The death of six marine mammals found May 4 in two closed floating traps below the Columbia's Bonneville Dam was likely caused by overheating, according to the findings of a necropsy performed on each of the animals.
State and federal officials "are pretty confident that this is the cause of death," Brian Gorman of NOAA's Fisheries Service said Wednesday. NOAA, Washington Department of Fish and Wildlife, Oregon Department of Fish and Wildlife and U.S. Army Corps of Engineers officials reviewed the necropsy findings on the four California and two Steller sea lions.
The findings for all six animals are consistent with death from heat prostration, according to a NOAA press release. More conclusive results may be available once studies are completed, in about 10 days, of tissue samples taken from the animals.
The findings were the conclusions of Bob Delong of the National Marine Mammal Lab and its necropsy team. The lab is located at NOAA's Sand Point facility in Seattle.
Necropsy reports and other documents associated with the investigation will be made public once the investigation has been completed.
The investigation into the circumstances relating to the deaths of these animals continues, one of its mysteries now potentially solved and another not. The trap doors were left open and investigations are focused on how they got closed. The doors could have been tripped by natural forces, such as by sea lion jostling or potentially by rising and falling water elevations, or by humans.
Foul play has "not been ruled in or out," Gorman said. "We're looking at the human element."
Anyone with information that may assist in the investigation is asked to call the NOAA Enforcement Hotline at 1-800-853-1964.
One theory is that the blubber encased pinnipeds were kept high and dry for too long and died of heat exhaustion.
"Clearly, they were in the traps and they couldn't get in the water," Gorman said. But, he said, the weather was cool. The air temperature at Bonneville that night fell to 39 and only rose to 56 on May 4, according to NOAA Weather Service data.
The deaths occurred between 7 p.m. that Saturday night when U.S. Army Corps of Engineers observers saw the trap doors open, and when the dead animal were found just before noon the next day.
The traps were positioned at the dam as part of an effort by the states of Oregon and Washington to trap California sea lions for relocation to zoos and aquariums around the country. The goal of that program is to reduce the predatory sea lions' impact on spawning salmon and steelhead runs.
The states' departments of fish and wildlife had scheduled trapping each Monday and Thursday. Between trapping days the traps are left open so the sea lions could "haul out" onto the platforms and become comfortable with their presence.
Officials have acknowledged that trap doors have in the past closed spontaneously without having been triggered by humans. The traps are triggered by ropes tethered in blinds on a nearby island. A theory being investigated is whether falling water levels could have put tension on the ropes and triggered the trap doors. The dam's average daily tailwater elevation dropped by more than 3 feet from Friday, May 2 to May 4.
The Humane Society of the United States' Sharon Young said she had discussed the overheating hypothesis with a marine mammal physiologist who said it was possible, though the odds of six different animals succumbing at once are long. The animals ranged from a young sea lion weighing about 300 pounds and one weighing 1,300 pounds, according Gorman.
"It would seem a short period of time for that to happen," said Young, who pointed out that sea lions in the past have been trapped in Northwest and hauled in cages as far as Southern California.
"Humans killed them -- either the government through neglect or they had a grotesque breach of security" if someone trespassed and deliberately closed the cages, Young said.
They traps were in a "boat restricted zone" below the federally owned dam where public access is prohibited.
Both California and Steller sea lions are protected under the federal Marine Mammal Protection Act. Steller sea lions, which are not subject to removal, are also federally protected under the Endangered Species Act. Penalties of up to $20,000 and one year in federal prison can be imposed for each animal protected under the MMPA, and up to $50,000 and one year in prison for each animal protected by the ESA.
Each trap held two dead California sea lions and one dead Stellar sea lion
In March, NOAA-Fisheries granted Washington, Oregon and Idaho the authority to lethally remove or relocate up to 85 California sea lions annually from the area below the dam to reduce predation on salmon. Among the spawning fish passing the dam each spring are five stocks listed under the ESA. The sea lions, rarely seen at the dam in recent decades, began to congregate at Bonneville in greater numbers each late winter and spring since the turn of the century.
Sea lion trapping and removals have been postponed until at least next March, according to the terms of an agreement reached recently between by the states, HSUS and federal government. HSUS has challenged NOAA's authorization decision in U.S. District Court.
The agreement calls for an expedient legal review of the issues both at the district court and appellate level. U.S. District Court Judge Michael W. Mosman last week adopted the agreement as an order. Briefing is set to begin in June with oral arguments scheduled Sept. 3. A Mosman decision soon after would leave the autumn and winter for any potential appeal to play out.
State officials initially announced the deaths the result of an apparent shooting. An x-ray examination identified metal fragments in soft tissue around the neck area of two of the dead animals. And a metal slug was found in the blubber of one animal. But neither the fragments nor the slug appear to have caused death, and may have been associated with old wounds, according to NOAA.
The sea lions appeared to have nearly ended their annual stay at Bonneville. The daily pinniped count peaked April 16 at 63, the highest total recorded over the course of research that began in 2002. That number included 46 California sea lions.
During the week that ended May 11, an average of eight Steller and fewer than 20 California sea lions were observed at the dam, according to Monday's weekly status report prepared by Corps researchers Robert Stansell, Sean Tackley, and Karrie Gibbons. Researchers have since 2002 been studying the marine mammals, evaluating their eating habits and other behaviors.
The report says many of the animals have been spotted at Astoria in recent days, more than 140 miles away at the river mouth. Numerous sea lions carry brands so they can be identified for research purposes.
Preliminary data indicates that 75 different California sea lions visited the dam this year, which would be down slightly from the 80 or so spotted at the dam the previous two years and the 100 seen the two years before that. The report stresses that the 2008 data is preliminary and due for further analysis and proofing.
Observers at the dam have seen from Jan. 1 through May 11 3,669 chinook and 285 steelhead taken by, principally, California sea lions. That surpasses last year's record (over the course of the research) total of 3,589 chinook with pinnipids still taking 80 per day over the week ending May 11. The species of another 681 fish observed taken by sea lions could not be identified.
One branded California sea lion has taken at least 106 salmon over a 68-day period; another has taken at least 101 over 51 days, according to the weekly report. The previous record for an individual was 79.
The report says the smaller animals still lingering at the dam seem to be taking advantage of the fact that many of the larger, dominant sea lions have left the scene. Some have been observed taking up to 10 salmon per day.
Observers have also seen 607 white sturgeon taken in the water immediately below the dam. Most were the prey of Steller sea lions.
The reports can be found at:
http://www.nwd-wc.usace.army.mil/tmt/documents/fish/