Funding Program: Fisheries: Aquatic and Endangered Resources
Statement of Problem: Sturgeon populations in the Missouri River, as elsewhere, appear to be in decline. This decline may be due in part to poor reproductive success. Evidence suggests that recruitment of pallid sturgeon to the adult population is limited or non-existent in the Missouri River. In contrast the closely-related shovelnose sturgeon is reproducing and recruitment is occurring in the Missouri River. While their spawning requirements and behavior may be similar in many respects the reasons behind the apparent difference in reproductive success of the two species are not easily discerned. Unfortunately the specifics of the reproductive physiology and spawning behavior of both species are poorly documented. Shovelnose and pallid sturgeon are assumed to spawn in current over coarse substrate in, or adjacent to, the main river channel. Migrations of shovelnose sturgeon into smaller streams, presumably for spawning, have been reported, but similar use of small tributaries by pallid sturgeon has not been recorded. The relationship of migration and spawning activity to hydrology has not been clearly described for these species though authors speculate that spawning runs are variable and somewhat dependent on river flow. Eggs of most sturgeon species are broadcast over the spawning area, become adhesive soon after release, attach to the substrate, and remain attached until hatch. The sequence of spawning behavior from migration and aggregation at the spawning site through egg deposition has not been documented for the shovelnose or pallid sturgeons. The timing, periodicity of spawning events, and the location of spawning in the water column and in relation to the substrate and overlying water conditions (i.e. turbidity, flow and velocity) are not known. Numerous factors may play a role in limiting spawning activity and reproductive success for sturgeon. These may include hydrology, temperature, impediments to migration, lack of spawning substrate, inadequate numbers of reproductive adults, hybridization with closely related sympatric species, predation and contaminants. Recent evidence suggests that some reproduction and recruitment may be occurring in the Lower Missouri River and in the Mississippi River. Larval pallid sturgeons were identified from samples collected in these locales in 1998, 1999 and 2000. Preliminary evidence also suggests that pallid sturgeon are successfully spawning below Fort Peck Dam in the Upper Missouri River, though recruitment apparently has not occurred there for decades. These findings suggest that physical and hydrological conditions consistent with successful pallid sturgeon spawning exist within or upstream of these areas. What is not known is the exact location of spawning or the relative suitability of these conditions for the sturgeon. This inability to identify specific conditions that contribute to successful reproduction limits the ability of biologists to evaluate or define conservation or engineering criteria for habitat rehabilitation efforts specific to the needs of pallid sturgeon. Increased understanding of the reproductive physiology of these sturgeon and the ability to predict or assess relative reproductive success will increase the ability of managers to tailor prescribed management actions to promote species recovery.
Objectives: The goal of this project is to improve fundamental understanding of reproductive ecology of the endangered pallid sturgeon, with the intent that improved understanding will inform river and species management decisions. The objectives of this study are to: 1. Determine the direction, magnitude, and habitat used during spawning migrations for shovelnose sturgeon and pallid sturgeon at two geographically and hydrologically distinct reaches of the lower Missouri River. 2. Describe the reproductive physiology of shovelnose sturgeon and pallid sturgeon prior to and after successful and unsuccessful spawning. 3. Identify and rank proximate cues necessary for successful spawning by Missouri River sturgeon. 4. Evaluate the effect that a semi-natural increase in flow has on the reproductive status, movements, and habitat use of pallid sturgeon shovelnose sturgeon. These objectives are strongly supportive of the Fisheries: Aquatic and Endangered Resources program goal (FAER): Quantify and describe functional relationships among aquatic species and habitats to provide information to conserve or restore aquatic community structure and function. In addition, the project supports the Terrestrial, Freshwater, and Marine Ecosystems Program goal (ECO): Devise restoration and adaptive management frameworks for impaired ecosystems. The task objectives are also supportive of USGS Science Strategy Themes. This research contributes directly to the USGS Ecosystems science theme as it provides fundamental understanding of the ecological requirements of an endangered large river umbreall species. The needs of this species are directly tied to the physical, chemical, and biological controls on river ecosystem structure and functions. This understanding is critical to informed river restoration and managment. The project also relates to the USGS Water Census theme as it addresses large rivers can be restored and managed to provide for a critically endangered speices as well as ecosystem services and human needs. Similarly, understanding of the fundamental ecology of a widely ranging large river species that requires 100's of river kilometers to complete its life history will be critical in mitigating effects of climate and/or associated land-use change (Climate Theme).