A new study modeling glacier retreat hints at a bright spot for salmon as new habitat opens up from underneath melting glacier ice.
The study, “Glacier retreat creating new Pacific salmon habitat in western North America,” led by Kara Pitman at Simon Fraser University in Vancouver, British Columbia hypothesizes an additional 6% more salmon habitat, mainly in Alaska, by the end of the century.
“The hot spot is the central coast of the Gulf of Alaska,” said University of Alaska Southeast environmental science professor Eran Hood, one of the study’s authors. “The area north of the Alsek and south of the Copper River. That’s where we estimated a 27% increase in river habitat that could be colonized by salmon. That area has some very large glaciers and flat terrain creating the potential for several thousand kilometers of new salmon habitat by the end of the century.”
The additional habitat could lead to “new, sizable increases in salmon production in some locations,” the study says. One kilometer of spawning habitat can produce 500 to 1,500 juvenile coho, according to the study.
“Thus, with hundreds to thousands of kilometers of new habitat being created from glacier retreat, there is a potential to produce hundreds of thousands to millions of additional juvenile salmon, depending on species,” the study says.
Researchers estimated that streams exposed by glacier retreat that had a gradient above 10-15% would be too steep for salmon to colonize. They modeled five distinct climate change scenarios driven by temperature and precipitation projections in response to two climate emissions scenarios, and focused on a model that modeled mid-range climate impacts on glacier retreat.
In the “Northern Southeast” region in the study, which contains the Chilkat Valley, it was estimated that glacier retreat could open up 150 km of new spawning habitat by the end of the century. This is compared to 1,930 kilometers of new spawning habitat through the entire study region, which spans from Cook Inlet to the southern coast of British Columbia.
“We identified 315 retreating glaciers at the headwaters of present-day streams that will create salmon-accessible streams assuming a 10% stream gradient threshold for upstream salmon migration, and 603 glaciers assuming a 15% stream gradient threshold,” the study states.
Some percentage of salmon are prone to stray from their home streams, Hood said. The tendency to stray is an evolutionary adaptation to protect a population from dying out if a particular stream becomes compromised.
“That tendency is what allows them to recolonize new streams. There’s very good evidence of this in Glacier Bay,” Hood said. “You see streams that have been exposed in Glacier Bay. Some of the streams created by glacier retreat now have thousands of salmon in them. They were completely inaccessible to salmon if you go back about a hundred years because they were covered in ice.”
Hood also warned that future salmon population increases are still at risk from the effects of climate change such as ocean acidification, warming waters, sea-level rise and extreme floods and droughts.
“We don’t want to make people think ‘Oh everything’s going to be great for salmon.’ In some areas glacier retreat will create new salmon production, but we also have to keep in mind the problems that climate change pose for salmon,” Hood said.