Oncorhynchus sp. nov. 'Northern Conchos Trout'

TAXONOMIC NOTES Undescribed species. Affinity appears to be with Yaqui trout in the adjacent basin, but genetic work shows this trout to be unique. JUSTIFICATION Extensive surveys show the trout to occupy only one section of a tiny headwater stream in the Hojasichi sub-basin of the Río Conchos. Habitat is evidently restricted to 1 km of stream and the population has not expanded its range in the past 14 years, despite some protections. the total population size is unlikely to exceed 250 individuals. Threats include fishing pressures, livestock overgrazing, and inbreeding. Given its highly restricted extent of occurrence and area of occupancy, an observed decline in the area, extent, and quality of available habitat in the recent past, and expected future declines, this species is assessed as Critically Endangered (CR) under criterion B1ab(iii)+2ab(iii). GEOGRAPHIC RANGE INFORMATION This species is currently known from about 1 km of stream in the Hojasichi sub-basin of the Río Conchos. Its extent of occurrence (EOO) does not exceed 2.33 km² (although for the purpose of the Red List assessment, this measurement is raised to 4 km² to ensure the EOO is not smaller than the area of occupancy). Its area of occupancy (AOO) is 4 km² (but the actual area occupied by the species does not exceed 2 km²). It occurs in one location. John Woodhouse Audubon (1906) mentioned trout in the Conchos basin seen during his 1849 overland trip through Chihuahua. POPULATION INFORMATION Pennington (1963) described a fish which could only be referred to trout, while studying the culture of the Rarámuri near Sisoguichi. Anecdotal reports of "aparique" (trout) are frequently reported by the indigenous Rarámuri, but they typically mention that they haven't seen the fish for 10 or 20 years. Flechsig noted that residents of Panalachi told him of existence of a trout but were unable to produce the fish because of severe drought in the early 1950s (A. Flechsig Pers. Comm. 2004). We found native trout in 2005 near Panalachi, but subsequent trips to that site over the next 11 years failed to produce any trout. A tiny population was found in a remote stream to the north of Panalachi in 2006. That population is restricted to about 1 km of stream in a remote area, but appears not to be expanding it's range, and is the only known population of this species despite repeated efforts to find more. Total population size is unlikely to exceed 250 mature individuals. HABITAT AND ECOLOGY INFORMATION This species is currently thought to be restricted to a single headwater stream in the northern Río Conchos, excluding the Río Balleza sub-basin. Historical reports suggest it was more widespread in the upper Conchos proper. The single location where this species occurs is between an elevation of 2350-2400 masl. Basic life history and basic ecology are uncertain and require additional research. THREATS INFORMATION Historical declines are the result of overfishing, particularly anglers that take the fish by poisoning the waters, either with clorox, lime, or poisonous roots. Overgrazing by livestock has degraded stream banks and helped to eliminate the fish from most of its former range. Currently, these are not considered major threats to this population because access to the public and livestock is restricted. However, a recent trip showing some fish with a severe overbite suggests that the population has become inbred. Use of detergents in the streams by native peoples washing clothes may also have contributed to the reduction in range of this species. Future genetic introgression with rainbow trout is expected, given government initiatives that promote the development of hatcheries within the region. USE AND TRADE INFORMATION Historically, this species was targeted by subsistence fisheries through the use of clorox, lime, and other indiscriminate fishing methods. Currently, there is no known trade in this taxon. CONSERVATION ACTIONS INFORMATION Currently the species is known to subsist only in one stream, a northerly flowing tributary to the Río Hojasichi. Sections of this stream are crudely fenced with barbed wire to keep livestock out of the riparian, and there is currently a "streamkeeper" (hired by the WWF) that lives on the stream to control public access. Continued site protection is imperative to the survival of this species. Future conservation should seek to employ habitat restoration, species recovery, and education and awareness initiatives.