Technical Report
1999 Population Monitoring of Rio Grande Silvery Minnow
Date: 2000/03/23
Author(s): Dudley R.K., Platania S.P.
Publication: Final report prepared for U.S. Bureau of Reclamation and U.S. Army Corps of Engineers, 50 p.
Abstract:
Population information on Rio Grande silvery minnow and the associated Middle Rio Grande (Rio Grande between Velarde, New Mexico and Elephant Butte Reservoir) fish community has been gathered regularly since 1987. The first studies were conducted by Platania (1993a) from 1987-1992 to determine spatial and temporal changes in the ichthyofaunal community and to provide resolution of species-specific habitat use patterns. A key purpose of those preliminary studies was to supply additional information on the conservation status of Rio Grande silvery minnow. Quarterly sampling efforts during the summer and autumn of 1989 and 1990 revealed that densities of Rio Grande silvery minnow were extremely low. Based on previous samples, these low densities indicated a rapid decline of this species in its already greatly reduced range. The 90-95% reduction in the range of Rio Grande silvery minnow and threats to its continued persistence in the Middle Rio Grande were central to this species being listed as endangered by the U.S. Fish and Wildlife Service (U.S. Department of Interior, 1994).
From 1992 until present, the U.S. Bureau of Reclamation, U.S. Fish and Wildlife Service, New Mexico Department of Game and Fish, and U.S. Corps of Engineers have cooperated to fund numerous ichthyofaunal studies in the Middle Rio Grande. Among these studies was the long-term monitoring of the distribution and relative abundance of the Middle Rio Grande fish community at numerous sites between Angostura Diversion Dam and Elephant Butte Reservoir. While Rio Grande silvery minnow was the primary focus of these efforts, these research activities were designed to provide information about the entire fish community.
The objective of the 1999 collecting activities was to monitor populations of Rio Grande silvery minnow and the associated fish community. Seasonal and spatial differences in population structure and species densities were examined to determine the ecological dynamics within this system. Annual changes in the distribution, abundance, and composition of all fish species were also assessed. Information obtained from this study will allow a more thorough understanding of the current conservation status and population dynamics of Rio Grande silvery minnow both of which are important components for the recovery of this species.