Large rivers and their associated fish communities have undergone major alterations over the last century. Habitat fragmentation caused by both large and small dams, channelization to promote river transportation, and increased sedimentation from land use changes have all altered large river habitat and affected large-river fishes. Paddlefish are an archetypical large-river migrant that have experienced population declines as a result of overexploitation and large-river habitat alteration, so may serve as an indicator of habitat condition and connectivity. Paddlefish in the lower Osage River are believed to be a naturally self-sustaining population, yet may be vulnerable to interruptions in reproductive habitat and behavior caused by both a low-head dam and large hydroelectric facility. I developed a series of comprehensive research objectives to assess the critical components required for successful paddlefish reproduction in the lower Osage River and identify potential limiting factors. This information will help focus future management efforts to sustain natural reproduction of lithopelagophilic spawners in altered rivers.
Sex steroid information clearly identified gravid male and female paddlefish were present in the lower Osage River and provided a timeframe for physiological spawning readiness that occurred during a decrease in discharge release as opposed to a natural rise. Over all three study years, 41 of 86 transmittered paddlefish moved upstream over Osage River Lock and Dam #1, allowing for the successful development of a discharge and temperature model to predict upstream passage. Historical analysis of discharge and temperature conditions during the spawning period (1 March – 31 May) from 1939-2009 indicate that upstream passage likely occurs in most years (69% of those studied) but may be restricted in low water years that occurred as frequently as 31% of the years studied. Movement and habitat use downstream of Bagnell Dam were affected by large decreases (> 550 cms) in river discharge that were a result of Missouri River flood mitigation. No spent females or eggs were collected below Bagnell Dam, and only one larval paddlefish was collected, suggesting that natural reproduction was limited in the three years studied.
Despite the presence of gravid fish and access to upstream spawning habitat, we observed a strong weight of evidence that suggests paddlefish reproduction downstream of Bagnell Dam is most likely limited by altered discharges, resulting in disrupted spawning behavior or insufficient environmental conditions for spawning. Altered flows are suspected in the decline of many riverine species, yet the effects of these flows are still poorly understood. Successful management of regulated river systems for societal and biological benefits requires a more comprehensive understanding of specific species life history traits that are vulnerable to alterations in natural flow regimes.
|Advisor:||Galat, David L.|
|Commitee:||Jacobson, Robert, Millspaugh, Joshua, Rabeni, Charlie|
|School:||University of Missouri - Columbia|
|Department:||Fisheries and Wildlife|
|School Location:||United States -- Missouri|
|Source:||DAI-B 74/07(E), Dissertation Abstracts International|
|Subjects:||Wildlife Conservation, Conservation, Natural Resource Management, Water Resource Management|
|Keywords:||Osage River, Paddlefish, Reproductive success|
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