Scientists help the silvery minnow rebound in the Rio Grande.
By Megan Wilde
Usually, when a species disappears from a place, it’s gone forever. But the Rio Grande silvery minnow (Hybognathus amarus) may become an exception. For the first time in more than 50 years, biologists have found a Texas-born silvery minnow in the Rio Grande. That bodes well for the herculean effort to return this endangered species to Texas, as well as for the beleaguered river.
The Rio Grande silvery minnow was once one of the most common piscine residents of the Pecos River and the Rio Grande, from the Texas coast into northern New Mexico. But by the 1970s, this hardy desert fish had disappeared from all but a 170-mile stretch of the Rio Grande near Albuquerque, N.M. — about 5 percent of its historic range. Drought in the 1990s brought these remaining minnows perilously close to extinction, prompting the federal government to list the species as endangered in 1994.
“This is a minnow that was here for thousands and thousands of years, doing just fine. And suddenly it wasn’t,” says fisheries biologist Gary Garrett, who also directs the Texas Parks and Wildlife Department’s watershed conservation program. “As biologists, that tells us something went wrong.”
What went wrong is still a mystery, but biologists suspect changes in the Rio Grande were to blame for the minnow’s disappearance. Over the past century, dam building, water diversion for thirsty cities and farms, and pollution from mining and agriculture conspired to make the Rio Grande a lot less grand.
“All of these changes would not be the best news for a small minnow,” says Bob Edwards, a University of Texas–Pan American fish biologist.
Since the 1970s, though, the river has changed for the better in some ways. Water quality improved after DDT and other harmful chemicals were banned.
And in the Big Bend, the river still flows free of dams and major diversions for about 300 miles between Presidio and Amistad Reservoir. Plus, other fish similar to silvery minnows have managed to hang on in this stretch of river. That’s why biologists chose this region as the best place for the minnow to make a comeback.
The minnow’s Texas homecoming began in December 2008, when the U.S. Fish and Wildlife Service — in collaboration with TPWD and other groups — released 445,000 hatchery-raised minnows into their namesake river. Now almost a million minnows have been released at four sites in Big Bend Ranch State Park, Big Bend National Park and a private ranch near Black Gap Wildlife Management Area. In October, another 400,000 minnows joined them, and more releases are planned for future years.
Edwards and Garrett are on the team of biologists monitoring the minnows, and so far, they’ve found healthy survivors every time they’ve looked. But in order for the species to re-establish itself in Texas, the minnows will need to do more than survive — they need to find enough habitat to spread out and, most important, make more minnows.
This past summer, the team found the first signs of reproduction. In April and May, they collected silvery minnow eggs and larval fish, and in August, they found a juvenile. Garrett says the juvenile fish was probably one of thousands of young Big Bend native minnows, the first of their kind to be born and raised in Texas in half a century.
These discoveries are making the team increasingly hopeful, though they say it’s too soon to draw conclusions about how the minnows will ultimately fare here.
“If they make it, at least we can assume that portion of the river has rebounded from whatever was wrong and is closer to its natural, functioning, healthy state,” Garrett says. “I’m trying not to be too optimistic, but we’re starting to hit a few of the milestones that we’d like to hit. So far, so good.”