River Otters Return to the San Francisco Bay Area

Latest update September 13, 2019 Started on February 15, 2012

After a decades-long absence due to habitat loss and trapping, river otters are returning to the Bay Area. Join our community of conservationists as we document and explore the natural recovery of this charismatic carnivore.

February 15, 2012
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In The Field
We Launched the Trident First, a bit of news. The Open Explorer platform, which hosts our expedition reports, is being discontinued. We'll be gone for a time, but since our Expedition is sponsored by the SEE Initiative, we will return at some point on a new National Geographic platform. As for the Trident... We were out on Tomales Bay recently, using Captain Brett Miller's catamaran to do our research work. We bought the Trident along to take a look under the water. The first thing was found was that driving the Trident is an acquired skill that we had not yet acquired. We'll need to practice at our Test Facility before we try a live dive again. The second thing we found is that the video can be pretty amazing when the Trident is under proper control, as happened a few times just through random chance. Thanks to Brett for the use of his boat and his deft handling of the Trident's tether, to ROEP co-founder Megan Isadore for her logistics expertise, and to our guest explorers Jackie and Jim for their steadfast encouragement and exceptional snacks. We're sure we'll have mastered the Trident by the time our Expedition returns on the new Explorer platform. Until then, you'll still find us at our website https://riverotterecology.org or on Facebook / BayAreaOtters or Instagram riverotterecology
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Our Ship Came In

We got a Trident, and we're really happy about it.

We're grateful to the SEE Initiative for the generous donation. And it wouldn't have been possible without the active support of all of you who signed up to follow our expedition.

The Trident arrived today at River Otter Ecology Project's world headquarters. We're planning to practice driving it soon at our new Trident Testing Facility in Fairfax.

We have a few ideas on where to use the Trident in its first real underwater foray. We'll post here about our new adventures, of course.

Thanks to the SEE Initiative, we have a new horizon to explore.

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What If We Could See Underwater?

Many of the reports we receive from our community of Otter Spotters end with something like, "...then it dove underwater, and I lost sight of it."

We certainly know how that is.

River otters use all kinds of aquatic habitats: near-shore ocean, bay, estuary, lake, and, yes, rivers. They use protected streams on public lands, man-made ponds on agricultural lands, channelized creeks in urbanized areas, and reclamation ponds maintained by sanitary districts. Water is water, as long as it's clean, and it's where river otters forage for food, do some of their traveling, and is often where they mate.

But we can only see the surface.

We're hoping to change that. We've applied to the Science Exploration Education Initiative for a grant of a Sofar Trident underwater drone. With a Trident drone, we'd be able to gain a better understanding of habitats river otters occupy, and their role in the life of those habitats.

We'd use the Trident in all three of our main programs: research, education, and community science.

In our research program, the Trident would allow us to explore underwater habitat areas in places river otters occupy now, like Rodeo Lagoon and the near shore habitat at Muir Beach. We could also explore habitats river otters don't occupy yet, like the Salt Pond restoration sites in the southern part of San Francisco Bay.

In our Hands on Science education program, we could put the Trident in the hands of the students who work along side us in the field as we demystify the reality of working in biology, and try to inspire them to continue their science education.

Our community science program is designed to gather landscape-scale data on river otter presence while at the same time engaging the public in active support of watershed conservation. Underwater video from the Trident would be a powerful addition to the community presentations we do all over the San Francisco Bay Area.

And maybe, against all odds, we'd be able to capture underwater video of river otters interacting with their wild habitat.

We hope SEE Initiative will approve our grant request, and we can get started on our new underwater adventure.

Meanwhile, we'll wait patiently on land...

In The Field

A Sense of Wonder

Fun! I love this. Thanks for sharing Terence.

I headed out on a quiet Tomales Bay morning. A few fishermen dotted the bay, and I nodded a greeting to a fellow kayaker putting in at the launch. I stowed my field gear in my trusty research vessel, the aging inflatable kayak that has carried me dutifully to my camera sites through the years.

I paddled in no particular hurry toward the far shore. The harbor seals were all hauled out on Hog Island. A few cormorants bobbed in the water, doing that disappearing dive that’s so quick and unprefaced it seems like something they just thought of for the first time. I kept an eye out for bat rays, since I had seen quite a few my last time out. Today there were no signs of them, no tips of their black wings jutting just out of the water. A V of seven pelicans glided low overhead. I stopped paddling to watch them pass, then turned north. An osprey observed all from a snag high above the shoreline.

At my first camera site I spent an hour or so collecting scat samples, installing a new camera, sitting on a rock looking at the water. A group of young people paddled by in double kayaks. I watched the bay a little longer. Then I packed up and pushed off for my next site. A juvenile loon, making vaguely disapproving sounds, paddled along in front of me as I headed south. Unlike other water birds, loons don’t usually seem bothered by my presence, but this one had soon had enough of me, and veered off out of my path.

