“They’re very difficult to find in the rivers’ main stems,” Zipfel added. “You might set a net in one place and catch one or two, but you can set that same net 100 yards upstream or downstream and get nothing.” Fisheries biologists usually sample fish populations by electrofishing — running a low-voltage current through the water and forcing fish to the surface. “That works great for scaled fish, but paddlefish don’t have scales,” Zipfel said. “To catch paddlefish, we have to use gill nets.”