Sea otters control populations of kelp-grazing sea urchins, so dramatic changes in these ecosystems have followed the collapse and recovery of sea otter populations.
The California sea otter population, listed as threatened under the Endangered Species Act, has grown since last year, according to a recent population census published by the U.S. Geological Survey.
The otter population is reported annually as a three-year-running average, and rose to 2,941 this year, up from last year's average of 2,792. The animal still retains its threatened species status, and will continue to do so until it reaches an average of 3,090 individuals for three consecutive years, according to a USGS statement.
A large group of volunteers and researchers from several different science institutions, including the Monterey Bay Aquarium and the University of California, Santa Cruz, collaborated to conduct the survey, which spanned more than 300 miles (480 kilometers) from the San Francisco Bay area south to Rincon Point near Santa Barbara. The animals were observed from April through June, primarily through telescopes and from low-flying aircraft. [Marine Marvels: Spectacular Photos of Sea Creatures]
This year's growth is attributed, in part, to the expansion of the survey area to include San Nicolas Island, a region of Southern California that had been excluded from the survey in the past. An increase in pup numbers also accounts for some of the growth, the USGS reports.
Those involved in the survey remain cautiously optimistic about what this year's count means for future population trends.
"A high pup count is always encouraging, although the number of adult otters counted along the mainland was almost identical to last year's count, so we'll have to wait and see if the positive trend continues," Brian Hatfield, USGS biologist and coordinator of the survey, said in the statement.
Sea otters play an important ecological role in the kelp forests of California's near-shore coastal ecosystems by eating sea urchins and other kelp grazers that, if left unchecked, would decimate kelp beds.
The thick-furred animals were nearly hunted to extinction along the California coast by the fur trade that operated in the 18th and 19th centuries, and were thought to have been completely wiped out until several dozen were spotted off the coast of Big Sur in the 1930s. Since then, the population has steadily grown, though numbers fluctuate annually and from region to region.
"Certainly, sea otters have made an impressive recovery in California since their rediscovery here in the 1930s," Tim Tinker, a biologist with the USGS who supervises the survey, said in a statement. "But as their numbers expand along California's coast, they are facing different 'growing pains' in different locales. Our research partnership is investigating the factors responsible for these local trends."
In addition to their annual census, the USGS maintains an annual database of sea otters found dead or stranded on shore to help track potential causes for changes in population trends.