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At Kirby Park, the accessible trail is currently closed due to storm damage.

News Release: Volunteer Monitoring Reveals How Sea Otters Use Elkhorn Slough

Ron and ROMP volunteers
byElkhorn Slough Team
onNovember 29, 2022


November 28, 2022

Dr. Kerstin Wasson, Elkhorn Slough Reserve Research Coordinator
(831) 332-9938

Ron Eby, Reserve Otter Monitoring Program Lead Volunteer
(831) 383-8784

Joe Mancino, Elkhorn Slough Safari Captain/Owner
(831) 633-5555

Dave Feliz, Elkhorn Slough Reserve Manager
(831) 595-6605

Volunteer Monitoring Reveals How Sea Otters Use Elkhorn Slough
New scientific paper highlights the value of community natural history observations

MOSS LANDING, CA – Hundreds of people come to Elkhorn Slough every day to hike coastal trails, revel in the diversity of shorebirds, or kayak among otters and seals. What if the energy of these people could be harnessed to answer important scientific questions about the estuary? A new paper published in the international journal Ecosphere shows how community members can play a key role in our growing understanding of how sea otters use estuaries.

“The Elkhorn Slough Reserve is dedicated to protecting the biodiversity of this estuary and to engaging the community in this effort, for the benefit of many different species and habitats,” says Reserve manager Dave Feliz. Volunteers support education, stewardship, and research at the Reserve. One of the most dedicated groups of Reserve volunteers are those that form the Reserve Otter Monitoring Program (ROMP).

ROMP volunteers go out twice per month to count otters and observe their behaviors at over a dozen locations around Elkhorn Slough. For many of these volunteers, otter monitoring has become a passion. “Watching otters is the highlight of my day, and I always learn something new,” says volunteer Ron Eby, who plays a leadership role in ROMP and is the first author on the new paper.

One of the most exciting patterns detected by the ROMP team is how closely sea otters are associated with seagrass beds in the estuary. Volunteers note exact locations of each otter during their monitoring efforts. When the records for five years were combined, it became clear that sea otters are found in seagrass about six times more often than in immediately adjacent open water. The Reserve is engaged in seagrass restoration, and this finding highlights how important such restoration is for generating vital sea otter habitat.

Another striking pattern detected by ROMP: differences in otter distribution and behavior based on the tide. Where the otters are and what they are doing differs significantly at low versus high tides. For instance, the new paper demonstrates that quiet tidal creeks through salt marshes on the Reserve are used primarily at high tide, when otters can scramble up the banks and nap on the marshes, warming up and saving energy. “Volunteer data really allow us to understand how salt marshes are used by otters, and this helps us design the best strategies for conserving and restoring these habitats,” comments Reserve Research Coordinator and adjunct UCSC professor Dr. Kerstin Wasson, the senior author on the new paper.

The new study also highlights the value of amateur observations as a part of ecotourism ventures. In 1994, Captain Yohn Gideon started the Elkhorn Slough Safari, which takes visitors out on pontoon cruises along the main channel of the estuary. He designed these tours specifically to provide opportunities for close-up encounters with sea otters. On each trip, he handed one participant a clicker and asked them to press the button every time they saw a new otter. Passengers always took this duty seriously and counted carefully. At the end of the voyage, the otter counts were recorded. In 2015, Gideon sold the Slough Safari to Captain Joe Mancino, who continued the tradition of counting otters on each voyage. “We’re out on the water every day, showing locals and visitors from far away the beauty of the Slough and the diversity of animals in the estuary,” says Mancino. “Since we’ve got eyes on the water every day, it just makes sense for us to count the otters and seals on our voyages.” Currently Mancino is logging about 400 pontoon trips, thus 400 otter counts per year.

The new paper compares long-term patterns of otter abundance in Elkhorn Slough from Slough Safari otter counts with data collected by a professional team of scientists headed up by the USGS, which conducts annual surveys of southern sea otters across the entire range. Remarkably, the patterns were nearly identical: both show the same peaks and valleys in otter abundance over time, and both yield very similar estimates for current otter numbers in the lower estuary (around 80 animals). Since the Slough Safari data were clearly reliable, they were then used to examine seasonal differences, and it turned out that there are more otters in the lower estuary in summer than in winter. Volunteer data can detect such patterns and other short-term dynamics that professional surveys cannot, since they are only conducted once per year.

Dr. Wasson hopes that the results of this paper will encourage more community members to get involved in monitoring habitats and species in the natural world around them—and that it convinces the scientific community that such observations can be accurate, complementing those of professionals. “All those eyes on our habitats can help us understand and protect the places we love,” she notes. “So find a place you care about and start watching! My doctoral advisor used to love to quote Yogi Berra, who said ‘you can observe a lot by watching.’”


This investigation and the new paper were led by the volunteers and staff of the Elkhorn Slough Reserve, owned and operated by the California Department of Fish and Wildlife, in partnership with the National Oceanic and Atmospheric Administration and the Elkhorn Slough Foundation. Visit for more information about the Elkhorn Slough Reserve and the Elkhorn Slough Foundation. For more information on USGS sea otter surveys, see:

Elkhorn Slough Foundation (ESF) is a nationally accredited nonprofit land trust whose mission is to conserve and restore Elkhorn Slough and its watershed. ESF protects more than 4,200 acres of rare habitat including oak woodlands, maritime chaparral, sand dunes, coastal prairie, and freshwater and tidal wetlands. Since 1982, ESF has been the nonprofit partner of the Elkhorn Slough Reserve, promoting community involvement in conservation through award-winning education, volunteer, and research programs.

Celebrating more than 40 years since its designation in 1979, Elkhorn Slough National Estuarine Research Reserve (ESNERR) is one of 30 National Estuarine Research Reserves established nationwide and administered by the National Oceanic and Atmospheric Administration (NOAA) to support long-term research, water-quality monitoring, environmental education, and coastal stewardship. The California Department of Fish & Wildlife (CDFW) owns and manages the 1,700-acre Reserve, which includes five miles of public trails winding through a variety of rare habitats.

Seal laying in salt marsh

Photo by Kiliii Yuyan

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