Oncorhynchus chrysogaster

TAXONOMIC NOTES The taxon Oncorhynchus chrysogaster currently includes the drainages of the ríos Fuerte, Sinaloa, and Culiacán. Here we treat only the Río Fuerte subpopulations as O. chrysogaster. Sinaloa and Culiacán subpopulations are different phenotypically from each other and from those subpopulations in the Fuerte watershed. JUSTIFICATION This species is known from a number of localities within the Urique, Loera, and Verde sub-basins in Chihuahua, Mexico. Its extent of occurrence (EOO) is estimated to be 3,289 km² and its area of occupancy (AOO) is estimated to be 44 km². Anecdotal evidence suggests population decline and possible extirpation in some areas where this species. However, it is still considered common in the Río Verde and Loera sub-basins. Primary threats include deforestation, livestock overgrazing, hybridization with Rainbow Trout, and localized fishing pressure. Therefore, this species is assessed as Near Threatened (NT) because it meets the threshold for a threatened category under B1 and B2 and there is evidence of continuing decline in the area, extent, and quality of available habitat, but it occurs in more than 10 locations, the population is not severely fragmented, and currently there is no evidence of major range-wide population decline. GEOGRAPHIC RANGE INFORMATION This species is known from 22 localities and more than 10 locations in the sub-basins Urique, Loera, and Verde in Chihuahua, Mexico. It is found in headwater streams of all three sub-basins and in the mainstem of the Río Verde above about 1,900 m. The Río Verde and its tributaries have the largest populations of this trout. Arroyo las Truchas in the Loera basin also has a strong population. Extent of occurrence (EOO) for the species is estimated to be 3,289 km² and area of occupancy (AOO) is estimated to be 44 km². The population is not considered to be severely fragmented. POPULATION INFORMATION Total population size is unknown for this species. Range-wide population trend is unknown, but it is suspected to be declining at a rate that precludes this species from being assessed in a threatened category under criterion A. Mexican Golden Trout are rare and possibly have been eliminated from the upper Urique basin. Trout in the Los Loera system are common in the Arroyo las Truchas, but other streams in that area have not been surveyed. The Río Verde sub-basin populations appear to be stable. Trout are rare in Arroyo San Vincente, and appear different phenotypically from the rest of the basin. The Río Verde and its tributaries have the largest populations of this trout. Arroyo las Truchas in the Loera basin also has a strong population. HABITAT AND ECOLOGY INFORMATION Mexican Golden Trout prefers cold, clear streams above 1,900 m altitude. Their preference appears to be for deeper water beneath boulders and undercuts. Spawning individuals have been taken in mid-February. The specific habitat uses, basic life history, and basic ecology of this species are uncertain and require additional research. THREATS INFORMATION There are multiple threats to the Mexican Golden Trout. Habitat degradation from the effects of overgrazing and logging is principal. These activities cause siltation and warming of the stream waters, and increase flash flooding which can disturb spawning regimens. The Río Verde populations are easily accessed from the highway and are subject to exploitation by anglers. Grow-out facilities in the Fuerte basin are common and Rainbow Trout (Oncorhynchus mykiss) escape from these operations is likely to lead to introgression. To date we have not collected any Mexican Golden Trout that we suspected were hybridized with Rainbow Trout. 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 traded. It is occasionally targeted in subsistence and sport fisheries. However, the magnitude of harvest is unknown. CONSERVATION ACTIONS INFORMATION Currently there are no species-specific conservation measures directed towards Mexican Golden Trout. Recommended conservation actions include implementation of harvest limits in the Rio Verde, and education and encouragement of of cattle ranchers to reduce accessibility to riparian vegetation. More information regarding population size, population trend, and the impacts of major threats would be useful in guiding future conservation action.