Duckweed Removal for Gila Topminnow Habitat Improvement

In 1967 the Gila Topminnow was listed as endangered by U.S. Fish and Wildlife under the Endangered Species Act. The Gila Topminnow is a small (2.5-5 cm), silvery, guppy-like fish without dark spots on the fins. Topminnow are unique in that they bear live young rather than lay eggs.

The Az Game and Fish Department is working to improve habitat for the Gila Topminnow. The Friends of San Rafael Valley worked with Az Game and Fish on their most recent attempt to improve dissolved oxygen levels in riparian area streams and pools by removal of duckweed. Duckweed is a very small floating plant that can cover the entire water surface cutting off oxygen to fish.  

The volunteers mechanically removed the duckweed utilizing long handle dip nets and pool skimmers to scoop the duckweed off the surface of the water and remove it from streams and pools.

The Arizona Game and Fish Department has deployed dissolved oxygen loggers in each of the stream/pool for the duration of removal efforts, to track whether mechanical removal of duckweed improves dissolved oxygen levels over the course of the season. The Gila Topminnow population is being monitored to evaluate whether duckweed removal leads to greater survival and reproduction of topminnow.