Electrofishing for Crayfish

Estimating populations with multipass electrofishing

three people stand in a stream with nets and gear
From left to right, Carl Smith (biological technician), Gordon McWhirter (retired hydrological technician), and Ethan Liles (volunteer) electrofish for crayfish in Alabama streams. USDA Forest Service photo by Zanethia Barnett.

Since its origin, more than 40,000 years ago, fishing has taken a variety of forms — from spearing to hook-and-line fishing. In the 1960s, scientists began using a method called “electrofishing” to study aquatic populations.

In a study published in the North American Journal of Fisheries Management, USDA Forest Service scientist Zanethia Barnett researched the factors that impact the accuracy and efficiency of electrofishing for crayfish.

Barnett is a research fisheries biologist on the Aquatic Conservation Ecology team at the Southern Research Station. “Our team focuses on how humans impact the environment of native stream populations,” says Barnett. She studies freshwater aquatic organisms, such as crayfish, and recently turned her attention to one of the team’s key data collection methods: electrofishing.

Electrofishing introduces an electric current into the water. This electric current stuns aquatic organisms, allowing them to be collected, observed, and later released back to the water with little to no harm.

With these observations, scientists can learn about the population size, average weight, and number of males and females in a population.

Listen to a brief audio clip by author Zanethia Barnett describing this publication. • Text Transcript

“Electrofishing is one of the most common ways to sample for fish, and it’s becoming an increasingly common way to sample for crayfish.” But Barnett knew of no research on how efficient electrofishing was for sampling crayfish within rocky, highly diverse southeastern streams. “We wanted to know how accurate our assessment method was, especially compared to other sampling methods.”

By sampling crayfish from streams in Alabama, Barnett and her team came to two conclusions about electrofishing. First, multipass electrofishing — or electrofishing throughout the same area two or more consecutive times — allowed them to collect more crayfish than when they made only one pass.

Barnett explains that when crayfish find cover under rocks and vegetation, one electrical pass may dislodge them, but they often times are still out of reach or unseen by scientists. “When you sample an area one time, you may not see some of the crayfish. But after a second disturbance, we found that we were collecting more.”

By collecting more crayfish, scientists and stream managers can obtain more accurate data about the populations.

a crayfish
Cambarus coosae, one of the many crayfish species collected during the study. Photo by Guenter Schuster of Eastern Kentucky University.

“There are numerous crayfish species that are up for listing as endangered species right now. But before species can be listed as endangered, we have to evaluate the population status,” says Barnett.

Second, Barnett determined that the efficiency of electrofishing was impacted by stream and crayfish characteristics, such as water quality, water conductivity, and crayfish size. In other words, electrofishing is not a one size fits all technique, as its effectiveness depends on environmental factors. For example, a smaller crayfish species may be harder to collect and thus require more electrofishing passes than sampling for a larger crayfish species would.

The southeastern U.S. is a hub for crayfish diversity, so Barnett was able to look at multiple crayfish species at one time. “It was interesting to see how when collecting a suite of species, there may be two or three that were more susceptible to electrofishing than others — which means population estimates were more accurate for these species than for other species which were not as susceptible. This also showed that more electrofishing passes were needed for the less susceptible species for more accurate estimates,” adds Barnett.

Read the full text of the article.

For more information, email Zanethia Barnett at zanethia.c.barnett@usda.gov.

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