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    Author(s): Joseph L. Bonneau; Russell F. Thurow; Dennis L. Scarnecchia
    Date: 1995
    Source: North American Journal of Fisheries Management. 15: 563-568.
    Publication Series: Scientific Journal (JRNL)
    Station: Rocky Mountain Research Station
    PDF: Download Publication  (553.74 KB)


    Relative efficiencies of sampling methods were evaluated for bull trout Salvefinus 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 were pooled in 1991, but no differences were found in 1992. Observations from the bank sometimes improved the accuracy of the population estimates; more than one-third of the juvenile bull trout observed in Trestle Creek in 1992 were observed from the bank, whereas bank observers saw fewer fish (both species) than snorklers in Granite Creek. Both snorkelers and bank observers effectively captured juvenile bull trout with specially designed nets at night. The snorkeler captured 71% of the juvenile bull trout observed, whereas the bank observer captured 86%. Visible polymer implants allowed us to identify marked fish at night without the need for recapture.

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    Bonneau, Joseph L.; Thurow, Russell F.; Scarnecchia, Dennis L. 1995. Capture, marking, and enumeration of juvenile bull trout and cutthroat trout in small, low-conductivity streams. North American Journal of Fisheries Management. 15: 563-568.


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    bull trout, Salvefinus confluentus, cutthroat trout, Oncorhynchus clarki, sampling methods

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