Eradication of Nonnative Brook Trout with Electrofishing and Antimycin‐A and the Response of a Remnant Bull Trout Population

Abstract

AbstractA remnant population of native Bull Trout Salvelinus confluentus was threatened with extirpation by competition and hybridization with introduced Brook Trout S. fontinalis in Sun Creek, a second‐order headwater stream in Crater Lake National Park, Oregon. Between 1992 and 2005, artificial barriers were installed to exclude nonnative fish, and multiple applications of electrofishing and the piscicide antimycin‐A were used to remove Brook Trout from 14.6 km of stream. Several novel methods were employed, including diver‐directed and trap‐net electrofishing and the use of a portable raceway to hold Bull Trout during piscicide treatments. Electrofishing likely eradicated Brook Trout from a small headwater section of the stream but required more effort (54 person‐days/km) than antimycin treatments (17 person‐days/km) in the same reach to ensure eradication. For eradication of Brook Trout from larger downstream reaches, antimycin treatments applied in consecutive years were more successful than multiple treatments applied within a single year. Brook Trout have not been detected by annual surveys in the project area since 2005. The total effort expended to eradicate Brook Trout from 14.6 km of stream was approximately 138 person‐days/km. Between 1989 and 2010, Bull Trout abundance increased approximately tenfold, and distribution increased from approximately 1.9 km to 11.2 km. These results exemplify the response of an imperiled Bull Trout population after removal of Brook Trout. The large investment of time and resources required to restore small populations like this one may be warranted only for critical population segments with special status or local management importance.Received November 10, 2011; accepted October 31, 2012