Climate Change and Hatcheries

Over the last decade or so, the North Pacific has warmed faster than any other ocean basin on Earth. A marine heat wave that lasted from 2014 to 2016 led to the collapse of the Gulf of Alaska cod fishery as well as to the death of more than half of Alaska’s common murres. Four million of these black and white penguin-like seabirds died of starvation when the North Pacific experienced the multi-year spike in ocean temperatures. Warming temperatures also led to a near disappearance of snow crab in the Bering Sea, and the death of thousands of sea lions and dozens of whales.

Rising temperatures can mean trouble for salmon, too. Warmer water holds less oxygen, which fish need to survive. Higher temperatures also make salmon more susceptible to disease, and certain parasites are on the rise. And the metabolism of fish, as with other marine creatures, speeds up when temperatures rise. Essentially salmon get hungrier as the water warms.

Hatcheries are releasing billions of young salmon into a transforming North Pacific. In warmer seas, fish need to eat more to survive. But warming temperatures are also altering the availability and quality of prey. This is likely to exacerbate the problem of competition for food between hatchery and wild salmon.

On top of that, pink salmon populations are booming as temperatures warm. These fish are already the most numerous type of salmon in the North Pacific, making up 70% of all salmon in the region. As other species of Pacific salmon dwindle with rising temperatures, pink salmon’s rapid two-year life span allows them to rebound quickly after population drops and colonize new areas.

In recent years, pink salmon populations have been moving north into the Arctic Ocean, and pinks straying from Russian hatcheries have invaded North Atlantic rivers in Scandinavia, where they’re considered an invasive species.

While pinks are thriving, Chinook salmon populations are plummeting. Across Alaska, British Columbia, and the U.S. West Coast, Chinook salmon runs are showing record low numbers. In some regions, these population drops are directly linked to warming ocean temperatures and changing conditions in rivers as rising temperatures alter rain and snowfall.

Hatcheries, which release over a billion pink salmon into the North Pacific each year, are piling onto the pink salmon bounty, introducing marine competitors to wild fish at a time when rising temperatures mean that there might not be enough food to go around.

--Miranda Weiss