"When the otters are gone the kelp forests change to a barren land," Jim Estes, an otter expert and marine biologist with the US Geological Survey, told AFP.

Sea otters are known as a keystone predator. They eat sea urchins, which feed on kelp, thus maintaining the environmental balance for other species.

"The kelp in places that no longer encompass the range of the sea otter is massively degraded," said Estes.

New legislation would beef up the budget to protect the otters on a federal level and fund scientists like Estes hoping to unravel the mystery of the flatlining otter population.

The Southern Sea Otter Research and Recovery Act, recently introduced by California Congressman Sam Farr, would authorize 25 million dollars over five years of otter study and conservation.

"We've been fighting to bring them back from the brink of extinction for more than 60 years, and this bill would be a big step in that direction," Farr said.

"Sea otters are a California icon, attracting tens of thousands of visitors to the Central Coast and playing a crucial role in maintaining our unique kelp-bed communities."

Officially listed as a threatened species since 1977, the southern sea otter was hunted nearly to extinction by 19th century fur traders who decimated the historic population of 16,000.

The population has rebounded to roughly 2,900 now, but has suffered a high mortality rate in recent years, particularly among reproductive age females.

"Otter mortality is a warning beacon of a degraded marine environment," said David Jessup, researcher with the California Department of Fish and Game.

"Look at the San Francisco Bay. It used to be so clean that game wardens had to chase down oyster pirates. Now an oyster could not be supported there even in a glass cage."

The sources of pollution have turned out to be surprising. In 2006, the state of California began labeling bags of cat litter with warnings to discourage flushing it down the toilet after scientists found it to be a source of toxoplasma, a deadly single celled infectious organism found in roughly half of the dead otters.

Another land-spawned bug infecting otters, sarcocystis, is traceable to opossum droppings.

A recent study from the American Veterinary Medical Association determined that three central California coastal towns collectively produce over 100 tons of outdoor feline fecal deposits annually.

"The laws are clear that it is illegal to pollute the marine environment, but it is difficult to track the sources of pollution and it is not just cat feces," said Jessup.

Conservationists and marine researchers hope to draw attention to the land-sea connection, and mitigate the sources of "non-point" pollution, hazardous material and toxins that are more difficult to isolate than a factory discharging waste directly into the Pacific.

"There are things we can do to encourage social and biological change," said Jessup.

"Right now we have a straight pipe from us to them, but we could create artificial wetlands to replace the ones we have destroyed, and regulate the pollution from street and agricultural run-off, septic systems, and other effluents."

The southern sea otter is a concentrated species, with a range from Half Moon Bay, south of San Francisco, to Santa Barbara, spanning only 420 kilometers (250 miles).

Most of the otters stay close to Monterey, but historically the species ranged from the northern California coast all the way to the northern Mexican coast.

The concentration of the population puts it further at risk, scientists say. "If a large oil spill happens on the California central coast," said Jim Curland of Defenders of Wildlife, "those otters will get hammered."

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