Technical Report

Augmentation and Monitoring Plan for Rio Grande Silvery Minnow in the Middle Rio Grande, New Mexico

URL: https://webapps.usgs.gov/mrgescp/documents/Remshardt_2001_Augmentation%20and%20Monitoring%20Plan%20for%20RGSM%20in%20the%20MRG%2C%20NM.pdf

Date: 2001/12/01

Author(s): Remshardt W.J.

Publication: U.S. Fish and Wildlife Service Report, 16 p.

Abstract:

The Rio Grande silvery minnow (Hybognathus amarus) was historically found in the mainstem Rio Grande and its larger tributaries (Chama River and Jemez River) from near Española to the Gulf of Mexico, and in the Pecos River from Santa Rosa downstream to its confluence with the Rio Grande (Bestgen and Platania 1991). Currently, H. amarus has been found in the middle Rio Grande, New Mexico, between Cochiti Dam and Elephant Butte Reservoir, representing 283 km (176 mi) or 5-7% of the historical range. The species has declined and it is estimated that more than 70% of the known population of H. amarus inhabits the reach from the San Acacia diversion dam downstream to Elephant Butte Reservoir (U.S. Fish and Wildlife Service 1999).

Throughout much of its historic and current range, the decline of H. amarus may be attributed in part to modification of stream discharge patterns and sediment loads, channel dessication, obstructions to upstream movement (e.g., impoundments and diversion dams), channelization, competition and predation by introduced nonnative species, and water quality degradation. One factor of considerable importance is the loss of nursery habitat. During spawning, fertilized eggs could passively drift up to 390 km downstream before being able to move out of the drift (Platania 2000). If spawning were to occur at the uppermost location (Cochiti Dam), many larvae could be transferred past Angostura and Isleta diversion dams before being able to actively seek out low-flow nursery areas given current uniform channel conditions. In a more natural channel, eggs may only drift as much as 100 m downstream in a day (W. L. Minckley pers. comm.). It is likely that some or all of the factors may have contributed to the decline of H. amarus which ultimately resulted in the listing of this endemic cyprinid as a federal endangered species (U.S. Department of the Interior 1999).