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 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. 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 Nation. "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 phenomenon.
For years, the annual jack count has served as a key indicator for forecasting next year's harvest. The more jacks, 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."
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.
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.