Scientists mix salmon stocks to learn about their survival

By Kate Golden
Juneau, Alaska (AP) 4-08

In a small, cold room next to Auke Creek, two women are two-thirds of the way through clipping the fins of 50,000 inch-long pink salmon fry. These humpies in the current batch aren’t wriggling; they’ve been bathed in an anesthetic. After their surgeries, they’ll be released into the wild next week to swim free.

If all goes as planned, perhaps 1 percent, or 500 full-grown fish, will return next summer.

They are grandchildren of the first fish in their experiment, and they will help researchers figure out how salmon populations adapt to their environments.

“The more you know about what makes these populations tick, what makes them strong and vigorous, the better management decisions you make,” said lead researcher Tony Gharrett, a professor of fisheries at the University of Alaska Fairbanks.

His work helps tackle a central question of fishery conservation and management: What happens when you mix two genetically isolated populations, as hatchery and wild stocks of salmon might be?

Hatcheries in Alaska have a constitutional mandate to preserve healthy wild stocks, which in part means preserving biodiversity, according to Scott Kelley, who oversees salmon enhancement programs in Southeast Alaska for the Department of Fish and Game. He relies on research such as Gharrett’s to make good decisions.

It wasn’t always this way. Alaska learned a lot from the mistakes of the Pacific Northwest, said UAF fisheries professor Bill Smoker, Gharrett’s colleague.

By the 1950s, much salmon habitat in Washington had already been destroyed by urban growth, logging and hydroelectric dams. Hatchery salmon were introduced to offset the habitat loss.

They didn’t. The salmon populations never recovered and in some cases were eradicated.

“Genetics and conservation really weren’t on the radar screen,” Gharrett said.

Fish managers didn’t know then that introducing hatchery stock into wild habitat could compromise wild populations, not only because of genetic mixing, but also from increased competition and disease.

Problems in the gene pool are some of the hardest to detect – and to fix, according to Gharrett.

Hatchery management in the Lower 48 has improved “leaps and bounds” as scientific tools have improved, Kelley said.

Alaska was ahead of the game from the start. Hatcheries here were never intended to mitigate disaster, but to enhance healthy wild stocks for sport and commercial fishing or provide fish where there were none naturally.

There are definitely issues that people want to address, said Rick Faucht, director of operations at the local hatchery, Douglas Island Pink and Chum Inc. But they’re not the dire-straits type of issues that have been experienced elsewhere.

At Auke Creek, Gharrett has been looking at humpy genetics since the late 1970s. It turns out pink salmon are a great species for investigating population genetics, particularly the pink salmon at Auke Creek.

Like all salmon, they come back to their spawning creek on their own, so researchers don’t have to track them down. And in Auke Creek, a permanent weir across the creek allows researchers to control what goes out and see every full-grown fish that comes back.

Pinks’ two-year life cycle is also much more convenient for research than, say, chinooks’ five-year cycle. Hybridization experiments depend on seeing what happens two generations – in this case, six years – down the line.

Finally, full-grown pinks are easy to age: They’re always two years old, so you know which fish were their parents.

“It’s just a really nice, clean system,” Gharrett said.

But most interesting, these pinks are quite strict about when and where they come back. Fish that spawn on even-numbered years don’t mix with the ones from odd years. And Gharrett found that even in the same year, the salmon that come in August generally don’t mix with the ones that return in September.

Gharrett’s experiments involve mating these fish that would never meet on their own. He has hybridized the even-year with the odd-year fish. By the second generation, hybrids don’t survive as well as the pure stock. Now he is testing to see whether the same holds true for hybrids of early run and late-run fish.

It’s known that loss of genetic diversity hurts populations. But by breeding two different populations Gharrett is adding diversity. So why don’t these fish thrive?

The theory goes that each population evolves separately to its own slightly different situation, such as a slightly warmer creek. Then by hybridizing the fish, Gharrett muddies the genetic makeup of those adaptations. The hybrids are less likely to survive in either of the parents’ environments.

It’s called “outbreeding depression.”

Gharrett will look at when the hybrids come back and how well they survive.

With these and other studies, Gharrett can start to tease out how local adaptation works.

It’s the kind of information conservation biologists everywhere – whether here, in zoos or in agriculture – need to preserve wild stocks.

An indirect benefit is that the UAF research also provides seed stock for more state fish biologists, according to Kelley, who was himself once Gharrett’s graduate student.

About 80 percent of the graduate students in the fisheries program at UAF end up working in resource management in Alaska, Gharrett said.

Laurinda Marcello, a first-year master’s student at UAF, spent her winter raising the salmon fry now undergoing surgery. The floor of the Auke Creek laboratory was covered with ice at times. But she grins as she pulls out a tray of tiny fry, and points to a dense silvery frenzy.

“They’re hungry,” she says.

They won’t get to eat until after their surgery, though.