Friday, July 3, 2020

Hopes for the Healing of a River: Northern River Otters on the Tuolumne

I had the delightful privilege of watching a River Otter family hanging out along the Tuolumne River the other day. There were three of them, two adults and a juvenile. It's the most time I've ever seen any of them out of the water. It's a good sign that recovery is possible in a river system despite the abuses we've heaped on our wonderful gift of nature.

The Gold Rush of 1848 was catastrophic to the Tuolumne. Miners dug up river vegetation and processed literally all the river gravels for the elusive metal. Gold dredges did incalculable damage to stretches of the rivers in the Great Valley by ripping out the riparian vegetation and destroying the soils along the river floodplain. Underground mines brought minerals to the surface that oxidized to form acids and other toxins. Mercury used in the gold recovery process leaked into river waters. In the twentieth century we built massive dams that altered the water quality and flow levels. These have wreaked havoc with what remains of the natural ecosystem.

One of the bellwethers of the health of a river system is the presence or absence of apex predators and other native species. The predators cannot thrive if their prey species are not present, whether from pollution, drought or other cause. I'm always looking for signs that the native species are present and hopefully thriving. In the last few years I've run across bobcats, foxes, raccoons, beavers (gnawed trees, anyway), hawks and ospreys and Northern River Otters (Lontra canadensis). There was even a report recently of a Mountain Lion downstream in Modesto.

There used to be an even more diverse group of predators and prey species along this river. In historic times there were California Grizzly Bears, Black Bears, and Gray Wolves, along with the California Condor. In prehistoric times, the tally included Sabertooth cats, Dire Wolves, and several other rather scary beasts. The river was populated by gigantic tusked salmon up to nine feet in length.

Geologically, our river otters were a relatively late addition to the river ecosystems of North America. Their family evolved more than 30 million years ago, and spread throughout the Old World and migrated into the Americas, including the Giant Otter of South America. But the Northern River Otter fossil record only goes back to the beginning of the ice ages about 1.9 million years ago. They are related to European species, and probably came across the Bering Land Strait when sea levels were lower (although being an aquatic species, they could have swam the relatively short distance between Russia and Alaska).

The current range of the otter ends in our region. It's their frontier. According to the River Otter Ecology Project, there have been sightings on the Tuolumne River, and just one or two in the Merced River one drainage to the south (some otters were spotted in Yosemite Valley for the first time in decades recently). I'm hoping they will be able to spread farther south into the San Joaquin River drainage. I have seen them on the valley floor in the San Luis National Wildlife Refuge in a slough of the San Joaquin.

The otters cooperated long enough that I was able to get some video too. Enjoy!


Anonymous said...

I wonder where they come from. If they didn't used to be seen on that river, what was their origin?

Garry Hayes said...

They are comfortable on land and in water. They are known to walk miles between rivers sometimes, so it makes sense that they migrated, perhaps down the coast and inland through the Sacramento Delta into the Great Valley

Noah's ARk said...

I grew up on the Stanislaud River in Riverbank. For the last 15 years or so, my parents have been seeing river otters along the undevelped north side of the river, downstream of Jacob Meyers park. Before that, I don't recall ever seeing them when I was growing up in the 70s-90s. They are really fun to watch. Remind me of dogs in their behaviour, socialization, etc