Technical Report
Final Rio Grande Silvery Minnow Annual Augmentation Plan 2023-2028
Date: 2022/08/01
Author(s): Archdeacon T.
Publication: Prepared by U.S. Fish and Wildlife Service, New Mexico Fish and Wildlife Conservation Office.
Abstract:
Rio Grande Silvery Minnow (Hybognathus amarus; hereafter RGSM) is an endangered, small-bodied fish now found only in the Middle Rio Grande (MRG) of central New Mexico. Rio Grande Silvery Minnow was listed as endangered in 1994 primarily due to extirpation from 90-95% of its former range. In 2000, the U.S. Fish and Wildlife Service (USFWS) developed policy for the controlled propagation of endangered species. In 2001, the first RGSM Augmentation Plan (hereafter Augmentation Plan) was introduced to guide the USFWS’s efforts to propagate and augment the wild population and contribute towards recovery of the species.
The purpose of augmentation is to increase the resilience of RGSM and improve the species’ ability to persist through time. This is achieved by increasing overall abundance and distribution of RGSM following years of low recruitment by augmenting wild populations with genetically diverse hatchery-reared fish. Since 2001, over 3 million hatchery raised RGSM have been released into the MRG. Initially, stocking and monitoring efforts focused on the Angostura Reach where catch rates were low and the benefit of augmentation was expected to be higher than other reaches. Eventually, all reaches received hatchery fish and hatchery constraints have limited production for the Middle Rio Grande to 300,000 or less per year.
Rio Grande Silvery Minnow densities decline during years of low spring runoff. Recovery from population bottlenecks is hindered by lack of spawning adults in some years. While hatchery released individuals cannot count directly towards recovery goals, their presence and successful reproduction can contribute to recovery though increased demographic resilience by increasing spawner numbers and preventing loss of genetic diversity. Long-term population and genetics monitoring confirm augmentation increases the number of potential spawners in spring and genetic diversity has been maintained in the wild population.
The revised augmentation plan was effective 2018-2022 and requires revision for 2023-2028. Minor changes from the 2018 Augmentation Plan include:
- Updated early spring planning calculation to reflect inclusion of additional years of long-term population monitoring data
- Comparison of autumn release calculations based on September monitoring and October monitoring to determine if adjustments to fish releases are required