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# of Endemic Species
137: Rio Salado
Major Habitat Type:
xeric freshwaters and endorheic (closed) basins
Salvador Contreras Balderas, Universidad Autónoma de Nuevo León. Additional text was modified from Abell et al. 2000. Freshwater Ecoregions of North America: A Conservation Assessment
Largely defined by the watersheds of the Río Sabinas and Río Salado, this ecoregion includes central and eastern Coahuila, northern Nuevo León, and a small portion of Tamaulipas.
Drainages flowing into:
Río Salado is a tributary of the Rio Grande (Río Bravo), which flows into the Gulf of Mexico.
Main rivers or other water bodies:
Rivers in the ecoregion include the Río Salado, Río Sabinas, Northern Río San Juan, and Southern Río Salado de Nadadores. The Cuatro Ciénegas spring complex drains eastward into the headwaters of the Río Salado.
The Río Salado originates in low mountains of the Sierra Madre Oriental, and flows in a southeasterly direction through plains.
The climate of this ecoregion is primarily arid and semiarid (Köppen 1936). The Chihuahuan Desert in the western part of the ecoregion is characterized by dry summers and occasional winter rains (Davis et al. 1997). The mean annual temperature ranges between 14-23 ºC, and mean annual precipitation ranges between 200-675 mm.
The ecoregion is characterized by clear headwater streams, mostly piedmont, and slow plains in the middle to lower reaches. This basin has two ecologically very distinctive tributaries: the Northern Río San Juan, with strictly freshwater, hilly headwaters and hard bottoms; and the Southern Río Salado de Nadadores along the plains, which is highly saline for the most part. The mainstem of the Río Salado has high salt content, is muddy, and is low gradient.
The ecoregion is characterized by the Chihuahua desert in the west, with pockets of Sierra Madre Oriental pine-oak forests. Tamaulipan mezquital is the dominant vegetation type in the east, with small areas of Tamaulipan matorral. Mesquite-grassland is characteristic within Tamaulipan mezquital. Creosote bush (Larrea tridentata) is dominant in the Chihuahuan Desert (World Wildlife Fund 2001).
The fish assemblage in the lower course is notorious due to its big river forms and the euryhaline character of most species. These species do not invade the upper course – they do not go above the Lower Rio Grande Valley. Some of the euryhaline species include the longnose gar (Lepisosteus osseus) and spotted gar (L. oculatus) (Lepisosteidae); mosquitofish (Gambusia affinis), Tex-Mex gambusia (G. speciosa), and robust gambusia (G. marshi) (Poeciliidae); and Rio Grande cichlid (Herichthys cyanoguttatus) (Cichlidae).
Description of endemic fishes:
Several near-endemic species characterize each section of the ecoregion: Devils River minnow (Dionda diaboli), spotted minnow (D. melanops), and Mexican red shiner (Cyprinella rutila) in the San Juan, Río Salado darter (Etheostoma segrex) in the Salado de Nadadores, Salado shiner (Notropis saladonis) in the Río Salado, and Mexican blindcat (Prietella phreatophila)in subterranean waters. The Salado shiner is the only species considered to be a strict endemic to the ecoregion.
Other noteworthy aquatic biotic elements:
The Río Salado ecoregion possesses no known endemic mussels, crayfish, or aquatic herpetofauna.
Usually speciation has developed in allopatry, mostly through a combination of barriers and dispersals. The divergence may be exemplified by a number of cases. The series of the cyprinid Cyprinella is represented by forms in different major tributaries of the Río Bravo/Rio Grande. For example, the Mexican red shiner (Cyprinella rutila) occurs in the Río Salado.
Justification for delineation:
Ecoregion delineations were based on qualitative similarity/dissimilarity assessments of major basins, using the standard administrative hydrographical regions of the Mexican federal government.
Abell, R. A., Olson, D. M., et al. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.
Carranza, J. (1954). "Descripción del primer bagre anoftalmo y depigmentado encontrado en aguas mexicanas" Ciencia 14(7-8) 129-136.
Contreras-Balderas, S. (1985). "Lista zoogeográfica y ecológica de los peces de Coahuila, México" Mem. VIII Cong. Nal. Zool. (Méx.) 1 156-174.
Contreras-Balderas, S., Edwards, R. J., et al. (2002). "Fish biodiversity changes in the Lower Rio Grande/Rio Bravo, 1953-1996" Rev. Fish Biol. and Fish 12 219-240.
Hubbs, C. L.,Hubbs, C. (1958). "Notropis saladonis, a new cyprinid fish endemic in the Rio Salado of northeastern Mexico" Copeia 1958(4) 297 - 307.
Norris, S. M.,Minckley, W. L. (1997). "Two new species of Etheostoma (Osteichthys: Percidae) from central Coahuila, northern Mexico" Ichthyol. Explor. Freshwaters 8(2) 159 - 176.
World Wildlife, Fund (2001). "Terrestrial Ecoregions of the World" 2005 (2005; www.worldwildlife.org/science/ecoregions/biomes.cfm).