The Chihuahuan Desert Native Fish Conservation Network contains six NFCAs (Upper Big Bend, Lower Big Bend, Guadalupe Mountains Streams, Davis Mountains Streams, Pecos River, and Devils River) that are comprised of the most remote watersheds in the state and contain a wide variety of habitats with many uniquely adapted plants and animals. In addition to flows from the Rio Grande, Río Conchos and Pecos River, three major (Hueco-Mesilla Bolsons, Pecos Valley and Edwards-Trinity Plateau) and six or more minor aquifers provide water to the region.

Deep trenching of streams by erosion from overgrazing and deforestation (Ohmart and Anderson 1982), introductions of exotic species and extinction of native species may cause irreversible damage to these ecosystems. Under these conditions droughts are even more devastating. Droughts not only reduce rainfall, but also cause an increase in groundwater pumping for agricultural and municipal uses. Such extreme conditions put stress on fish community equilibrium with more tolerant species gaining a competitive and numerical advantage. Tributary creeks tend to be impacted more severely, yet are critical to the breeding and rearing of young of many of the indigenous species. These changes have been gradual and long-term, taking place since the mid-1800s (Miller 1961), but their effects have been compounded over time and are now becoming dramatic. While perturbations such as pollution, reduced groundwater and dam construction are theoretically fixable, recovery to a pristine state is unlikely.

Approximately half of the native fishes of the Chihuahuan Desert are threatened with extinction or already are extinct (Hubbs 1990). Likely extinctions from this area include: Maravillas Red Shiner Cyprinella lutrensis blairi, Phantom Shiner Notropis orca, Rio Grande Bluntnose Shiner Notropis simus simus and Amistad Gambusia Gambusia amistadensis (Miller et al. 1989). Extirpations include Rio Grande Shiner Notropis jemezanus in the New Mexico portion of the Rio Grande (Propst et al. 1987) and Shovelnose Sturgeon Scaphirhynchus platorynchus, Rio Grande Silvery Minnow Hybognathus amarus, Rio Grande Cutthroat Trout Oncorhynchus clarki virginalis and Blotched Gambusia Gambusia senilis in Texas (Hubbs et al. 2008). Endemic species other than fishes are also being lost from this region (e.g., Rio Grande Monkeyface Quadrula couchiana, False Spike Quincuncina mitchelli, and Mexican Fawnsfoot Truncilla cognata; Howells and Garrett 1995). Left unchecked, this trend of species extirpation and extinction is likely to continue.

Another significant threat to a substantial portion of the Chihuahuan NFCN is the establishment of invasive Giant Reed Arundo donax and Saltcedar Tamarix spp. These non-native plants have effectively channelized stream segments and the resulting constricted flow has reduced shallow, backwater habitat and changed bottom sediments from a mixture of sand and gravels to one of primarily larger gravels and cobble. The effect of the dense stands has also armored and stabilized the riverbanks, thus preventing natural sediments and sand to be available for habitat within the river itself (Garrett and Edwards 2014).

The streams of the Chihuahuan NFCN hardly resemble their natural state where many of the original water courses were lined with gallery forests and diverse riparian zones. Exploitation of limited resources, particularly groundwater pumping, has degraded that environment, caused extirpation and extinction of species and ultimately, loss of habitat and ecosystems (Smith and Miller 1985). The few relatively natural faunas and fairly intact ecosystems that remain need careful management if they are to be preserved.

Sources

Garrett, G. P., and R. J. Edwards. 2014. Changes in fish populations in the Lower Canyons of the Rio Grande. Pages 396–408 in Proceedings of the sixth symposium on the natural resources of the Chihuahuan Desert region (C.A. Hoyt and J. Karges, editors). Chihuahuan Desert Research Institute, Fort Davis, TX. http://hdl.handle.net/2152/62996

Howells, R. G., and G. P. Garrett. 1995. Freshwater mussel surveys of Rio Grande tributaries in Chihuahua, Mexico. Triannual Unionid Report 8:10.

Hubbs, C. 1990. Declining fishes of the Chihuahuan Desert. Pages 89-96 in Third Symposium on Resources of the Chihuahuan Desert Region (Powell, A.M. et al. eds.). Chihuahuan Desert Research Institute.

Hubbs, C., R.J. Edwards, and G.P. Garrett. 2008. An annotated checklist of the freshwater fishes of Texas, with keys to identification of species. Second Edition.  Texas Journal of Science Supplement (July):2–87. https://doi.org/10.15781/T22Z13563.

Miller, R. R. 1961. Man and the changing fish fauna of the American Southwest. Papers of the Michigan Academy of Science, Arts, and Letters 46:365-404.

Miller, R. R, J. D. Williams, and J. E. Williams. 1989. Extinctions of North American fishes during the past century. Fisheries 14(6):22-38.

Ohmart, R. D., and B. W. Anderson. 1982. North American desert riparian ecosystems. Pages 433-466 in G.L. Bender, editor. Reference handbook on the deserts of North America. Greenwood Press, Westport, Conn.

Probst, D. L., G. L. Burton, and B. H. Pridgeon. 1987. Fishes of the Rio Grande between Elephant Butte and Caballo reservoirs, New Mexico. Southwestern Naturalist 32:408-411.

Smith, M. L., and R. R. Miller. 1985. Conservation of desert spring habitats and their endemic fauna in northern Chihuahua, Mexico. Proceedings of the Desert Fishes Council 13:54-63.