Statement of Problem: The pallid sturgeon (
Scaphirhynchus albus) was listed as federally endangered in 1990 and is currently the focus of intense recovery efforts. The pallid sturgeon and the closely related, but more common shovelnose sturgeon (
Scaphirhynchus platorynchus) are endemic to the Mississippi and Missouri Rivers and lower sections of their larger tributaries from Montana to the Gulf of Mexico. Despite a described range exceeding 3,500 miles of river, no part is without substantial alteration from habitat modification or alteration of flow and temperature regimes (U.S. Fish and Wildlife Service, 1993). Despite evidence of pallid sturgeon spawning (DeLonay and others, 2014; DeLonay and others, 2015a; DeLonay and others, 2015b), evidence from various monitoring efforts suggests that young-of-the-year survival and recruitment to the adult population is limited or nonexistent throughout most of the Missouri River (U.S. Fish and Wildlife Service, 2000). In contrast, shovelnose sturgeon are successfully recruiting in the Missouri River (Moos, 1978; Keenlyne, 1997). Recovery of the imperiled pallid sturgeon is likely dependent on successful spawning and survival through early life history stages. Early life stages are typically highly susceptible to mortality and may represent a potential bottleneck to species recovery. Biotic and abiotic factors operating during the free-embryo life stage (hatch to exogenous feeding) may limit survival and population growth (Dettlaff and others, 1993). As is typical for most sturgeon, little information is available for the free-embryo life stage. Water temperature is considered to be the most important environmental factor influencing the development this early life stage. Understanding the environmental requirements , specifically temperature and how it effects development, growth and survival during the early life history stage, is essential for successful pallid sturgeon recovery. Developing embryos and free embryos may experience a wide range of temperature variation in the Missouri River and its tributaries. Limited information exists on the effect of water temperature on the early development of Scaphirhynchus sturgeon. Therefore, it is imperative to describe the effect of temperature on developing embryos and free embryos. Understanding the environmental effects of temperature on developmental trajectories will allow the correlation of behavioral endpoints with developmental stages and provide the basis for refining critical dispersal models to guide management actions.
Objectives: Characterize growth and development of pallid sturgeon free embryos incubated and reared at 3 to 6 constant temperatures. Identify critical developmental milestones and map the developmental trajectory of free embryos under different environmental conditions.