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You are here: Home / Publications / Periodicals / Natural Outlook / Natural Outlook, 2011 / Little Fish Makes Big Bend Comeback

Little Fish Makes Big Bend Comeback

The TCEQ plays a part in reintroducing the endangered Rio Grande silvery minnow. (Natural Outlook, Winter/Spring 2011)

A Rio Grande silvery minnow lays on the fingers of Gary Garrett, Texas Parks and Wildlife.
A Rio Grande silvery minnow lays on the fingers of Gary Garrett, Texas Parks and Wildlife.
Photo courtesy of Ray Mathews/TPWD.

The Rio Grande silvery minnow was once the most common native fish in the Rio Grande, found in large schools all along the river, from northern New Mexico to the Gulf of Mexico. But by the 1970s, the species had dwindled to occupying only a small stretch of the middle Rio Grande near Albuquerque, New Mexico, about 7 percent of its historic range. In 1994, the silvery minnow was placed on the federal endangered species list.

Today, the future looks a little brighter for the small fish. After an absence of nearly fifty years, the silvery minnow swims again in the Big Bend reach of the Rio Grande.

Silvery Minnows Released in Texas

In 2008, the U.S. Fish and Wildlife Service (FWS), in collaboration with the TCEQ and other members of the Rio Grande Silvery Minnow Recovery Team, released 445,000 minnows from New Mexico breeding facilities into the Rio Grande—at Big Bend Ranch State Park, Big Bend National Park, and the Adams Ranch del Carmen, a privately owned conservation area. Another 509,000 were released in 2009 and 448,444 in 2010. More releases are planned in future years.

"The silvery minnow in the Big Bend is designated as an experimental non-essential population," said Herman Settemeyer, who, as coordinator of the TCEQ's Interstate River Compact Program, was a member of the team that developed the minnow's recovery plan.

This designation is allowed under section 10(j) of the Environmental Species Act, which encourages the reintroduction of a species by reducing regulations, giving local communities flexibility in establishing parameters for reintroduction.

Comeback in the Rio Grande

In the spring of 2010, biologists collected eggs in the Big Bend reach to see what species were spawning, and identified some silvery minnow eggs. During subsequent monitoring efforts, biologists also documented larval and juvenile silvery minnows.

"This was the first reproduction that we'd documented from this population," said Aimee Roberson, a wildlife biologist with the FWS who worked on silvery minnow conservation out of the FWS's New Mexico Ecological Services Field Office until taking a position in the Alpine, Texas, office several years ago to coordinate the Big Bend reintroduction.

Future monitoring efforts will be targeted to document the survival of these eggs to larval, juvenile, and adult life stages.

"After working several years on this project, it's exciting to see this result," added Roberson. "I think it's indicative that we are moving in the right direction and moving toward successfully reestablishing this species in the Big Bend reach."

The Rio Grande Silvery Minnow

(Hybognathus amarus)

Photo of silvery minnow courtesy of Aimee Roberson/FWS.
Photo courtesy of Aimee Roberson/FWS.

Description | The Rio Grande silvery minnow is a small, stout fish with moderately small eyes and a small mouth. Adults rarely exceed four inches in length.

Habitat | Rio Grande silvery minnows prefer slow-moving water with a sandy or silty bottom.

Diet and Feeding | Rio Grande silvery minnows eat algae and diatoms (microscopic algae) from the nutrient-rich silty bottoms of quiet stretches. They also pick up pollen, bacteria, and organic debris while nibbling.

Reproduction | The Rio Grande silvery minnow is a pelagic spawner, meaning that it releases its eggs directly into the water to incubate when the conditions are right. One female can release more than 4,000 eggs in a 12-hour period. In contrast to some fish eggs that take months to incubate, the minnow's eggs hatch in about 24 hours into larvae that can swim in just three to four days.

Endangered Species | The Rio Grande silvery minnow was placed on the federal endangered species list in 1994. The exact reason for the silvery minnow's dwindling numbers is unknown, but biologists hypothesize that changes in the Rio Grande—construction of dams, decreasing water quality, introduction of non-native fish, and channelization that narrowed and sped up the river—led to the decline.

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