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.
Southern sea otters are a common sight in the ocean waters from Monterey south to Big Sur but the endangered mammal has a long way to go before it can be removed from the threatened species list.
The USGS study released Tuesday says the latest numbers show the population of sea otters is shrinking faster than any time since the late 1990s. The past three years saw the most shrinkage in sea otter numbers.
"This year's census results demonstrate that sea otters continue to experience levels of mortality sufficient to limit their recovery" said Dr. Tim Tinker, lead scientist for the USGS sea otter research program in California.
But there's hope for future sea otter generations.
"This slight dip of the sea otter growth trend has happened before, most recently in the mid- to late 1990s, so hopefully this will be just a brief set-back to the recovery of the population." USGS biologist and survey organizer Brian Hatfield said. "The fact that the pup counts have continued to increase slowly is encouraging."
Scientists say pollution and people are partly to blame for the decline, the Chronicle reported. Lab tests show sea otters are dying from diesease carried by bacteria, viruses and parasites found in sewage and urban and farm runoff contaminating coastal waters.
More studies in the works are focusing on the reasons behind the sluggish rate of recovery and variable population trends.