A federal court judge on Thursday denied a request that he put on hold state plans to begin in March trapping and removing salmon-eating California sea lions from below the Columbia River's Bonneville Dam.

At the end of hourlong oral arguments, U.S. District Court Judge Michael W. Mosman told the attorneys involved that "the balance of equity tips in favor of protecting the salmon run."

The killing of sea lions represents irreparable harm, one of the legal standards that must be present if a stay is to be issued. But the killing of salmon, by the big marine mammals, is also irreparable harm.

The heightened level of pinniped predation below the dam could potentially have dire consequences for upriver spring chinook salmon stocks, which include both hatchery produced fish and wild Upper Columbia and Snake River wild salmon that are listed under the Endangered Species Act, according to state officials.

While the sea lions take a relatively small percentage of the overall run below Bonneville, they could potentially wipe out uniquely evolved, wild tributary populations that are each species building blocks.

"There's nothing comparable" that could befall the California sea lions if the removal plan moves forward, the judge said. NOAA Fisheries in March of 2008 approved the states of Idaho, Oregon and Washington's application under the Marine Mammal Protection Act to lethally remove sea lions, which congregate each spring below the dam to feast on salmon, steelhead and other stocks as they search for fish ladders.

The 5-year authorization allows the removal, lethal or otherwise, of up to 85 California sea lions, although NOAA officials have said it was doubtful that more than 30 could actually be removed annually. The candidates are "individually identifiable predatory California sea lions that are having a significant negative impact on the decline or recovery of ESA listed salmonids at Bonneville Dam," according to language in the MMPA's Section 120.

The agency in 2007 estimated that the total population of the United States stock of California sea lions is 238,000 and stable, if not growing. The stock has reached its "optimum sustainable population size, as defined by the MMPA, and carrying capacity for ocean and breeding conditions.

Agency documents and testimony say that the planned Columbia River removals won't have a significant effect on the California sea lion as a species because the population is large and robust.

On the other hand, many of the salmon populations are depressed and listed under the ESA. Congress amended the MMPA to add the lethal removal provision in response to a situation at Seattle's Ballard Locks in the mid-1990s in which sea lion predation helped push a steelhead stock over the brink to functional extinction.

"Congress has a slightly greater concern abut their loss," Mosman said of ESA listed salmon.

The Humane Society of the United States, which launched the litigation, said it would immediately take its request for a stay to the U.S. Court of Appeals for the Ninth Circuit. Its goal is to prevent sea lion removals while an appeal of an earlier Mosman decision is being heard and is decided.

The HSUS asked for, and got, expedited consideration of its stay request from Judge Mosman. It intends to make the same request of the appellate court.

Mosman in a Nov. 25 opinion and order ruled that the federal government complied with the law in granting permission for the lethal removals.

"Viewing NMFS's actions in light of the APA's deferential standard, NMFS properly evaluated whether individually identifiable pinnipeds were having a significant negative impact on the decline or recovery of salmonids," Mosman said. The judge said the lawsuit's legal bottom line hinged on the Administrative Procedures Act.

The APA requires that a challenged action be upheld unless it is "arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law."

An appeal of Mosman's November ruling was filed by HSUS in mid-December. The briefing schedule for the appeal set by the Ninth Circuit begins March 23 and stretches into May.

The HSUS, the Wild Fish Conservancy and individual plaintiffs on July 3 had asked the district court to set aside the NOAA approval.

HSUS during the litigation pressed the argument that NOAA have not proven the marine mammals were having a "significant" impact on listed fish, particularly when compared to other permitted causes of mortality such as harvest or the hydro system. Some level of mortality of ESA listed stocks is allowed under NMFS' biological opinion "incidental take statements" for the dams and state and tribal harvest.

HSUS also contended that the federal agency erred by failing to do an environmental impact statement as required by the National Environmental Policy Act.

But Mosman ruled that NMFS followed the proper legal course.

"MMPA section 120 addresses a relatively narrow interaction between two species -- pinnipeds and salmonids," Mosman's opinion says. "NEPA and the ESA, which generally provide broader frameworks for assessing the 'other reasons for the decline,' address different issues.

"As discussed above, because the inquires and factual circumstances are so different, the agency could reasonably conclude that an action is not significant for purposes of NEPA or the ESA but is significant for purposes of MMPA section 120," Mosman said in his Nov. 25 order. "Thus, even if NMFS had to consider 'other reasons for the decline,' its decision to authorize a lethal take of California sea lions under MMPA section 120 does not "fl[y] in the face of more than a decade of past administrative decisions" as HSUS had alleged.

"NMFS was not obligated to discuss and explain other decisions made under other statutory schemes. Given the factual circumstances, NMFS's decision was not inconsistent with previous decisions under other statutory schemes."