Population prediction and viability model for pallid sturgeon (Scaphirhynchus albus , Forbes and Richardson, ) in the lower Missouri River

Abstract

Summary Long‐term population trends of pallid sturgeon Scaphirhynchus albus in the lower Missouri River were evaluated via a discrete and stochastic age‐structure population viability model. The intent of this model was to (i) estimate the local pallid sturgeon population size, (ii) quantify the contribution of hatchery‐reared fish to the overall population, (iii) predict the level of natural production needed to create a self‐sustaining population, and (iv) determine the parameters that produce the largest model sensitivity. The model estimated that the wild, adult population size was approximately 6000 fish that remained in the lower Missouri River in 2012 compared to approximately 42 000 hatchery‐reared pallid sturgeon. Under the assumption of no natural recruitment, the population size will continue to decline at approximately 8% annually, with an annual egg to age‐1 survival rate of 0.00011 predicted to maintain a stable population. The model was most sensitive to survival rates of fish ≥ age‐1 and less sensitive to age‐0 survival rates and fecundity. Decreasing or increasing the female spawning interval by 1 year had minimal effect on the overall population trajectory. Recovery management planning for a species such as pallid sturgeon, which is slow‐growing, late‐maturing, and has intermittent spawning would require several years to access recovery potential and management decisions. Barring any unforeseen natural catastrophe, the pallid sturgeon population in the lower Missouri River is not in immediate danger of local extirpation; however, the population appears to be far from viable and self‐sustaining.

Flood Effects Provide Evidence of an Alternate Stable State from Dam Management on the Upper Missouri River

“…It has also been documented that the bank attachment allows predators from the floodplain to access the habitat, which would not be possible if the islands were mid‐channel and separated by flow (Catlin et al ., ; Anteau et al ., ; Lott et al ., ). Fish populations have also been impacted by changes in geomorphology; research has directly linked dam‐induced changes to the decline of the Pallid Sturgeon as a result of loss in spawning habitat, reduction in food supply, altered temperature and flow of water and reduced sediment loads and turbidity (Keenlyne and Evenson, , Pegg et al ., ; Steffenson et al ., ). Declines in the Fort Peck reach's subpopulation have been linked to the large reservoirs, which create zones with reduced dissolved oxygen resulting in increased larval mortality (Guy et al ., ).…”

“…The Least Tern and Piping Plover populations, which utilize sandbars for breeding season habitat, have declined as dams have diminished sediment loads causing a loss of islands (Lott et al ., ). The decline of the Pallid Sturgeon, once abundant along the Missouri, has been attributed to the loss and modification of its habitat by human activities, which have blocked fish migration, destroyed spawning areas, reduced food sources, altered temperature and flow of water and reduced sediment loads and turbidity (Keenlyne and Evenson, , Pegg et al ., ; Steffenson et al ., ). Subpopulation declines in the Fort Peck reach have been linked to the large reservoir, which interrupt downstream drift of the larvae and create zones of reduced dissolved oxygen resulting in larval mortality (Guy et al ., ).…”

Using the robust design framework and relative abundance to predict the population size of pallid sturgeon Scaphirhynchus albus in the lower Missouri River

“…Steffensen et al . () used the population estimate from Steffensen et al . () to extrapolate across the entire lower Missouri River.…”

Assessment of pallid sturgeon relative condition in the upper channelized Missouri River

“…Finally, overall pallid sturgeon condition was correlated against several hypothesized factors that may contribute to the variation in pallid sturgeon condition. The hypothesized, independent variables that were acquired and tested included (1) the mean annual discharge of the Missouri River at the Omaha (USGS 06610000) and Nebraska City gages (USGS 06807000), (2) intraspecific competition which used the Steffensen et al (2013b) population viability model to estimate the current pallid sturgeon population in the lower Missouri River, (3) interspecific competition which used the standardized, long-term electrofishing catch per unit effort (CPUE) for flathead catfish Pylodictis olivaris (Porter et al 2011 and M. Pegg, University of Nebraska-Lincoln, Pers. Comm.…”