River otters coming back to Sonoma County

Winter rains have swollen streams and rivers, recharging groundwater, filling ponds and lakes, and making more visible the network of waterways that traverse Sonoma County. One species that makes good use of this aquatic web is the river otter. Have you seen a river otter recently? If so, you’re one of a growing number because river otters are on the comeback.

River otters are large, fish-eating members of the weasel family. They are energetic animals about three feet long that depend upon fish and crayfish for over 90 percent of their food. Otters are aquatic, which means that they live almost exclusively in or near water. You may see them swimming in places like Spring Lake, traveling along Sonoma Creek, feeding along the Petaluma or Russian rivers or even working the mouths of coastal streams in places like Pinnacle Gulch or Gualala Point.

The Bay Area is seeing a rebound in river otter populations. Experts speculate that this is a testimony to many overlapping efforts to improve water quality and restore habitat. Megan Isadore of the River Otter Ecology Project says, “The most amazing thing about the otters’ return is they have done it completely on their own. There have been no efforts to reintroduce otters. What we are seeing is the response of the species to improved conditions.”

This time of year, female otters are denning and having pups. Maternal dens can be under large fallen trees or even inside old beaver dams. Each female gives birth to between one and four pups and then, shortly after, will breed with a male in preparation for the following winter. One amazing fact is that females experience “delayed implantation,” harboring fertilized eggs and then keeping the pregnancy dormant for up to 10 months.

Most young otters live with their moms for at least a year, with females often staying to act as helpers with the new pups. Young adult males leave after a year and strike out on their own to find and establish their own territory. Otter observations are often made during the February through March time frame as these disbursing juveniles take chances crossing subdivisions, ridges, roads and farm fields in search of a new and abundant source of fish.

A river otter can actually look like a mid-sized dog swimming through the water until it pulls itself on shore and you see their long, sleek bodies and thick tails that easily double their length. You also can look for otter tracks in the mud and sand near streams. The track is nearly 3 inches wide and shows five toes with webbing in between. You may even notice otter scat, which is unmistakable because of its pungent fishy smell.

If you do get to see otters, you will be delighted with their playful nature. They can be seen sliding down mud banks and plunging into the water, engaging in what looks like a game of tag.

Otters are at the top of the freshwater food chain, but they do occasionally become prey for coyotes, mountain lions, bobcats and foxes. Today, domestic dogs have the largest potential to harm, harass, displace or even kill otters, so otter researchers urge us to keep our dogs on a leash near water.

Otters have benefited from on-the-ground habitat improvements and from the evolution of environmental policy. In 1961, California outlawed commercial otter trapping. Otters were trapped for two reasons: to sell their rich, thick pelts to the garment industry and sometimes to protect localized fish populations. Otters have large home ranges and are constantly on the move, so large scale fish populations remain intact even if individual fishing holes get temporarily depleted.

However, land owners with high-value fish in private ponds and lakes often have called for the removal of otters. Today, wildlife managers work with landowners to devise systems to deter the otters and push them on to the next fishing spot.

Another policy assist came from the 1972 passage of the Clean Water Act. This ushered in a generation of investments in cleaning the bay and eliminating many sources of industrial and agricultural pollution. Like bald eagles and peregrine falcons, otters illustrate that policy decisions do matter, and that we can repair degraded environments. As recently as 1995, state maps did not even show Marin and Sonoma counties as part of the river otter’s range. Today, scientists confirm that otters occupy much of their former Bay Area territory.

So next time you visit Sonoma County’s parks and open space preserves, keep an eye out for river otters. The River Otter Ecology Project invites you to join the growing league of “otter spotters” by posting observations to its interactive map at riverotterecology.org. You also can upload your observations of otters and other species on INaturalist.org, a citizen-science app and website.

And if you haven’t seen a river otter yet, take heart. Your chances are pretty good this year, and getting better.

Melanie Parker is the Natural Resource Manager for Sonoma County Regional Parks.