A fish story

Researchers on the San Juan River, below Piute Farms falls.

Piute Farm, the “unrunnable” waterfall below the must-make take-out at Clay Hills, has long struck fear in the hearts of San Juan River runners. However, new research shows at least a few river runners are successfully navigating the 20-foots falls – at least one way.

A new study from the Bureau of Reclamation has found a large population of endangered razorback sucker and pikeminnows in the San Juan below the waterfall and above Lake Powell.

Using radio transmitters and antenna, researchers counted 1,000 razorback and dozens of Colorado pikeminnow downstream of the waterfall. The study was conducted in 2015-17 and appears in the journal River Research and Applications.

The new information will help guide future recovery and conservation efforts of the endangered fish. “Even though we knew the waterfall existed, nobody knew how it affected the Colorado pikeminnow and razorback sucker,” BuRec’s Mark McKinstry, coauthor of the study, said.

The waterfall formed in the 1980s, as changing reservoir levels and sediment redirected the San Juan over a 20-foot ledge. Until recently, little was known about its effect on the two endangered fish. Although the number of razorback downstream of the waterfall is proportionally larger than the population upstream, biologists do not fully understand the ability of the fish to spawn and grow in river-reservoir conditions.

The situation is not unique to the San Juan. Downstream at the Grand Canyon, the recently formed Pierce Ferry rapid is also believed to be stymying endangered fish moving between Lake Mead and the Grand Canyon. It’s a scenario that’s expected to play out more in coming years, given changing climate and dropping reservoir levels.

“We know connectivity is important but these emergent river-reservoir processes could be further stressing populations,” Casey Pennock, a study co-author, said. “It’s challenging researchers to better understand the resiliency of populations in systems that may never return to historical conditions.”

To help further that understanding, Reclamation recently funded a $3.4 million study in the Lake Mead and Grand Canyon areas – the only self-sustaining population of razorback. Researchers will look at habitat, flows, water temperatures, as well as other factors impacting the fish.

The razorback sucker is one of four large fish native to the Colorado River Basin. Listed on the Endangered Species List in 1991, it was historically abundant throughout the main stem of the Colorado as well as major tributaries in Arizona, California, Nevada, New Mexico, Utah and Wyoming. Although current populations of razorback are greatly reduced from historic levels, the fish has survived thanks to aggressive stocking efforts.