Killing one fish to save another in Yellowstone

White-breasted gulls are following a slow-moving boat in Yellowstone Lake. The crew on board is up to something fishy. It’s four fishermen letting out an awful lot of net. The net sinks into the lake’s deep depths in a large S-curve created by the swerve of the captain’s turns. The crew manages up to 40 miles of netting. That netting collects 300,000 lake trout every summer. “We are aggressively netting non-native lake trout in Yellowstone Lake to reduce their predation on our native cutthroat,” says Todd Koel, Yellowstone National Park native fish conservation leader. An angler turned in an unusual catch in 1994. It was a fish that wasn’t supposed to be in Yellowstone Lake — a lake trout. The surprise catch hooked biologists with an unexpected problem. They had an invader in a fishery carefully monitored for the persistence of the park’s coveted native fish, Yellowstone cutthroat trout. “We’re not going to allow that in Yellowstone National Park,” Koel says. “This place is much more than that. We’re way better than that.” Lake trout have aggressive appetites. They made quick work of eating native swimmers. By mid 2000s, 90 to 95 percent of the native Yellowstone cutthroat trout in Yellowstone Lake were gone. “The problem is lake trout are like large wolves on the landscape, only in the lake,” Koel says. “Large, highly predatory, fish-eating machines essentially.” The park’s fisheries biologists are fighting those fish-eating machines with intensity. The goal is a lake trout population crash. That’s what the commercial fishing boat from the Great Lakes region is for. The crew, with gulls in their wake, put out gillnets as fast as they bring fish in. They work the waters from May to October. They fill stacks of black bins with dead lake trout. Cut open any of the dead fish and there’s up to eight cutthroat trout inside...more