The allowed catch of white sturgeon in the lower Columbia River (from Bonneville Dam down to the mouth of the river) could be reduced by as much as 35 percent from recent years' levels, Oregon and Washington department of fish and wildlife officials said during a meeting Thursday in Vancouver, Wash.

Fishery managers for both states say new catch guidelines for sturgeon will likely reflect recent declines in the lower Columbia River sturgeon population.

State biologists see signals that populations of "sub-legals" and of 42- to 60-inch fish that are legal targets have been on a downward trend in recent years.

Both developments are warning signs. The fish measuring 42 inches or less are those about to grow or "recruit" into the category of fish that are eligible for harvest and the legal-size fish are approaching the age where they will join the "oversize" population of spawners.

The decline in legal size white sturgeon appears to have started in 2007 according to catch data and accelerated in 2008 according to abundance estimates produced from data collected via the netting, tagging, release and recapture of fish.

"We did experience a pretty big decline" in 2008, the ODFW's John North said. Abundance estimates had been near 100,000 or higher from 1995 through 2007 for 42- to 60 inch white sturgeon in the lower Columbia. But the estimate dropped from 135,400 in 2007 to only 97,000 in 2008.

The catch and catch rates in sport fisheries for sub-legal sturgeon, which must be released, have also tumbled in recent years.

"It's about half of the longtime average," North said of the sub-legal catch rate.

"The decline started a couple of years earlier in this data set" as compared to the legal-size sturgeon, he said.

The story seems quite different for members of the species at either end of the age scale.

The oversize population estimate, as gauged by sport landings, in the Columbia River gorge upriver of Portland dropped from an average of about 4,000 in 1995 to a catch average annual catch of 1,500 since 2004 but has been stable, perhaps slightly on the rise, in recent years.

That drop could be as a result of a broadened sanctuary around the primary lower river sturgeon spawning ground, North said.

The spawner news is brightened, however, by the fact that catches of the oversize sturgeon in the estuary have jumped from 1,500 or fewer from 1995 through 2005 to nearly 2,500 this year.

When combining the two totals the oversize population seems to be relatively stable, North said.

Age 0 sampling surveys conducted since 2004 with bottom set nets have shown "a dramatic increase in young of the year," North said of sturgeon that are typically less than 14 inches long.

Thursday's meeting was called in part to help determine "what changes do we need" in fishing regulations and guidelines for 2010 to help halt the sub-legal and legal population declines, North said. In recent years the lower Columbia sport and commercial fisheries have been allowed to harvest up to 40,000 legal white sturgeon with 20 percent of that total going to the gill-net fleet and 80 percent to anglers.

ODFW and WDFW staff outlined three possible scenarios for adjusting the allowable harvest.

The first would reduce the 40,000 guideline in proportion to the recent decline in the population estimates for legal fish, about 12 to 24 percent.

The second would reduce the allowable harvest in proportion to the estimated decline in legal and sub-legal abundance, from 16 to 35 percent.

The most conservative option would drop the allowable catch even further as a buffer because of the uncertainty surrounding the status of the broodstock population.

The broodstock issue could prompt such remedies as an expansion of the time period when fishing in the sanctuary is prohibited and expanding the sanctuary boundaries.

Harvest is not the only cause for reduced sturgeon number. But it is the only known factor over which state managers have control, Tweit said.

An increase in the number of Steller sea lions feeding below Bonneville since 2005 has resulted in a large increase in predation on sturgeon.

A U.S. Army Corps of Engineers study estimates that sturgeon catch in the area immediately below the dam rose from 413 in 2006 to 664 in 2007 to 1,139 in 2009.

Tweit said that plunging populations of smelt and lamprey in recent years may have affected sturgeon. Both fish have historically been a part of the big fishes' prey base.

Any number of factors or a combination of factors could be prompting the population declines, or it could just be a case of elongated natural inter-annual variability.

"But we don't have evidence that any one of them is the cause," Tweit said.

Anglers at the meeting suggested a clamping down, and tighter monitoring, of lower river commercial fisheries.

One of them suggested that the gill-netters may be releasing fish at the lower end of the legal range so that they can replace it with a large, more profitable fish. Those larger fish are more valuable in the water, because they are at or near spawning size, he said.

Another angler said commercial fisheries targeting sturgeon should be prohibited during the warm months of August and September when sub-legals and oversize fish are less likely to survive a bout with a gill-net.