Comparing White Bass Recruitment Sources and Population Demographics Among the Large Rivers of Illinois..

White Bass Morone chrysops is a native, migratory sportfish that is found throughout the central United States in large rivers and riverine impoundments. White Bass migrate into tributaries and riverine portions of reservoirs to spawn during spring. These spawning migrations concentrate fish and may make them more susceptible to angling pressure. White Bass have been well studied in reservoirs throughout the central United States since the early 2000’s when fisheries management practices shifted from population management to fish assemblage management. However, despite the increase in White Bass research in reservoirs, large river populations remain understudied. My thesis research used otolith microchemistry to assess the role of tributaries in supporting White Bass populations in the Ohio, Wabash, Middle Mississippi, Upper Mississippi and Illinois rivers and to compare population demographics (recruitment, growth, and mortality) among rivers. Water samples were collected from each of the five rivers and their tributaries and analyzed for strontium, barium, and calcium concentrations to calculate molar elemental ratios (Sr:Ca, Ba:Ca) and determine if differences in water Sr:Ca and Ba:Ca observed in prior studies persisted among large rivers and their tributaries. Otoliths from White Bass collected from locations where their movement was constrained (e.g., impoundments where dam passage is not possible) were analyzed to characterize relationships between water chemistry (Sr:Ca and Ba:Ca) and White Bass otolith chemistry. I then applied these regression relationships in conjunction with water chemistry data from each of the five large rivers and tributaries in the study area to estimate ranges of otolith Sr:Ca and Ba:Ca for White Bass in each of the rivers and tributaries. Otolith core Sr:Ca and Ba:Ca from White Bass collected from the Ohio, Wabash, Middle Mississippi, Upper Mississippi, and Illinois rivers were compared with predicted river-specific ranges of otolith Sr:Ca and Ba:Ca to identify natal river for each fish. All fish utilized for microchemistry were aged and used to create an age-at-length key from which vital rate parameters were calculated. Microchemistry results indicated that White Bass origin proportions differed among rivers. In rivers with more prominent differences in water Sr:Ca compared to their tributaries and upstream river segments, natal river assignments were more definitive and indicated that large river White Bass stocks are being strongly supplemented by tributaries and other upriver locations. In areas with small differences in water chemistry among potential natal rivers, origin designations were less definitive due to partially overlapping ranges of Sr:Ca and Ba:Ca among locations. A study using genetics to assess natal river fidelity in spawning White Bass should be conducted to better assess stocks and population structure in the large rivers. White Bass populations were dominated by age 0 fish (young of the year). Vital rate parameters were consistent with those of reservoir populations in the central United States, with riverine White Bass exhibiting fast growth, high mortality, and variable recruitment. My results indicated that a holistic approach to large river management should be considered when managing White Bass. Management regulations should reflect those in well studied reservoir populations based upon my findings, but future projects should expand upon our data and focus on population modeling of White Bass in these systems to better understand fishing and natural mortality, especially in areas of concentrated fish during the spawning season