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Peter Westley grew up fishing for salmon in Prince William Sound.
“Some of my fondest memories are actually spending time fishing in front of Wally Noerenberg Hatchery and other things, ” Westley said. “So, I’ve been tied to hatcheries in one way or another for a really long time.”
Now, Westley is a salmon researcher at the University of Alaska Fairbanks looking at how hatchery and wild fish interact. He’s one of a dozen authors of a study focusing on years of data on pink salmon hatcheries in Prince William Sound. It was funded through universities in Alaska, Washington, and Oregon through the Cooperative Institute for Climate, Ocean and Ecosystem Studies (CICOES) and supported by hatchery operators, the Alaska Department of Fish and Game, and nonprofit science groups. They all want to know more about salmon. So, Westley and the other researchers combined their data and their questions.
“What are some of the potential trade-offs regarding the use of hatchery fish as a part of the fabric of Alaska’s fisheries?” Westley said.
Salmon hatcheries are a huge part of Alaska’s fishing economy. Over two dozen of them provide harvests for thousands of commercial fishermen and are worth over half a billion dollars each year. The state owns some of the hatcheries, which are mostly managed by private nonprofits. They carefully rear salmon from eggs and then release the fry at specific sites along the coast. Their hatchery stocks originally came from wild local fish runs.
But what happens when the hatchery fish join the wild stocks? They’re known as “strays”.
“Individuals that are showing up to the wild population, interbreeding with those wild fish,” explained Samuel May, another author of the study.
May is a research geneticist with the U.S. Department of Agriculture and worked with the University of Alaska Fairbanks on modeling for the study. He and the other researchers found that some hatchery salmon are straying from their groups and mixing with wild stocks. They’re traveling with the wild salmon to spawning grounds and creating a larger overall population but at the same time, potentially changing the traits of the wild fish.
May said there aren’t many stray hatchery pinks – roughly 1-5% of the population — but that could still make a difference, especially in streams with just a small run of wild fish.
And that’s because of run timing, a trait that’s deeply ingrained in the salmons’ genetics.
“Pink salmon, in particular, probably [have] the strictest timing of all of the different salmon species,” May said. “They have this really strict two-year life cycle and they actually return to the stream in which they were born within just a few days generally of when their parents returned.”
Hatcheries release juvenile salmon at different times and locations than nearby wild runs to keep the stocks separate. But some still mix, May said. This can cause wild populations to increase, which could be a good thing for harvesters, but the hatchery fish can also cause the wild stocks to change the timing of their routine. And timing is everything. Wild salmon have evolved to return during the best temperatures and food availability for their juveniles when they hatch.
“[Strays] can end up pulling the wild population off of that optimum and changing the dynamics of the wild system,” May said. “And the fear is that this is going to reduce the populations productivity or resilience to future changes.”
Conditions change from stream to stream. And specific salmon runs have adapted to them for thousands of years.
“So, if that timing changes just a little bit, then the population as a whole could be at risk of kind of missing the ideal optimal, or the ideal environmental conditions that they need in order to go on and produce that next generation,” May said.
As for why salmon occasionally stray? That’s unknown and would take more research. Yet, Westley said what they’ve learned from this study is still important – that some hatchery and wild salmon mix and create larger populations, which can be a good thing, but it can also potentially change those wild stocks – forever.
“It is a blessing and a curse, double-edged sword, whatever you want to call it,” Westley said.
The authors say this hatchery pinks study doesn’t end here. The methods can also be used for hatchery chum salmon in Southeast, which is another multi-million dollar industry in Alaska’s fisheries.
