Mystery Crayfish Highlights Conservation Challenges

Forest Service crayfish detectives get creative

Researchers collect fish and crayfish from a river upstream of the Lewis Smith Reservoir in Alabama. Photo by Susie Adams.
Researchers collect fish and crayfish from a river upstream of the Lewis Smith Reservoir in Alabama. Photo by Susie Adams.

On a recent sampling trip to the Bankhead National Forest in northwest Alabama a team led by U.S. Forest Service scientist Susie Adams scooped up a crayfish from a river flowing into the Lewis Smith Reservoir. The crayfish had a distinctive black, orange, and white color pattern on the tips of its largest claws, which quickly caught the team’s attention because it didn’t look like any crayfish known to live in the streams and rivers where they were working.

The team collected several more crayfish and took them to Adams’ research lab in Oxford, Mississippi, for a closer look; what they found only deepened the mystery. The physical features of the crayfish they collected were most similar to two types of crayfish (Orconectes juvenilis and O. ronaldi) native to rivers in Kentucky and Indiana, far north of the Bankhead National Forest. Genetic analysis indicated that they were most similar to O. ronaldi, native to Kentucky, but there was no perfect genetic match. So, they wondered, what exactly is this crayfish and where did it come from?

Adams and other crayfish researchers are left to ponder these types of questions far too often. The southeastern U.S. is home to the most diverse crayfish community on the planet, with over 80 different species in the state of Alabama alone. For many of these crayfish, there’s not a complete description of their native range – the areas where we should expect to find them – or much other information on how they live. Without this basic information it is difficult to know if crayfish species are native or introduced to an area — and if populations are stable or if they are in need of conservation efforts.

Adams decided the mystery crayfish warranted additional investigation. She sent her team of crayfish detectives back to take a closer look at the waters in and around Lewis Smith Reservoir. Crayfish spend most of their time beneath rocks, in wood, or in burrows, and this secretive lifestyle makes them a challenge to collect, so the team had to get creative. They used electricity and nets in shallow streams and rivers, boats and baited traps in deeper rivers.

They also employed a unique sampling approach — using hungry bass to get at crayfish in the deep water of the reservoir. Bass frequently feed on crayfish, so Adams acquired the stomach contents of bass that had been collected during another study in the reservoir. Within many of the bass stomachs were bits of crayfish that helped Adams to more completely describe the crayfish community in the area.

In total, Adams found seven types of crayfish in the area, including the mystery crayfish and a second unexpected, but more easily identified, species. Three possible scenarios could explain the presence of the unexpected crayfish: 1) they are native to the area but were previously undetected (with one possibly being a new species), 2) they are not native but moved into the area on their own, or 3) they were introduced by humans, either intentionally or unintentionally.

Adams believes that the third scenario is the most plausible for the mystery species and noted that crayfish introductions in reservoirs are being discovered more frequently in recent years. She added, “Determining how these crayfish arrived in the Bankhead National Forest is an important step in developing conservation and management strategies for the area.”

Read more in the article just published in the journal Freshwater Crayfish.

For more information, email Susie Adams at 

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