Nest survival, nesting behavior, and bioenergetics of redbreast sunfish on the Tallapoosa River, Alabama
Type of DegreeThesis
Fisheries and Allied Aquacultures
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Adaptive management has been implemented in the Tallapoosa River, Alabama; one objective of the process is to determine how discharge and temperature affect redbreast sunfish reproductive success. Nesting male redbreast sunfish Lepomis auritus were monitored via snorkeling and video during 2006 and 2007 to estimate nest survival and quantify nesting behavior in a regulated reach of the Tallapoosa River (Alabama) below R.L. Harris Dam. In addition, males were collected during 2007 to determine if metabolic constraints were evident when caloric contents and bioenergetic models from the regulated Tallapoosa River and an unregulated tributary were compared. A priori hypotheses were constructed relative to how biological and environmental factors might affect nest survival. Nest survival estimates were determined in Program MARK and competing environmental and biological models were evaluated using Akaike’s information criterion (AIC). These data allowed for assessment of the functional response of daily survival rate of nests in relation to discharge. One year in the study was an extreme drought year (2007) allowing for nest survival estimates during an atypical water management year. Findings from this study support use of spawning windows (e.g., low flow releases from dam) to increase reproductive success for redbreast sunfish. Spawning window timing could be as early as mid-May, which is earlier than previously suggested. Spawning flows provided earlier in the year could enhance reproductive success for other fish species. Video of nesting behavior indicated that male redbreast sunfish primarily exhibited the defend and leave behavior during ‘baseflow’ (e.g., low flow conditions) observations. During higher discharge events (i.e., one-unit or turbine; ~ 200cms) spawning behaviors (e.g., milt and court) ceased and the defend behavior decreased; whereas, the leave and the clean behaviors increased. Behavior observations indicated that increased flow caused disruption of spawning and nest abandonment. Behavior during two-unit discharge events was only minimally observed because of drought conditions; however, data did indicate detrimental effects of two-unit discharge on nests (i.e., destruction). Bioenergetic modeling predicted decreased growth, and weight for males during the spawning season at both the regulated and unregulated sites. At the unregulated site consumption rates increased as temperature increased; when the thermal maximum was reached (33ºC), consumption decreased precipitously. In contrast, consumption rates at the regulated site were always positively related to temperature and did not decline when the thermal maxima was reached (28ºC) suggesting that thermal mitigation occurred from hypolimnetic releases from the dam. Reducing uncertainty regarding how biota respond to management actions is a goal of adaptive management and results from this study are applicable to flow management and its subsequent effects on nesting centrarchids.