Oncorhynchus sp. nov. 'Baluarte Trout'

TAXONOMIC NOTES Some museum specimens appear to be introgressed with Rainbow Trout. JUSTIFICATION This species is currently known only from three localities in the headwaters of the Baluarte watershed. Total population size and population trend are unknown as there have been no repeat collections at any sites within the Baluarte, and the purity (extent of ingression) of current collections are uncertain. Severe population fragmentation is likely, given the most widespread and major threat to this species is genetic introgression with Rainbow Trout (Oncorhynchus mykiss). Its area of occupancy (AOO) and extent of occurrence (EOO) are both highly restricted and this species is not thought to occur in more than three locations. Decline in the number of mature individuals, as well as continued decline in EOO and AOO are inferred. As such, this species is listed as Critically Endangered (CR) under criterion B2ab(i,ii,iii,v). Additional field research in the Baluarte watershed may find more native populations. More information regarding population status, distribution, and the impact of introgression would be useful in guiding future conservation action. GEOGRAPHIC RANGE INFORMATION This species is known only from three collection localities in the Sierra Madre Occidental, Durango, Mexico. Arroyo Santa Barbara represents the largest subpopulation. at high elevation in the Sierra Madre Occidental, Durango, Mexico. The area of occupancy (AOO) for the species is estimated at 6 km² and its extent of occurrence (EOO) is estimated at 113 km², based on available georeferenced point records, and both are inferred to be declining based on apparent introgression with Rainbow Trout (Oncorhynchus mykiss). We expect that more field research in the Baluarte watershed would find additional native populations. POPULATION INFORMATION There is insufficient information to establish trends regarding the population status of this species. It is suspected that the pure populations of Baluarte trout are under threat of introgression with introduced Rainbow Trout. HABITAT AND ECOLOGY INFORMATION This species is restricted to the headwaters of the Baluarte watershed in the Sierra Madre Occidental. Elevation ranges from 2,500-2,700 m asl. Basic life history and basic ecology are uncertain and require additional research. THREATS INFORMATION The presence of, and introgression with native Rainbow Trout (Oncorhynchus mykiss) is an immediate threat to the species, and is expected to have resulted in declines in the extent of occurrence, area of occupancy, habitat quality, and the number of remaining mature individuals. 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 fish CONSERVATION ACTIONS INFORMATION No conservation actions currently in place. One reasonable option would be to isolate a native population and try to reproduce that in a troutless stream that is inaccessible to upstream movement of Rainbow Trout. Additionally, more research regarding distribution, population status, and the effects of introgression are needed.