Scientific Investigations Report 2009–5201
This report provides a synthesis of results obtained between 2005 and 2008 from the Comprehensive Sturgeon Research Program, an interagency collaboration between the U.S. Geological Survey, Nebraska Game and Parks Commission, U.S. Fish and Wildlife Service, and the U.S. Army Corps of Engineers’ Missouri River Recovery—Integrated Science Program. The goal of the Comprehensive Sturgeon Research Program is to improve fundamental understanding of reproductive ecology of the pallid sturgeon with the intent that improved understanding will inform river and species management decisions. Specific objectives include:
Management actions to increase reproductive success and survival of pallid sturgeon in the Lower Missouri River have been focused on flow regime, channel morphology, and propagation. Integration of 2005–08 Comprehensive Sturgeon Research Program research provides insight into linkages among flow regime, re-engineered channel morphology, and pallid sturgeon reproduction and survival.
The research approach of the Comprehensive Sturgeon Research Program integrates opportunistic field studies, field-based experiments, and controlled laboratory studies. The field study plan is designed to explore the role of flow regime and associated environmental cues using two complementary approaches. An upstream-downstream approach compares sturgeon reproductive behavior between an upstream section of the Lower Missouri River with highly altered flow regime to a downstream section that maintains much of its pre-regulation flow variability. The upstream section also has the potential for an experimental approach to compare reproductive behavior in years with pulsed flow modifications ("spring rises") to years without.
The reproductive cycle of the female sturgeon requires several years to progress through gonadal development, oocyte maturation, and spawning. Converging lines of evidence support the hypothesis that maturation and readiness to spawn in female sturgeon is cued many months before spawning. Information on reproductive readiness of shovelnose sturgeon indicates that sturgeon at different locations along the Lower Missouri River between St. Louis and Gavins Point Dam are all responding to the same early cue. Although not a perfect surrogate, the more abundant shovelnose sturgeon is morphologically, physiologically, and genetically similar to pallid sturgeon, and thereby provides a useful comparative model for the rarer species. Day length is the likely candidate to define a temporal spawning window. Within the spawning window, one or more additional, short-term, and specific cues may serve to signal ovulation and release of gametes. Of three potential spawning cues – water temperature, water discharge, and day of year – water temperature is the most likely proximate cue because of the fundamental physiological role temperature plays in sturgeon embryo development and survival, and the sensitivity of many fish hormones to temperature change. It also is possible that neither temperature nor discharge is cueing spawning; instead, reproductive behavior may result from the biological clock advancing an individual fish’s readiness to spawn day after day through the spawning period until the right moment, independent of local environmental conditions. Separation of the individual effects of discharge events, water temperature, and other possible factors, such as proximity to males, will require additional well-controlled field experiments (for example, pulsed flow modifications from Gavins Point Dam) combined with focused laboratory studies.
Telemetry derived movement and behavior data for shovelnose and pallid sturgeon indicate consistent patterns of upstream spawning migrations before spawning. Shovelnose sturgeon seem to be spawning at many locations, and spawning of the population occurs for an extended time (1 to 2 months). Movement patterns vary between sexes; female sturgeon generally move upstream and spawn at the apex of their migration, whereas males choose to migrate upstream to one or several spawning locations, or choose to remain relatively sedentary. Environmental changes such as temperature fluctuations or extreme flow events may slow or disrupt spawning migrations or inhibit spawning. Limited information indicates that patterns of migratory behavior of pallid sturgeon are similar to shovelnose sturgeon. Additional information is needed on pallid sturgeon to determine whether or not this species spawns during the same period, spatial extent, or range of environmental conditions.
Tracking gravid (reproductive) female shovelnose and pallid sturgeon from 2004–07 narrowed delineations of spawning habitat. In 2008, three separate pallid sturgeon spawning patches were resolved to areas of several hundreds of square meters by intensive tracking of three gravid female pallid sturgeon of hatchery origin. Each of the three geographically separated patches was on the outside of a revetted bend, with deep, relatively fast, and turbulent flow. Because this is a common habitat on the Lower Missouri River, these results support the hypothesis that spawning habitat availability is not a limiting factor in pallid sturgeon reproduction in the Lower Missouri River.
