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The Development and Application of a Larval Pallid Sturgeon (Scaphirhynchus albus) Bioenergetics Model
Pallid Sturgeon Scaphirhynchus albus are native fish of the Missouri and lower Mississippi River basins and currently listed as an endangered species under the Federal Endangered Species Act. As a result of anthropogenic alterations within the Missouri River, including dredging, channelization, and construction of large reservoirs, Pallid Sturgeon reproduction is reduced or eliminated throughout the species range. Due to a lack of wild progeny, little is known of the larval Pallid Sturgeon and their habitat or environmental requirements. To increase knowledge on the larval Pallid Sturgeon’s physiological requirements for growth and survival, the objective of this study was to develop a bioenergetics model to determine optimal temperature for growth of young-ofyear Pallid Sturgeon and apply the model in a realistic simulation. To develop this model, I estimated metabolic demands and growth over a range of temperatures and sizes. Pallid Sturgeon (0.005 to 9.094 g) were subjected to a range of temperatures commonly found in the Missouri River (13 – 28°C). Exogenously feeding larval fish were fed chironomids at ad libitum rations three times daily over multiple days to determine maximum consumption and estimate growth. I used static respirometry to quantify the routine respiration rate of larval Pallid Sturgeon. Using this model, I estimated daily consumption (g/d) for a 1-g fish, ranging from 0.15 g/d at 13°C to 0.31 g/d at 24°C. I also estimated daily oxygen consumption (M, g O2/d) of a 1-g larval fish to range from 0.006 g O2/d at 13°C to 0.016 g O2/d at 28°C. The independent observations of daily consumption (g/d) fit the bioenergetic estimates of daily consumption (F2,35= 477, r2 = 0.96, P-Value < 0.001). I then used the bioenergetics model to simulate and compare growth potential between historical and contemporary water temperatures in two reaches of the Missouri River. For these simulations I looked at the difference in end weights in a Spawning Scenario, estimating larval growth across a growing season starting from hatch, and a Stocking Scenario, estimating larval growth across a growing season starting with larvae stocked on July 1st. Temperature data were collected from Booneville, Missouri, hereafter referred to as the lower Missouri River (LMR) and Bismarck, North Dakota, hereafter referred to as the Garrison Reach (GR). In the Spawning Scenario, with feeding rate set at 50 % maximum consumption, I found a 1.0 % increase and a 65.2 % decrease in end weights from the Pre-Dam to Post-Dam time periods in the LMR and GR, respectively. This simulation resulted in 4.1 % fewer days and 5.0 % fewer cumulative thermal units (CTU) in the LMR and 38.3 % fewer days and 53.6 % fewer CTU in the GR. In the Stocking Scenario, with a feeding rate set at 50% maximum consumption, I found a 7.5 % increase and 37.4 % decrease in end weights from the Pre-Dam to Post-Dam time periods in the LMR and GR, respectively. This simulation resulted in 1.1 % fewer CTU in the LMR and 24.1 % fewer CTU in the GR. Our findings suggest that the cold waters of the deep-release storage reservoirs could negatively impact the growth potential of larval Pallid Sturgeon within at least 110 km downstream proximity; however, at approximately 960 km below impoundment, the negative impacts from temperature are no longer detected. With six major dams along the main stem upper Missouri River, thermal depression may be a leading cause of recruitment failure in Pallid Sturgeon and I recommend additional research into the geographic range of cold water impacts on larval Pallid Sturgeon growth and survival.