This year's late-timed rush of spring chinook salmon up the Columbia River may have done as much to save their number as did elaborate human efforts to keep the fish from the jaws of sea lions lurking at Bonneville Dam.

"There was a bigger run (of upriver spring chinook) but fewer fish were taken" this year by sea lions than in 2005, according Robert Stansell of the U.S. Army Corps of Engineers.

The Corps of Engineers operates the dam, and has for the past five years monitored the sea lions' impact on migrating salmon. An increased sea lion presence at the dam has caused concern because the salmon are easy prey as they search for passage routes over the structure. Portions of the run, Upper Columbia spring and Snake River spring/summer stocks, are protected under the Endangered Species Act.

Preliminary data shows that at least 2.5 percent of the salmon approaching the dam this year were picked off by, primarily, California sea lions between Jan. 1 and the end of May.

That's the second highest rate since monitoring began in 2002, but below last year's 3.4 percent. It includes only predation witnessed by observers on the dam so it is a minimum estimate of the sea lion impacts.

Observers saw about 2,800 salmon being consumed this year below the dam, slightly fewer than the 2,920 eaten last year by the marine mammals. That's despite an increased availability of salmon this year. About 82,000 salmonids had made it to Bonneville by the end of May last year as compared to more than 104,000 this year.

The shape of that upriver run may have been a factor, Stansell said.

The return was more prolonged last year. This year numbers of fish passing Bonneville were small until the very end of April, fewer than 3,000 through the 28th. In a year with "normal" run timing about half of the run will have passed the dam by the end of April.

"It was my impression they were hauled out more" on rocks and structures this year than in the past, Stansell said of the California sea lions. The first was spotted at the dam on Feb. 9, the earliest arrival in the five years of monitoring.

"They didn't have the fish to take and they were waiting and waiting," Stansell said. The large salmon pulse did arrive eventually with daily dam counts exceeding 4,000 for eight days in a row beginning May 5, essentially swamping the waiting predators. During the 2005 run, daily counts surpassed 4,000 three times, twice in April and once in May.

"They were catching as many as they could," Stansell said, but sheer strength in numbers and their late arrival may have allowed a higher percentage of the fish to escape this year.

An estimated 87 individual pinnipeds were observed at the dam. Most were California lions but 10 Stellar sea lions and three harbor seals also visited the dam.

The Stellars and harbor seals are resident to Oregon/Washington coastal areas; the California sea lions are mostly males that swim north in winter to feed and build strength for their early summer breeding period off the coast of Southern California. The pinnipeds swim about 140 river miles inland from the mouth of the Pacific Ocean to reach the dam. All had left the dam by the end of May.

The number of pinnipeds at the dam was about the same number as last year, and about 20 fewer than in 2003 and 2004. When monitoring first began in 2002 only 31 pinnipeds made the trip to the dam and prior to that only a handful were seen each year.

"All of the other trends have continued," Stansell of the sea lions' behavior.

They have been arriving earlier each year, and staying longer each year. The daily average number of pinnipeds at the dam was about 27 this year as compared to 4.4 in 2002. At least some pinnipeds were in evidence at Bonneville for 59 days in 2002; this past spring there were sea lions at the dam 110 days.

The marine mammals have gradually gotten more skilled as well. In 2002 nearly 12 percent of the fish initially caught by the sea lions escaped. By 2005 less than 1 percent of the fish were escaping. That escape percentage rose slightly to 2.6 percent.

Most of the California sea lions' diet is salmon. About 9.9 percent of their diet this past year was lamprey and 2.6 percent was shad. The shad percentage has been relatively constant over the years while the lamprey consumption steadily rose to hit a peak of 25.1 percent of the sea lions' diet last year.

Stansell cautioned that all of the data is preliminary and data analysis is ongoing.

"We're proofing the data right now" Stansell said this week.

In progress also is an evaluation of what various data means. The Corps will meet with state and other federal officials over the coming months to review the data and decide on possible courses of action for next year to reduce impacts on salmon.

The federal agency this year for the first time launched a "hazing" effort at the dam, using acoustic and percussive devices, flares, and rubber bullets from the dam in an effort to unsettle the animals and potentially chase them away. The hazing was done in two-day blocks, followed by two days without hazing, so that researchers could evaluate what difference it made.

Beginning April 1, the Oregon and Washington departments of fish and wildlife began a hazing effort of their own several miles downstream from the dam in hopes of keeping the animals on the run. The state and federal biologists are forbidden by the Marine Mammal Protection Act from harming the pinnipeds.

Preliminary numbers indicate that the sea lions actually captured more salmon while the dam hazing activity was ongoing than they did when there wasn't hazing. The raw numbers show they took slightly fewer salmon while the state boats were conducting hazing.

Stansell said there has been no analysis yet of the statistical significance of those numbers.

The hazing did seem to make the huge but shy Stellar lions uneasy. They had arrived at the dam earliest, in January, and began preying on white sturgeon before the salmon arrived. In all, observers on the dam saw 264 sturgeon taken, mostly by the Stellars. Once the hazing began in earnest in March, the Stellar sea lions disappeared.

The California sea lions, however, seemed imperturbable. Some reacted to the hazing but most predatory behavior quickly resumed amidst the hubbub. A large percentage of the California sea lions have made the pilgrimage to Bonneville year after year.

Among the tasks of the researchers is to dig deeper into the data to find out who is eating what, and how much. Many of the sea lions have brands as a result of other research efforts and/or identifying natural markings. That should allow researchers to single out the pinnipeds that are the most persistent and voracious.

Oregon and Washington fish and wildlife officials are at work on an application to the Secretary of Commerce for Section 120 authority under the MMPA that could increase their authority to deal with the marine mammals.

"We're moving forward with what the commissions asked us to do," the WDFW's Guy Norman said of springtime directives from the Oregon and Washington fish and wildlife commissions. The states hope to complete the application the next couple months.

"The application will, really, just identify the problem," Norman said. It will detail the status of the salmon stocks and the extent of the predation, as well as status of the pinniped populations and their Columbia River activity. The Stellar sea lions are themselves listed under the ESA but the California sea lions are not.

"The California sea lions are the primary problem," Norman said. Approval of the Section 120 authority could allow the states pursue lethal removal of particularly troublesome animals.

The section says states can seek federal authorization to lethally take "individually identifiable pinnipeds that are having a significant negative impact on the decline or recovery of a salmonid stock that is being considered for or are listed" under the Endangered Species Act. An approval of the initial application would allow for establishment of a task force made up of fish and wildlife specialist that would judge any lethal removal request.

Such approval has been granted only once. The Washington Department of Fish and Wildlife, after several years, received permission in 1995 to lethally remove three California sea lion that could not be deterred from preying on steelhead at Ballard Locks in Seattle. That fish stock was decimated. The sea lions were shipped to Sea World in Florida.

Norman also said that there are initiatives in Congress seeking to increase the flexibility of the MMPA.

"We're hoping it can be streamlined," Norman said.