Spawning at many locations scattered over a large spatial extent and over an extended period may decrease the likelihood of sturgeon finding suitable mates, and thereby increase the potential for reproductive failure or hybridization. Widely distributed spawning also may reduce the effectiveness of short-duration flow modifications or discrete habitat restoration projects in species recovery.
This study was the first to document spawning of pallid sturgeon in the Lower Missouri River. Two wild pallid females were tracked to apices of their migration in 2007; when subsequently recaptured, they were determined to have spawned completely. We have also documented spawning of hatchery-propagated pallid sturgeon in the Lower Missouri River, indicating that hatchery progeny are surviving, growing, reaching reproductive maturity, and are now potentially contributing a new generation of fish. Although this is a significant measure of success for the species recovery program, uncertainties remain about whether or not spawning results in successful recruitment to the population.
Our results support the hypothesis that spawning location, water velocities, growth rates, and drift dynamics determine the spatial and temporal distribution of pallid and shovelnose sturgeon larvae and juveniles in the Missouri River. Calculations based on mean reach velocities indicate that drifting larvae that hatch along much of the Lower Missouri River have the potential to drift into the Mississippi River. Habitat restoration activities that facilitate spawning further upstream, increase river length (by restoring cut-off channels), or decrease drift distance (for example, by decreasing mean velocities or increasing channel width and habitat complexity) may assist in recruiting Scaphirhynchus sturgeon in the Missouri River. Moreover, understanding of typical drift distances of larval Scaphirhynchus sturgeon may provide useful guidance for placement of channel-restoration projects intended to provide rearing habitat. Our drift calculations indicate that with present (2009) reach-averaged velocities, rearing habitat would be most beneficial to pallid sturgeon downstream from river mile 378, near the Kansas River confluence. Whether or not such habitat is limiting for survival of larval sturgeon has not yet been determined. The potential for Missouri River larvae to drift into the Mississippi River indicates a need to understand habitat functions and fate of larvae far downstream from spawning sites and to integrate understanding of sturgeon life history for a geographic area that includes the Missouri and Mississippi Rivers.
Assessments of habitat dynamics indicate that most habitat categories change little in area with changes in discharge that would occur with proposed pulse-flow modifications. In contrast, morphodynamic assessments indicated that flows similar in magnitude to pulse-flow modifications are capable of transporting sediment and altering habitat substrate at the local scale. Whether or not pulsed flows can "condition" spawning substrate at the right time, in the right place, and in patches of the right size for successful pallid sturgeon spawning remain unknown. Improved understanding of where and when sturgeon spawn will be necessary to address these questions. Our assessments of habitat availability and use indicate that migrating adult sturgeon use specific areas within available habitats, characterized by high variability of depth and velocity, and low ratios of velocity to depth. Selection of these habitats provides insight into combinations of flow and channel form that support the energetic requirements of migrating fish. Diminished areas of these habitats in the upper channelized section of the river may indicate that habitat is more limiting in this part of the river compared to upstream and downstream sections. Lack of suitable migration habitat in the upper channelized section may indicate a reproductive bottleneck if fish are energetically limited in their migration to spawning areas or in finding mates.
Posted September 21, 2009
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DeLonay, A.J., Jacobson, R.B., Papoulias, D.M., Simpkins, D.G., Wildhaber, M.L., Reuter, J.M., Bonnot, T.W., Chojnacki, K.A., Korschgen, C.E., Mestl, G.E. , and Mac, M.J., 2009, Ecological requirements for pallid sturgeon reproduction and recruitment in the Lower Missouri River: A research synthesis 2005–08: U.S. Geological Survey Scientific Investigations Report 2009–5201, 59 p.
Missouri River Background
Summary and Discussion