Technical Report
Rio Grande Silvery Minnow Population Monitoring Results From April 2016
Date: 2016/05/20
Author(s): Dudley R.K., Platania S.P.
Publication: Prepared for U.S. Bureau of Reclamation, 26 p.
Abstract:
The April population monitoring efforts were conducted at 20 sites throughout the Middle Rio Grande. Five sites were located in the Angostura Reach, six sites in the Isleta Reach, and nine sites in the San Acacia Reach. A list of collection localities is appended (Table A-1). Adult and juvenile fish were obtained by rapidly drawing a 3.1 m x 1.8 m small mesh (3/16th inch) seine through discrete mesohabitats. Larval fish were also collected with a 1.0 m x 1.0 m fine mesh (1/16th inch) seine in all seasons except winter. All fishes were identified to species and enumerated. We measured and aged all Rio Grande Silvery Minnow. As age-0 individuals are only present after annual spawning occurs (ca. May–June), their absence in the months preceding spawning is to be expected. Figures illustrating fish densities (i.e., fish per 100 m2 ) were prepared for the ten focal species to facilitate comparisons among reaches.
During April, sampling covered 10,365.7 m2 (surface area) of water and yielded 1,394 fish. Cumulative fish density during April was 13.4 individuals/100 m2 sampled. The three most common species were Red Shiner (n = 1,054), Flathead Chub (n = 174), and Channel Catfish (n = 52). The 20 sampling sites yielded a total of 13 fish species. Rio Grande Silvery Minnow was present in 29 of the 231 seine hauls that yielded fish. We collected Rio Grande Silvery Minnow at 12 of the 20 sampling sites, and its overall density was 0.35 (n = 36) individuals/100 m2 sampled. Densities of unmarked and marked individuals were 0.22 (n = 23) and 0.13 (n = 13) individuals/100 m2 sampled, respectively. Densities of age-0, age-1, and age-2+ individuals were 0.00 (n = 0), 0.32 (n = 33), and 0.03 (n = 3) individuals/100 m2 sampled, respectively.