Stream Fragmentation Thresholds for a Reproductive Guild of Great Plains Fishes

Impoundments, diversion dams, and stream dewatering have created a mosaic of large river fragments throughout the Great Plains of central North America. Coincident with these habitat changes are massive declines in the distribution and abundance of Great Plains fishes belonging to the pelagic-spawning reproductive guild. We analyzed longitudinal fragment lengths (measured in river kilometers, rkm) and literature accounts of population status for eight species from this guild across 60 fragments to derive thresholds in stream length associated with extirpations. Fragment length predicted population status (F-2,F-21 = 30.14, P < 0.01), with lengths averaging 136 +/- 21 rkm for extirpated, 226 +/- 69 rkm for declining, and 458 +/- 137 for stable populations. Fragment length explained 71% of reported extirpations and estimated thresholds in fragment length explained 67% of variation in population persistence. Our findings provide insight into appropriate spatial scales for conducting riverscape conservation approaches that address the hierarchical effects of fragmentation on stream-dwelling fishes.