Summary This study evaluated the effects of environmental parameters on the probability of capturing endangered pallid sturgeon (Scaphirhynchus albus) using trotlines in the lower Mississippi River. Pallid sturgeon were sampled by trotlines year round from 2008 to 2011. A logistic regression model indicated water temperature (T; P < 0.01) and depth (D; P = 0.03) had significant effects on capture probability (Y = −1.75 − 0.06T + 0.10D). Habitat type, surface current velocity, river stage, stage change and non‐sturgeon bycatch were not significant predictors (P = 0.26–0.63). Although pallid sturgeon were caught throughout the year, the model predicted that sampling should focus on times when the water temperature is less than 12°C and in deeper water to maximize capture probability; these water temperature conditions commonly occur during November to March in the lower Mississippi River. Further, the significant effect of water temperature which varies widely over time, as well as water depth indicate that any efforts to use the catch rate to infer population trends will require the consideration of temperature and depth in standardized sampling efforts or adjustment of estimates.

Loss of habitat, targeted removals, and overharvest has contributed to the decline of Alligator Gar Atractosteus spatula. There is agreement among commercial fishers, some recreational anglers, conservationists, and natural resource managers that this species warrants conservation. Appropriate management actions require research to further understand the life history and ecology of Alligator Gar populations. We conducted a movement study of 16 Alligator Gar in the lower Ouachita River, Arkansas–Louisiana, for 1 year using acoustic telemetry. The Alligator Gar were stationary at least 28% of the year. We documented 1,552 movement events during the study. The mean (SD) movement rate during the movement events was 1.13 (0.18) km/h, but it varied among individuals. Only 2 of the 16 Alligator Gar were detected upstream of Felsenthal Dam. The tailwater habitat just below Felsenthal Dam was used heavily by the Alligator Gar. The linear home range was 11.9 (7.1) river kilometers. Due to the hydrology of the system, access to the floodplain is not a hindrance to the lateral movement of Alligator Gar in the Ouachita River. The Felsenthal Dam did seem to hinder longitudinal movement, even though high water allowed the fish to move over and around the dam during spring and early summer. Management plans to rebuild Alligator Gar populations in regulated river systems should consider the negative consequences of barriers to lateral or longitudinal movement.

Shovelnose sturgeon Scaphirhynchus platorynchus are a large-river fish distributed throughout the Mississippi River basin, including the lower 1,533 km of the Mississippi River where riverine habitat has been and continues to be modified for navigation and is a potential site for development of instream hydrokinetic electric power generation.Information about habitat use and preference is essential to future conservation efforts. Shovelnose sturgeon have previously been found to select particular habitat types, and these selected habitats vary seasonally; although these past analyses do not consider the selected habitats in a landscape context. We used ecological niche factor analysis (ENFA) that uses distributions of telemetry locations and environmental variables to model habitat suitability in a landscape context. We recorded 333 locations of shovelnose sturgeon during July-December 2013 that included periods of relatively high and low river stages. The ENFA analysis indicated high-suitability locations were in or near deep water during both high and low river stages. During high river stages, high-suitability locations were near island tip habitat, deep water, and steep bottom slope and far from main channel habitat. During low stages, high-suitability locations were in or near deep water and main channel habitat and far from secondary channel and wing dike habitats. This landscape-scale analysis supports seasonal shifts in habitat use and provides insights that can be used to inform habitat conservation and management to benefit shovelnose sturgeon in the lower Mississippi River and possibly other large rivers. and input by J. Bies, M. Quist, J. Porter and E. Wengert. Funded by U.S. Fish and Wildlife Service, U.S. Geological Survey, and Mississippi State University. ORCID Dylan A. Hann

Inputs of nutrients, sediments and detritus from catchments can promote selected components of reservoir fish assemblages, while hindering others. However, investigations linking these catchment subsidies to fish assemblages have generally focussed on one or a handful of species. Considering this paucity of community-level awareness, we sought to explore the association between land use and fish assemblage composition in reservoirs. To this end, we compared fish assemblages in reservoirs of two sub-basins of the Tennessee River representing differing intensities of agricultural development, and hypothesised that fish assemblage structure indicated by species percentage composition would differ among reservoirs in the two sub-basins. Using multivariate statistical analysis, we documented inter-basin differences in land use, reservoir productivity and fish assemblages, but no differences in reservoir morphometry or water regime. Basins were separated along a gradient of forested and non-forested catchment land cover, which was directly related to total nitrogen, total phosphorous and chlorophyll-a concentrations. Considering the extensive body of knowledge linking land use to aquatic systems, it is reasonable to postulate a hierarchical model in which productivity has direct links to terrestrial inputs, and fish assemblages have direct links to both land use and productivity. We observed a shift from an invertivore-based fish assemblage in forested catchments to a detritivore-based fish assemblage in agricultural catchments that may be a widespread pattern among reservoirs and other aquatic ecosystems.

Pallid sturgeon Scaphirhynchus albus (Forbes & Richardson, 1905, Bulletin of the Illinois State Laboratory of Natural History, 1905, 7, 37) are an endangered riverine sturgeon native to the Mississippi and Missouri rivers, and declining numbers have been attributed to multiple stressors, including habitat loss and alteration. The lower Mississippi River provides a useful context to assess pallid sturgeon habitat selection because, although altered for flood control and navigation, it provides a free‐flowing system with a diversity of habitats and a minimally altered hydrograph. A discrete choice model of data collected year‐round from two reaches for 3–5 years revealed changes in habitat selection across water temperatures and river stages representative of seasonal variation in habitat for 116 telemetry‐tagged pallid sturgeon. Natural bank, island tip, and secondary channel were positively selected and main channel, although frequently used, was avoided. The degree of selection varied among river stages, water temperatures, and reaches. Habitat selection appears to be strongly influenced by preference for locations with moderate depth (median 11.7 m; lower and upper quartiles 8.1 m and 16.3 m) and moderate current velocity (median 0.9 m/s; lower and upper quartiles 0.7 m/s and 1.2 m/s).