A California sea lion captured Monday as part of a state effort to remove the animals from below the Columbia River's Bonneville Dam died the next day during a health examination at a Tacoma zoo.

The animal, a 1,454-pound adult male being held temporarily at the Point Defiance Zoo and Aquarium failed to resume breathing after being anesthetized for the examination. A team that included an Oregon veterinarian, a state marine mammal biologist and a federal animal-care expert had concluded the health exam and were attempting to bring the animal out of anesthesia when the death occurred.

A necropsy is being performed to determine the exact cause of death. Results will be announced when available, according to a press release issued by the Washington Department of Fish and Wildlife.

The sea lion is one of seven captured during the past week for relocation to designated zoos and aquariums. The goal of the Oregon-Washington initiative is to reduce the number of California sea lions preying on protected salmon and steelhead passing the dam on their upriver spawning run.

PDZA spokeswoman Sheelah Medved said that three of the captured animals were shipped out early Wednesday morning, bound for Sea World San Antonio and she thought three more would be transported today (Friday).

The animals are being held in temporary quarantine at PDZA for disease testing in preparation for permanent placement at designated zoological facilities around the country. PDZA staff were not involved in the health examination.

U.S. Army Corps of Engineer researchers began evaluating the pinnipeds' behavior and eating habits in 2002. The number of California sea lions trekking the 146 miles upriver to the dam had grown rapidly in the previous few years raising the concern of NOAA Fisheries and others.

The sea lions await with open jaws spring chinook salmon and steelhead, including five stocks listed under the Endangered Species Act. Researchers observed sea lions taking 3,589 salmon last year, which amounted to about 4.2 percent of the passing run.

The states of Idaho, Oregon and Washington sought and won authority under a Marine Mammal Protection Act to lethally remove as many as 86 California sea lions annually. NOAA Fisheries, charged with protecting listed fish as well as the sea lions, granted the authority in March.

The Humane Society of the United States on Wednesday immediately called on the federal government to immediately halt the live captures and conduct an investigation to get to the bottom of the incident.

That states' authority was trimmed last week in federal court with an order staying lethal removal activities but allowing the relocation of California sea lions to captive display facilities. The HSUS requested the stay.

"Given that sea lions eat so few of the salmon compared to overfishing and other impacts, there should be no rush to remove these animals from the wild, especially in light of the apparent problems with capture and relocation," said Michael Markarian, executive vice president of The HSUS.

State officials resumed the trapping effort Thursday but came up empty when no animals strayed onto the trap. Trapping is planned each Monday and Thursday until further notice, according to Rick Hargrave, Oregon Department of Fish and Wildlife.

The initial attempt on April 24 snared six California sea lions, including three that qualified for removal (three were released). To make the removal list, a sea lion must be individually identifiable through brands or natural body markings. They must have also rebuffed ongoing state and federal efforts to chase them away, been observed eating salmon and been at the dam for five days or more.

Included in the first bunch captured was a California sea lion dubbed C319, who has been seen at Bonneville each year since 2002. C319 weighed in at 1,151 pounds last year, a record among animals trapped by the states.

He pushed that record higher, to 1,236 pounds by the time of his capture, with a steady diet of fatty salmon. The animal had been at the dam since Feb. 25 and has been observed catching at least 39 salmonids and eight unknown fish over 59 days.

"He probably ate at least twice that many," said Robert Stansell, who heads the Corps research. The documented catch includes only predation within sight of observers in the area immediately below the dam.

The deceased sea lion, B198, broke C319's weight record. His tonnage is evidence of plentiful forage. A species description on the Marine Mammal Center's web site says males may reach 1,000 pounds but the average is closer to 850. Other descriptions, including NOAA's, put the average adult male's weight in that same range.

"That really points to the fact that this is not the norm," Stansell said of Bonneville situation, where salmon are easy prey for the pinnipeds and allows them to pile on calories while burning few.

The ODFW has trapped, tagged or marked and weighed more than 800 sea lions over the years for a variety of research purposes. A similar effort, with similar pinniped handling statistics, in ongoing in the Puget Sound. None of those marine mammals weighted as much as B198 and C319.

"These are some of the heaviest California sea lions known," said ODFW marine mammal biologist Bryan Wright.

B198 spent 45 days below the dam in the spring of 2006 and was observed taking 77 salmonids, two lamprey and seven fish that observers could not identify. He skipped the trip in 2007 but returned this year on March 19, taking 13 salmonids before his capture, according to research data.

Stansell speculated that his relatively low observed salmon take this year may be because ongoing hazing forced a shift in the sea lion's predation strategy. The researchers, in a summary report of 2005-2007 observations, noted that some animals respond to the hazing by becoming more "secretive," spending more time underwater.

The male California sea lions forage north from their Southern California breeding grounds and begin to make their Bonneville appearance in mid-winter. The number grows as the salmon run builds. The pinnipeds usually have exited the Bonneville feeding ground by the end of May.

The Bonneville California sea lions population is in that growth stages just as the salmon run appears to be climbing toward a peak (the five highest daily salmon counts of the year at Bonneville's fish ladders have been the past five days). The sea lion count on April 16 was 63, including 17 Steller sea lions and 46 California sea lions. That total is the highest for any given day over the course of the research. The previous high was 54 last year, according to the most weekly report produced by Stansell's research group.

"A preliminary look at individuals identified at Bonneville Dam so far suggests we have seen about 70 different California sea lions, and at least 17 Steller sea lions and 2 Harbor seals," according to the report. "At least 38 of the California sea lions have been seen in previous years."

Of the 60 animals initially listed for potential lethal take, 32 have been seen at Bonneville Dam so far this year. An additional 5 branded animals now qualify.

Preliminary, unexpanded data indicates that 2,416 chinook, 268 steelhead, 606 sturgeon (21 larger than 5 feet), 8 lamprey and 574 unidentified fish were taken by sea lions for between Jan. 11 and April 27. The take is on pace to surpass last year's salmon take, the highest recorded in the first six years of the study. The sturgeon take is nearly double last year's total. The California sea lions are responsible for the vast majority of the salmon take; the Stellers focus on sturgeon.