Restoring Bull Trout at Crater Lake – Fall 1996

Restoring Bull Trout at Crater Lake

Park Science, Vol. 16, No. 4
Fall 1996, pp. 6-7

National Park Service

Dept. of Interior

Bull trout (Salvelinus confluentus) is the only native fish known to inhabit Crater Lake National Park today. Within the park, bull trout abundance has been reduced to between 100 and 300 adults; their distribution has been restricted to a 1.9-km reach along Sun Creek. Hybridization and competition with nonnative brook trout (S. fontinalis)threatened the Sun Creek bull trout population with extinction. Last year, a generous grant from Target Stores, through the NPF “Expedition Into the Parks” program, supported bull trout research and management, which led to improved management techniques.

From the research, the park learned that standard electroshocking techniques for brook trout removal within the bull trout zone injured bull trout and caused delayed mortality. Resource managers refined their techniques and began using snorkel divers to count bull trout and remove brook trout. The divers counted bull trout by size-age class. When they encountered brook trout, the divers immediately removed them with suction samplers or electroshockers. This technique was successful in reducing brook trout abundance and allowing bull trout to increase in number. However, the technique is not likely to result in the eradication of brook trout, due to the structural complexity of the stream channel.

In future studies, the park will continue to remove brook trout from Sun Creek using the snorkel diver electroshocking technique. They will also monitor bull trout recovery. Removal of brook trout from Lost Creek, where no native fishes are found, will be conducted with electroshocking and treatments of Antimycin, which proved successful during early phases of the project at Sun Creek. The establishment of a bull trout population in an alternate watershed will serve as a backup in the event that the Sun Creek population becomes extinct or as a source of fish to enhance the restoration of the Sun Creek population.