Using Species Distribution Models to Infer Potential and Restricted Ranges of a Fluvial-Specialist Black Bass Species

Fluvial fishes face increased imperilment from numerous anthropogenic activities, yet specific factors contributing to species declines are often poorly understood.  Species distribution models (SDMs) can disentangle numerous relevant factors to discern which factors are contributing most to species range loss.  We applied a presence-only SDM approach in Maxent to address what factors are contributing to range loss of Shoal Bass (Micropterus cataractae), a fluvial-specialist sportfish vulnerable to extinction.  We estimated the species’ potential distribution as well as three current restricted distributions, each featuring different fragmentation intensities.  All SDMs had high predictive performance and accuracy.  Results revealed that Shoal Bass potentially occurred in 6,533 km of ≥3^rd order streams.  The restricted SDMs estimated 5,574 km present with no riverscape fragmentation to 4,146 km present at the highest fragmentation level.  Response curves depicted Shoal Bass probability of presence increasing in free-flowing fragments >600 km as fragmentation increased.  Interestingly, the apparent relationship between Shoal Bass and non-native congeners changed as fragmentation intensified, moving from a 1:1 positive linear relationship to a slightly negative effect on Shoal Bass presence at >0.75 probability of presence of non-native congeners.  Applying similar SDM approaches to other imperiled fluvial fishes could facilitate large-scale conservation planning.