Hatchery Fish Smothering Native Salmon

Photo: Alaska Region U.S. Fish & Wildlife Service/Flickr

Hatchery salmon have been used to bolster the wild salmon stocks in Alaska for years, and that practice’s ill-effects have been well-documented. But another, previously unknown, impact of stocked salmon coexisting with wild fish is playing out in Southeast Alaska.

According to an article in the Craig Medred, hatchery-born salmon are inflating salmon runs so much in some streams that they’re literally choking out all other fish within the river. When hatchery salmon return to rivers to spawn – instead of returning to their hatcheries – they can artificially inflate the salmon numbers in a given river. That many fish end up consuming more of the dissolved oxygen in the water than can be quickly replaced, which leads all salmon to suffocate.

According to the article, “The problem is self-correcting in a natural system. Hypoxic events reduce spawning and survival, fewer fish return in future years and the issue is resolved. This is not the case if returns are being boosted by straying hatchery fish.”

This presents a unique problem that fisheries managers in Alaska will have to solve. But it serves as a reminder to the rest of the fly fishing community that, even when well-intentioned, our efforts to meddle in the natural world can often have unforeseen consequences.