In 1989, Joseph Fitzpatrick discovered the Yalobusha rivulet crayfish (Hobbseus yalobushensis). After the species description was published, silence reigned. For the next 29 years, no studies focused on the species.
“That’s not uncommon,” says USDA Forest Service aquatic ecologist Susan Adams. “We know very little about the ecology and life history of many crayfish species.”
In 2015, Adams contributed to a global assessment of crayfish conservation status. The assessment reports that 21 percent of all crayfish are data deficient, and 20 percent of North American species are threatened. The Yalobusha rivulet crayfish falls into both categories.
“We wanted to learn more about the Yalobusha rivulet crayfish and its distribution, habitat associations, ecology, and life history,” says Adams.
Before Adams’ study, the Yalobusha rivulet crayfish had been documented in only six localities.
In 2011, Adams and her colleagues were studying Shutispear crayfishes (Procambarus lylei),which is also rare. “During that study, we found a Yalobusha rivulet crayfish where it had never been documented before,” says Adams.
The discovery led to a new study, with results recently published in the American Midland Naturalist.
Adams and her colleagues surveyed parts of the Yazoo River system in southern Calhoun County, Mississippi. The study sites were on Weyerhaeuser pine plantations where best management practices were used, and Adams’ coauthors were Weyerhaeuser scientists.
Over the course of three years, the scientists sampled 16 streams. “We found Yalobusha rivulet crayfishes in 13 new localities in eight of the streams,” says Adams. The scientists conducted all sampling in February and March.
During each sampling visit, the scientists measured stream size and water quality variables. They also assessed whether streams flowed year-round or dried up at times.
The scientists captured 2,225 Yalobusha rivulet crayfish. Eighty-one percent of the crayfish were juveniles, captured in 2012 and 2013.
What species occurred alongside the Yalobusha rivulet crayfish? The scientists also captured many other crayfishes, amphibians, and fishes.
“The presence of fishes was strongly correlated with the absence of crayfish,” says Adams. “The presence of predatory fishes was the best indicator of crayfish absence.”
Crayfish also prey on each other. Three other crayfish species were associated with absence of the Yalobusha rivulet crayfish.
The crayfish were most abundant in small, intermittent streams, where fish cannot live. “The importance of intermittent streams is often overlooked,” says Adams. “But these small streams provide crucial habitat for some species.” Fitzpatrick and his colleagues had observed that the species occurred in small streams in 1989.
“There are several potential explanations, including predation,” says Adams. “But other factors such as stream flow duration, water table depth, and food availability could also play a role.”
The Yalobusha rivulet crayfish is small and relatively short-lived. It persists in pine plantations, and perhaps alongside other land uses as well.
It is one of more than 60 crayfish species found in Mississippi. “The southeastern U.S. is a global hotspot of crayfish diversity,” says Adams. “We hope future research will facilitate conservation planning for this and other crayfish species.”
Weyerhaeuser provided some funding for this research.
For more information, email Susie Adams at email@example.com.