Canyon Ferry Reservoir risk assessment : the potential impacts of introduction of five non-native species

Abstract

Water chemistry Summertime turbidity in the Missouri River at Toston averaged 11.34 NTUs during the 1980's. The maximum turbidity recorded by the USGS was 60 NTUs on May 5, 1981. Typical late summer turbidity readings are 2-5 NTUs. Dissolved oxygen in the Missouri River at Toston rarely falls below 8.0 mg/1 and 90% saturation. The average minimum DO (based on 9 years of record) is 8.7 mg/1. The Ph of the Missouri River at Toston ranges from 7.6-8.7, with the average pH being 8.17. Summertime turbidity in Canyon Ferry Reservoir ranges from 4.0-100.0 {% trans.), with an average of 85.1, based on USEPA data collected in 1975. The pH levels in Canyon Ferry vary between 7.2 and 8.6, with the average being 8.1. Dissolved oxygen in Canyon Ferry, measured near the dam, ranges from 0.6 mg/1 to 11.6 mg/1, with an average of 7.6 mg/1. The percent saturation ranges from 5.3% to 100.0%. DO levels typically vary with depth, with surface waters being more oxygenated. Canyon Ferry is no exception, with lowest DO readings coming from a depth of 145 feet. The minimum DO at 27 feet (the approximate depth of the thermocline) was 4.0 mg/1, 39.2% saturation. During 1975, the minimum DO recorded in the surface water was 8.2 mg/1, 74.3% saturation. SMALLMOUTH BASS Review of life history of smallmouth bass The smallmouth bass is native to the eastern and central United States and Canada. The species has been introduced across the United States and much of the world. Smallmouth are not native to Montana. The first known introduction occurred in Horseshoe Lake (near Bigfork) in 1914 (Brown 1971). Smallmouth bass are currently distributed in a variety of coolwater habitats across Montana, including Noxon Reservoir in western Montana and the Tongue River in southeastern Montana. The smallmouth is divided into two subspecies, the northern smallmouth Micropterus d. dolomieui and the Neosho smallmouth Micropterus d. velox (Hubbs and Bailey 1940). It is the northern smallmouth that is reviewed in this report. Smallmouth bass are not currently known to exist in Canyon Ferry Reservoir. Age and growth. Smallmouth are generally a long lived species. Individuals to 15 years old have been reported (Scott and Crossraan 1973). Smallmouths seem to live longer in the Pacific northwest than the mid-west, with a 13 year old smallmouth reported from the Snake River, Washington (Bennett et al 1983).