Fishes of the Peloncillo Region: Rarity and Endemism in an Arid Region
Outstanding Features:
Aquatic habitats harboring native fish populations have become increasingly scarce in the Southwestern US and Northwestern Mexico. As water use and drought have increased, aquatic habitats have diminished drastically. By many estimates Arizona has lost over 90 percent of its riparian habitat. In most of the aquatic ecosystems that remain, introduced species of fishes, amphibians, and crustaceans have had a devastating impact on the native fish fauna. These losses have made preservation of surviving aquatic ecosystems and their native fish populations a major conservation priority. The Peloncillo region is highly significant for preserving some of the last intact assemblages of indigenous fishes left in the Chihuahuan Desert Ecoregion. Much of the following information and recommendations comes from the United States Fish and Wildlife Service (USFWS) 1995 Yaqui fishes recovery plan.
Geographic Scope
For purposes of discussing fish populations, the Peloncillo region includes a large portion of the northern Rio Yaqui watershed. This basin as a whole comprises 73,000 km2, with 2% of that in the U.S. (portions of southern Cochise County, Arizona, and Hidalgo County, New Mexico; see map, page 12). The Rio Yaqui begins in western Chihuahua and is significantly augmented by the Río de Bavispe as it enters Sonora on its way to its final destination, the Gulf of California. Near its mouth, the Río Yaqui discharges an total annual average of 2,800 ha3, of water, earning it the rank of one of the largest rivers in the region. In addition to collecting runoff from US territory in the southern San Simon Valley and the northern San Bernardino Valley, this river system’s watershed includes a significant portion of Mexico’s western and northern Sierra Madre.
This report addresses fish communities at the northeastern edge of the Río Yaqui system. The area covered here by current GIS data on native fishes encompasses the area extending from the north end of the Peloncillo range, just north of Interstate 10 in Arizona, south across the U.S./Mexico border to the Sierra San Luis and the upper reaches of the Río Bavispe in Sonora, and from Leslie Canyon, at the southern tip of the Chiricahua Mountains, east to the Animas Mountains in New Mexico.
Habitats – Overview
Diversity of aquatic habitats throughout the Río Yaqui basin is high, including both perennial and ephemeral representatives of high, medium, and low gradient streams at elevations ranging from some 2500m to sea level; low salinity warm and cool springs; cienegas; and temporary lagunas. Mountain creeks (high elevation, high gradient streams) support both indigenous and non-indigenous trout, but most fishes in the basin occupy intermediate- to low-elevation, mid- to low-gradient warm water creeks, cienegas, and moderate- to large-sized rivers. Creeks typically have alternating riffles and pools in which heterogeneity is enhanced by undercut banks, boulders and woody debris. Gravel bottoms in swift areas are vegetated with algae. Rivers vary from pool-riffle types with boulder and gravel bottoms to long, strongly flowing reaches over gravel and sand. Cienegas, stream-associated marshlands with low, emergent aquatic plants and hydric- adapted trees (e.g., Salix spp.), were historically common but have suffered severe degradation in the past two centuries.
The Upper Yaqui area addressed here includes almost all of these features, at elevational ranges from approximately 2500m to 1000m. Most streams in this region are ephemeral, mid- to low- elevation and mid- to low- gradient systems, but a few key reaches are perennial. The Upper Yaqui region has historically had numerous warm and cool springs; some of these still exist. Several cienegas also remain, and some are recovering well from past disturbances. Within the Upper Yaqui, three sites are emphasized here because of their extant fish populations: Cajon Bonito, the San Bernardino National Wildlife Refuge and affiliated habitats on adjacent ranches, and Leslie Creek. More detailed habitat descriptions have been made for both US sites,4 and for portions of the Mexican sites.
Fish Populations in the Region
According to GIS data compiled by W.L. Minckley and Heidi Blasius, three main areas within the greater Peloncillo region/upper Río Yaqui basin support native fish populations, with 13 species, including two undescribed. These areas are Cajon Bonito and the upper Bavispe watershed in northern Sonora; and two sites on the northern Bavispe watershed in the United States—the San Bernardino Wildlife Refuge, and Leslie Creek.
