Date of Award
Master of Science
Sauger Sander canadensis is a native, migratory sportfish found in large rivers and riverine impoundments, primarily in the central United States. The migratory nature of this species requires access to un-impounded sections of river in order to complete reproduction and other aspects of life history. This requirement, along with their popularity as a gamefish, has resulted in widespread declines in sauger populations throughout their range due to habitat alteration and fragmentation combined with harvest pressure. The lower Ohio River supports a sauger population that is impeded by multiple high head dams and is heavily exploited by recreational anglers. However, despite high popularity among anglers, relatively little is known about large-scale movement patterns of sauger in the lower Ohio River. Additionally, the contribution that tributaries make to the population in terms of both recruitment and use by adults has not been assessed. I identified analysis of trace elements and stable isotopes in otoliths as techniques that could help quantify the role that tributary habitats play in the Ohio River sauger fishery. First, I collected water from the Ohio River and its larger tributaries in order to test the null hypothesis that there were no persistent differences in Sr:Ca, δ18O, and Ba:Ca among rivers. Water and otolith Sr:Ca, δ18O, and Ba:Ca from Sander spp. were then compared to test the null hypothesis that there is no significant relationship between Sr:Ca, δ18O, and Ba:Ca in the water and Sr:Ca, δ18O, and Ba:Ca measured in the otolith. I applied this relationship to Sr:Ca, δ18O, and Ba:Ca measured in the core of sauger otoliths collected in four navigational pools to test the null hypothesis that there were no differences in sauger recruitment sources among the four pools sampled on the lower Ohio River. Finally, I analyzed changes in Sr:Ca, δ18O, and Ba:Ca across otolith transects of the same fish to identify movements between the Ohio River and tributary habitats and test the null hypothesis that there were no differences in movement probability by age or assigned origin. Analysis of water chemistry indicated significant differences in Sr:Ca between the Ohio River and its tributaries, but not among tributaries. There were no significant differences in either water Ba:Ca or δ18O between the Ohio River and its tributaries. Comparison of water and otolith chemistry of known origin individuals yielded significant relationships for Sr:Ca and δ18O, but not Ba:Ca. As a result, only Sr:Ca was used for origin and movement assessments. Analysis of otolith core Sr:Ca indicated that tributaries are an important source of recruitment for the lower Ohio River sauger fishery. Otolith Sr:Ca consistent with reaches upriver of the study area were also prevalent in otolith core samples, indicating upriver sources are important for maintaining population density in the study area. Movement analysis indicated high probabilities of movement to upriver habitats in all pools, along with high movement probability to tributary habitats among fish collected in all pools. The data indicated that adult sauger in the lower Ohio river were recruited from multiple sources, and there is a high degree of exchange between the Ohio River and its tributaries. High recruitment and movement probability from upriver areas of the Ohio River indicated that the study area I identified does not encompass all of the river used by the population(s) sampled. Managers should focus on unification of regulations and sampling protocol to reflect this expansive range.
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