Graduate student Ken Skipper maneuvered the team's bright blue pontoon boat, loaded with a generator to power two electro-fishing wands, a cooler for stunned fish and other scientific equipment. They worked a few bends from the South Fork's confluence with the pristine North Fork of the Coeur d'Alene River near the Enaville Resort. Maret and USGS biologist Mike Beckwith jolted fish with up to 1,000 volts of direct current. A couple of technicians and fellow biologist Dorene MacCoy netted the fish that floated up, white bellies flashing in the muddy water. Later, MacCoy sliced open 10 brook trout, taking out their livers.
Heavy metals tend to accumulate in fish livers.
The organs will be frozen and shipped Monday to the National Water Quality Laboratory in Denver. Fish such as trout are much more mobile than sculpin, researchers hypothesize, so if mine waste is an issue they can better avoid metals. Another surprise came last month when they found cutthroat trout and brookies in a river reach near Silverton, which is heavily influenced by mine waste. Researchers are careful to point out these findings. USGS scientists have weathered years of criticism from the mining industry and others on the controversial issue of heavy metals.