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.

Fishes introduced outside of their native distributions have the potential to negatively affect their recipient ecosystems. Since their illegal introduction into the Green River, Wyoming, in the 1990s, Burbot Lota lota have been sampled in lotic and lentic environments throughout the Green River system, where they pose a threat to native fishes and valuable sport fisheries. In response to this invasion, managers of the Green River have begun to explore the efficacy of a suppression effort targeting Burbot. We sought to the describe population dynamics of Burbot in the lentic portions (i.e., reservoirs) of the Green River system in comparison with Burbot population dynamics in lotic areas of the Green River. We also sought to evaluate potential management scenarios for a suppression program. Burbot for this study were collected from Fontenelle and Flaming Gorge reservoirs in October and November 2016. Growth rates of Burbot in the lentic portion of the system were higher than those for fish in the Green River. Total annual mortality rates (A) of Burbot were approximately 10% lower in the reservoirs (33%) than in the Green River. Additionally, lentic Burbot matured earlier than lotic Burbot. An age‐structured population model indicated that Burbot populations were growing rapidly (population growth rate λ = 1.18) in the study reservoirs. Annual exploitation (μ) of juvenile Burbot would need to reach 7%; the μ of mature Burbot would need to increase to 33% or greater (A ≥ 57%) to effectively suppress Burbot in this system. Sensitivity analysis suggested that mortality of age‐1 and age‐2 Burbot had the greatest influence on λ. However, due to difficulties in collecting juvenile Burbot in the Green River system, focusing removal efforts on mature individuals may be the most realistic option for suppressing Burbot populations in this system.

Burbot Lota lota were illegally introduced to the Green River, Wyoming, in the mid-1990s and pose a threat to recreational fisheries and native fish conservation. Although much is known about Burbot population dynamics, little is known about their movement patterns. Our objectives were to describe the movement dynamics of Burbot in the upper Green River system to provide information on the ecology of Burbot and insight on possible management actions. In total, 875 Burbot were tagged with PIT tags in the upper Green River and Fontenelle Reservoir; their movements were tracked from August 2016 to March 2018. Additionally, 22 Burbot were tagged with radio transmitters in Fontenelle Reservoir in November 2017, and 13 Burbot were tagged with radio transmitters in the upper Green River in November 2018. Of these fish, 11 Burbot tagged in Fontenelle Reservoir and all river-tagged Burbot were tracked as they migrated into the Green River and associated tributaries during the spawning season. Upstream and downstream movements of Burbot tagged with PIT tags in Fontenelle Reservoir and the upper Green River peaked during December-January and were synchronized with river temperatures reaching 0°C. Of the total number of PIT-tagged Burbot, 10-15% of those tagged in Fontenelle Reservoir were detected in the Green River during the spawning season and 15% of those tagged in the Green River were detected moving downstream toward Fontenelle Reservoir during the spawning period. Movements of radiotelemetered Burbot were synchronized with river ice-up in mid-December. Maximum upstream distance traveled by adfluvial Burbot was 5.8 km. Fluvial Burbot primarily migrated downstream during the spawning period, and maximum downstream distance traveled was 17.7 km. Detection data suggest that both fluvial and adfluvial Burbot occupy the same reaches