Record Count for Dead Otters
January 21, 2011
According to preliminary data released this week by the US Geological Survey Biological Resources Division, a 2010 was a record year for otter strandings, with 304 otters dead or found with life-threatening injuries. About a dozen were stranded alive, says Brian Hatfield, a wildlife biologist for USGS.
USGS adjusts its findings to account for proportion, and 2010 also holds the record when adjusted as rate for the total population. The Otter Project, a non-profit organization dedicated to contributing to sea otter recovery, calculates more than 11 percent of the otter population was found dead last year. Of the 304 stranded otters, about 25 percent were found between Moss Landing and Carmel.
Hatfield says, "Any increase in mortality is of concern to us," and this record year is disconcerting to otter advocates. The increase is "not a good sign" for the otter population, he says. Otters are listed federally as a threatened species under the Endangered Species Act.
As to causes of mortality, Hatfield says there was an unusually high number of shark bites last year. Scientists are still exploring whether there is an increase in the shark population, but there is "evidence linking protozoa infection to shark attacks." Infected otters may be less cognizant of their surroundings and hence are more vulnerable, or such infections may cause tremors that produce vibrations, making otters easy targets for sharks.
Last year was the first for recording otter deaths as a result of toxic algal blooms in freshwater, another subject of further inquiry for scientists.
USGS also found the otters' habitat range shrinking both from the north and the south along the coast. A similar otter range retraction occurred about ten years ago, but Hatfield says there is no known cause for the retracted range. What is certain, he says, is that "we would like to see the range expanded and numbers increased."