Date of Award
Master of Science
Insight into environments and habitats that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfishes are important recreational species in the Mississippi River and are commercially harvested. However, contributions from main channel and tributary habitats to catfish recruitment in large rivers such as the middle Mississippi River (between St. Louis, MO and Cairo, IL) are unknown. Stable isotope and trace elemental signatures in otoliths have been useful for determining environmental history of fishes in a variety of aquatic systems, including the Mississippi River. The objectives of this study were to identify the principle natal environments of channel catfish Ictalurus punctatus and blue catfish I. furcatus in the middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ18O) and strontium:calcium ratios (Sr:Ca). Catfish were sampled in the MMR during July-October 2013 and 2014 and lapilli otoliths were analyzed for δ18O and Sr:Ca. Water samples from the MMR and tributaries were collected seasonally from 2006-2014 to characterize site-specific signatures. Persistent differences in water δ18O and Sr:Ca among the MMR and tributaries (including the upper Mississippi, Illinois, and Missouri rivers as well as smaller tributaries) were evident, enabling identification of natal environment for individual fish. Results indicated that blue and channel catfish stocks in the MMR primarily recruited from the largest rivers (Missouri and Mississippi rivers) in our study area and received minimal influence from smaller tributaries. Recruitment and year class strength investigations and efforts aimed at enhancing blue and channel catfish spawning and nursery habitats should be focused in the large rivers with less emphasis in the smaller tributaries.
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