Annual Report

Experimental Augmentation and Monitoring of Rio Grande Silvery Minnow in the Middle Rio Grande, New Mexico Annual Report June 2003-May 2004

URL: https://webapps.usgs.gov/mrgescp/documents/Remshardt_2005_Experimental%20augmentation%20and%20monitoring%20of%20RGSM%20in%20the%20MRG%20NM%20Annual%20Report%20June%202003%20-%20May%202004.pdf

Date: 2005/05/17

Author(s): Remshardt W.J.

Publication: Report prepared for Middle Rio Grande Endangered Species Act Collaborative Program, 38 p.

Abstract:

Rio Grande silvery minnow (Hybognathus amarus) was historically found in the mainstem Rio Grande and its larger tributaries (Rio Chama 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). Recently, Rio Grande silvery minnow was found in the Middle Rio Grande, New Mexico (MRGNM) below Cochiti Dam downstream to Elephant Butte Reservoir, representing 283 km (176 mi) or 5-7% of its historical range. Within the last several years, continued river drying in Isleta and San Acacia reaches has dramatically decreased densities to a level where Angostura Reach now has the highest catch rates of Rio Grande silvery minnow (Dudley et al. 2004). Direct and indirect evidence indicates that augmentation efforts in the Angostura Reach are partially contributing to the increase in upstream catch rates. In comparison, 5 years ago it was estimated more than 70% of Rio Grande silvery minnow inhabited the San Acacia Reach (San Acacia diversion dam downstream to Elephant Butte Reservoir) (U.S. Fish and Wildlife Service 1999). With frequent river intermittency downstream of Isleta Dam and unknown population status above Angostura Dam, these areas currently do not provide adequate and/or continuous population status. Human and environmental factors have reduced the continually flowing range of Rio Grande silvery minnow to the Angostura Reach (below Angostura Dam to Isleta Dam), which is only 65 km (40.4 mi) or 1% of its historic range. Nevertheless, the potential for intermittency should not outweigh the potential for continued occupation and existence in the lower reaches.