While walking around Whitehouse Pool on Sunday morning, Megan Isadore slowed her gait as she passed by some feces, mentally checking whether it came from a river otter. (It didn’t.) “I’m always looking for scat. I’m always looking at scat,” she laughed.
For Ms. Isadore, the executive director of the River Otter Ecology Project, based out of her home in Forest Knolls, collecting scat is a crucial part of the research her group pursues, along with the genetic analysis of it. The project’s scat collection—which she emphasizes is non-invasive—takes place in its focus study area, Marin County, where all its cameras are, too; the nonprofit’s citizen science project, an effort to document the Bay Area population, covers nine counties.
The return of sea otters to the Bay Area in recent decades provides a source of hope that changes in the way humans treat the environment can truly benefit wildlife, Ms. Isadore said. “It shows that humans can actually have a positive effect on our watershed.”
There is little documentation about historic river otter populations in the Bay Area other than 19th century trapping records. (The animal’s constant search for food—swimming takes enormous energy—means it is not a common sight.) The otters were likely extirpated around the middle of the 20th century; since then, a host of environmental measures, including a state ban on otter trapping and the federal Clean Water Act, have improved the health of waterways.
The first new recorded siting of a river otter in Marin was in 1989, in Walker Creek.
Ms. Isadore started working for SPAWN as a naturalist in 1998, and in the following years she spotted more and more otters as she led spawning surveys and undertook field work. Still, population maps for the otters from the state Department of Fish and Wildlife showed virtually none in the Bay Area.
Ms. Isadore founded the nonprofit in 2012 to address this absence of data. A major prong of her work is the citizen’s science project, which asks residents across the nine-county Bay Area to submit otter sightings. So far, she has collected over 1,000 from Gualala to San Jose. “They’re really thriving,” she said.
Fish, mussels, crabs and water birds comprise much of otters’ diet. They like to eat “anything that’s slow and easy to get,” Ms. Isadore said, but they aren’t afraid to launch a sneak attack, too. Once, while watching a flock of gulls at Tennessee Cove, she saw an otter suddenly reach its paw around one of the birds. With its mouth digging into the gull’s neck, the otter dragged the bird into the reeds. Ten minutes later, it did it again, hunting for her pups.
They hunt for fish in the eelgrass beds of Tomales Bay, but they also protect young fish, she said. The eelgrass beds are nurseries for coho smolts and other young fish that eat and grow before heading out into the ocean. Adult fish in the bay like to make meals of smolts, but the presence of the river otters, which prefer the big fish, spooks the smolt’s predators. That gives the young a fighting chance to make it to the Pacific. The river otters may very well eat them when they return to Tomales Bay as adults. “But they do their part in the earlier part of their life cycle to protect them. It’s such an elegant example of the circles of life,” Ms. Isadore said.
River otters are an indicator species of watershed health: as long as water quality is generally fair and there are fish to eat, the otter can survive. (They don’t seem to be particularly bothered by some hustle and bustle.) Their tenacity was epitomized in 2013 by the appearance of an otter, named Sutro Sam, in the Sutro Baths, a defunct public swimming area in San Francisco. It was one of the first sightings in the city in decades, and it’s likely he came from Marin.
The nonprofit’s online map that documents every citizen sighting shows a robust otter population—but it also shows where the otters have failed to make a home. None have been spotted in San Mateo, a gap that leads to more questions than answers, at least for now.
“There’s fabulous otter habitat in San Mateo on the coast… but we have found no trace of river otters. So our question is, have they simply not arrived there yet? Is there something stopping them? There are two big freeways, there’s the coastal mountains, so I don’t know,” Ms. Isadore said.
In addition to the citizen science effort, the project has set up cameras, mostly in state and federal parkland, and collected scat along the 100 miles of coastline in Marin—from Rodeo Lagoon up to Point Reyes, into Tomales Bay and up Lagunitas Creek all the way to water district reservoirs. The cameras help track otter behavior and pup numbers, but the inability of researchers to distinguish between individual otters limits the amount of information that can be gleaned from video alone.
The scat provides concrete evidence of the otters’ location. The mammals use “latrine sites,” areas where they can both use the bathroom and smell other scat to get information about who else is in the area. (The odor is distinctive, Ms. Isadore said. “Once you’ve smelled otter scat, [latrine sites are] not too hard to find. It’s pretty smelly.”)
The nonprofit has been taking swabs of the scat to test for two bacteria, salmonella and vibrio. They haven’t found salmonella and though they’ve discovered evidence of vibrio—a bacteria found in shellfish that can cause vomiting, fever and diarrhea in humans—it doesn’t seem to have an effect on otter health, Ms. Isadore said.
In October, the project started sending scat to San Francisco State University for genetic analysis. When they are complete, these analyses can provide information on otter ranges (how far they hunt for food), dispersal (how far they travel from their place of birth) and food sources. Just like with fingerprints, the DNA extracted from the scat will allow the project to differentiate between otters. Through a matrilineal analysis, researchers could also determine if Marin otters descend from a single animal or if otters returned to the Bay Area from multiple sites, shedding a bit more light on their return.
But it’s not cheap; genetic analysis will likely cost $10,000 to $15,000 a year, and the group has put out a call for donations to help fund the effort.
The long-term goal for much of the group’s research is both to continue ongoing education efforts and to help agencies consider effects on the slippery mammals when making land-use decisions, such as in the restoration or conservation of wetlands and streams.
To send in a river otter spotting anywhere in Bay Area, visit riverotterecology.org/submit-your-sightings-online-here.html.