|Red List Category & Criteria:
||Gante, H., Santos, C.D., Alves, M.J. & Rodrigues, J.
||Snoeks, J. & Pollock, C.M.
The Lisbon Arched-mouth Nase is restricted to three small rivers, with its extent of occurrence estimated to be less than 10 km² and area occupancy of ca. 3 km². Its distribution is highly fragmented with little or no contact between the three subpopulations. One of the subpopulations is known to be severely declining over the last two decades. Historical records in additional tributaries, where the species no longer exists, indicates a contraction of the extent of occurrence.
The species is rare within its range and it is affected by high human pressure on water resources (including water extraction for agricultural purposes); presence of exotic species; industrial, domestic and agricultural sources of pollution; and land reclamation. These threats are especially problematic during extreme drought events, which lead to an overall degradation of habitat quantity and quality. Furthermore, the species was found to hybridize with a critically endangered sympatric relative (Iberochondrostoma lusitanicum) (Gante et al. 2010). Continued introgression from this comparatively more abundant species could lead to its genetic dilution.
|Range Description:||This species occurs only in restricted areas of three small tributaries in the terminal portion of the Tagus (Tejo) River Basin in Portugal. These are Rio Trancão, Rio Maior and Ribeira de Muge (Gante et al. 2007, 2010). Material available in museum collections confirms its presence in historical times in two additional tributaries in which present day populations have not been found (Ribeira de Ulme and Ribeira de Magos) (Gante et al. 2007). This suggests that the species’ areas of occurrence and occupancy are likely regressing. Many other tributaries of the Tagus (Tejo) River have been sampled over the years but no additional subpopulations have been found. Further sampling effort in the tributaries where the species occurs was unsuccessful in finding more individuals, indicating a very restricted area of occupancy.|
Conservative area calculations of the extent of occurrence (i.e., assuming that the species can be found in all of the extent of the basins where it was found) indicate an area below 10 km². The area of occupancy, based on proven occurrence or the presence of adequate habitat, is ca. 3 km².
Portugal (Portugal (mainland))
|♦ Estimated area of occupancy (AOO) - km2:||4||♦ Continuing decline in area of occupancy (AOO):||Yes|
|♦ Extreme fluctuations in area of occupancy (AOO):||No||♦ Estimated extent of occurrence (EOO) - km2:||4-10|
|♦ Continuing decline in extent of occurrence (EOO):||Yes||♦ Extreme fluctuations in extent of occurrence (EOO):||No|
|♦ Number of Locations:||3-4||♦ Continuing decline in number of locations:||Yes|
|♦ Extreme fluctuations in the number of locations:||No|
|Range Map:||Click here to open the map viewer and explore range.|