Assessment of Native Salmonids Above Hells Canyon Dam, Idaho, 2004-2005 Annual Report.
In the western United States, exotic brook trout Salvelinus fontinalis frequently have a deleterious effect on native salmonids, and biologists often attempt to remove brook trout in streams using electrofishing. Although the success of electrofishing removal projects typically is low, few studies have assessed the underlying mechanisms of failure, especially in terms of compensatory responses. We evaluated the effectiveness of a three-year removal project in reducing brook trout and enhancing native salmonids in 7.8 km of an Idaho stream and looked for brook trout compensatory responses such as decreased natural mortality, increased growth, increased fecundity at length, or earlier maturation. Due to underestimates of the distribution of brook trout in the first year and personnel shortages in the third year, the multiagency watershed advisory group that performed the project fully treated the stream (i.e. multipass removals over the entire stream) in only one year. In 1998, 1999, and 2000, a total of 1,401, 1,241, and 890 brook trout were removed, respectively. For 1999 and 2000, an estimated 88 and 79% of the total number of brook trout in the stream were removed. For the section of stream that was treated in all years, the abundance of age-1 and older brook trout decreased by 85% from 1998 to 2003. In the same area, the abundance of age-0 brook trout decreased 86% from 1998 to 1999 but by 2003 had rebounded to near the original abundance. Abundance of native redband trout Oncorhynchus mykiss decreased for age-1 and older fish but did not change significantly for age-0 fish. Despite high rates of removal, total annual survival rate for brook trout increased from 0.08 {+-} 0.02 in 1998 to 0.20 {+-} 0.04 in 1999 and 0.21 {+-} 0.04 in 2000. Growth of age-0 brook trout was significantly higher in 2000 (the year after their abundance was lowest) compared to other years, and growth of age-1 and age-2 brook trout was significantly lower following the initial removal years but recovered by 2003. Few other brook trout demographic parameters changed appreciably over the course of the project. Electrofishing removals required 210 person-days of effort. Despite experiencing slight changes in abundance, growth, and survival, brook trout in Pikes Fork appeared little affected by three years of intensive removal efforts, most likely because mortality within the population was high prior to initiation of the project such that the removal efforts merely replaced natural mortality with exploitation.
- Research Organization:
- Idaho Department of Fish and Game
- Sponsoring Organization:
- United States. Bonneville Power Administration.
- DOE Contract Number:
- 00022947
- OSTI ID:
- 903196
- Report Number(s):
- DOE/BP-00022947-1; R&D Project: 199800200; TRN: US200720%%208
- Country of Publication:
- United States
- Language:
- English
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