Ecoregion Description

162: Sinaloa

Major Habitat Type:

tropical and subtropical coastal rivers

Author:

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

Countries:

Mexico

Boundaries:

This ecoregion is bordered by the Gulf of California to the west and the Continental Divide to the east. It encompasses all of the coastal state of Sinaloa, from the southern tip of Sonora along the coast to the state of Nayarit, and inland to Chihuahua and Durango.

Drainages flowing into:

Pacific Ocean via the Gulf of California

Main rivers or other water bodies:

Rivers in the ecoregion include the Río Fuerte basin in the north to the Río Acaponeta in the south. The Río Presidio is another major basin. The ecoregion does not include headwaters (Río del Fuerte, Río Presidio) east of the Sierra that were former tributaries of the Río Bravo.

Topography:

The ecoregion spans the rugged western slopes of the Sierra Madre Occidental down to the coast. Elevations in the ecoregion range from sea level to over 3000 m asl.

Climate:

Along the coast the climate is primarily humid subtropical with a long dry season, whereas higher elevations experience generally mild winters and wet summers. Semiarid steppe characterizes the extreme northern part of the ecoregion. Mean annual temperature averages 20 ºC, but varies in different parts of the ecoregion between 10 and 25 ºC. Mean annual precipitation is 870 mm.

Freshwater habitats:

Freshwater habitats in the ecoregion range from high sierra headwaters to coastal plain rivers and some coastal lagoons. The coastal rivers of this ecoregion have short courses and narrow floodplains.

Terrestrial Habitats:

Dry forest dominates the coast with dry forest trees and columnar cacti, including the kapok tree (Ceiba pentandra) and desert fern (Lysiloma watsonii). Higher elevations are dominated by Sierra Madre Occidental pine-oak forests, which boast some of the greatest terrestrial diversity in North America. Pseudotsuga and Pinus constitute the biggest trees. Unfortunately, overharvesting has left only two percent of the original habitat.

Fish Fauna:

Compared to the other Nearctic tropical and subtropical coastal river ecoregions, this ecoregion has few species. It is, however, dominated by the euryhaline Poeciliopsis genus, with species such as the lowland livebearer (Poeciliopsis latidens), clearfin livebearer (P. lucida), headwater livebearer (P. monacha), Sinaloa livebearer (P. presidionis), blackstripe livebearer (P. prolifica), and chubby livebearer (P. viriosa).

Description of endemic fishes:

The Sinaloa ecoregion does not exhibit extraordinarily high levels of aquatic endemism. Endemics include the lowland livebearer (Poeciliopsis latidens), clearfin livebearer (P. lucida), shorttail chub (Gila brevicauda), and one endemic species of crayfish. However, near-endemic species include the Sinaloa livebearer, blackstripe livebearer, chubby livebearer, blackfin silverside (Atherinella crystallina), and mountain clingfish (Gobiesox fluviatilis).

Ecological phenomena:

Rivers are short and floodplains narrow, with little exchange between rivers except through marine waters.

Evolutionary phenomena:

Speciation of the genus Poeciliopsis, especially adaptation of all-female species complexes and hybridization. 

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. There are a high number of near-endemics in this ecoregion, particularly in the all-female strains of Poeciliopsis. 

Level of taxonomic exploration:

Relatively good, excellent along the lowlands, but poor in the high sierras.

References/sources:

Abell, R. A., Olson, D. M., et al. (2000). "Freshwater Ecoregions of North America: A Conservation Assessment" Washington, DC, USA: Island Press.

Hendrickson, D. A. (1983). "Distribution records of native and exotic fishes in Pacific drainages of Northern Mexico" Journal of the Arizona-Nevada Academy of Science 18(2) 33-38.

Hendrickson, D. A., Minckley, W. L., et al. (1980). "Fishes of the Rio Yaqui Basin, Mexico and United States" Journal of the Arizona-Nevada Academy of Science 18(2) 65-106.

Hendrickson, D. A.,Varela-Romero, A. (2002)"Fishes of the Rio Fuerte drainage" In Lozano-Vilano, M. (Ed.). Libro Jubilar en Honor al Dr. Salvador Contreras Balderas. Dir. Gral. De Publicaciones. (pp. 171-195) Monterrey, México: Universidad A. de Nuevo León.