Rapid quantitative assessment to assist in identification of imperiled fishes
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Methodologies for ranking conservation status of fishes range from a rapid qualitative method (e.g., expert opinion) commonly used by state agencies to time-consuming quantitative method (i.e., Species Status Assessment; SSA) currently used by US Fish and Wildlife Service. Purpose of this study was to develop a rapid but quantitative methodology for ranking conservation status of freshwater fishes. Using parameters of SSA, redundancy (i.e., occurrence in numbers of independent drainages and semi-independent reaches, occurrences outside of the study area), representation (i.e., commonality within reaches), and resiliency (i.e., number of reaches with recently reported absences) were compiled for 50 species of fishes within the Edwards Plateau, Chihuahuan Desert, and South Texas Plains ecoregions of Texas. The 50 species represented 12 families of fishes and consisted of narrowly distributed fishes (i.e., occurring in one drainage) and widely-distributed fishes (i.e., occurring in up to six drainages) and among 1 to 50 reaches. Twenty-six percent (N = 13) of the fishes occur only within the study area. Parameters were analyzed with multivariate analysis. Principal component axis I described a redundancy gradient, contrasting narrowly distributed fishes from widely distributed fishes, and principal component axis II described resiliency and representation gradient, contrasting fishes with greater percent absence or percent rare from those with fewer percent absences and occasional to abundant in relative abundances. Weighted summation of species scores for axes I and II were sorted from least (i.e., towards low redundancy, representation, and resiliency) to greatest (i.e., towards high redundancy, representation, and resiliency), and species were ranked. Species ranks were similar to the list of Texas Species of Greatest Conservation (SGCN), which were developed from rapid qualitative method, but discrepancies highlighted limitations of qualitative methods and expert opinion. Most notably, charismatic and well-studied fishes with moderate redundancy, representation, and resiliency were listed as SGCN, whereas less-studied fishes with lower redundancy, representation, and resiliency were not listed as SGCN. Among life history traits, majority of the top 50% ranked fishes were small-bodied fishes associated with aquifer dependent surface waters. Reproductive and trophic guilds were similar between the top and bottom 50% ranked fishes.