More spring chinook salmon are beginning to show up at the lower Columbia's Bonneville Dam and, right on cue, the numbers of predatory California sea lions present below the hydro project are growing as well.

Meanwhile, the steady presence of the larger Steller sea lions has fishery officials fretting about the toll on white sturgeon.

Recent springs have seen a surge in marine mammal visitations to the dam as compared to historic levels. Bonneville is located about 145 miles upstream from the mouth of the Columbia. Researchers monitoring the situation since 2002 have observed one species, the California sea lions, zero in on salmon, steelhead, lamprey and other smaller fish while the Stellers have a decided preference for sturgeon. The big fish's primary spawning grounds stretches from below the dam downriver.

U.S. Army Corps of Engineers' observers witnessed the taking of 584 sturgeon between Jan. 11 and March 30, all but six by Steller sea lions, according to preliminary, unexpanded data compiled by researchers. Included were 21 sturgeon estimated to be over 5 feet in length.

The total far surpasses last year's total of 361 sturgeon, which was a record over the seven years of the study. Last year the Stellers were observed preying on more of the larger, spawning size fish, taking 55 that were larger than 5 feet long. The totals include only witnessed predation during daylight hours.

The states of Idaho, Oregon and Washington hope to take action to reduce what they say is a significant California sea lion impact on spring chinook salmon and steelhead runs, including stocks that are listed under the Endangered Species Act. They received last month authorization under the Marine Mammal Protection Act to lethally remove specific pinnipeds.

That authorization is stalled, at least temporarily, by litigation but the states intend to soon begin trapping California sea lions and shipping some of the animals to zoos and aquariums.

The Steller sea lions have a double layer of protection that includes the ESA while the Columbia River white sturgeon are unlisted.

The Stellers are divided into a western stock and an eastern stock. The eastern stock, which includes animals that call the Columbia home, is listed as threatened and its population is estimated by NOAA Fisheries to be increasing by about 3 percent per year. The western stock has the more stringent "endangered" status.

"The eastern stock would probably qualify for delisting," said Charlie Corrarino, Oregon Department of Fish and Wildlife Conservation and Recovery Program manager.

The lower Columbia's sturgeon, meanwhile, "are probably the healthiest population of white sturgeon in the world," he said. Still, the pinniped-sturgeon interaction is worrisome. The fish take up to 20 years to reach breeding age so taking big chunks from limited broodstock can eventually cause problems.

"I think it is more of a conservation issue than the California sea lion-spring chinook" interaction, Corrarino said.

The Steller-sturgeon interaction escalated greatly last year but hazing activities designed, principally, to deter California sea lions served to spook the Stellers. Only 19 sturgeon were observed being taken after rubber and crackershells began flying last spring.

"It appears as though they're becoming smarter" and realize that the pyrotechnics cause them no harm, Corrarino said.

As many as nine Steller sea lions were seen below Bonneville last year on any one day. The number is 12 this year.

"It's been growing every year," Corrarino said of the Steller sea lion presence.

Boat based harassment by state crews has been carried out two to five days a week at the dam since Dec. 12 targeting Steller sea lions preying on sturgeon and has continued for California sea lions to date. The effort was boosted to seven days a week recently with tribal hazers joining the fray.

Dam based harassment by U.S. Department of Agriculture Wildlife Service agents began on March 3.

Corps researchers had through March identified at least 42 different California sea lions. That number has grown from 18 on March 13, according to data compiled by Corps' researchers Robert Stansell, Sean Tackley, and Karrie Gibbons. At least 27 of the California sea lions seen at the dam have visited in previous years.

California sea lions had primarily been taking steelhead, but during the past few weeks they have begun catching numerous chinook, according to preliminary data through March 31. Pinnipeds have been observed taking 264 chinook and 192 steelhead as well as 388 unidentified fish. Most of those unidentified fish are believed to be salmonids.

Just over half (225 of 610 or 37 percent) of the prey taken by California sea lions has been attributed to specific individuals, or 43 percent (191 of 442) for salmonid prey specifically, according to the preliminary data.

The upriver spring chinook salmon run seems to have arrived as well. Anglers have been doing well downstream and counts at Bonneville's fish ladders are starting to pick up. Sunday through Wednesday saw the first daily counts of the year of more than 20 chinook. A total of 241 chinook and 1,128 steelhead had passed the dam (through Wednesday) so far this year. The upriver spring chinook return is predicted to total 269,300.

That information on particular pinnipeds' eating habits is necessary if the states are to exercise their California sea lion removal plan. The authorization only allows the removal of idenfiable predators that:

-- have been observed eating salmonids in the "observation area" below Bonneville Dam between Jan. 1 and May 31 of any year; and

-- have been observed in the observation area below Bonneville Dam on a total of any five days (consecutive days, days within a single season, or days over multiple years) between Jan. 1 and May 31 of any year; and

-- have been sighted in the observation area below Bonneville Dam after they have been subjected to active non-lethal deterrence.

The authorization lists 61 individuals that qualify for "immediate removal."

NOAA's authorization letter says qualifying sea lions that are captured in a trap must be held in a temporary holding facility for at least 48 hours prior to being euthanized pending a determination of the availability of pre-approved permanent holding facilities such as zoos or aquarium to accept the animal.

Free-ranging individually identifiable predatory sea lions may be shot by a qualified marksman when hauled out on the concrete apron along the North side of Cascade Island, on the flow deflectors along the base of the dam's spillway, or in the water within 50 feet of the concrete apron or the face of the dam at power houses one and two.

The states are planning to begin trapping and branding animals within two weeks with some potentially headed for zoos or aquariums. One trap that has been used by the ODFW to trap and mark animals at Astoria has been moved to Bonneville so the pinnipeds become comfortable with its presence.

Stansell said that as many as eight or nine sea lions have squeezed into the cage at once.

"It's looking like the animals are doing what we hoped they would do," said NOAA's Garth Griffin.

Of the 61 animals listed for potential lethal take or removal, 22 have been seen at the dam so far this year and about 15 have been seen on the single trap with several others hauled out nearby, according to Stansell.

The states are having three additional traps built. A transfer barge will also be brought to the site once trapping begins.