Climate change and extreme droughts are shrinking the breeding grounds of California’s wild salmon, with experts warning that Australia could face similar threats to its freshwater ecosystems.
Climate Change Shrinks Wild Salmon Habitat in California
A new international study has revealed that prolonged droughts, intensified by climate change, are significantly reducing the natural breeding range of wild salmon in California. The research, published in the Proceedings of the National Academy of Sciences (PNAS), was led by the University of California in collaboration with Associate Professor Sally Thompson from the University of Western Australia (UWA).
“Salmon are incredibly important in north-west America—not only as a cultural symbol for Indigenous communities, but also as a vital part of forest ecosystems and the fishing industry,” said Associate Professor Thompson, from UWA’s Center for Water and Spatial Science.
How Drought Disrupts the Salmon Life Cycle
Salmon are migratory fish species that hatch in freshwater rivers, migrate to the ocean to mature, and then return to their birthplace to spawn. However, between 2011 and 2014, California experienced a one-in-a-1,000-year drought that drastically altered river flows.
“Typically, winter stream flows begin in November, triggering the salmon’s return upstream,” Thompson explained. “But during this extreme drought, water didn’t begin to flow until January, leaving many breeding grounds inaccessible.”
As a result, salmon in several northern Californian rivers were unable to spawn, leading to widespread breeding failures. Since salmon tend to return to their birthplace to reproduce, this lack of access could mean future generations won’t repopulate these areas.
A Shrinking Range with Long-Term Impact
The researchers warn that the breeding range of California’s wild salmon is contracting—a trend that may become permanent if climate change continues to drive extreme drought events.
“Our study shows that the valuable Californian salmon population is losing ground,” said Thompson. “When salmon are unable to spawn in specific locations, we risk losing them from those ecosystems forever.”
Why Australia Should Pay Attention
While Australia does not have wild salmon, the findings are highly relevant to the country’s own freshwater systems. Australia is home to several migratory fish species—such as lampreys—that also rely on freshwater access to breed.
“Climate extremes that occur in California—like bushfires and droughts—are often mirrored here in Western Australia,” said Thompson. “We’re already seeing declining rainfall and shrinking river flows, which pose a significant threat to our native fish populations.”
Urgent Need for Freshwater Conservation
This study underscores the growing need for sustainable water management and climate resilience planning in both the U.S. and Australia. Protecting freshwater ecosystems and ensuring migratory species can access breeding habitats must be a priority in the face of global climate change.
Reference:
Stephanie M. Carlson et al. (2025). Anatomy of a range contraction: Flow–phenology mismatches threaten salmonid fishes near their trailing edge. Proceedings of the National Academy of Sciences (PNAS). DOI: 10.1073/pnas.2415670122
Provided by: University of Western Australia