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Salmon thrive now; can they survive warming?

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The float plane coasts above southwest Alaska just low and slow enough for a bird’s-eye view of why this is salmon country: pristine streams and rivers that provide a birthplace for tens of millions of wild salmon each year.

Our destination is a research station in Wood-Tikchik State Park that becomes home each summer to scientists studying the resilience of salmon.

Station manager Daniel Schindler greets us, a smile breaking through his Grizzly Adams beard as we shake hands. With him on the shore of Nerka Lake are his wife, daughter and eight other researchers.

Walled-in by fjord-like peaks and hills thick with white spruce, the station run by the University of Washington is reachable only by boat or plane. It was built in 1947 and, with few renovations, it shows.

‘Diverse portfolio’ is key
But this rundown outpost has produced the longest continuously recorded history of salmon runs in the world. It's a record that shows that while runs shift from year to year, they are healthy because of what Schindler calls the “diverse portfolio” of salmon populations and habitat.

The summer of 2006 was exceptional for salmon: More than 4 million made it up to the Wood-Tikchik watershed, nearly three times the average over the past half century. Half of those salmon spawned in Nerka.

Nerka salmon have actually benefited from slightly warmer temperatures. Schindler says spring has come about two weeks earlier in recent years, giving salmon fry more time to grow before they have to fend for themselves in the ocean.

But the salmon could be forced to seek cooler waters if temperatures rise any more, he says.

That's what happened on the Yukon River in central Alaska, where the water is 10 degrees warmer than in the past. Research suggests the increase has created a thriving environment for a parasite that kills many salmon before they reach the ocean.

Coring back in time

Back at Nerka, researchers are looking at the past for clues to the future. Bruce Finney, a paleoecologist at the University of Alaska-Fairbanks, is studying the remains of salmon taken from Nerka’s floor to see what salmon runs were like thousands of years ago.

Finney chose what turned out to be a cold, wet week for the actual coring. After battling a hard rain and even harder lake bottom for hours aboard a small skiff, he got what he wanted: several 8-foot-long, clear plastic tubes that looked like huge chocolate push-up bars.

The sediment should reveal the density of salmon remains over time for a comparison with  climate and geological records.

Earlier corings showed a connection between natural climate changes and salmon populations. Finney says this is an indication that higher carbon levels in the atmosphere could have played a role then, just as carbon emissions from cars and industry are believed to be contributing to warming today.