Purdue Researchers Track Oil Spill's Effects On Sea Otters

November 20, 1997

WEST LAFAYETTE, Ind. -- Studies on the health of sea otters in Alaska are helping scientists understand how an ecosystem responds to an environmental disaster.

Paul W. Snyder, a Purdue University veterinary pathologist, is studying the effects that the 1989 Exxon Valdez oil spill in Prince William Sound has had on the Alaskan sea otter population. He's part of a team investigating why the otter population in the spill area has not rebounded to pre-spill numbers.

Snyder and Alan Rebar, dean of Purdue's School of Veterinary Medicine and a veterinarian who has studied healthy and sick California sea otters, will present data on the otter studies today (Thursday, 11/20) in Albuquerque, N.M., at a meeting of the American College of Veterinary Pathologists.

"Trying to establish whether the lack of population recovery is a direct result of the spill or not is difficult," Snyder says. He says there are estimates that up to 15 percent of the almost 11 million gallons of crude oil spilled by the tanker may still be in the environment.

Snyder, an expert on animal immune systems, has studied the Alaskan sea otter's blood and tissues for the past two years. In the course of his field investigations, he developed a technique to determine the level in the otter of an enzyme that metabolizes aromatic hydrocarbons -- a biomarker that may indicate the level of exposure to oil.

Initial results indicate that otters living in the spill area have a higher level of this enzyme, called cytochrome P450, than control otters living in a nearby, non-spill area.

"Increased levels of this enzyme may be the result of continued exposure to low levels of oil, to other environmental contaminants, or to some yet to be determined factors," Snyder says. "We need to continue these studies to evaluate the significance of these findings."

Snyder works on the project with Rebar, one of the world's leading experts on the clinical pathology of the sea otter, who was asked by the U.S. Fish and Wildlife Service in 1989 to review the direct effects of oil on the organ systems of sea otters that died in the Exxon spill. He also was one of the scientific reviewers of the impact the spill had on wildlife in general.

Snyder says there could be a multitude of reasons for the low otter numbers. They may simply have moved to a noncontaminated area, or the oil may be affecting the food supply or the otter's reproductive capabilities.

"Evidence of oil in the animal's blood suggests they may be exposed by ingesting oil when they groom their fur, or they may be eating contaminated food," Snyder says. "These studies should shed light on the mechanism."

Snyder's otter study is part of a larger research project to investigate the recovery of the ecosystem in Prince William Sound. About 15 researchers, ranging from biostatisticians to veterinarians to expert divers, are using funds from the $900 million spill settlement to study the near-shore ecosystem, which includes ducks, invertebrates, marine mammals, terrestrial mammals and sediments. Institutions involved include Purdue, the University of Alaska, the University of Washington and the National Geologic Survey, as well as the private sector.

"This is the first time a significant comprehensive effort has been made to follow the impact such a disaster has on an entire ecosystem, including predators, prey and the environment," Rebar says.

Rebar, who was asked by the Justice Department to serve as an expert witness before the Exxon case was settled out of court, says there are legal lessons to be learned as well.

"In circumstances where this type of environmental damage has occurred, the key to establishing the level of responsibility is to determine the level of damage induced by the spill itself," he says. "By being able to track the biomarkers of oil-induced injury, such as cytochrome P450, we have a way of directly linking death or damage to oil exposure. Also, by assembling this group of scientists, we now have a blueprint for who should be mobilized in the event of a similar situation."

Rebar became involved with the project in 1989, when project scientists found abnormalities in the sea otters' blood. Snyder joined the team in 1995.

"The researchers wanted to know whether the animal's immune system had been compromised," Snyder explains. "I have a clinical immunology lab here at Purdue, where we've evaluated the immune systems of animals from all over the country, from wallabies at the Indianapolis Zoo to domestic species such as cats, dogs and livestock. So when Dr. Rebar asked me if we could evaluate the immune system of a sea otter, I said 'we can try.'"

Snyder went to Alaska in the summer of 1995 to determine if it was logistically possible to obtain blood and tissue samples from the otters, preserve the specimens cryogenically with liquid nitrogen and transport them back to his Indiana lab. Once he demonstrated it could be done, he went back the next two summers to gather more specimens from about 50 to 60 animals each trip.

The analytical techniques Snyder developed have applications in Indiana as well, where river otters recently have been reintroduced.

"Working with the Department of Natural Resources, I've harvested similar samples from the Indiana animals, evaluated them, and stored them for future reference," he explains. "In the event that the population does not thrive as it should, we can re-evaluate the animals, comparing their current condition to before they were introduced, and try to determine if something in the environment is affecting them.

"Ultimately, I'd like to apply what we learn in Alaska to other marine ecosystems that may become contaminated with pollutants, such as busy harbors and channels. It would be interesting to compare the level of exposure in animals in contaminated areas to those in remote areas, and perhaps develop some kind of risk assessment for animals in various locales."

Purdue University

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