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Probing the link between wild, hatchery salmon in Prince William Sound

The existence of interactions between hatchery fish and wild stock salmon in Prince William Sound was established in the late 1990s after hatcheries started marking eggs, making straying samples possible. The state of Alaska set a 2 percent threshold for hatchery salmon straying in the sound.

A three-year study by the Alaska Department of Fish and Game released in 2010, revealed much more widespread mixing, with up to 98 percent of hatchery fish in wild-stock streams. The question of the genetic impact of such a blend and potential interbreeding, however, remained unexplored for years, despite numerous calls from experts and the Marine Stewardship Council.

In May the Department of Fish and Game announced it was looking for researchers to submit proposals to study the impact of hatchery and wild salmons in Prince William Sound and Southeast Alaska. The Cordova-based Prince William Sound Science Center (PWSSC) won the project against many competitors, including universities around the country.

DNA from parents, offspring

The study aims to answer major questions about pink and chum salmon populations, as asked by the state in its request for proposals. First, scientists will look into the fitness of hybrid salmon and whether or not interbreeding weakens species over time. The department's aerial surveys are also put into question, as the state wonders if annual assessments are erroneous and misleading due to the presence of hatchery fish among wild stocks. That could mean overfishing in some wild spawning areas.

The lead researcher is Michele Buckhorn from the Prince William Sound Science Center, who earned a Ph.D in Ecology from the University of California Davis in 2009. "What makes the study so unique, is that it will be collecting DNA from both parents and their offspring," Buckhorn said. Geneticists will then be able to compare generations of pink and chum salmon in wild streams that have either high or low hatchery-straying rates.

A large number of otoliths, the only bone structure located in the ear of the fish, will be collected to establish the number of wild and hatchery salmon spawning in the wild.

The Cordova-based science center will team up with the Sitka Sound Science Center to gather data over the next few years. R.J. Kopchak, development director of the PWSSC, said his role wasn't to interpret findings, but to ensure the data is transferred elsewhere for analysis. "I was a commercial fisherman for 33 years, I know how fleet feels about these issues," Kopchak said. "But these are questions we need to answer."

Clue in fish jaws

Studies from other areas show that hatcheries could impact wild stocks several ways including the loss of genetic diversity, shifts in adult run timing and earlier maturity. Ultimately, wild and hatchery fish compete for food, spawning sites and mates.

According to Buckhorn, small changes such as the length of a salmon's bottom jaw could impact the natural cycle of any species, making, for instance, males less attractive to females and disturbing mating patterns. "But as long as the study isn't completed, we just don't know what we'll find," Buckhorn insisted.

The amount of fish the four hatcheries in Prince William Sound produce has soared recently. The state, which is in charge of managing hatchery productions, allowed an increase of 35 million eggs for pink salmon. The production went from 152 million eggs to 187 million. The chum egg production jumped from 17 million to 44 million over the past three years.

"In the past five years, there has been a steady request to increase production," said Alaska Department of Fish and Game Biologist Bert Lewis. Currently, 30.8 percent of the fish harvested in Alaska waters for commercial fishing, sport fishing and subsistence comes from hatcheries. In some places, hatchery juveniles outnumber wild stocks.

The study is funded not only by the state, but also by hatcheries and processors.

Many players recognize the necessity of hatcheries to smooth out salmon population fluctuations, a need that was first felt in the 1970s. One of the most extreme crashes came in 1971, when the salmon population dropped from more than 7 million to 54,000 the next year. However, the study will add substance to the way the state manages resources.

"This is a decade-long effort," Kopchak of the Prince William Sound Science Center said of the study, which should start later this year. "You need generations to deal with genetics."

Diane Jeantet is a reporter with The Cordova Times.  Contact her at djeantet@thecordovatimes.com.  Used with permission.