Habitat Use of Juvenile Pallid Sturgeon and Shovelnose Sturgeon with Implications for Water‐Level Management in a Downstream Reservoir

Abstract

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, age-1 hatchery-reared juvenile pallid sturgeon were released in 1998. The objective of this study was to evaluate the habitat use of these fish and compare it with that of indigenous shovelnose sturgeon S. platorynchus. Twentynine juvenile pallid sturgeon and 21 indigenous shovelnose sturgeon were implanted with radio transmitters in 2003 and 2004. The two species showed no differences in habitat use in terms of mean depth, cross-sectional relative depth, longitudinal relative depth, column velocity, bottom velocity, and channel width. However, there were seasonal differences within both species for cross-sectional relative depth, column velocity, and channel width. Both shovelnose sturgeon and juvenile pallid sturgeon were primarily associated with silt and sand substrate. However, shovelnose sturgeon were associated with gravel and cobble substrate more than juvenile pallid sturgeon. Shovelnose sturgeon and juvenile pallid sturgeon both selected reaches without islands and avoided reaches with islands; the two species also selected main-channel habitat and avoided secondary channels. Mean home range was similar between juvenile pallid sturgeon (15 km; 90% confidence interval, 65.0 km) and shovelnose sturgeon (16.5 km; 64.7 km). Spatial distribution differed between the two species, with shovelnose sturgeon using upstream areas more often than juvenile pallid sturgeon. Twentyeight percent of juvenile pallid sturgeon frequented 60 km of lotic habitat that would be inundated by Fort Peck Reservoir at maximum pool. Stocking juvenile pallid sturgeon can successfully augment the wild pallid sturgeon population in the Missouri River above Fort Peck Reservoir, which is crucial to the long-term recovery of the species. However, water-level management in downstream reservoirs such as Fort Peck can influence the amount of habitat available for pallid sturgeon.

Resource selection by juvenile pallid sturgeonScaphirhynchus albus(Forbes and Richardson, 1905) in the channelized Missouri River, Nebraska, USA

“…() and Gerrity et al. () contrast habitat selection observed in this study; these differences suggest that juvenile pallid sturgeon are selecting best available habitat in the highly‐modified NMR although habitat types not present might be more suitable for promoting fitness. These differences also demonstrate the ability of juvenile pallid sturgeon to adapt to their environment.…”

“…Similarly, Gerrity et al. () noted that hatchery‐reared juvenile pallid sturgeon avoided off‐channel habitat in the Missouri River, Montana, USA, possibly because main channel habitats in the unchannelized river provided suitable habitat. Findings from both Snook et al.…”

Seasonal resource selection by blue suckers Cycleptus elongatus

“…Although seasonal habitat selection has been observed for several large‐river fish species (Zigler et al , 2003; Daugherty & Sutton, 2005; Gerrity et al , 2008), habitat requirements of many lotic fishes are not fully understood. Understanding this for large‐river fishes, especially imperilled species, will probably become increasingly important as aquatic system manipulations continue worldwide (Jelks et al , 2008).…”

Considering a species-loss domino-effect before endangered species legislation and protected area implementation

“…For the shovelnose-pallid sturgeon system, protection of shovelnose sturgeon may actually jeopardize the recovery of the pallid sturgeon-the opposite of the intended effect. Given their morphological similarity during early life, the two species may occupy similar niches or habitat (Gerrity et al 2008). Both species are thought to be invertivores as juveniles (ages 0-1) and thus may occupy similar habitats and consume similar food resources.…”