Technical Report
Rio Grande Silvery Minnow Population Monitoring Program Results From 2003
Date: 2004/04/12
Author(s): Dudley R.K., Platania S.P., Gottlieb S.J.
Publication: Report prepared for U.S. Bureau of Reclamation, 168 p.
Abstract:
Rio Grande silvery minnow, Hybognathus amarus, has been declining in distribution and abundance in the Rio Grande Basin over the past fifty years. It has been extirpated from the Pecos River and from the vast majority of its historical range in the main stem Rio Grande. The remaining population of this imperiled species resides in a 280 km reach of river between Cochiti Dam and Elephant Butte Reservoir in the Middle Rio Grande of New Mexico. The remnant population of this once widespread taxon has also been steadily declining in abundance despite its listing as a federal endangered species in 1994. Multiple pronounced river drying events over the past decade have eroded the ability of this species to recover in its current range. In addition, fragmentation of its remaining range into four segments (35.9, 65.2, 85.5, and 90.4 km long) by diversion dam structures (Angostura, Isleta, and San Acacia) pose continued threats to the species’ long-term persistence.
Analysis of Rio Grande silvery minnow catch rates revealed a significant interaction (p<0.05) between mean catch rate and locality. The highest catch rates of silvery minnow were generally recorded at upstream sampling localities in each of the respective reaches (i.e, close to diversion dams). This spatial distribution of individuals was most pronounced in the Angostura and Isleta reaches. Diversion dams allow passive downstream movement of silvery minnow eggs and larvae but block upstream movements of juveniles and adults>< 0.05) between mean catch rate and locality. The highest catch rates of silvery minnow were generally recorded at upstream sampling localities in each of the respective reaches (i.e, close to diversion dams). This spatial distribution of individuals was most pronounced in the Angostura and Isleta reaches. Diversion dams allow passive downstream movement of silvery minnow eggs and larvae but block upstream movements of juveniles and adults.