LEABURG - State fish biologist Mark Wade, thigh deep in a pool full of thrashing fish, grabbed a wriggling 35-pound salmon by its tail and belly and hoisted it out of the water.

The adipose fin on the big buck's back was still intact, meaning it had not been marked at a hatchery when it was a smolt.

Wade heaved the big fish through an opening in the Leaburg Dam fish ladder, allowing the big salmon to join several others he had passed upstream so they can spawn in the gravel beds of the upper McKenzie River in the coming weeks.

But 15 of the chinook Wade found in the depths of the fish ladder were fin-clipped and faced a different fate. They were hauled up a ladder, stuffed into a portable fish tank and trucked back to the McKenzie salmon hatchery, where they will be spawned by hand.

The Oregon Department of Fish and Wildlife took the unusual step of turning the Leaburg Dam fish ladder into a temporary fish trap as part of its ongoing effort to preserve the McKenzie's naturally reproducing spring chinook run.

And that run is in trouble.

As of Friday, cameras in the fish ladder had recorded only 948 spring chinook passing upstream. That compares with 1,239 at this time last year.

"Last year was bad, this is very bad," said Wade.

The last "good" years were 1992 and 1993, when about 3,000 salmon passed above Leaburg Dam by the end of August.

This year's McKenzie run is all the more disappointing because it turned out so low in spite of the most restrictive salmon angling regulations in history of the Willamette basin.

Salmon fishing was prohibited on the McKenzie River. In addition, a quota was placed on the salmon harvest in the lower Willamette River. Fishing there was halted after only 1,950 fish had been caught in the Portland area. The Portland fishery was cut back because the Oregon Fish and Wildlife Commission wanted to make sure that enough spring chinook "escaped" over Willamette Falls to meet the egg needs of the upriver hatchers - and in hopes of providing a natural spawning run of 1,400 fish on the McKenzie River.

Just as disappointing this year was the lack of any hint of a rebound in salmon numbers.

"The jack count down at Willamette Falls was a record low this year, and jacks are a pretty good indicator of future run size," Wade said.

Jacks are immature male salmon. Their numbers are considered one of the most-reliable tools for forecasting the size of the following year's run.

Preliminary forecasts are that the 1998 run will be "similar or worse" than this year's, Wade said,. "The early indication is between 30,000 and 35,000 Willamette spring

chinook entering the Columbia River," he said.

"This year, there were 36,000." Wild fish comprise only 5 to 10 percent of the total run. The rest of the run is produced by various hatcheries in the Willamette Valley.

Most of the wild fish are bound for the McKenzie River, home of the basin's last significant run of naturally reproducing spring chinook.

The makeshift fish trap at Leaburg Dam is part of an ongoing effort to bring the McKenzie run into compliance with Oregon's Wild Fish Management Policy.

Biologists have long suspected that too many salmon reared at the McKenzie Hatchery have been straying past the hatchery, swimming above Leaburg Dam and spawning among the wild fish.

To monitor that, they inserted coded wire tags in snouts of a small percentage of the hatchery salmon when they were juveniles. The adipose fin also was removed from the fish, providing a visual clue that they carried a coded wire tag.

Last year, the ODFW tried to recover tags from the carcasses of salmon that had already spawned in the upper McKenzie and died. That method proved to be ineffective, Wade said. "We spent a lot of time looking for carcasses and tags and didn't recover that many."

Using the fish ladder as a trap allows researchers to recover the coded wire tags from hatchery fish that clearly had strayed past McKenzie Hatchery.

It also allows biologists to reduce the proportion of hatchery- reared fish breeding with native fish - an important consideration under the Wild Fish Management Policy.

"The Idea is to protect the gene pool of wild fish," Wade said.

Because there are still a lot of unmarked hatchery fish straying upstream, Wade said, sorting out the tagged fish is not a cure-all for

that problem.

In the future, a higher percentage of hatchery fish will be marked. All 1996 brood year fish at the McKenzie Hatchery were clipped and tagged, for example, and the ODFW hopes to continue that in the future, finances permitting.

But salmon from other Willamette drainage hatcheries will not necessarily be tagged. That means the dilemma facing ODFW harvest managers would continue.

On the one hand, the Wild Fish Management Policy dictates that wild runs of fish not be over-harvested. On the other hand, there is intense public pressure to maintain the showcase spring chinook salmon fishery in the lower Willamette River at Portland.

Wade said preliminary discussions concerning next year's spring salmon season are already being held, and recommendations will probably be announced in December.