Why Salmon Might Disappear From the Menu
Americans eat more than 624 million pounds of salmon a year, and about a third of it comes from the Pacific Ocean.
But will we (and our grandchildren) be fishing for or dishing up wild Pacific salmon in 50 years? How about 150 years? The answer depends on what we decide about climate change in the next few years.
A new study by a group of Canadian scientists, published in the journal Nature Climate Change, looks at how Pacific chinook salmon will fare as their streams become warmer in the next several decades.
On the upside, the researchers found that young chinook showed the capacity to endure stream temperatures that were somewhat warmer than historic averages. That means that climate change alone isn’t likely to cut off our supply of Pacific salmon steaks or sushi in the next few decades at least.
But they also found that there is just so much change that salmon can stand. The chinook died in water temperatures above about 76 degrees Fahrenheit, which was about 7.2 degrees warmer than their natural river habitat.
Because climate change is set to warm most Pacific salmon streams of the U.S. and Canada by at least that much in the next 100 to 150 years, “we need as a society to decide what is an acceptable level of risk and come up with solutions,” said study coauthor Bryan Neff, a biologist at Western University in London, Ontario.
“Studies like these are important because they make us ask ourselves, ‘Do we care?’ ” Neff said. “And if the answer is yes, then how are we going to prevent this from happening?”
“Tackling climate change is one avenue,” he added, because it would reduce our dependence on energy sources that create the most carbon pollution: oil, gas, and coal.
Neff and his colleagues focused their study on chinook salmon of Canada’s Quinsam River. To learn more about the chinooks’ reaction to warmer water, they looked at “aerobic scope”: the ideal temperature for the fish to do activities crucial to their survival, such as swimming, feeding, and evading predators.
Fish are ectotherms: Their body temperature falls or rises based on the cold or warmth of their surrounding environment, with their metabolism slowing down or speeding up accordingly.
In one set of experiments, the researchers found that if an individual young chinook from the Quinsam was raised in water 7.2 degrees Fahrenheit warmer than it would normally encounter in the wild, the fish’s ability to get oxygen into its blood and tissues adjusted, and it was able to go about its normal activities.
In another experiment, they bred chinook and then tracked how different genetic strains responded to gestating, hatching, and maturing in the warmer water.
“We found that there were genes in the population that allow fish to perform optimally at a slightly higher temperature or at a slightly lower temperature, regardless of what environment they were raised in,” Neff said.
Put another way, the species adapted somewhat to the changing temperature environment. But they could only adapt so much.
The scientists hooked up individual chinook from the two groups to an EKG to measure how well their hearts performed in warmer temperatures. If the water’s temperature rose above about 76 degrees, the heart could not pump enough oxygen into the animal’s tissues—including the heart itself, which began to beat erratically. Essentially, the chinook had the fish equivalent of a heart attack and died.
Neff hopes this research will inspire more investigation into how different salmon runs will fare in a warming world and inform action in the present, when it has the best chance to have an impact. “There’s always more information that we need to make a confident decision,” he said. “That aside, we do have to make decisions now.”