Boundaries

This ecoregion includes all Pacific slope rivers from the Golfo de San Miguel in western Panamá southward through the Panamanian Darién, Colombian Chocó, and all of western Ecuador to the Río Piura drainage in northernmost Peru.

Topography

Elevations rise dramatically from the coastal plain to peaks exceeding 5750 m along the Cordillera Occidental of the Andes.  The Río Atrato flows north between the Cordillera Occidental and the Serranía del Baudó. The Serranía del Darién separates this basin from the Tuira basin in Panamá.

Freshwater habitats

This ecoregion is composed of many independent, short rivers in small watersheds. These are high-gradient narrow rivers with little or no floodplains and base-level channels that are short and shallow. Those on the Pacific side have a significant tidal flux. Discharge and silt-loads are historically low, except during heavy rains, especially in the Colombian Chocó and Panamá (annual rainfall varying from 9000 to 12,000 mm in several of the drainages). There are few small lakes on the coastal plains. However, a complex system of cienagas is present in the lower Atrato.

Terrestrial habitats

Terrestrial habitats range from predominantly moist and dry forests and mangroves along the coast to montane forests at higher elevations. The beginning of the Sechura Desert begins around the Río Piura at the southern tip of the ecoregion.

Description of endemic fishes

This ecoregion contains high endemism, exceeding 70% at the species level. Astroblepus (Astroblepidae) contains 15 endemic species and Pseudocurimata (Curimatidae) contains six species, with a significant degree of species-level endemism in relatively discrete geographic areas along the western versant of the Andes (Vari 1989).  On the western versant of the Andes, the southernmost confirmed record of any species of curimatid is that of Pseudocurimata peruana in the Río Piura, Peru (Vari 1989).  Other endemics include the curimatid Steindachnerina atratoensis and characids Cynopotomus atratoensis and Gilbertolus atratoensis.  The monotypic Iotabrycon praecox, a glandulocaudine characid, is reported only from the Río Vinces in Ecuador (Weitzman and Fink 1985). Within the cetopsid catfishes the genus Paracetopsis (with three species) is completely endemic to this ecoregion, and an additional four species of Cetopsis are also endemic (Vari et al. 2005). Endemic genera include Chilobrycon, Iotabrycon, Landonia, Phenacobrycon (Characidae); Aspistor (Ariidae); and Cruciglanis (Pseudopimelodidae).

Other noteworthy fishes

Many mountain stream fishes (astroblepids, trichomycterids, loricariids, characids) live in Andean and coastal uplands and mountains.  Distributions of several species (curimatid Cyphocharax magdalenae, characids Creagrutus affinis and Roeboides dayi) and genera (Argopleura, Characidae) are shared by rivers in this ecoregion and the easterly adjacent Magdalena–Sinú ecoregion [302].  Argopleura is considered the most primitive genus among the Xenurobryconini, a tribe of Glandulocaudinae (Weitzman and Fink 1985).  One species, A. chocoensis, is endemic to the Río San Juan and several species of Argopleura also occur in the Río Magdalena basin (Weitzman and Fink 1985).  The ctenoluciid Ctenolucius beani, a high-level predator, occurs in the Río Atrato and several Pacific slope drainages from the Río San Juan to the Río Santa Maria system in central Panama (Vari 1995).  Distributions of a few Pacific Coast species (e.g., characid Roeboides occidentalis) also extend into central Panama (Lucena 2000).

The fish fauna of eastern Panamá is of special interest because it contains peripheral species or populations of South American groups that likely entered the area from the south after the emergence of the Isthmus.  Bussing (1985) lists the South American fishes that reach their northern limits in the ríos Tuira or Bayano: Characidium, Creagrutus, Bryconamericus, Phenagoniates, Gasteropelecus, Apteronotus, Ageneiosus, Pimelodus, Hoplosternum, Ancistrus, Astroblepus, Chaetostoma, Crossoloricaria, Dasyloricaria, Lasiancistrus, Leptoancistrus, and Geophagus.  Fewer South American groups extend farther into Central America (Bussing 1985).

Justification for delineation

This ecoregion comprises an assemblage of trans-Andean fishes highly distinct at the species, and sometimes generic, level to their counterpart in the Cis-Andean region. Such high level of allopatry makes this one of the most unique freshwater fish assemblages in the South American continent.

Level of taxonomic exploration

Fair