Geology topics

D. A. Hann

Publications and source records attributed to D. A. Hann.

3 recordsLinked to original sources

USGS2020

Pallid sturgeon seasonal habitat selection in a large free-flowing river, the lower Mississippi River

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).

Alabama, Arkansas, Louisiana, Mississippi↗

USGS2015

Increasing capture efficiency of pallid sturgeon Scaphirhynchus albus (Forbes and Richardson, 1905) and the reliability of catch rate estimates

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 − 0.06 T + 0.10 D ). 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.

Mississippi↗

USGS2015

Land use structures fish assemblages in reservoirs of the Tennessee River

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.

Tennessee River↗