Earth Notes
4:04 am
Wed March 20, 2013

Earth Notes: Rio Grande Silvery Minnow

The Rio Grande silvery minnow may sound like it has a name out of a children's book. But the problems it faces are unfortunately real.

Silvery Minnow
Silvery Minnow
Credit Aimee Roberson/USFWS

Once among the most widespread and abundant fish in the Rio Grande, it's now restricted to about 150 miles of the central river, in and around Albuquerque. Dams, water diversions, and channelization, compounded by recent drought, have dried up much of its former habitat.

In summer, when irrigation demand is greatest, that habitat shrinks even more, and part of the river downstream from the city dries up. Despite stocking efforts and some reserved instream flows, densities of silvery minnows last year were the lowest ever recorded in the middle stretch of the river.

Another population has been stocked in the Big Bend reach of the river in Texas. And experimental efforts are underway to rear the fish in specially built facilities in New Mexico.

In these refugia, the minnows are put into outdoor ponds and streams built to mimic nature. They feed on natural and artificial foods until they reach adequate size, then are released into the river. But to spawn, they've typically had to be injected with fertility hormones.

Recently, silvery minnows did spawn naturally in a new refuge - taking cues from a staged springtime runoff like that of the actual river. Once back in their native environment, the small silvery minnows can survive. But only with one key ingredient: some river water flowing down the channel as it used to do.