Salmon splashing near a gate at a salmon hatchery.
Copyright 2019 Photography by Adri.

Wild salmon’s been ecologically, culturally and commercially important in the Pacific Northwest for centuries. Drastic population declines due to overfishing and habitat loss has resulted in government-funded salmon hatcheries to “enhance” wild stocks, with so-called “restoration aquaculture.”

Of the five Pacific salmon species in North America, Chinook (or King salmon) is the most severely depleted, with some populations listed as endangered in the U.S. and Canada. As Chinook is an important fishery (for humans and killer whales) it has the highest hatchery production, releasing a staggering 3.7 billion Chinook into the Salish Sea since 1950—that’s 50 million salmon every year!

What impact does adding 50 million fish annually have on such an ecosystem? “Ecological implications of changing hatchery practices for Chinook salmon in the Salish Sea” sheds new light on the complex results of this grand experiment with nature. This study (and others) note that hatchery production doesn’t automatically increase the number of salmon available for fishers or fish-eating orcas. In fact, the total catch continues to fall most years, and with it the highly interdependent population of Southern Resident killer whales.

Farmed and wild salmon are not created equal: healthy wild salmon populations are genetically diverse, whereas hatchery-raised fish are genetically similar. They’re released en masse from only a few locations, and over a short time period which often results in an unnatural distribution of salmon in the ecosystem.

According to the study’s authors, a Vancouver Island hatchery releases 60% of its Chinook into the Georgia Strait, though historically the Strait only accounted for 5% of the wild Chinook stock. Likewise, South Puget Sound historically accounted for 4% of wild Chinook stocks, yet the hatchery release is 25% of their raised fish. These salmon then appear to stay local, unlike wild Chinook that spend 2-6 years foraging in the Pacific. This unnatural residency adds thousands of predators to the Salish Sea ecosystem, who ironically are thought to eat up to 50% of subsequent releases of hatchery salmon, not to mention juvenile wild salmon, and their prey.

Milt being extracted from a salmon at a hatchery.
Photo courtesy of U.S. Fish and Wildlife Service.

The timing of release of hatchery fish also impacts their future chance of survival. In 2015, over half of the Georgia Strait hatchery Chinook were released over a two-week period in mid-May. By comparison, wild Chinook migrations vary from river to river over many months, spreading genetic diversity and managing risk. A mass release of clones from hatcheries doesn’t build in such safeguards, and a predictable, abrupt release makes them more vulnerable to predators. Especially since at release they’re almost twice as large as their wild counterparts, and so are the perfect size for seals and birds, who quickly learn the timing of these releases.

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The study’s authors suggest a more diverse, experimental approach to hatchery management in the Salish Sea (and beyond). Hatchery managers should explore the potential for improving juvenile hatchery survival rates by better mimicking natural systems. It’s also imperative to develop a better understanding of all the ecological impacts hatcheries can have on wild Chinook.

However, it’s clear that very little time remains to continue to experiment within a system that has evolved over millennia. Wild salmon are at risk of extinction and these orcas need food now. The Southern Residents need a share of the annual Chinook catch and in the longer term, wild salmon populations need to be restored, so that hatcheries become unnecessary. Breaching dams would restore access to critical upstream spawning habitat, which ultimately could return millions of wild Chinook back to Pacific waters. Whatever we decide to do, it needs to be soon. Time is simply running out.