Technical Report

Rio Grande Silvery Minnow Rescue and Salvage Report Fiscal Year 2003

URL: https://webapps.usgs.gov/mrgescp/documents/SmithandBasham_2003_RGSMRescueandSalvageReportFiscalYear2003.pdf

Date: 2003/01/01

Author(s): Smith J., Basham K.

Publication: Prepared by U.S. Fish and Wildlife Service, 13 p.

Abstract:

Despite recent water management to benefit the Rio Grande silvery minnow (silvery minnow), some portions of the Rio Grande have gone intermittent yearly since 1996. The location, magnitude, and duration of the intermittency are dependent on many environmental events including spring runoff, summer thunderstorms, amount of supplemental water stored in upstream reservoirs, and other general climatic conditions. Stream drying causes direct mortality to fish when the pools in which they are trapped in dry up.

The fate of fish trapped in isolated pools has been studied in the Rio Grande and other drainages to determine the effects of river drying on the fish community. These studies have determined that the trapped fish become stressed due to crowding, increasing water temperatures, increasing ambient temperatures, decreasing dissolved oxygen, aquatic predation, terrestrial predation, interspecific competition, and intraspecific competition (Trammer 1977, Capone and Kushlan 1991, Smith and Hoagstrom 1997, Ostrand and Marks 2000, and McClinton et al. 2000). All of these potential factors make survival of fish in isolated pools questionable.

Over the last 5 years, the U.S. Fish and Wildlife Service New Mexico Ecological Services Field Office (Service) with assistance from other agencies, has salvaged silvery minnows from isolated pools during river intermittency and translocated these fish to areas with permanent flowing water. In 2001, the Service determined that salvage of silvery minnows was an appropriate reasonable and prudent measure for minimizing incidental take of the silvery minnow during river intermittency. This determination was based on the available information on fish survival in isolated pools, the endangered status of the silvery minnow, and the possibility of the minnow population declining throughout the middle Rio Grande.

The first notable silvery minnow salvage was performed in 1996 and salvages have continued to some degree each year since then. Prior to 2001, one attempt was usually made to collect as many silvery minnows stranded in isolated pools as possible. These early attempts usually consisted of one crew entering the Rio Grande at available access points, collecting silvery minnows, and translocating them upstream to flowing water. These salvages were usually conducted only once a year, and in most cases no attempts were made to collect silvery minnows from isolated pools in remote and inaccessible portions of the Rio Grande. During 2001 and 2002 organized and extensive minnow salvage was accomplished by the service.

In 2003, the Service performed approximately 54 individual silvery minnow salvages within the Isleta and San Acacia Reaches, salvaging 713 silvery minnows. Access points were located for all drying portions of the Rio Grande, regardless of how remote. Approximately 70 river miles were salvaged with some river miles being salvaged several times due to re-wetting caused by rainstorm events (“acts of nature”), bringing the total up to approximately 90 river miles salvaged.