Wild salmon has been ecologically, culturally and commercially important in the Pacific Northwest for centuries. Sharp population declines due to overfishing, habitat loss and climate change spawned the growth of hatcheries to “subsidize” these losses with fish bred and raised in captivity and released into the wild. Of the five Pacific salmon species Chinook (or King salmon) is the most severely depleted, with populations listed as endangered in the US and Canada. It’s also the primary fisheries target (for humans and killer whales) and so has the highest hatchery production. Since 1950, a staggering 3.7 billion Chinook salmon have been released into the Salish Sea—that’s 50 million a year!

However, simply adding more salmon into an ecosystem does not automatically increase the number reaching maturity to be caught by fishers or Chinook-dependent species like the Southern Resident Killer Whales. The total catch declines each year, and this highly interdependent population of endangered killers whales with it.

Salmon have a complex life history, dependent on fresh water for the start and end of their lives, with the intervening years in salt water. Their routes to-and from the ocean are likely unchanged for centuries and salmon-eating killer whales have co-evolved with them. Land ecosystems also benefit from this rich abundance of nutrients and nitrogen delivered by the salmons’ annual return to the rivers, sustaining bears, wolves and forest food webs.

While healthy wild salmon populations are rich, diverse and complex, hatchery-raised salmon resemble more of the monoculture of modern-day farming. Hatchery release sites do not mimic the streams and tributaries of complex river systems, and the mass release of genetically similar salmon from a small number of sites results in an unnatural distribution of Chinook in the ecosystem. For example, Vancouver Island releases 60% its hatchery-raised Chinook into the Strait of Georgia, but that river system historically only produced 5% of wild salmon. South Puget Sound historically accounted for 4% of wild Chinook, but is 25% of Salish Sea hatchery production. In addition, these Puget Sound releases appear to be “resident”—whereas wild Chinook spend 2-6 years foraging in the open ocean—thus thousands of predators remain in this finely balanced ecosystem predating on up to 50% of subsequent releases from the hatcheries, not to mention juvenile wild salmon, or their prey.

USFWS

A mass release of captive fish brings risk of disease transfer to wild counterparts, and severely increases competition for food. Together with the risk of interbreeding there are many possible threats to genetic diversity—critical to salmon and whale survival.

Other factors such as release date also appear to be compromising the success of hatchery-raised Chinook. For example, in 2015 over half of the Strait of Georgia hatchery fish were released in a two-week period in mid-May. By comparison, wild Chinook in the Skagit River were at peak migration throughout February and March, whereas the Dungeness River population peaked in June. This natural, staggered timeframe over different river systems over many months reduces the risk of the entire population encountering unfavorable ocean conditions that might limit survival. A mass release from hatcheries does not build in such safeguards and a predictable abrupt release makes them more vulnerable to predators.

The size of US hatchery-raised Chinook at release also increases the risk of predation. Almost twice as large as wild Chinook, they’re the optimal size for seals and birds. Evidence suggests that smaller wild fish can survive at higher rates in their first months and thus increase their chances of reaching full-size to reproduce.

The study’s authors suggest a more diverse, experimental approach to hatchery management in the Salish Sea (and other west coast sites) to explore the potential for improving juvenile hatchery survival rates by better mirroring natural systems, in addition to developing a better understanding of the ecological impacts of hatcheries on wild Chinook.

However, it is clear to Wild Orca that very little time remains to experiment within a system that has evolved over millennia. The whales need food now. In the short term, Wild Orca believes that the whales should be apportioned a share of the annual Chinook quota, to ensure there are sufficient salmon left in the ecosystem each season for their needs. In the longer term, breaching dams would restore access to critical upstream spawning habitat, which ultimately could return millions of wild Chinook back to the Salish Sea.

Read the complete study here.

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