Climate change is wreaking havoc on Pacific Ocean salmon populations: overheating spawning streams, triggering storms that scour stream beds and droughts that dry them up, and upending food webs in the Pacific. But a warming world could bring one silver lining, at least for a while. A new computer model shows retreating glaciers in British Columbia and Alaska could open up thousands of kilometers of new river habitat by 2100.
“This study helps quantify what we might see in the future at a time when salmon are struggling,” says Greg Knox, executive director of SkeenaWild Conservation Trust, a salmon conservation nonprofit not involved in the work.
Pacific salmon occupy a wide range off the coast of the western United States and Canada, from southern California up to northern Alaska, and along Russia in the western Pacific Ocean. They require pristine streams with cool, plentiful water to thrive, but habitat destruction has taken a toll. Today, populations are believed to be just 1% to 3% of their historic numbers. Many of the healthiest communities live along the coast of British Columbia up through southeastern Alaska, where thousands of glaciers—vestiges of the last ice age—used to terminate in the Pacific. A lot of those glaciers have been melting away for decades, creating new rivers as the ice recedes. Salmon have been able to move into and spawn in those newly opened rivers in as little as 10 years.
“Once conditions stabilize in the newly formed streams, salmon can colonize these areas quite quickly,” says Kara Pitman, a geomorphologist at Simon Fraser University (SFU) and lead author of the new study. Her fellow author, Alexander Milner, a river ecologist at the University of Birmingham, previously found that as many as 5000 salmon spawned in regions of Stonefly Creek in northern British Columbia, where just 10 years prior there had been a glacier. “It shows you how adaptive and resilient salmon are,” Knox says.
To get a better sense of how climate change might impact the fish over a broader region, Pitman and her colleagues modeled glacial retreat under modest predicted temperature rise throughout British Columbia and south-central Alaska, a region that includes some 46,000 glaciers. Today in Nature Communications, they report that Pacific salmon river habitat will likely expand by 6150 kilometers, nearly the length of the Mississippi River. This habitat consists primarily of streams with an incline of less than 10%, which makes it possible for fish to traverse; 2000 kilometers of the new river habitat is expected to be suitable for spawning and rearing young. In the Gulf of Alaska alone, melting glaciers are expected to increase salmon habitat by as much as 27%.
The outlook isn’t all good. The region is home to rich deposits of gold and copper. Mining companies are racing to stake claims in territory that was previously buried under ice. “There’s a gold rush happening,” says Jonathan Moore, a river ecologist at SFU, who led the study. And mining in riverbeds can rapidly degrade salmon spawning and rearing habitat.
Good times for the fish that do colonize new rivers likely won’t last. That’s because the ice feeding the rivers will eventually melt away entirely, says Tara Marsden, who runs sustainability projects for the Gitanyow Hereditary Chiefs, a Canadian Indigenous nation negotiating conservation treaties with the Canadian government. Waters could warm and ultimately disappear.
The findings are “somewhat hopeful,” Marsden says. “There may be a period when things look good. But there is something bigger on the horizon that is not good.”
To give the fish the best opportunity to survive, Marsden, Moore, and others say, fisheries managers in British Columbia and Alaska must be proactive in protecting newly opened river habitat.
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