Bighead and silver carp are well established in the Mississippi River basin following their accidental introduction in the 1980s. Referred to collectively as Asian carp, these species are filter feeders consuming phytoplankton and zooplankton. We examined diet overlap and electivity of Asian carp and three native filter feeding fishes, bigmouth buffalo, gizzard shad, and paddlefish, in backwater lakes of the Illinois and Mississippi rivers. Rotifers, Keratella spp., Brachionus spp., and Trichocerca spp., were the most common prey items consumed by Asian carp and gizzard shad, whereas crustacean zooplankton were the preferred prey of paddlefish. Bigmouth buffalo diet was broad, including both rotifers and crustacean zooplankton. Dietary overlap with Asian carp was greatest for gizzard shad followed by bigmouth buffalo, but we found little diet overlap for paddlefish. Diet similarity based on taxonomy correlated strongly with diet similarity based on size suggesting filtration efficiency influenced the overlap patterns we observed. Although rotifers were the most common prey item consumed by both bighead and silver carp, we found a negative relation between silver carp CPUE and cladoceran density. The competitive effect of Asian carp on native fishes may be forestalled because of the high productivity of Illinois and Mississippi river habitats, yet the potential for negative consequences of Asian carp in less productive ecosystems, including Lake Michigan, should not be underestimated.

Shallow‐water habitat is hypothesized to provide nursery habitat for young fish. The construction of side‐channel chutes to restore shallow‐water habitat is common in the lower Missouri River; however, a recent adaptive management strategy document (developed by a multiagency, multidiscipline team), as well as previous research, has suggested that the accessibility of chutes to age‐0 Scaphirhynchus spp. (sturgeon hereafter) may be limited. Access is a critical prerequisite for young fish utilizing chute habitat; thus, we investigated chute‐specific accessibility for age‐0 sturgeon at seven chutes (constructed and natural). Age‐0 sturgeon were capable of accessing most chutes; however, accessibility appeared limited at sites with highly restrictive inlet structures. Our results suggest that future consideration of chute inlet designs that meet authorized Missouri River purposes while providing improved fish access is warranted. Additionally, capture sites for exogenously feeding age‐0 sturgeon were usually deeper (>1.5 m) and faster (>0.5 m/s) than sites without sturgeon in chute and adjacent main‐stem habitats. This finding is consistent with previous research that suggests that slow and shallow habitats may not be used by age‐0 sturgeon as frequently as other habitat types in the lower Missouri River.Received June 4, 2014; accepted September 24, 2014

Information regarding the life history and biological requirements and preferences for the razorback sucker Xyrauchen texanus is limited. Current recovery efforts involve rearing fish to juvenile or adult stages in hatcheries before they are released into areas of critical habitat that increase their survival. Our objectives were to develop a model based on habitat use by hatchery‐reared razorback suckers in the lower Colorado River of Arizona and California for predicting preferred habitat and to determine whether fish would use reconnected off‐channel habitats. To this end, we monitored the use of existing and reconnected habitats by hatchery‐reared razorback suckers implanted with sonic transmitters. Off‐channel (backwater) habitats were preferred over main‐channel or side‐channel habitats. We constructed a model using logistic regression to predict which types of backwaters (based on morphology and water quality) were most suitable for use by razorback suckers. The model works well for predicting sites that are less suited for use and can be used to prioritize habitats for reconnection purposes because razorback suckers were found to utilize reconnected habitats.