The most significant stream in the region is northern Sonora’s Cajon Bonito, which flows from the western slopes of the Sierra San Luis to join the Río Bavispe. About 20 miles south of the U.S./Mexico border, Cajon Bonito supports the most intact suite of native fish species in the Southwestern US and Northwestern Mexico, including Yaqui beautiful shiner, Mexican stoneroller, ornate shiner, Yaqui longfin dace, Mexican roundtail chub, Yaqui sucker, Yaqui topminnow, Yaqui catfish, and Yaqui chub, the last three of which are listed as endangered by the U.S. government. Compared to other Sonoran and Chihuahuan Desert streams, its species richness is very high.
Most reaches of the Cajon Bonito presently lack invasive non-native species. While it is part of the Río Yaqui system, which has experienced increasing invasion and introduction of non-native fishes such as black bullhead (Ameirus melas) and mosquitofish (Gambusia affinis), Cajon Bonito is protected from invaders present in lower parts of the Rio Bavispe by a dry downstream reach that prevents easy upstream migration of exotics. It remains vulnerable, however, to invaders present in stocktanks and other impoundments.
Records do exist for the river carpsucker Carpiodes carpio, which is native to North America east of the Rocky Mountains. This fish has apparently been in the system for several decades, and is not known to breed with or otherwise negatively impact native species. However, a fish farm stocked with non-native trout and non -native catfish has recently been established (with funding from Mexican federal aquaculture grant program) upstream from one of the most pristine reaches of the Cajon. This fish farm poses an imminent threat of introducing invasive fishes as well as diseases and parasites, and its diversion ponds could have other negative effects on water quality.
The suite of fishes in the Río Bavispe, one of the Río Yaqui’s major tributaries, reflect the same assemblage found in Cajon Bonito: Mexican stoneroller, Yaqui beautiful shiner, Yaqui chub, Yaqui catfish, Yaqui topminnow, Yaqui sucker, Yaqui longfin dace, ornate shiner, and Mexican roundtail chub. Higher elevations of the upper Río Bavispe have produced records of two as- yet undescribed species, the Yaqui trout and Yaqui mountain sucker. The Fleshylip sucker (also known as the Bavispe sucker) is also known only from the upper Río Bavispe.
According to Peter Unmack of Arizona State University (2005, pers. comm.), there is one record for desert chub (Gila eremica) at a small tributary of the Río Yaqui, 21 miles south of Agua Prieta, Sonora, near the village of Cabullonas. However, that record has been questioned due to an inability to find any specimens since that collection in 1959. North of Cajon Bonito and the Río Bavispe, about 17 miles east of Douglas in the U.S., is the San Bernardino National Wildlife Refuge, which protects a third source of the Río Yaqui. Historical records indicate that this area once supported around a quarter of the 35 known indigenous fish species in Arizona: Yaqui beautiful shiner, Mexican stoneroller, longfin dace, Yaqui chub, Yaqui topminnow, Yaqui catfish, Yaqui roundtail chub, and Yaqui sucker.
The upper reaches of the Río Yaqui watershed currently harbor four threatened or endangered taxa—the beautiful shiner (Cyprinella formosa), Yaqui chub (Gila purpurea), Yaqui catfish (Ictalurus pricei) and Yaqui topminnow (Poeciliopsis occidentalis sonoriensis). Additionally this region has provided historic habitat in the U.S. for four additional indigenous fishes: longfin dace (A gosia chrysogaster, Yaqui form), Mexican stoneroller (Campostoma ornatum),Yaqui roundtail chub (Gila minacea) and Yaqui sucker (Catostomus bernardini), all currently candidates for listing in both the U.S. and Mexico. Seven of the eight species are also considered imperiled by the State of Arizona. Livestock overgrazing, erosion, water diversion, aquifer pumping, non-indigenous species, destruction or alteration of most natural fish habitats and drought have caused the extirpation of all eight taxa in the U.S -portion of the Rio Yaqui basin, though four have since recolonized or been reintroduced.
