Date of this Version
Rugg, M.L. 2013. Shovelnose sturgeon reproductive ecology in the Lower Platte River, Nebraska. Masters Thesis. University of Nebraska, Lincoln, Nebraska.
Biodiversity and abundance of freshwater organisms are experiencing drastic declines. Anthropogenic disturbances have altered the natural flow regimes of large rivers, and have led to declines in species that rely on elements of natural flow. Similarly, shovelnose sturgeon distribution has diminished in the last 100 years due to habitat alteration, overharvest, and water contamination. To fully understand the status and viability of a fish population, basic knowledge of a fish’s reproductive strategy is needed. Aspects of reproduction that should be understood to manage for sustainability include maturation, fecundity, and spawning dynamics. There is currently little published information on age/size of maturity and fecundity of shovelnose sturgeon, and no such work on sturgeon in the Platte River. Therefore, the objective of this research was to characterize aspects of the reproductive ecology of shovelnose sturgeon in the Lower Platte River. Additionally, I assessed the validity of age estimates from fin ray cross sections to address age-related questions of reproduction using marginal increment analysis. Male shovelnose sturgeon reach maturity at a minimum fork length of 453 mm, and age-6. Males appear to spawn every three years once they have reached maturity. Female shovelnose sturgeon reached maturity at a minimum fork length of 449 mm, and age-6. Females appear to spawn every four to six years once they have reached maturity. Total fecundity of females was 16,098 + 1103 (mean+ SE), and egg size was 2.401 + 0.051mm (mean + SE). Fecundity of female shovelnose sturgeon was positively correlated with fish size (length and weight) and age, with weight being the best predictor of fecundity. The proportion of shovelnose sturgeon in spawning condition peaked during spring (March-May) and fall (September-October), indicating that shovelnose sturgeon spawning activities in the Lower Platte River may be bimodal. Monthly marginal increment measurements from fin rays did not display a yearly sinusoidal curve that would be expected if translucent and opaque bands represented 1 year of somatic growth. Therefore, the current method and interpretation of fish age from fin rays is likely leading to inaccurate age estimates.
Advisor: Mark Pegg