River Otters Stage a Comeback in Bay Area

As winter rains swell Bay Area waterways, river otters are likely to be on the move. Go outside this weekend and you might see one.

"When creeks rise and there's lots of water, they're more likely to explore and search out new places," says Megan Isadore, director of  River Otter Ecology Project, based in Marin County.

The small, weasel-related aquatic mammals are making a comeback after almost totally disappearing from the region during the last century. Otter populations were decimated, first by trapping, then by pollution. Isadore believes the population has been rebounding under the radar for decades, aided by the banning of trapping in 1961 [PDF] and the U.S. Clean Water Act of 1972.

"We started to notice them more and more often in our creeks in Marin in the early 2000s," says Isadore. "When we looked into what information there was on river otters in the Bay Area, we found that there was really no information."

Since Isadore started the River Otter Ecology Project as a citizen-science effort to map otter sightings, they've been found in nearly every county in the Bay Area, with the exception of San Mateo. One very famous otter -- dubbed Sutro Sam -- showed up at San Francisco's Lands End in 2012 and hung around for nearly six months.

While otters do eat endangered salmon species, it's not clear how they affect the fish populations. Scientists believe the otters' presence in the Bay's eel grass beds could help scare away larger fish that also eat young salmon.

"Compared to the other challenges salmon face ... ocean acidification, overfishing, dams, erosion from development," says Isadore, "where river otters stand in that whole array of problems is negligible."

If you spot a river otter, you can help track its spread at the River Otter Ecology Project website. The project has even created an interactive map of river otter sightings.