Before juvenile salmon make their way to the sea, they grow and feed in freshwater, including wetlands, for anywhere between a few months and several years.
But new research finds that as air temperatures rise with climate change, the water that flows through coastal Alaska’s ponds and marshes is warming rapidly, too. That could spell trouble for Pacific salmon, which can’t grow – or live – in waters above certain temperatures.
“I’ve never really hoped so much that I might be wrong,” said Amaryllis Adey, a researcher at Virginia Tech.
Adey is a co-author of the report, which was published in December in the journal Nature. The researchers compared nine years of water and air temperature data from 20 ponds near Yakutat and Cordova. They found that the water was keeping pace with increases in air temperatures.
That’s notable because it marks a departure from what’s happening with other freshwater ecosystems as temperatures rise, Adey said.
Past research shows that rivers and streams are warming more slowly than the air due to a range of factors, including that they move quickly and benefit from glacial runoff. Wetlands, meanwhile, are typically shallow, still, and more spread out across the landscape – leaving them more exposed to the air.
“It was really stark,” she said. If “one degree of air temperature results in one-degree increases in water temperature, that could be really concerning in the future.”
The researchers’ next step was using the historical data to model what might happen in the decades to come.
The researchers looked at two possible scenarios. One was a future in which humans continue producing greenhouse gases at the current rate. Adey called that the “business as usual scenario” and said it resulted in a “drastic increase” in water temperatures.
“It was like up to 22 degrees Celsius by the end of the century,” Adey said.
That’s about 71 degrees Fahrenheit, which is really warm – and dangerous – for these wetland ecosystems. Coho salmon, for instance, stop growing at around 68 F. And death becomes likely once temperatures surpass about 73 F.
Adey says it’s certainly possible that salmon would adapt. But if they can’t shift the timing of their migrations or habitat use, she said, “they won’t be able to continue to grow and survive in these systems that are very economically and culturally dependent on them.”
The second scenario was less grim. If humans continue emitting at current rates for another decade and then begin reducing carbon emissions, water temperatures would still rise. But they would be less likely to reach dangerous levels.
The study looked specifically at two areas – the Yakutat Forelands and the Copper River Delta. But the results have far-reaching implications, including in Southeast Alaska.
“We’d expect that there’s going to be kind of similar responses across that coastal region,” she said.
Other organisms, including algae and bottom-dwelling invertebrates, are also temperature sensitive, the study said. That means warmer water could be felt by the entire food chain, ranging from different fish species to migratory birds.