My second site is more constrained than the first, on a rocky part of the shoreline. There’s a sliver of beach, just big enough for my boat when the tide is low. I dragged my kayak up, and saw fresh otter tracks above the last high tide line. They seemed small. The camera is at the end of a seep that comes down off Pierce Point. In winter the seep spills down right into the bay, but at this time of year it peters out a little way above the shore. I unpacked my field gear, collected a fresh scat sample, and changed the video card in the camera. I stood by the camera, entering the data I had collected into my phone app, typing “fresh scat collected; fresh tracks, small, seen; batteries ok.” Someone was grunting and huffing at me. I heard it, but I was typing on my phone, in the world of my device.

Not for long. I looked to my left, and was right back where I belonged. A mother otter, three feet away up in the seep, was the someone grunting and huffing. The imperturbable and impossibly cute face of a baby otter peered over her shoulder. My first thought, “how many babies are there?” gave way immediately to the impulse to move away now, right now. But there was no away to move to except back to the water. I tossed my gear into my drybag, tossed my drybag into the boat, tossed my boat into the bay, tossed myself into the boat, paddled back ten yards or so, and waited. After five or ten minutes, the mother otter appeared and surveyed the scene. I was still too close. I moved back down the shore a little way – not out of her sight, but on the outskirts of it. After a minute or so, the mother otter came back, closely trailed by two trundling babies, then a third who was a little clumsy still. They all slid into the water and went gliding away up the shoreline away from me.

And I went gliding back to the boat launch, and glided through the rest of my very fine day.


What Are River Otters Eating?

River otters are carnivores and apex predators. They're also indicators of ecosystem health and environmental contamination. Although they depend on fresh water, river otters also use marine, estuarine, and terrestrial habitats. Their diet can be a window into ecosystem function.

Because they have high energy needs, river otters eat a lot -- and they're not particularly choosy. They tend to favor fish and crustaceans, but they'll take whatever is slow, nearby, and relatively easy to catch. Because they're so opportunistic, their diet can change seasonally and reflect the relative abundance of different prey.

We can learn something about what's going on in a habitat area by looking at what river otters are eating. We can also compare one area to another.

And that's what we did.

River Otter Ecology Project (ROEP) just completed a comparative of study of river otter diet at four locations in Point Reyes National Seashore and one in Martinez, on the east side of San Francisco Bay. This is first ever study of river otter diet at Point Reyes, and the first in the SF Bay Area since 1974.

Over a period of 4 years, ROEP scientists and our field volunteers and interns collected over 500 river otter scat samples from the 5 study sites. Students from our Hands on Science programs at Tomales High School and Marin Academy worked along with our scientists, volunteers, interns, and even ROEP Board members to dissect and analyze the samples. (In case you're wondering -- we dissolve the fecal matter in Efferdent and water and wash the samples before we dissect and analyze them.)

Overall, fishes were the most frequent prey item we found, followed by crustaceans and waterbirds. Fishes were the most frequent prey at all the sites, but consumption of crustaceans and waterbirds varied, with the river otters at Abbotts Lagoon eating relatively more waterbirds, and those in Southern Tomales Bay eating relatively more crayfish.

Because so little is known about river otters in the SF Bay Area, this study will serve as a baseline for future research. It's a starting point for measuring changes in river otter diet over time to give us insight into how their habitat may be altered by climate change and other factors.

You can read the whole report here.

Our prey study was funded by the Point Reyes Fund for Marine Science, the Sacramento Zoo Conservation Fund, and Mt. View Sanitary District. Our research and sample collection in Point Reyes National Seashore is performed under NPS permit #PORE2015SCI0003.

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Our Community Scientists Changed the Map

Understanding river otter range, or the area that river otters inhabit, is an important tool for land use planning, restoration decisions, and toxic spill planning and response.

The California Department of Fish & Wildlife maintains the range map, and the 1995 version, which was still considered current, showed river otters were absent from much of the SF Bay Area. We knew from our Otter Spotter program that wasn't right.

In 2017, we offered a portion of our Otter Spotter data set to the Department of Fish & Wildlife as a source for an updated range map. Now the new map has been published. Based on our Otter Spotter reports, 4100 square miles have been added to the river otter range in California.

Since 2012, we've received over 3,000 Otter Spotter reports from our community scientists. Thanks to their help, river otters are back on the map.

Here are images of the 1995 map, the new 2019 map, and the area added in the update.

Take a look at our interactive range map

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Awesome! Great job Terence and team!
Expedition Background

Decades ago river otters were extirpated from much of the San Francisco Bay Area due to habitat loss and trapping. They began to return, largely unnoticed, in the late 1980s. We were working on salmon recovery in Marin County when we began to notice the presence of rivers otters patrolling our watershed. We found that almost nothing was known about otters in the Bay Area, so we started River Otter Ecology Project in 2012 to document the natural recovery of this apex aquatic predator.
Through our community science Otter Spotter program, we collect information from the public about where river otters are present. At the same time, we study the progress and dimensions of river otter recovery through a long-term monitoring project of populations in Marin County. Above all, we engage our local communities in supporting conservation and restoration by linking river otter recovery to the health of our watersheds. We hope to inspire personal connections to our shared natural landscapes.

Love this expedition, Terence. Excited to be following.

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