Capture, Marking, and Enumeration of Juvenile Bull Trout and Cutthroat Trout in Small, Low-Conductivity Streams

Abstract

Abstract Relative efficiencies of sampling methods were evaluated for bull trout Salvelinus confluentus and cutthroat trout Oncorhynchus clarki in small, high-gradient streams with low conductivities. We compared day and nighttime observations by snorkelers to enumerate bull trout and cutthroat trout, and at night we also used a bank observer. Methods were developed for capturing juvenile bull trout in areas where traditional methods such as electrofishing were ineffective. Juvenile salmonids were counted during the day and night in two reaches (200 m) of Trestle Creek, Idaho, in August 1991. In July 1992, juvenile salmonids were counted during the day and night in 10 reaches (75 m) of three Idaho streams: Trestle, Rattle, and Granite creeks. Night counts of juvenile bull trout exceeded day counts in all reach comparisons; differences were significant (P < 0.05) in 1992 but not in 1991. In contrast, summer day counts of cutthroat trout were significantly higher (P < 0.05) than night counts when reaches we...