Of the 37 sea otters that ended up in zoos and aquariums after surviving the 1989 Exxon Valdez oil spill, all but nine are dead, researchers reported Friday.
Most of the ones that died in captivity over the past 10 years suffered "remarkably similar" fates to the ones that died while being treated in Valdez in the weeks after the spill, according to Terrie Williams, a biologist at the University of California at Santa Cruz. Williams managed the sea otter center in Valdez in 1989.
"The one organ that showed damage over and over again (is the) lung - the lung seems to be a target," said Williams, who shared her study at the Egan Center during the final day of a symposium marking the 10th anniversary of the 11-million-gallon spill.
Williams also found deteriorated livers and that about half of the pups born to the captive sea otters were stillborn.
In a separate study, Carol Gorbics, a U.S. Fish and Wildlife Service biologist, also tracked the rescued sea otters during the 10 years since the spill. The two biologists looked at clinic records, blood tests and necropsies for the captive animals. Their findings are similar.
In a report presented at the symposium, Gorbics said more than 450 sea otters were rescued from polluted water. Of the 197 released back into the wild, 45 were tagged and monitored for two years. At the end of two years, 15 were still alive, 14 were dead, 15 were missing and presumed dead, and one radio collar failed.
The 37 sea otters that were shipped to aquariums and zoos in the United States, Japan and Canada weren't released because they had severe health problems or because they were abandoned or orphaned pups, Gorbics reported.
Williams pointed out that there was no way to tell the exact age of the otters rescued but that generally biologists looked at weights and lengths to classify the animals as pups, immature adults or adults.
Sea otters generally live 15 to 20 years. And Gorbics reported that biologists believe permanent captivity likely increased long-term survival for at least some of the individuals.
During the first year in captivity, 13 died. Two of those were estimated to be 15 years or older at the time. Of the nine otters living today, five were pups at the time of the spill, she said.
Among the 28 captive sea otters that have died since the spill, death has been attributed to heart or pulmonary problems, gastrointestinal problems, neurological disorders, acute oil toxicity, trauma or other causes.
"We basically found that just about every organ system of these animals was affected (by oil) and it certainly showed up on the necropsies," Williams said.
The exposure to oil caused the lungs to "blow out," Williams said. "The lungs would become distended as a result of the inhalation or dermal absorption of oil. We believe it is related to the petroleum aromatics (benzene, toluene and xylene). ... Eventually the lungs would just rupture."
Liver damage was also a persistent problem, Williams pointed out. In some cases, the liver of an exposed animal was mottled in color and crumbly. "If you break the liver apart, it is very friable; it fell apart in your hands," she said.
The damage to the liver might also be related to hypothermia when oil ruined the insulated effects of their fur. That caused their cardiovascular system to shut down, she added. So it is hard to sort out whether the liver damage is because of the animal trying to metabolize oil or because of hypothermia.
Researchers also noted changes in reproduction. Of the 14 pups born to captive otters, seven were stillborn or survived only 24 hours. Two survived less than two weeks. One born in 1993 now lives in an aquarium in Antwerp, Belgium.
For comparison, Gorbics looked at pups born to captive sea otters before the spill and found those had a much higher survival rate. She pointed out that studies of the Sound's wild juvenile sea otters in the first year after the spill found that pups in the western stretches of the Sound, which was oiled, had a lower survival rate than pups born in the eastern sound, which was not oiled.
"The cause of the reduced survival both in the captive and wild is unknown," Gorbics wrote.
Williams found other reproductive problems. Many of the animals developed infections following pregnancy or associated with the pregnancy. "There is no reason I can give you just yet, but it certainly is something of concern," Williams said.
"Overall, this paints a bit of a bleak picture for reproductive activity for these animals," Williams said. "However, it is unclear how much of this is related to original oil exposure and how much is due to captive situation."
* Reporter Natalie Phillips can be reached at firstname.lastname@example.org