Spring 2014

Critter Census

Research Sheds Light on Elusive Humboldt River Otters

For years, scientists have wondered: Just how many river otters—considered by scientists to be a critical species in a healthy ecosystem—are out there? Recently, a team of HSU researchers used a unique combination of citizen science and genetic sampling to estimate the number around Humboldt Bay.


In the last century, river otter populations have dropped dramatically due to hunting and habitat loss. At the same time, relatively few studies have estimated their numbers, especially in California.
The team—which was led by graduate student Kristin Brezski, joined by HSU Wildlife Professors Micaela Szykman Gunther and Jeffrey Black—set out to create a demographic snapshot of the species in Humboldt Bay. They published their findings in the September issue of the Journal of Wildlife Management.

River otters sit at the top of the food chain, serving as an indicator of ecosystem health. But they are also notoriously elusive, making it hard for scientists to spot them and track their numbers.
For the study, the HSU team collected more than 300 samples of river otter scat over several months around Humboldt Bay. Their method was non-invasive, meaning no animals were trapped or handled.

“In recent years, non-invasive genetic sampling has become an increasingly popular method among wildlife biologists looking to reduce the potential of animal harm,” says Gunther. Common methods include extracting DNA from the animal’s hair, feces and saliva.

In this case, researchers analyzed the creatures’ scat to create unique genetic “fingerprints” for each otter. They then conducted a population analysis that included such variables as group size, geographic distribution and social structure.


Graduate student Kristin Brezski collects a sample as part of the river otter population survey. River otters are notoriously elusive, making it hard for scientists to spot them and track their numbers.

“Based on our data, we were able to track where these otters lived, where they moved and how they used their habitat,” Gunther says.

To complete the picture, they pooled their findings with visual observations from a citizen science project. Since 2000, the project has collected thousands of otter sightings from more than a hundred local residents. Citizen reports filled in important gaps that couldn’t be determined through DNA analysis alone.

The group determined that Humboldt Bay is home to 41-44 river otters—a larger number than previously expected. It also has a higher density of the creatures compared to other coastal systems. “Assessing how river otter abundance and density change over time will inform managers about the health of an apparently productive coastal system,” Gunther says.

About the Researchers

FOLLOWING HER GRADUATE STUDIES at HSU, Brezski is currently pursuing a Ph.D. at Louisiana State University, where she’s continuing her studies of population genetics examining population viability and hybridization of endangered red wolves.

Gunther is a professor in the Wildlife Department, where she focuses on the behavioral ecology of mammals. Since 2002, she has used non-invasive genetic analysis to inform reintroductions of endangered African wild dogs in South Africa.

Black is a professor in the Wildlife Department, where he focuses on the behavior and population dynamics of waterfowl. He has studied ducks, geese, Steller’s jays, and river otters.