Habitat use, diet, and growth of hatchery-reared juvenile pallid sturgeon and indigenous shovelnose sturgeon in the Missouri River above Fort Peck Reservoir
Gerrity, Paul Christopher
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Natural recruitment of pallid sturgeon Scaphirhynchus albus has not been observed in the Missouri River above Fort Peck Reservoir, Montana, for at least 20 years. To augment the population, 732 hatchery-reared juvenile pallid sturgeon (HRJPS) were released as yearlings in 1998. Evaluation of these HRJPS was necessary to determine their performance in a natural lotic environment. Habitat variables were measured at 666 locations obtained from 29 HRJPS (mean length = 511 mm, 90% confidence interval + 17 mm; mean weight = 434 + 37 g) and 21 indigenous shovelnose sturgeon Scaphirhynchus platorynchus (mean length = 497 + 29 mm; mean weight = 566 + 97 g) implanted with radio transmitters in 2003 and 2004. Mean home range was similar between HRJPS and shovelnose sturgeon. Mean river kilometer was different between the two species, with shovelnose sturgeon using upstream areas of the study reach more than HRJPS. Hatchery-reared juvenile pallid sturgeon frequented lotic habitat created by receding reservoir water levels, indicating that Fort Peck Reservoir influences the amount of available habitat for HRJPS. No differences existed in mean depth, cross-section relative depth, longitudinal relative depth, column velocity, bottom velocity, and channel width between HRJPS and shovelnose sturgeon. Shovelnose sturgeon and HRJPS were primarily associated with fines and sand substrate. However, shovelnose sturgeon associated with gravel and cobble substrate more than HRJPS. Shovelnose sturgeon and HRJPS selected reaches without islands and avoided reaches with islands. Additionally, HRJPS and shovelnose sturgeon selected main channel habitat and avoided secondary channels. The diets of 50 HRJPS and 155 shovelnose sturgeon were examined. Shovelnose sturgeon primarily consumed Chironomidae (percent occurrence = 70%; percent composition by weight = 67%), whereas HRJPS primarily consumed fish (percent occurrence = 54%; percent composition by weight = 90%). There was no difference in relative growth rate between recaptured HRJPS (N = 18) and shovelnose sturgeon (N = 11) from May through October in 2003 and 2004. It appears that HRJPS in the Missouri River above Fort Peck Reservoir are capable of living in a natural lotic environment. Therefore, stocking HRJPS can be used to successfully augment wild pallid sturgeon populations.