Studying otters

Studying otters -- Southern Illinois University Carbondale graduate student and field researcher Andrew Rutter is part of a team of researchers studying the status of the river otter in Illinois. The field team is live trapping otters in several locations. They are outfitting the otters with radio transmitters so they can study their movement, access the population health, and when needed, determine cause of death. (Photo by Russell Bailey)

December 04, 2014

Researchers studying Illinois’ river otters

by Andrea Hahn

CARBONDALE, Ill. -- Every species of animal presents its own challenge for researchers. For a team at Southern Illinois University Carbondale, the river otter poses several, including: How do you monitor an animal too sleek to wear a tracking collar? 

A team of researchers is at the beginning of a four-year project, funded by the Illinois Department of Natural Resources, to investigate the status of the river otter in Illinois. They hope to include at least 60 otters in a study that will help determine future management practices for the species. They’ll do this by radio tracking the animals to learn more about their individual home ranges, their role as the newly re-introduced top predator in aquatic ecosystems, causes of death, and the impact of a sanctioned trapping season. 

But first the research team has to catch the otters. And outfit them with radio transmitters. 

“An otter is not the easiest animal to capture,” Clay Nielsen, professor of wildlife ecology and conservation with the Department of Forestry and the Cooperative Wildlife Research Laboratory at SIU, said. “They are clever, and they are mobile and they can travel a long way in a short time.” 

Eric Schauber, wildlife ecologist with the Cooperative Wildlife Research Laboratory and associate professor of zoology, concurred. He and Nielsen are the principal investigators of the research team. 

“Otters cannot carry a powerful radio transmitter because it would be too heavy for them; they are low to the ground and often underwater so the signal does not carry very far; and they move long distances for their size,” Schauber said. 

For the capturing part of the problem, Nielsen and Schauber recruited graduate student Andrew Rutter, an experienced trapper from Chanute, Kan. Rutter graduated from Emporia State University with a bachelor’s degree in biology and some experience with field research. On this project, he’s had good success already. Rutter’s field research team caught 10 otters in the first five weeks of the research project and hope to double that number before the end of this year. 

Rutter explained that one of the challenges to capturing otters is their unpredictable and independent nature. 

“They don’t really respond to bait,” he said. “They catch their own fish, and they are very good at it. They really do their own thing. You have to guess where they will be and where they will go. Because they have such large home ranges, they may pass by our traps only rarely.” 

The only sure thing about otter behavior, he said, is that they will always swim when given the option. When water levels are lower, that can be an aid to the research team. Higher water levels that temporarily change water courses can wreak havoc on even the best-laid plans. 

And then there is the problem of tracking. The team is using a field-tested, minimally invasive technique to insert a small transmitter under the animals’ skin. At the same time, they record measurements and take tissue and DNA samples. 

The team expects to do most of its tracking from the ground, but Nielsen said they may enlist the aid of the SIU aviation program for some aerial tracking, owing to the otters’ mobility and adaptability. 

The main purpose for all this capturing and tracking is to assess otter ecology and response to harvest. The winter of 2012-2013 marked the first Illinois trapping season for river otters since 1929, when the animals were first protected by law. River otters had been abundant in the state, but beginning in the early 1900s, their numbers here began to decline due to a combination of fur harvest and habitat loss. They didn’t rebound, even with legal protection. In 1977, the State of Illinois listed the river otter as a “state threatened” species, and then as “state endangered” in 1989. 

Even with such protections, the river otter did not recover as ecologists had hoped. Finally, the IDNR brought in 346 otters from Louisiana, releasing them at sites in central Illinois from 1994 to 1997. That did the trick. By 2004, the population was well on its way to recovery and Illinois removed the otter from state lists of endangered and threatened animals. 

“I think 20 years ago, no one would have thought otters would take off as they have,” Nielsen said. “We are studying otter survivability and causes of mortality – this is the first time otters have been studied in this way in Illinois. It’s an opportunity for us to study the re-introduction of a top predator into an ecosystem.” 

Nielsen noted that SIU’s partnership with the IDNR on this and other research projects statewide  provides enhanced research and mentoring opportunities for graduate students, introduces undergraduate students to field research and provides the agency with the data it needs for informed wildlife management. He regularly involves students in his research projects to help them gain the field experience research teams seek. 

“The IDNR relies on us to be able to work statewide, and we’re proud of that,” Nielsen said. 

“This is another avenue for SIU to burnish its already well-established position as a leader in research on river ecosystems,” Schauber said. 

The team is already looking at opportunities for spin-off research. 

“I am very interested learning more about how interactions between otters may change as the environment fills in,” Schauber said. “River otters are essentially the top of the aquatic food chain here, and I am interested in finding out what, if any, level of control they have on populations of their prey. We are currently investigating how much otters eat invasive silver carp. This is an enormous potential prey base for otters that was not present in the past when otters were abundant.” 

The team will catch otters this year and the next two years. While they will analyze data as they receive it, the major analysis comes in the year following the three catch and tag years. 

The river otter is a member of the weasel family. Adult otters are 35 to 53 inches long tip to tip; approximately 30 to 40 percent of that length is tail. They weigh 10 to 25 pounds, with the males about a third bigger than the females on average. Their sleek bodies are perfect for agile swimming; they use their tails as rudders to help them navigate. Known for their cleverness and playful personalities, otters are also voracious predators. Their thick, water-repellent fur is dark brown to reddish brown, silvery or tan on the throat and belly.