Effects of Elevated Temperature on Growth and Survival of Smallmouth Bass

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Abstract
The long‐term effects (November 1977‐October 1978) of elevated temperature on smallmouth bass, Micropterus dolomieui (age 0+ at stocking) were evaluated in outdoor channels located on the Tennessee River in Alabama, the southern limit of the native range of this species. Temperature treatments, with three channels per treatment, were at the ambient regime of the Tennessee River and 3, 6, and 9 C above ambient. Actual temperatures ranged from 1 to 30 C in the ambient channels and from 10 to 38 C in the +9 C channels. Under extreme summer conditions there was a 10% (by volume) refuge zone of 35 C water in the +9 C channels. Mean annual survival rates ranged from 84% in the +3 C regime to 92% in the +6 C regime; survival was 87% in both the ambient and +9 C treatments. Substantial growth occurred throughout the range 20 to 32 C. After 322 days, net biomasses of smallmouth bass in the four thermal regimes were not significantly different (range, 85–105 kg/hectare). Reproduction at age I occurred in all four regimes. The broad thermal requirements for growth and survival of smallmouth bass in this study were characteristic of warmwater species. To protect smallmouth bass from elevated temperature, the following numerical temperature criteria were derived: (1) a mean weekly average temperature of 32–33 C in the mixed water body would permit satisfactory growth; and (2) a maximum temperature of 35 C for short‐term exposure during the summer growth period would avoid potential lethal effects.

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