Devils River Minnow

Devils River minnow are native to tributary streams of the Rio Grande in Val Verde and Kinney Counties, Texas, and in the State of Coahuila, Mexico. Monitoring of the species has occurred inconsistently across the range. Recent detections of Devils River minnow confirm its persistence in the Devils River and its tributaries, San Felipe Creek, and Pinto Creek. Streams within the range lacking recent surveys include Sycamore and Mud Creeks in Texas, the Rio San Carlos in Coahuila, and the Rio Salado drainage in Coahuila. Las Moras Creek in Texas, which lies within the historical range, is considered extirpated. The species does not occur in the mainstem Rio Grande, the Rio Conchos in Mexico, or other tributary streams not listed above.

Estimates of population size for Devils River minnow in any of its extant habitats are not available. In Pinto Creek, the population is very low and declining due to habitat loss and modification. In San Felipe Creek, the population is low (in the hundreds) and has declined due to habitat loss and modification. The Devils River is considered a stronghold for the species.

The Devils River minnow was listed as threatened on October 20, 1999 (64 FR 56596). Critical Habitat was designated on August 12, 2008 (73 FR 46988). A five-year review was completed in 2008.

Devils River minnow are associated with clean and clear streams strongly influenced by groundwater flows from the Edwards-Trinity (Plateau) Aquifer (73 FR 46988). They rely on the presence of channels of moderate- or fast-flowing, spring-fed waters over gravel substrates. They usually occur where spring flow enters a stream, rather than in the spring outflow itself. This species evolved in environmental conditions of large hydrologic variations inherent to desert river systems that are characterized by extended droughts and extreme flash floods.

Critical Habitat

The critical habitat rule for Devils River minnow does not identify specific physical and biological features (PBFs) used to develop critical habitat, but it does identify primary constituent elements (73 FR 46988–47026). These are the following habitat components:

1. Streams characterized by:
   1. Areas with slow to moderate water velocities between 10 and 40 cm/second (4 and 16 in/second) in shallow to moderate water depths between approximately 10 cm (4 in) and 1.5 m (4.9 ft), near vegetative structure structure
      Something temporarily or permanently constructed, built, or placed; and constructed of natural or manufactured parts including, but not limited to, a building, shed, cabin, porch, bridge, walkway, stair steps, sign, landing, platform, dock, rack, fence, telecommunication device, antennae, fish cleaning table, satellite dish/mount, or well head.
      
      Learn more about structure , such as emergent or submerged vegetation or stream bank riparian riparian
      Definition of riparian habitat or riparian areas.
      
      Learn more about riparian vegetation that overhangs into the water column;
   2. Gravel and cobble substrates ranging in diameter between 2 and 10 cm (0.8 and 4 in) with low or moderate amounts of fine sediment (less than 65 percent stream bottom coverage) and low or moderate amounts of substrate embeddedness; and
   3. Pool, riffle, run, and backwater components free of artificial instream structures that would prevent movement of fish upstream or downstream.
2. High-quality water provided by permanent, natural flows from groundwater spring and seeps characterized by:
   1. Temperature ranging between 17 °C and 29 °C (63 °F and 84 °F);
   2. Dissolved oxygen levels greater than 5.0 mg/l;
   3. Neutral pH ranging between 7.0 and 8.2;
   4. Conductivity less than 0.7 mS/cm and salinity less than 1 ppt;
   5. Ammonia levels less than 0.4 mg/l; and
   6. No or minimal pollutant levels for copper, arsenic, mercury, and cadmium; human and animal waste products; pesticides; fertilizers; suspended sediments; and petroleum compounds and gasoline or diesel fuels.
3. An abundant aquatic food base consisting of algae attached to stream substrates and other microorganisms associated with stream substrates.
4. Aquatic stream habitat either devoid of nonnative aquatic species (including fish,plants, and invertebrates) or in which such nonnative aquatic species are at levels that allow for healthy populations of Devils River minnows.
5. Areas within stream courses that may be periodically dewatered for short time periods, during seasonal droughts, but otherwise serve as connective corridors between occupied or seasonally occupied areas through which the species moves when the area is wetted.