Oncorhynchus sp. nov. 'Piaxtla Trout'

TAXONOMIC NOTES The Piaxtla Trout is the closest relative to the San Lorenzo trout, but is phenotypically distinct and Escalante et al. (2015) report genetic differences. JUSTIFICATION This species is restricted to few headwater streams of the Río Piaxtla drainage between 2,100-2,700 m asl in Durango, Mexico. While its extent of occurrence and area of occupancy are both restricted, this species appears to be abundant where it occurs and population status is suspected to be stable. There are no known major pervasive threats. Therefore, this species is assessed as Near Threatened because it meets the threshold for a threatened category under criteria B1 and B2, subpopulations are likely severely restricted, but there is no indication of major population or habitat decline. GEOGRAPHIC RANGE INFORMATION This species is found in a few headwater streams of the Río Piaxtla drainage between 2,100-2,700 m asl. The largest populations appear to be in Arroyo El Granizo, Arroyo Santa Barbara, and Arroyo de la Plazuela. Extent of Occurrence (EOO) for this species is estimated to be 334 km² and area of occupancy (AOO) is unlikely to exceed 10 km. Threats are expected to act independently on stream headwaters, therefore the number is locations is expected to be fewer than 10. Distribution is not considered to be very restricted, given a lack of major plausible threats with the capacity to drive this species towards extinction within a short period of time. There is one instance of intra-basin transfer of Piaxtla Trout to a fishless stream. However, the status of that introduction is unknown. POPULATION INFORMATION This species appears to be locally abundant at the few collection localities where it occurs. Current population trend is suspected to be stable. However, populations are inferred to be severely restricted, given they do not occur in main river reaches and likely encounter thermal barriers that limit the dispersal of individuals between headwater reaches. HABITAT AND ECOLOGY INFORMATION The Piaxtla Trout occupies cold and clear headwater streams. Virtually nothing is known of its reproductive or behavioural traits. THREATS INFORMATION Currently, there are no known major pervasive threats to this species. There are no known grow-out facilities for rainbow trout in the Piaxtla basin. However, future genetic introgression with Rainbow Trout is expected, given government initiatives that promote the development of hatcheries. Sportfishing occurs in the basin but is not thought to present a major threat at this time. USE AND TRADE INFORMATION There is no known trade in the taxon. CONSERVATION ACTIONS INFORMATION There are no known conservation actions in place at this time. Education of the local populace about the native trout is recommended. More research regarding distribution, population size, population status, and the impacts of potential threats would be useful in guiding future conservation action.