Earth Notes: Southwestern River Otters

Jul 18, 2018

For millennia, southwestern rivers have harbored an array of native creatures—including a unique subspecies of river otter. These sleek mammals once frolicked in streams and beaver ponds, using impressive swimming skills to hunt fish, frogs, turtles, and occasionally even birds.

Southwestern river otters have been successfully reintroduced in Arizona, Colorado, Utah and New Mexico.
Credit Dan Williams/New Mexico Department of Game and Fish

In the late 1800s fur trappers arrived and took otters for their coats. In 1953, the last southwestern river otter was trapped along the upper reaches of the Gila River in New Mexico. Wildlife managers stepped in, and over the last thirty-five years they’ve successfully reintroduced otters in Utah, Arizona, Colorado, and parts of New Mexico—hoping to restore not just the animals but entire river ecosystems.

A Nature Conservancy study along Arizona’s Verde River showed that reintroduced otters helped reduce numbers of non-native invasive crayfish, especially in summer. Otters also eat a variety of fish. They don’t just pick off the slowpokes either—with undulating body movements and their webbed hind feet, these members of the weasel family use bursts of speed, catching mostly abundant fish species.

In New Mexico, wildlife officials have delayed reintroducing otters to the Gila River, fearing they will eat endangered native fish. This year graduate student Gabriela Wolf is studying the otter diet by collecting scat along the Red River (formerly the Chama) and the upper Rio Grande. In the lab, she’ll sort out bone fragments, scales, and other debris and try to identify which fish the otters are actually eating.  Her results are much anticipated for those who love wild rivers—and their inhabitants.