Resilience to Extremes - Can Salmon Survive the Hot Water?
The Pleistocene Epoch was long. Well, in the grand scheme of things, I suppose two and a half million years is rather short.
What you can say about the Pleistocene is it was cold. It is commonly referred to as the “Ice Age”, but in a sense, this term can be misleading. It is only the most recent of several ice ages, and the Earth was not actually a consistent snowball for the entirety of the Pleistocene. Instead the period was marked by what scientists think could be as many as twenty different glaciation cycles, where glaciers crept from both poles toward the equator, then retreated, over and over again.
If there’s anything that is more difficult than extreme conditions for (most) living organisms, it’s changes to the stability of those extremes.
Enter the Pacific Northwest, about one million years ago. By then, the five recognizable Pacific salmon species we know of today (sockeye, Coho, Chinook, pink, and chum), had diverged from their common ancestor, in addition to further differentiating from their closest relative, the Asian masu salmon. Repeatedly, the ice cap reached far south into British Columbia, encroaching on much of the salmon’s habitat in the coastal rivers and streams.
A question that’s up for debate regarding the history of these fish is this: how did salmon survive such severe swings in their environment as the glaciers came and went?
In his book King of Fish: The Thousand-Year Run of Salmon, author and professor of earth sciences David R. Montgomery cites two different theories for the salmon’s resiliency. He states that the prevailing notion is that the salmon survived in ice-free areas in the Columbia River Basin, as well as in California and other areas in Oregon.
But today, the fact is salmon do in fact inhabit waters at the feet of calving glaciers in Alaska where the water can approach freezing temperatures. This has led some to suggest that salmon could have possibly survived farther north than previously thought. Due to the drastic increase in the size of the polar caps, sea level dropped by hundreds of feet, exposing more of North America’s continental shelf. Scientists argue that newer rivers that flowed across that expanse could have also provided a sanctuary.
The importance of studying salmon’s past is becoming ever more applicable in today’s world, but in this case, the opposite extreme is the threat. Earth is undoubtedly warming. The National Oceanic and Atmospheric Administration reported that 2014 was the hottest year globally on record, and as far as 2015 goes, it appears the bar will be raised yet again.
We know salmon were able to survive the freeze, but what will happen if their water begins to boil? Hyperbole aside, it still begs the question, how will the fish survive as river and ocean temperatures rise?
Not very well it seems. Already, we are seeing major die offs in the rivers and streams of the Pacific Northwest. In July 2015, the return of 500,000 sockeye salmon to Columbia River was marred by the deaths of about half that number, a quarter of a million salmon. They died because the water was too hot.
If you’re an avid skier you might know the reason. For the second year in a row, snowpack was abysmally lower than the norm in the Cascade Range. Thus, when the summer months rolled around and the fish began their trip back up the Columbia, there wasn’t any snowmelt runoff left to cool the river.
The fish mortality event wasn’t an isolated occurrence during Oregon’s summer either. Scientists reported the death of over one hundred spring Chinook in the Middle Fork of the John Day River, where the water reached seventy degree, swimming-pool-like temperatures.
Is the resilience of the salmonid species finally reaching a breaking point? Or will they simply adapt as they have for millions of years and search for more ideal water, perhaps farther north. Matt Piche, the natural resources coordinator for the Native Village of Eyak in Cordova, Alaska says, “As waters warm, we’re starting to see Chinook salmon in areas we’ve never seen before, they’re starting to migrate north.”
This could only be a temporary fix though; Alaska isn’t impervious to warming temperatures either. The Pleistocene was long and cold, but the Holocene epoch we find ourselves living is quickly becoming hot. Let’s hope the salmon can keep up.
