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Climate change has unpredictable effects on salmon migration

While climate change has recently led to earlier spring blooms for wildflowers and ocean plankton, its effects on salmon populations are more unpredictable and complicated, according to a new study led by Simon Fraser University (SFU). 

To better understand this phenomenon, the experts compiled the largest dataset in the world on juvenile salmon migration timing, including 66 populations ranging from Oregon to British Columbia and Alaska. These datasets focused specifically on wild salmon and were at least 20 years in length, with the longest one dating back to 1951.

“Field scientists from many different organizations work really hard to collect data on the migration of smolts [young salmon], day after day, year after year. Bringing this data together really showcases the importance of long-term monitoring,” said study lead author Samantha Wilson, a postdoctoral fellow in Biology at SFU.

The investigation revealed that, although many species of salmon significantly changed their migration patterns over the past few decades – such as the pink and chum salmon, which are now migrating seven days per decade earlier – others did not change them, despite the rapid warming of their habitats.

Surprisingly, the researchers found greater variation between populations within species than between different species. “We were really surprised. Yes, there were really strong signals of climate change as many salmon tended to be migrating earlier, but it was incredibly variable and unpredictable,” Wilson said.

A match between the migration timing of juvenile salmon and food availability creates ideal conditions for surviving the first months in the ocean, influencing how many adults return. However, since many salmon populations do not appear to be responding to changes in the coastal ocean, mismatches could become increasingly common under future climate change, leading to population declines.

As global warming continues to alter a variety of ecosystems, being able to predict which species or populations are the most vulnerable is crucial for conservation efforts. However, when such changes are difficult to predict – as in the cases of salmon – a precautionary management approach could work best for the long-term conservation of ecologically, culturally, and economically important species.

“Climate change is here and it is changing salmon and their ecosystems. Many of these changes are going to be unpredictable, which calls for the protecting of salmon biodiversity and their habitats,” said co-author Jonathan Moore, an expert in the Ecology and Management of Aquatic Ecosystems at SFU.

Moreover, as this study has proven, collaborations among a variety of scientists from different backgrounds and the use of large datasets spanning extended periods of time are essential to examine the dynamics of large-scale, unpredictable systems.

“This study brought together more than 50 scientists from government and community organizations, with everyone contributing their expertise and data to better understand this important, but often overlooked life stage. Long term monitoring projects are expensive and logistically challenging to run, and yet are increasingly important to better our understanding of how climate change may be affecting salmon,” concluded co-author Matthew Sloat, the director of science at the Wild Salmon Center.

The study is published in the journal Nature Ecology & Evolution.

By Andrei Ionescu, Staff Writer

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