater stressors effectively ‘squeezes’ some salmon populations by lowering survival in both the river and the sea.’ 

Particularly concerning is the survival rate of lower juvenile salmon, which are impacted by watershed logging.

Coupled with the reduced survival rates of adult salmon due to seals and competition from other salmon – wild and those released from hatcheries – and the populations are declining rapidly.

‘This study showcases the power and importance of careful monitoring of both adult and juvenile life-stages of salmon and steelhead in order to understand what parts of their life-cycles are driving overall population change,’ project collaborator and SFU biology professor Jonathan Moore added. 

Salmon populations in the Pacific Northwest have been declining for some time (Alaska salmon are actually shrinking in size), but the environmental factors that are causing the declines are only just becoming understood by experts. 

‘Some research attributes the decline to worsening ocean conditions while others point to climate change or overfishing,’ Wilson added.

‘There has even been great uncertainty about which is more responsible, freshwater or marine processes, for salmon and steelhead declines.’

The findings can help inform the U.S. government’s recent Pacific Salmon Strategy Initiative (PSSI), which will allocate $647.1 million to help recover the salmon through conservation and scientific efforts, Wilson said.

The study was published today in the journal Global Change Biology

In July, Pacific Northwest salmon were seen dying from red lesions and white fungus from the extreme temperature spike the western part of the U.S. experienced over the summer.

Separately that month, researchers said the heatwave – caused by a ‘heat dome’ that hung over the Western U.S. and Canada and spiked temperatures to 121 degrees Fahrenheit in some spots – killed over 1 billion sea creatures.  



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