Effects of hydrologic variation and water temperatures on early growth and survival of selected age-0 fishes in the Tallapoosa River, Alabama.

Abstract

Altered flow regimes resulting from the construction of hydropower dams can negatively affect aquatic organisms in a variety of ways. The effects of flow and temperature variation on early growth, survival, and hatching success were examined at regulated and unregulated sites in the Tallapoosa River, Alabama. Previous research on the Tallapoosa River has focused on community responses to altered flow regimes in adult populations. However, very little information exists on specific impacts and responses of fish in early life stages. The objectives of this study were to: 1) estimate daily incremental growth rate and back calculate hatch dates of age-0 Redbreast Sunfish Lepomis auritus 2) examine relations between average daily incremental growth rate and age, hydrology, temperature, site type (regulated or unregulated) and year; and 3) examine relations between hatch success and frequency and hydrology at regulated and unregulated sites in the Tallapoosa River; and 4) quantify the effects of fluctuating water flow and decreased water temperatures on early daily growth and survival of age-0 Channel Catfish Ictalurus punctatus and Alabama Bass Micropterus henshalli through a series of laboratory experiments. Effects of hydrology on early growth and hatching success of age-0 Redbreast Sunfish were examined at regulated and unregulated sites in the Tallapoosa River. Average daily incremental growth techniques were used to back calculate daily incremental growth and estimate hatch dates and predict hatch success. Early growth was impacted by site type and year

and hatching success was impacted by flow and temperature variables. Overall daily growth rate and incremental growth rate varied among years and was higher at regulated sites than unregulated sites. Model comparison indicated that the best overall model that described average daily incremental growth included: site type, age, year, the number of hours discharge was greater than 220 cms (FLOW1), the number of cumulative degree days, and the day of year that the growth increment occurred as independent variables. However, overall model fit was poor. Additional models, with flow and temperature variables excluded, were evaluated and compared with Akaike’s Information Criterion (AICc). The best overall model included site type, age, and year as independent variables and explained 33% of the variation in average daily incremental growth rate. These results suggest flow and temperature regimes are important predictors of hatching success, and that early growth is impacted more by site type and year. The number of reversals, number of hours discharge was between 0 – 60 cms, number of cumulative degree days, and year were predictors of hatch success. Hatch frequency was higher and occurred earlier in unregulated sites compared to later hatching in regulated sections. Managing instream flows to provide periods of low-stable flows and temperatures should positively affect growth rates, increase hatching success, and increase subsequent recruitment of redbreast sunfish downstream of R. L. Harris Dam. In experimental studies, results suggest that strong fluctuating flows and decreased water temperatures negatively affected daily growth rates and survival of age 0 Channel Catfish and Alabama Bass. Mortality was highest in treatments with decreased water temperatures. Daily growth rates were lower in treatments with decreased water temperatures. Older fish had higher daily growth rates and decreased mortality, and were not as susceptible to the negative effects of treatments. These data also suggest that growth and survival may be impacted more by fluctuations in temperature (Δ10 °C) versus flow variation. However, treatments with high flow also exhibited decreased growth and some mortality. Management efforts should consider both flow and temperatures regimes together in an effort to increase growth rates, survival, and increase subsequent recruitment of fish in regulated rivers. Managers are encouraged to use models and conclusions described in this dissertation as part of their decision-making and objective-setting processes, in an adaptive management framework, to manage flow regimes in regulated rivers. Specifically, we recommend 1) thermal modification technologies at hydropeaking dams be investigated for suitability and feasibility; 2) instream flow management include thermal regimes and variation as part of management objectives; and 3) spawning and rearing windows continue to be employed, with evaluations on an annual basis, as a management tool to increase recruitment of fish in regulated rivers. The models and variables herein described should be continually improved upon and updated as more information is learned and uncertainty reduced. Additional data collection and experimentation is necessary to monitor fish populations and their response to the flow and temperature regimes in regulated rivers.