Temporal and Spatial Patterns of Fish Distribution and Diversity in the Noxubee River, Mississippi and Alabama
The Mobile Basin has undergone extensive channel modification with corresponding declines in the distribution and abundance of native aquatic fauna. However, many of the declining aquatic species of the Mobile Basin may persist within unmodified sub-basins. The Noxubee River is a sub-basin of the Mobile Basin that is relatively unaltered throughout its watershed, and we hypothesized that the system could serve as a refugium for declining riverine species of the Mobile Basin. We characterized species richness and assemblage structure of fishes in the Noxubee River and its tributaries to determine whether or not contemporary fish assemblages resembled the historical assemblages as described before construction of the Tennessee-Tombigbee Waterway. We found that fish assemblages of the contemporary river are similar to those of the historical river, and many species now absent from another portion of the Mobile Basin are still present and maintain similar distribution and abundance patterns. Our results are informative because there is little existing information available regarding fish assemblages in the Noxubee River since major alterations were imposed upon the Mobile Basin through construction of the waterway. These results are discussed relative to findings from another Mobile Basin tributary that exhibited a marked change in many fish assemblage properties following construction of the waterway. Variable resiliency among tributaries to altered main-channel rivers illustrates the need for predictive tools that can be employed to prioritize conservation efforts.
Orientation of the Noxubee River drainage. Closed triangles represent contemporary collection sites that were used only for analyzing species/habitat relationships because they did not have a matching historical collection effort (n = 32). Closed squares represent sites with historical and contemporary collections that met our criteria for inclusion in three analyses (n = 12): rarefaction, non-metric multidimensional scaling (NMS), and multi-response permutation procedure (MRPP). Closed circles are sites with a contemporary and matching historical collection that qualified for NMS and MRPP but not rarefaction based upon our criteria (n = 2).
Ninety-five percent confidence intervals for the regional rarefaction analysis of historical and contemporary collections (solid line and dashed line, respectively) demonstrate a difference (P ≤ 0.05) in species richness emerges for collections containing approximately 2,000 or more individuals.
Historical and contemporary Noxubee River fish assemblages (open and closed circles, respectively) did not cluster separately in ordination space when non-metric multidimensional scaling was applied to our data set. The second and third axes accounted for 23.2% and 45% of the variance in the species abundance matrix, respectively.
Non-metric multidimensional scaling identified three distinct clusters in our data set of contemporary Noxubee River fish assemblages corresponding to main channel, oxbow, and tributary habitats (closed circles, open circles, and open triangles, respectively). Axis two and three explain 29.3% and 38.8% of the variance in the data set, respectively.
Contributor Notes
Associate Editor: J. F. Schaefer.