"Jack" salmon, small chinook males that spend only a year in the ocean before returning to freshwater to try and spawn, are showing up in record numbers in the Columbia River. Scientists are puzzled about why this is happening and what it means.

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BONNEVILLE DAM — In the world of salmon, size matters. That’s because big male fish have the best chance of fending off rivals to stake out a prime spot on the spawning grounds next to fertile females.

So what’s up in the Columbia River? Here, a record number of runt-sized males are surging upstream, a biological mystery that has stunned scientists and frustrated fishermen like tribal hoop-netter Frank Sutterlict.

As the spring run neared its May peak, Sutterlict pulled up his net in hopes of finding a big Columbia chinook, an oil-rich salmon weighing 20 or even 30 pounds. But in a frustrating replay of so much of this spring harvest, Sutterlict found only a small male that weighed about six pounds.

“It’s just a little itty-bitty fish,” said Sutterlict, a member of the Yakama Tribe. “It takes three of them to make a good meal for everybody.”

These jacks are chinook males that spend only a year, rather than two to four years, at sea before returning to freshwater to try to spawn. Their final spring tally is expected to top 70,000, nearly triple the previously recorded high. The jacks likely will represent about a third of this year’s chinook run.

During seven days around the May peak of the run, more jacks than adult salmon swam past the Bonneville Dam.

“Just looking at the Bonneville Dam count, it’s extraordinary,” says Brian Beckman, a National Marine Fisheries Service biologist in Seattle. “It’s just kind of jaw-dropping … There is a huge signal from the fish that something has changed.”

Scientists say part of the explanation for the bounty of jacks could reflect improvements in ocean conditions that offer more feed for salmon.

Some also are scrutinizing hatchery-bred fish, which have higher percentages of these jacks than the wild runs.

Scientists have more than an academic interest in studying the mystery.

For years, the annual jack count has served as a key indicator for forecasting next year’s harvest. The more jacks, the model went, the bigger the expected total run of salmon.

Those predictions are used to figure out how many fish will be allocated to commercial, sport and tribal fishermen.

But the model has not been working very well.

Last year there was a strong show of jacks, prompting a forecast of a chinook run of nearly 300,000 fish this spring. But biologists now expect about 160,000 adult salmon.

That’s caused plenty of frustration among fishermen. Harvest openings were cut short, and tribal fishermen who hoped for a brief commercial gill-net season in the main-stem Columbia were out of luck. Instead, they were allowed only to fish from shore with smaller hoop nets and hook-and-line.

This year’s record number of jacks, if plugged into the traditional forecasting model, would yield a blockbuster run of more than 1 million spring chinook salmon in 2010. That would be more than double the size of any previous spring run in the era since 1938, when fish counts began over the Bonneville Dam.

No one is expecting that kind of bonanza, so scientists are scrambling to try to explain the jack run and come up with a new model for forecasting the run size.

“The first rule of allocation is to know how many fish there are,” said Guy Norman, a biologist with the state Department of Fish and Wildlife. “Something is out of whack, and we need to figure out what this means.”

Could be trouble

The high percentage of jacks in the run, if it continues in the future, would be a troubling new wrinkle in the multibillion-dollar effort to restore Columbia River basin salmon. The payoff for that effort is reduced when a larger portion of the run comes back as undersized fish.

The spring surge of jacks also is a reminder about the limits of scientific knowledge of salmon. There are still plenty of unknowns about these complex creatures that are born in freshwater, migrate to the ocean, then head back to their birthplace to spawn and die.

Federal scientists who specialize in salmon physiology think the males do a kind of internal assessment of their growth at sea. They then make a fateful decision to stay at sea or return to spawn.

But just why some of these salmon, only four or five pounds in size, would think it’s time to reproduce is not well understood.

Scientists say one likely factor can be found in the ocean.

Offshore of Oregon and Washington, the young salmon that emerged last year from freshwater found excellent conditions in their critical first few months, according to Bill Peterson, a federal biologist in Oregon. Perhaps that strong start prompted a higher percentage of the males to opt to return as jacks.

Hatcheries may also play a role. Initial surveys indicate that hatchery fish have about triple the rate of jacks as wild fish, according to Stuart Ellis, a biologist with the Columbia River Inter-Tribal Fish Commission.

Hatchery nutrition will be one line of inquiry because how these fish are fed can greatly influence how many return as jacks.

In research in Seattle, as many as 90 percent of heavily fed juvenile males ended up turning into jacks, according to Walt Dickhoff, a division director at NOAA Fisheries Northwest Science Center. Hatchery scientists say there have been no major changes in the total calories fed to salmon.

But two years ago, an Oregon company producing a moist salmon feed went out of business, so some hatcheries shifted to a dry feed that has more nutrients packed in each pellet.

Beckman, the federal biologist, says the drier feed might produce salmon with higher fat content and a greater propensity to return as jacks.

Hatchery biologists are skeptical that the change to the dry diet affected jack rates.

“The feed still has the same nutrients,” said Ann Gannam, a U.S. Fish and Wildlife Service fish nutritionist. “The big difference is moisture.”

Big hopes

The spring chinook run ends June 15, and in the weeks ahead the tribal fishermen are hoping for an improvement that will bring more big salmon ashore. In their commercial sales, a small jack may fetch about $20 to $30, while a mature fish can bring in more than $100 in a roadside sale.

But the small jacks still offer firm, tasty meat prime for canning. Sutterlict says it is important to be grateful even when jacks show up in his net.

“No matter what, after everything is said and done, we’re still glad we got our fish. It’s still a salmon.”

Hal Bernton: 206-464-2581 or hbernton@seattletimes.com