Climate Sep. 21, 2016 11:28AM EST
Salmon have been swimming in Pacific Northwest waters for at least seven million years.iStockFor as long as people have lived in the area, salmon have been an important food source and have helped shape cultural identities. But something is happening to Pacific coast salmon.
This year, British Columbia’s sockeye salmon run was the lowest in recorded history. Commercial and First Nations fisheries on the world’s biggest sockeye run on British Columbia’s longest river, the Fraser, closed. Fewer than 900,000 sockeye out of a projected 2.2 million returned to the Fraser to spawn. Areas once teeming with salmon are all but empty.
Salmon define West Coast communities, especially Indigenous ones. The West Coast is a Pacific salmon forest. Today, salmon provide food and contribute to sustainable economies built on fishing and ecotourism. West Coast children learn about the salmon life cycle early in their studies.
Salmon migrations, stretching up to 3,000 kilometers, are among the world’s most awe-inspiring. After spending adult lives in the ocean, salmon make the arduous trip up rivers against the current, returning to spawn and die where they hatched. Only one out of every thousand salmon manages to survive and return to its freshwater birthplace.
So what’s going wrong? Climate change is amplifying a long list of stressors salmon already face. Sockeye salmon are sensitive to temperature changes, so higher ocean and river temperatures can have serious impacts. Even small degrees of warming can kill them. Low river flows from unusually small snowpacks linked to climate change make a tough journey even harder.
Oceans absorb the brunt of our climate pollution—more than 90 percent of emissions-trapped heat since the 1970s. Most warming takes place near the surface, where salmon travel, with the upper 75 meters warming 0.11 C per decade between 1971 and 2010. Although ocean temperatures have always fluctuated, climate change is lengthening those fluctuations. A giant mass of warmer-than-average water in the Pacific, known as “the blob,” made ocean conditions even warmer, with El Niño adding to increased temperatures. Salmon have less food and face new predators migrating north to beat the heat.
Beyond creating poor environmental conditions for salmon, climate change increases disease risks. Warm conditions have led to sea lice outbreaks in farmed and wild salmon, and a heart and muscle inflammatory disease has been found in at least one farm. Scientists researching salmon movement through areas with farms are finding wild fish, especially young ones, with elevated parasite levels. Diseases that cause even slight deficiencies in swimming speed or feeding ability could make these marathon swimmers easy prey.