Morpho-Meristic Variation of Native Cutthroat Trout in the Southern Rocky Mountains, with Comments on Range-Wide Variation in Oncorhynchus Clarkii

Morpho-meristic variation is described in 48 populations of Cutthroat Trout Oncorhynchus clarkii from the Rio Grande, and Colorado, South Platte, and Arkansas River basins in Wyoming, Colorado, Utah and New Mexico. These include presumptive Rio Grande (O. c. virginalis), Colorado River (O. c. pleuriticus), and Greenback (O. c. stomias) Cutthroat Trout subspecies and an unusual Bear Creek, Colorado, population. Ten morpho-meristic characters, including spot distribution and density patterns, were variable across taxa and classification analyses better supported assignment of populations to a newer Molecular Model of Cutthroat Trout distribution than the traditional Geographic Model. Bear Creek and Rio Grande lineages were distinct, as were Blue Lineage populations of the Upper Green River Basin. Green Lineage populations of the Colorado, Gunnison, and Dolores River drainages, as well as Front Range populations from the Arkansas and South Platte River drainages, may represent more than one taxonomic entity.  Classification success was also high within lineages at the drainage scale, suggesting smaller-scale organization of diversity. All lineages are rare and findings will be useful to managers tasked with listing decisions and conservation actions for these Cutthroat Trout. Morpho-meristic data will also be reviewed to determine utility for range-wide classification of Cutthroat Trout.