Oncorhynchus sp. nov. 'Acaponeta Trout'

TAXONOMIC NOTES There is evidence that most populations of native Acaponeta trout are likely to be introgressed with Rainbow Trout. JUSTIFICATION This species is known only from the headwaters of four streams (arroyos los Metates, Cebollas, Tanquecitos, and Las Moras) at high elevation in the Sierra Madre Occidental, Durango, Mexico. Severe population fragmentation is likely, given the most widespread and major threat to this species is genetic introgression with Rainbow Trout. 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 four 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). GEOGRAPHIC RANGE INFORMATION This species is known only from the headwaters of four streams (arroyos los Metates, Cebollas, Tanquecitos, and Las Moras) at high elevation in the Sierra Madre Occidental, Durango, Mexico. Area of occupancy (AOO) for the species is estimated at 8 km² and its extent of occurrence (EOO) is estimated at 187 km², based on available georeferenced point records. Both EOO and AOO are inferred to be in decline due to introgression with Rainbow Trout (Oncorhynchus mykiss). This species occurs at four locations, given that the spread of Rainbow Trout is likely to affect each stream separately. POPULATION INFORMATION There is no information regarding trends of the populations. This species was common at Tanquecitos and las Cebollas. Given its highly restricted range, total population size is suspected to be small. HABITAT AND ECOLOGY INFORMATION This species occurs only in headwater streams in the Río Acaponeta watershed. Elevation of habitat ranges from 2,300-2,800 m asl. The specific habitat uses, basic life history, and basic ecology of this species are uncertain and require additional research. THREATS INFORMATION The unique phenotype of the Acaponeta trout shows the population to have a native component that is in danger of introgression with Rainbow Trout (Oncorhynchus mykiss). Future genetic introgression with Rainbow Trout is expected, given government initiatives that promote the development of hatcheries within the region. USE AND TRADE INFORMATION This species is not utilized. CONSERVATION ACTIONS INFORMATION There are no conservation actions currently in place. Education of the populace about the native trout regarding the potential impact of introgression may be an effective course of action. Additionally, more research regarding distribution, population size, and population trend would be useful in guiding future conservation action.