Scientists puzzled by increasing mortality rates in sea otter populations along California's central coast say the animals' food source may be delivering deadly pathogens.
A new study released this week by the U.S. Geological Survey and University of California, Davis suggests that sea otters regularly eating marine snails, clams or fat innkeeper worms have a higher risk of exposure to parasites that cause disease.
By comparison, sea otters that eat mainly abalone had very low risk of infection by these pathogens. The study found that sea otters at the highest risk live along the southern end of Monterey Bay and further south along the coast near San Simeon and Cambria in San Luis Obispo County.
Tim Tinker, a research wildlife biologist with the USGS and co-author of the study, said identifying the cause of sea otters' increasing mortality rates presented a logistical challenge for scientists. Put simply, "Trying to find a microscopic item in a huge ocean is really difficult," he said.
Biologists observed sea otters that were exposed to these pathogens and noticed the incidents corresponded to the animals' diets, according to Tinker.
Obtaining long-term diet information for animals, especially marine animals, can be difficult. The Central California coast has a high density of sea otters feeding on different diets in the same concentrated area.
"Sea otters are unique because we can directly observe their foraging habits," Tinker said. "They bring all their prey up to the surface."
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Scientists are still learning why a group of animals in the same location would have different diets, although Tinker said it may be due to limited amounts of available food.
Tinker said researchers hope to use the sea otter study to learn more about how these deadly pathogens enter the ocean in the first place. Science has confirmed these particular parasites originate in opossums and members of the cat family, Tinker said.
The study appears in the Jan. 19 edition of the journal Proceedings of the National Academy of Sciences.
