Oncorhynchus sp. nov. 'Culiacán Golden Trout'

TAXONOMIC NOTES The Culiacán Trout is phenotypically and meristically distinct from Oncorhynchus chrysogaster in the rios Fuerte and Sinaloa. JUSTIFICATION The Culiacán trout is restricted to headwater streams in the Río Culiacán basin, Chihuahua and Durango, Mexico and occurs in no more than six locations. This species can be locally common, however, collection localities are few and far between. Localized threats include logging and livestock grazing, both of which have resulted in a continued decline in the extent, area, and quality of available habitat. Subpopulations are fragmented and cannot intermix due to thermal barriers in main river channels. 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 headwater tributaries in the Río Culiacán basin. It is most common in arroyos Agua Blanca, El Desecho, and El Río. Extent of occurrence (EOO) for this species is estimated to be 207 km² and area of occupancy (AOO) is estimated to be 14 km², based on current collection records. Continued decline of both EOO and AOO is inferred, based on a reduction in the quality, area, and extent of suitable habitat. This species occurs in fewer than 10 subpopulations and is restricted to no more than six locations. Habitat is restricted to elevations between 2,300-2,800 m asl. POPULATION INFORMATION There is no information available about population trends as no collection sites have been revisited in recent years. This species can be locally common, however, collection localities are few and far between. Total population size is suspected to be less than 1000 with approximately 200 individuals in the largest subpopulation.. Thermal barriers in the mainstem rivers prevent movement of the trout between headwater streams, and therefore subpopulations are considered severely fragmented. HABITAT AND ECOLOGY INFORMATION Virtually nothing is known of the biology of this species. They inhabit clear, cold headwater streams, particularly between 2,300-2,800 m asl. THREATS INFORMATION Localized threats include deforestation of the watershed through logging/road building and grazing of livestock in the riparian. These threats have resulted in an observed reduction in the area, extent, and quality of suitable habitat. Logging and grazing increase silt loads in the stream and decrease clarity of the water and have the potential to smother spawning gravels. 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 currently no known conservation actions in place. Education of the local people about the native trout is likely to be the most effective from of mitigation. Additionally, more research regarding distribution, total population size, population trend, and the magnitude of threats would be useful in guiding future conservation action.