Oncorhynchus sp. nov. 'Mayo Trout'

TAXONOMIC NOTES The Mayo trout is most closely related to the Yaqui trout. JUSTIFICATION The Mayo Trout is restricted to four streams (13 collection localities) and is abundant only in one location. This location is a headwater stream that is threatened by mining interests. Additional threats include subsistence harvest, human encroachment, and subsequent declines in water quality and habitat availability. Subpopulations are fragmented and cannot intermix. Total population size has been severely diminished in the last 40 years and continuing decline in the number of mature individuals is inferred, but exact estimates of decline are unknown. Its extent of occurrence (EOO) and area of occupancy (AOO) are both highly restricted. Therefore, this species is assessed as Endangered (EN) under criterion B1ab(i,ii,iii,v)+2ab(i,ii,iii,v). GEOGRAPHIC RANGE INFORMATION This species is restricted to small streams above Basaseachi falls, and to a few headwater streams (above 2,000 m) that intersect the Río Mayo below the falls. One individual was collected below Basaseachi in 2008 (L. Findley Pers. Comm. 2008). Arroyo El Concheño appears to have the strongest population. Extent of occurrence (EOO) for the species is estimated to be 240 km² and area of occupancy (AOO) is estimated to be 26 km²; both are inferred to be declining due to adjacent mining activity, human encroachment, subsistence harvest, and reductions in habitat quality. This species is reported from 13 collection localities. However, threats are acting at the stream scale and the number of locations is unlikely to exceed four. POPULATION INFORMATION The Mayo Trout is rare throughout its range. Cursory surveys show it to be common only in Arroyo El Concheño. The species is decreasing in abundance above Basaseachi falls because of developments and encroachment of civilization. Severe fragmentation is inferred based on habitat type and dispersal ability. HABITAT AND ECOLOGY INFORMATION The Mayo Trout needs cold, clear water. Virtually nothing is known of the spawning habits or behavior of this species. THREATS INFORMATION Mining is a threat to the Mayo Trout in Arroyo El Concheño. Effluent from new mining efforts have killed much of the aquatic life immediately downstream of a mine on El Concheño. There are still trout immediately above a waterfall that is adjacent to the mine. Mayo trout are uncommon above Basaseachi falls, are absent from the mainstem of the river, and are decreasing in the headwaters due to encroaching civilization and developments along the streams. Water quality and catch from local anglers are affecting the populations. 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 may occasionally be taken in subsistence fisheries. CONSERVATION ACTIONS INFORMATION There are currently no conservation actions in place. It is imperative that mining not be expanded on Arroyo El Concheño. Education of the local populace may be of help in preserving the small populations above Basaseachi. Additionally, more research regarding distribution, population size, population trend, life history and ecology, and the magnitude of threatening factors will be useful in guiding future conservation action.