Oncorhynchus sp. nov. 'Southern Conchos Trout'

TAXONOMIC NOTES Undescribed species. Affinity appears to be with Mexican golden trout in the adjacent Fuerte basin, but genetic work shows this trout to be unique. Nathaniel Thomas Lupton collected two specimens of trout from this region in 1884 (Cope, 1886), but the location of the specimens and the collection locality remain a mystery. JUSTIFICATION This species is known only from about 2 km of the Arroyo del Molino and a tiny headwater tributary in the Río Porvenir sub-basin of the southern Río Conchos watershed. While there are currently no major threats affecting this species or its known habitat, total population size is unlikely to exceed 250 individuals. Therefore, it is assessed as Endangered (EN) under criterion D. More rigorous sampling in adjacent areas is needed to determine if additional populations exist. GEOGRAPHIC RANGE INFORMATION This species is currently known only from about 2 km of the Arroyo del Molino and a tiny headwater tributary in the Río Porvenir sub-basin of the southern Río Conchos watershed, which occurs at an elevation between 2,300-2,350 m asl. Therefore, extent of occurrence (EOO) and area of occupancy (AOO) are both estimated at 2 km². Localized threats are expected to affect the entire known range of this species. Area of Occupancy and EOO are currently stable, given the single location is highly isolated and free of major threats. POPULATION INFORMATION Total population size is unknown. However, given a highly restricted range, habitat specificity for cold headwater streams, and preliminary population surveys in 2007, population size is inferred to be between 100-250, and unlikely to exceed 1,000. Population trend is suspected to be stable, given the lack of major pervasive threats, and no evidence of habitat decline. The current known population is not considered to be severely fragmented. However, if additional subpopulations exist, genetic exchange between subpopulations is likely severely restricted given an inability to disperse through thermal barriers in river mainstems. HABITAT AND ECOLOGY INFORMATION This species is restricted to one headwater stream of the Río Porvenir sub-basin in the Conchos watershed. Cold and clear water is required. Nothing is known of the behavior, life cycle, or growth patterns of this species. THREATS INFORMATION There appear to be no immediate threats to the existing population, as it is remote and not easily accessible. Limitations to range expansion include overgrazing by livestock and the effects of logging and road building in this sub-basin. Future genetic introgression with rainbow trout is expected, given government initiatives that promote the development of hatcheries within the region. USE AND TRADE INFORMATION There is no known trade in this taxon. CONSERVATION ACTIONS INFORMATION There are no species-specific conservation actions in place. Recommended conservation actions include education of the local peoples regarding conservation status and efforts to keep livestock out of the lower reaches of the arroyo. There appears to be minimal impact in the species' actual habitat. More rigorous sampling to identify additional subpopulations of the species is recommended, given the area is remote and difficult to survey. Additionally, more detailed information regarding population size, population trend, and life history and ecology would be useful in guiding future conservation action.