Scaphirhynchus sturgeons are species of concern throughout their ranges. To revitalize their populations, a thorough understanding of their habitat use during all life stages is critical. However, limited information exists about fine-scale habitat use during early life. To determine the feasibility of using radio telemetry to monitor habitat use in the field, I assessed growth and survival of age-0 sturgeon tagged with 0.2 g, non-functioning telemetry tags during an eight-week period in a controlled setting and then tested field performance in the Middle Mississippi River (MMR). Three treatments were evaluated: 1) control, 2) internally implanted tags, and 3) externally attached tags. Growth and survival varied across treatment groups (all comparisons P<0.05). Sturgeon with internally implanted tags grew slowly and had low survival, while sturgeon within the control group and those with external tags grew faster and had higher survival (~100%). A trial was conducted to determine swimming performance of each of the treatment groups, which resulted in no differences in critical swimming speed among the tag types. Based on these results, a field-based telemetry evaluation was performed to determine if it is feasible to monitor fine-scale habitat use. Four wild, age-0 Scaphirhynchus sturgeon were externally tagged with functioning radio transmitters in the MMR. After less than 24-h, the tagged fish were no longer detectable, likely due to environmental conditions (e.g., extreme depths and high conductivity). Thus, efforts should be directed to creating a small telemetry transmitter that uses technology (e.g., ultrasonic) that transmits well in deep rivers while maintaining a minimum tag weight and maximizing battery life. Fine scale habitat use of age-0 sturgeon may ultimately be able to be quantified in the MMR and other deep rivers in the future, if technologies improve.

Research developing artificial propagation, husbandry, and nutrition of sturgeon species has developed greatly since the collapse of the Caspian Sea fisheries in the 1980s. Sturgeon species are commercially prized for their unfertilized roe which is marketed as the delicacy, caviar. Sturgeon production units commonly utilize commercial salmonid feeds, which contain large proportions of fish meal (FM) and fish oil (FO). Concerns regarding economics and sustainability have put pressure on aquafeed manufactures to efficiently utilize FM and FO, and to incorporate alternative protein sources, such as soybean meal (SBM). Therefore, the present studies estimated the optimal protein:energy ratio of juvenile Pallid Sturgeon Scaphirhynchus albus and evaluated the effects of increasing SBM composition on growth, feed efficiency, body and liver composition, and intestinal morphology of juvenile Shovelnose Sturgeon Scaphirhynchus platorhynchus, two species of Scaphirhynchus sturgeon of regional commercial importance. Protein:energy ratios were investigated using casein and dextrose based, semi-purified diets. Results indicated that Scaphirhynchus sturgeon are able to perform similarly across a wide range of protein:energy ratios (79 - 147 mg protein kcal-1), so long as adequate dietary energy (3,800 kcal kg-1 gross energy) is provided and essential amino acids are not limiting. Soybean meal was evaluated utilizing practical, isocaloric, isolipidic, isoenergetic test diets, designed to replace FM with increasing SBM. Juvenile Scaphirhynchus sturgeon were found to perform similarly on diets with up to 50% of FM replaced with SBM (336 g kg-1 diet). Evaluation of liver composition revealed that juvenile Shovelnose Sturgeon store less glycogen and crude lipid than other fish species, although no dietary differences were observed. Histological evaluation of the distal intestine revealed indications of SBM induced enteritis, though no statistical differences in measures were detected between treatments. This research is the first to describe optimal dietary formulation for the culture of Scaphirhynchus sturgeon.

Rehabilitation of sturgeon populations requires an understanding of sturgeon autecology during all life stages, especially during early life when high mortality occurs. To begin to understand sturgeon early-life history I determined river of origin on a multi-basin scale (i.e., potential rivers of origin). I then determined habitat needs and early life demographics on a more localized scale (i.e., specific river). Trace elements differ between river reaches of the central US and may be used to determine origin of age-0 sturgeon. My trace element analyses suggested that age-0 sturgeon captured in the Middle Mississippi River, which extends from the confluence of the Missouri River downstream to the confluence of the Ohio River, drifted from as far upstream as the Gavins Point Dam on the Missouri River (> 1200 km), while other individuals originated locally in the Middle Mississippi River. On a more refined scale of habitats, I used trawling to identify habitat features used. Age-0 Scaphirhynchus sturgeon catch rates were highest around artificial structures (i.e., wing dikes) and island areas while main channel habitat comprised the lowest catch rates. Within these habitats, young sturgeon frequently occupied low velocities (i.e., ~0.1), moderate depths (i.e., 2 to 5 m), and sand substrate. Although determination of river of origin and specific habitats used are imperative for restoration, sturgeon populations are likely regulated by factors within habitats that affect early-life dynamics. Mean sturgeon growth rates ranged from 1.42-1.50 mm/d over the four years but did not differ among years. Individuals hatched over a 25 to 50-d period and peak hatch dates were between 10- 20 May during all years. Hatching coincided with optimum spawning temperatures of 17-20oC and a rise in river stage. Abundance was positively related to river stage, with longer durations of high water related increasing abundance. Mortality of age-0 sturgeon increased with the number of days where water temperature exceeded 28 oC. In the end this study has set benchmarks for understanding factors affecting the early-life ecology of Scaphirhynchus sturgeon.