PORTLAND, Ore. -- The authorized killing of California sea lions at Bonneville Dam on the Columbia River would be postponed under a proposal agreed to Tuesday by the Humane Society of the United States and federal and state governments.

Steller sea lion. (NOAA photo)

The Humane Society filed a motion for a preliminary injunction against the authorization for killing the animals on March 28 and said it would seek a temporary restraining order if it wasn't granted by Friday, the earliest date the "lethal removal" was likely to begin.

Those favoring the removal say the sea lions are damaging salmon runs listed under the Endangered Species Act and protected at great expense.

The states estimate the sea lions eat up to about 4 percent of the spring chinook run as it schools at the base of the dam to pass through fish ladders en route to upriver spawning grounds.

The Humane Society contends the animals are only a small, although visible, pressure on the health of the runs and that the required "significant negative impact" hasn't been established.

The proposal, sent Tuesday to U.S. District Court in Portland, would delay the killing authorized by the National Marine Fisheries Service until the court could rule on the request for the preliminary injunction.

Under the agreement the Human Society will not seek a temporary restraining order against the entire sea lion removal project until the preliminary injunction issue is resolved if the defendants, the U.S. Commerce Department and the states of Oregon and Washington, don't kill sea lions before April 18.

However nonlethal removal of the animals to authorized permanent facilities such as zoos or marine theme parks would be allowed.

Both parties asked the court for a hearing on the preliminary injunction request before April 18. Otherwise, the agreement said, the plaintiffs can seek the temporary restraining order until the case is decided.

The Humane Society said it opposes the removal of sea lions but agreed to it so no animals would be shot before a ruling on the removal authorization.

Sharon Young, the marine issues field director for the Humane Society, said Tuesday,"We see this as a stay of execution for the sea lions."

The National Marine Fisheries Service authorized the killing or capture of up to 85 California sea lions a year for five years at the base of the dam but recommended the removal of a smaller number.

The animals are protected by the Marine Mammals Protection Act of 1972 but an amendment allows for lethal removal of some animals at the request of the states.

While the species was nearly wiped from hunting by the 1930s, it has prospered in recent decades and now is thought to number about 240,000.

The authorization to kill or remove sea lions also has strong support from Columbia River Indian tribes.

Oregon and Washington with the support of Idaho, made the request in 2006.