The California Department of Fish and Wildlife (CDFW) recently updated its distribution map for the state’s river otters, reflecting sightings by citizen-scientist “otter-spotters.” River Otter Ecology Project director Megan Isadore says the map fills in major gaps in the North Bay and East Bay, increasing otters’ documented range by 4,100 square miles. “It’s interesting to find how well they’re doing in very populated cities,” she says. Absent from the Bay Area for decades, river otters were observed near Tomales in 1989 and sightings have proliferated since then, possibly due to cleaner waterways. In addition to “Sutro Sam,” who frequented San Francisco’s Sutro Baths, they’ve been reported in Walnut Creek, Petaluma, and even at the Golden Gate Fields racetrack on the Albany-Berkeley line. South Bay otter sightings are rarer, but beavers are expanding in Santa Clara County. Steve Holmes of the South Bay Clean Creeks Coalition found a pregnant beaver on the Guadalupe River in 2013; others have been spotted in San Jose, Campbell, and Sunnyvale, and this spring De Anza College student Ibrahim Ismail discovered a den on Los Gatos Creek. Nineteenth-century records place beavers in the South Bay before their local extirpation, but CDFW does not issue permits for beaver relocation because of their nuisance potential. Although there are beaver colonies in Martinez and a few other Bay Area sites, the origins of the South Bay colonies are not known; the beavers may have moved downstream from Lexington Reservoir, where they were reportedly introduced in the 1990s under unclear circumstances. Holmes welcomes the return of the furry ecosystem engineers, whose activities have been shown elsewhere to improve habitat for salmonids. However, Santa Clara Valley Water District biologists Doug Titus and Navroop Jassal note that those studies may not match South Bay conditions, and explain that dams could affect threatened steelhead by blocking migration, increasing water temperatures, and providing habitat for exotic predators. However, they say that so far no negative impacts from dam-building or other beaver work have been observed.

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Photo by Romain Kang
 

Two long-scarce freshwater mammal species are staging a comeback in Bay Area waterways.

The California Department of Fish and Wildlife (CDFW) recently updated its distribution map for the state’s river otters, reflecting sightings by citizen-scientist “otter-spotters.” River Otter Ecology Project director Megan Isadore says the map fills in major gaps in the North Bay and East Bay, increasing otters’ documented range by 4,100 square miles. “It’s interesting to find how well they’re doing in very populated cities,” she says. Absent from the Bay Area for decades, river otters were observed near Tomales in 1989 and sightings have proliferated since then, possibly due to cleaner waterways. In addition to “Sutro Sam,” who frequented San Francisco’s Sutro Baths, they’ve been reported in Walnut Creek, Petaluma, and even at the Golden Gate Fields racetrack on the Albany-Berkeley line. South Bay otter sightings are rarer, but beavers are expanding in Santa Clara County. Steve Holmes of the South Bay Clean Creeks Coalition found a pregnant beaver on the Guadalupe River in 2013; others have been spotted in San Jose, Campbell, and Sunnyvale, and this spring De Anza College student Ibrahim Ismail discovered a den on Los Gatos Creek. Nineteenth-century records place beavers in the South Bay before their local extirpation, but CDFW does not issue permits for beaver relocation because of their nuisance potential. Although there are beaver colonies in Martinez and a few other Bay Area sites, the origins of the South Bay colonies are not known; the beavers may have moved downstream from Lexington Reservoir, where they were reportedly introduced in the 1990s under unclear circumstances. Holmes welcomes the return of the furry ecosystem engineers, whose activities have been shown elsewhere to improve habitat for salmonids. However, Santa Clara Valley Water District biologists Doug Titus and Navroop Jassal note that those studies may not match South Bay conditions, and explain that dams could affect threatened steelhead by blocking migration, increasing water temperatures, and providing habitat for exotic predators. However, they say that so far no negative impacts from dam-building or other beaver work have been observed.

About the author

Joe Eaton writes about endangered and invasive species, climate and ecosystem science, environmental history, and water issues for ESTUARY. He is also "a semi-obsessive birder" whose pursuit of rarities has taken him to many of California's shores, wetlands, and sewage plants.