Current Habitat Conditions
Since the late 1880s stream channels became incised and altered. Diversion and modification of stream channels themselves and excessive exploitation of underground aquifers; all reduced the quantity and quality of natural surface waters. Streams from springs and wells were channeled to fields and tanks. Black Draw, which collects water from the southwestern slopes of the Peloncillo mountains and has fed much of the San Bernardino wetlands, changed from a marshy swale (cienega ) in the 1850s to a creek lined with cottonwoods (Populus fremontii) in the 1890s, to an arroyo by the 1960s that was three to five meters deep, to 25 m wide and usually dry. Similar patterns typified the region. Introduction of non-indigenous species into stock-watering ponds and elsewhere came later, and their spread to remnant natural habitats contributed further to a general decline in aquatic communities. Included were highly predatory taxa such as largemouth bass (Micropterus salmoides), bullfrog, and western mosquitofish, and competitors/predators such as bullhead catfish (Ameiurus spp.), bluegill (Lepomis macrochirus) and black crappie (Pomoxis nigromaculatus).
Yaqui chub reappeared in Black Draw in 1987, either from the 1980 stocking or through upstream dispersal from Mexico. Considerable effort had by then been expended in erosion control and revegetation, and positive results of this, coupled with consecutive wet years and appearance of Mexican stoneroller (not before recorded from the stream), make the latter more probable. While these activities proceeded, further plans were implemented to acquire extirpated species from Mexico for culture and ultimate reintroduction back into historic habitats.
Personnel from USFWS, AZGFD, AZSU and El Centro de Ecologico, Hermosillo, Sonora, collaborated o n two trips for Yaqui catfish and one for beautiful shiner. The Yaqui catfish remain at Dexter National Fish Hatchery and Technology Center (NFHTC), where it has been studied morphologically and genetically for positive identification and to ascertain basic information required for successful culture. The Yaqui beautiful shiners were held at Dexter NFHTC, then 400 individuals were reintroduced in May 1990 on San Bernardino NWR. It has established and expanded into today’s subpopulations.
Conservation Targets
Two of the existing fish refugia in the Peloncillo region—Cajon Bonito and the San Bernardino National Wildlife Refuge—are extremely important for the viability of the fishes in the Peloncillo region. The San Bernardino NWR, while fully protected by the US government, is not immune to accidental introductions of non-native species. Careful management should remain a priority for the USFWS.
Cajon Bonito in Mexico is a series of privately owned ranches, each with varying degrees of knowledge and sensitivity to issues of fish conservation. While many biologists from the US and Mexico recognize the value of the Cajon’s fish assemblages, and The establishment of a non -native fish farm upstream of the most intact stream segment creates tremendous risks to native fish assemblages. This farm operation is currently supported by funding through the Mexican federal agency SAGARPA (Secretario de Agricultura, Ganadería, Desarrollo Rural, Pesca y Alimentación). Coordinated management, protected area status, and acquisition of segments by conservation buyers are all options for reducing threats along particular reaches of Cajon Bonito.
The Río Yaqui system has experienced increasing invasion and introduction of non- native fishes such as black bullhead (Ameirus melas) and mosquitofish (Gambusia affinis), although not yet to the extent of rivers north of the U.S. border, such as the Gila. This lag is most likely due to the relative inaccessibility of the upper Río Yaqui, and the relatively recent origin of government -funded introduction programs in Mexico.
Knowledge Gaps
Given the known reduction in riparian habitat within the Chihuahuan Desert Ecoregion, it is probable that the Peloncillo region historically supported more perennial streams and thus more native fish populations than it does today,24 for example in canyons such as Guadalupe, which even now flows much of the year. Natural cyclic droughts would, however, be sufficient to eradicate species in watercourses that might totally dry up during such periods. More study on potential reintroductions is warranted.
More study is needed to determine the possible historical occurrence of fishes in other areas of the Peloncillos, such as Guadalupe Canyon. Any reintroduction efforts to restore lost populations would require an assured permanent supply of water. Restricting or eliminating cattle access to riparian areas and providing them with other sources of water (e.g., - tanks) is one known way to reduce incision and help retain stream flow, a measure completed or underway in many grazing areas. However, cattle tanks might promote the spread of unwanted exotic species such as bullfrogs (Rana catesbeiana), so further study is needed here as well.
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Section Authors:
FISHES - Jonathan M. Hanson. Ecologist and Naturalist. Jonathan is the author of more than a dozen books on nature and outdoor subjects, including the award-winning 50 Common Reptiles and Amphibians of the Southeast and Southern Arizona Nature Almanac.
