Heat Killed Six Sea Lions
by Michael Milstein
Six sea lions found dead below Bonneville Dam about a week and a half ago apparently died when they overheated inside floating cages set out by state officials on the Columbia River, federal authorities said Wednesday.
Investigators looking into the deaths said they still don't know whether the doors of the cages closed inadvertently or someone yanked on ropes to shut them.
The disclosure of how the animals died raises the possibility that the federally protected sea lions were killed not by foul play, but by a state trapping program gone awry.
Marine mammal experts said sea lions used to swimming in cold water could quickly overheat even when air temperatures are not very high. The animals' thick blubber -- which insulates them from the cold ocean -- could act as an uncomfortable blanket when it's warm.
Panic as the sea lions realized they were trapped could also have caused them to exert themselves, further elevating their body temperatures, said Steven Brown, veterinarian for the Oregon Coast Aquarium in Newport. He compared it to a person wearing a double wetsuit and then strenuously exercising.
At least one of the sea lions had lacerations believed to be inflicted by another animal, a hint of tension inside the cages.
Sea lions cool themselves primarily by getting in the water, but those trapped inside the cages at the dam didn't have that option. Their temperatures might have risen faster as the floor of the cages warmed in the sun.
"Evidence seems to show this can happen in a relatively short period of time even in temperatures that don't seem that extreme to us," said Perry Hampton, director of animal husbandry at the Aquarium of the Pacific in Long Beach, Calif., where two sea lions died of heat exhaustion in 2006 while cut off from water.
Federal and state officials first blamed the sea lion deaths at Bonneville on vigilantes, concluding that the sea lions apparently had been shot. But they backtracked after necropsies by state and federal experts found no evidence to support that.
The National Marine Fisheries Service said Wednesday the results of necropsies on all six animals were consistent with death from heat prostration, or heatstroke.
State officials had positioned floating cages below the dam as part of an effort to control a sea lions that gather there to gobble protected chinook salmon headed up the dam's fish ladder. The Fisheries Service authorized the program.
The doors of the cages were supposed to remain open when state crews were not present, so the sea lions would get used to resting on the platform. But somehow the doors of two cages closed, trapping three sea lions inside each one, and no one noticed until it was too late.
The cages were last reported open about 7:30 p.m. May 3 and the six sea lions were discovered dead about noon the next day. High temperatures reached 65 at Bonneville Dam on May 3 and 56 the next day, according to the National Weather Service.
Oregon Department of Fish and Wildlife officials have acknowledged that the doors of a cage below Bonneville and others used near Astoria had inadvertently closed in the past.
But Brian Gorman, a spokesman for the National Marine Fisheries Service, said it's difficult to see how the doors of two cages would accidentally close at the same time.
State crews typically pulled on ropes from shore to shut the doors of the floating cages, and Gorman said the agency is investigating whether fluctuating water levels below the dam may have put tension on the ropes. The ropes were tied to a railing on shore and might have pulled tight as releases of water through the dam changed overnight.
"We are pursuing all the leads we can think of," he said. The probe remains a criminal investigation, he said.
He declined to point any fingers at Oregon and Washington state officials responsible for the sea lion trapping project. Federal officials spelled out specific standards for the project, and there's no indication they were violated.
"As far as we can tell at this stage, standard practice and standard protocols were followed all along," Gorman said.
Four of the dead animals were California sea lions, which are protected by the Marine Mammal Protection Act. The two others were Steller sea lions, protected by the Endangered Species Act. Killing either species is a federal offense.
Regardless of how the cage doors closed, state officials should have monitored them more closely so that sea lions could not have been left inside to die, said Sharon Young of the Humane Society of the United States. The Humane Society had fought state efforts to remove sea lions by killing them.
"The expectation is that the animals are going to be safe there, but obviously they weren't," she said. "Whether these animals were deliberately killed or they died of heat exhaustion, humans are responsible."
Charlie Corrarino of the Oregon Department of Fish and Wildlife declined to comment on the findings, except to say that state officials will respond to any federal findings in the case. "We want to know, 'Was there a problem, what was it, and how do we address it?' "
Bruce Mate, director of Oregon State University's Marine Mammal Institute, said he was surprised the sea lions would have died so quickly. But he said they carry all their fat on the outside of their body as insulating blubber, which makes it more difficult for them to cool their bodies when they need to.
Beached whales typically die of heatstroke -- even in cool weather -- because they cannot get rid of heat fast enough through their blubber when they are out of the cold ocean, he said.
One sea lion trapped and removed from Bonneville Dam this spring weighed 1,452 pounds, making it the largest ever captured, probably because it had put on so much weight eating fat-rich salmon. A 5-inch layer of blubber covered its sternum. The animal died under anesthesia, probably because its tremendous size weighed down its organs, officials said.
Sea lions that lie in the sun on beaches keep their temperature under control by not exerting themselves, Brown said.
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