Insight into environments that contribute recruits to adult fish stocks in riverine systems is vital for effective population management and conservation. Catfish are an important recreational species in the Mississippi River and are commercially harvested. However, contributions of main channel and tributary habitats to catfish recruitment in large rivers are unknown. Stable isotope and trace elemental signatures in otoliths are 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 principal natal environments of channel catfish Ictalurus punctatus and blue catfish I. furcatus in the middle Mississippi River (MMR) using otolith stable oxygen isotopic composition (δ 18 O) and strontium:calcium ratios (Sr:Ca). Catfishes were sampled during July-October 2013-2014 and lapilli otoliths were analyzed for δ 18 O and Sr:Ca. Water samples from the MMR and tributaries were collected seasonally from 2006-2014 to characterize sitespecific signatures. Persistent differences in water δ 18 O 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. Blue and channel catfish stocks in the MMR primarily recruited from the large rivers (Missouri and Mississippi) in our study area, with minimal contributions from smaller tributaries. Recruitment and year class strength investigations and efforts to enhance spawning and nursery habitats should be focused in the large rivers with less emphasis in smaller tributaries.

The effectiveness of pelvic fin ray microchemistry of muskellunge Esox masquinongy Mitchill to identify stocked individuals along with the potential to identify naturally reproduced fish were evaluated. Fish and water samples were obtained from one hatchery and seven lakes with natural differences in water Sr:Ca to determine whether locationspecific environmental signatures were recorded in sectioned muskellunge pelvic fin rays, including fish of known environmental history. Water and fin ray Sr:Ca were strongly correlated. Six lakes in Illinois possessed Sr:Ca signatures that were distinct from the hatchery where muskellunge were raised, resulting in pronounced shifts in Sr:Ca across sectioned fin rays of stocked fish. Hatchery and lake-specific Sr:Ca signatures were stable across years. Sixteen of 19 individual fish known to have been stocked based on PIT tags implanted at stocking were correctly identified as hatchery-origin fish using fin ray core Sr:Ca. Results also indicated that the hatchery Sr:Ca signal can be retained for at least seven years in fin rays of stocked fish. Fin ray microchemistry is a non-lethal approach for determining environmental history of muskellunge that could be used to assess movement patterns in lake and river systems and the degree to which muskellunge populations are supported by natural reproduction and stocking.

Mark–recapture studies require knowledge of tag retention rates specific to the tag types, fish species and size, and study duration. We determined the probability of tag loss for passive integrated transponder (PIT) tags implanted into dorsal musculature, T‐bar anchor tags attached to dorsal pterygiophores, and both tags in relation to years posttagging for double‐marked adult muskellunge Esox masquinongy over a 10‐year period. We also used PIT tags as a benchmark to assess the interactive effects of fish length at tagging, sex, and years posttagging on T‐bar anchor tag loss rates. Only five instances of PIT tag loss were identified; the calculated probability of a fish's losing its PIT tag was consistently less than 1.0% for up to 10 years posttagging. The probability of T‐bar anchor tag loss by muskellunge was related to both the number of years posttagging and the total length (TL) of the fish at tagging. The T‐bar anchor tag loss rate 1 year after tagging was 6.5%. Individuals of less than 750 mm TL at tagging had anchor tag loss rates less than 10% for up to 6 years after tagging. However, the proportion of fish losing T‐bar anchor tags steadily increased with increasing years posttagging (∼30% after 6 years) for larger muskellunge. Fish gender did not influence the probability of T‐bar anchor tag loss. Our results indicate that T‐bar anchor tags are best suited for short‐term applications (≤1 year) involving adult muskellunge. We recommend use of PIT tags for longer‐term tagging studies, particularly for muskellunge larger than 750 mm TL. Received November 19, 2010; accepted March 28, 2011

We investigated the environmental life history of widely distributed threatened and endangered sturgeons in large rivers of the central United States that experience different regulatory regimes and management priorities. Using microchemistry techniques, our goal was to assess how to improve species conservation by dampening the incongruity that often occurs between management and species’ ecological requirements, particularly at large spatial scales. Pallid sturgeon (Scaphirhynchus albus), shovelnose sturgeon (Scaphirhynchus platorynchus), and their hybrids were analyzed for 88Sr and 44Ca and related to a geographically relevant range of Sr:Ca values for the Missouri and Mississippi rivers to quantify large-scale environmental history. We found natal origin of 81% of all wild sturgeon collected was the lower Missouri River. Pallid and hybrid sturgeon used the middle and upper Mississippi rivers more frequently as they aged, whereas shovelnose sturgeon occupied the lower Missouri River more often throughout life. Our results highlight a mismatch between conservation boundaries and sturgeon river use. Managers should consider expanding current protections for pallid sturgeon to include the unprotected sections of the Mississippi River and that research and conservation actions consider the importance of Mississippi River habitats to Scaphirhynchus sturgeon throughout their life history. Our findings have implications for conserving wide-ranging riverine species at large spatial scales using the framework described here.

7Fatty acid (FA) analyses of fish tissues offer the potential to gain new knowledge of habitat-or 8 forage-specific energy inputs to fishes in river-floodplain ecosystems, although limited 9 information exists regarding among-habitat differences in FA biomarkers. The goal of this study 10 was to determine if differences in fish FA profiles among main channel and connected and 11 disconnected floodplain lakes exist in large river-floodplain systems. Bluegill Lepomis 12 macrochirus FA profiles were generated to assess differences among two reaches of the Illinois 13 River, USA and its connected and disconnected floodplain lakes and determine whether FA 14 signatures could be used to reclassify fish to their source habitat. Bluegill FA profiles differed 15 among habitats and river reaches, including differences in levels of individual FAs (e.g., 16 an indicator of allochthonous inputs, was higher among main channel fish) and FA groupings 17 (e.g., n-3:n-6 FA ratio, an indicator of aquatic primary productivity, was higher among 18 floodplain lake fish), which enabled >87.5% reclassification accuracy of fish to their source 19 environment. We demonstrated that bluegill FA profiles differed among reaches and laterally 20 among river channel and floodplain habitats, suggesting that FA profiles can be used to infer 21 recent habitat use and habitat-specific foraging of fishes in large river-floodplain ecosystems.