Date of Award
Master of Science
Sauger Sander canadensis are a native top level predator and popular sport fish. They are native to large, turbid midwestern rivers and are a highly migratory species that relies on unrestricted access to specific habitats throughout their lifespan. Due to specific habitat requirements and popularity as a sport fish, Sauger are in decline across much of their range. Habitat alterations including barriers, channelization and sedimentation, as well as overharvest, have resulted in population declines. Sauger are often subject to relatively high levels of exploitation because of their tendency to concentrate below dams during migrations, which leaves them vulnerable to anglers. The lower Kaskaskia River below Carlyle Lake dam and the lower Ohio River contain important Sauger sport fisheries despite the presence of multiple dams on both rivers and the potential for high levels of exploitation. However, effects of current and potential harvest regulations on Sauger stocks in the Kaskaskia and Ohio rivers have not been assessed. From previous annual monitoring surveys, Sauger in the Ohio and Kaskaskia rivers have very different size and age structures and are managed under different regulations. Additionally, the Kaskaskia River and its largest reservoir (Carlyle Lake) are stocked annually with Sauger, but the contributions of stocked Sauger and immigrants from the Mississippi River to the Kaskaskia River Sauger stock are unknown. I first sought to assess population demographics of Sauger in the Kaskaskia and Ohio Rivers to gain a baseline understanding of both populations and then used these data to evaluate harvest regulations on each river. This objective tested the null hypothesis that no differences in recruitment indices, growth rates and mortality rates exist between Sauger populations within each river. Sauger in the Kaskaskia River are currently managed under a 356-mm minimum length limit and a 6-fish daily bag limit. Prior to 2018, the lower Ohio River was managed under no minimum length limit and a 10-fish daily bag limit. To assess the contribution of Sauger from different environments to the Kaskaskia River stock, I used otolith microchemistry to infer recruitment sources of fish and assess movement of fish between the Kaskaskia and middle Mississippi rivers. This objective tested the null hypothesis that no difference existed in the contribution of different rivers to the Kaskaskia River sauger population. The Ohio River Sauger population had a small age and size structure relative to the Kaskaskia River. Sauger from each river exhibited fast growth rates and high annual mortality. Population modeling indicated that the current 356-mm minimum size limit for Sauger in the Kaskaskia River is sufficient at preventing growth overfishing and is likely resulting in the larger size structure compared to the Ohio River. Sauger were likely experiencing growth and recruitment overfishing in the Ohio River under no minimum length limit and will likely benefit from the 356-mm minimum length limit implemented in 2018. Otolith microchemistry revealed that Sauger from the Mississippi River represented a small contribution to the Kaskaskia River Sauger stock; however, some fish showed evidence of moving between the Kaskaskia and Mississippi rivers. Similar water chemistry between the hatchery and Carlyle Lake prevented the identification of hatchery origin Sauger. Because the Sauger stock in the Kaskaskia River appears to be primarily supported by stocking of fish into Carlyle Lake or natural reproduction within the Kaskaskia River, fisheries managers should focus on quantifying the contribution of hatchery fish to the Kaskaskia River stock.
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