Boundaries

The upper Usumacinta ecoregion lies within eastern Chiapas and southeastern Tabasco within Mexico, and northwestern Guatemala. It covers the upper Usumacinta basin above the confluence with the San Pedro River near the town of Multé.

Topography

The western part of the ecoregion is bounded by the rugged Sierra Madre de Chiapas in Mexico, and Sierra de los Cuchumatanes in Guatemala. Along the eastern edge of the ecoregion lie the western slopes of the Maya Mountains in Guatemala. The center and northern part of the ecoregion lie at lower elevations, sloping toward the Gulf of Mexico in the north.

Freshwater habitats

Freshwater habitats in this ecoregion include mountain streams, lowland rivers, periodically flooded wetlands, springs, cenotes, and freshwater lagoons. In many areas, especially within the expansive Montes Azules Biosphere Reserve of Mexico, aquatic habitats are surrounded by relatively pristine moist forests. 

Terrestrial habitats

The terrestrial habitats are dominated by Petén-Veracruz moist forests at lower elevations and pine-oak forests and montane forests at higher elevations.

Description of endemic fishes

Lacantuniidae, represented by the Chiapas catfish (Lacantunia enigmatica), is endemic to the Usumacinta drainage in both the Upper Usumacinta and Grijalva-Usumacinta [173] ecoregions. Other near-endemics include Scolichthys greenwayi, S. iota, Grijalva studfish (Xenodexia ctenolepis), Heterandria attenuata, H. dirempta, H. cataractae, and H. oblique, Amphilophus nourissati, ‘Cichlasoma grammodes’, ‘C.’ ufermanni, Theraps lentiginosus, Thorichthys pasionis, Vieja bifasciata, and V. heterospila. Many of these are restricted to tributaries in Guatemala.

Other noteworthy fishes

The Usumacinta endemic poeciliids Scolichthys greenwayi, S. iota and Xenodexia ctenolepis, and the characid Bramocharax baileyi appear to represent relict populations, the former which may have a close relationship to South American poeciliids. The Mayan tetra (Hyphessobrycon compressus) is the northernmost species of this large South American genus.

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.