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Why the Fate of a Tiny Rio Grande Fish Is So Important

Lots of rain and snow this year bode well for the endangered Rio Grande silvery minnow and that’s good news for the whole river and the riparian ecosystem.

Written by Jerry Redfern Published on Read time Approx. 4 minutes
U.S. Fish and Wildlife Service biologists Tristan Austring, left, and Angela James use a seine net to search for endangered Rio Grande silvery minnow in isolated pools in the riverbed near Socorro, N.M., in June 2013.AP/Susan Montoya Bryan

Heavy winter snows and a wet spring have filled the Rio Grande River through New Mexico with more water than it has seen in years, and water managers predict the river could stay up well into the summer. That’s good news both for people who rely on the river and for one of the river’s most threatened tiny inhabitants: Hybognathus amarus, a.k.a. the Rio Grande silvery minnow.

“I just think it’s going to be a really good year for the minnow,” said Carolyn Donnelly, a water operations supervisor at the Albuquerque office of the United States Bureau of Reclamation.

But for more than 20 years, that fish – an endangered species that grows to the size of a skinny finger – has been the center of a debate over how to save its minuscule population from extinction. It’s a debate that pivots on water in the Rio Grande.

The silvery minnow is a reflection of its river. Much as the Rio Grande is a heavily managed version of what it was a century ago, so is the fish. The fish needs water to live, and it needs special river conditions to breed in the wild. But several recent years of drought exacerbated the plight of the minnow, which has a short lifespan. Further, sections of the Rio Grande regularly run dry during summer as water is diverted for agriculture and other uses. Without hatcheries, relocation and dam diversions, the silvery minnow likely would have died out long ago.

“It’s not like a long-lived species where you have a bad year and there’s still all of these adults out there,” said Thomas Archdeacon, a fish biologist with the U.S. Fish and Wildlife Service. “Basically two bad years in a row will essentially wipe it out, and we’ll be relying almost entirely on that hatchery safety net.”

As water diversions increased, the Rio Grande silvery minnow numbers have dwindled in New Mexico, and without hatchery programs the fish would have likely died out. (U.S. Fish and Wildlife Service)

Once native to more than 2,000 miles of the Pecos and Rio Grande rivers from central New Mexico to the Gulf of Mexico, the minnow now lives in a nearly 200-mile reach of the Rio Grande between two major dams. (While extirpated in Texas, some hatchery minnows were reintroduced in 2008 near Big Bend.)

The minnow’s presence is a telltale of the state of the river’s health. “I think that they are somewhat a canary in the coal mine,” said Jack Williams, senior scientist with Trout Unlimited. “I think that’s maybe among their largest values to us.”

Over the past century, dams, irrigation diversions and drought have drastically altered the shape of the Rio Grande and depleted much of the fish’s natural range and spawning areas – namely the bosque or cottonwood forest that still lines parts of the river. Traditionally this forest floods in spring when the silvery minnow spawns.

“It absolutely is incredibly important for their spawning and survival,” said Kathy Lang, curator of the Silvery Minnow Refugium breeding program at the Albuquerque BioPark. “And obviously in low-flow years, we don’t have any of that habitat.”

Archdeacon said that what remains of the bosque “may not exist if there wasn’t an endangered species there that required protection.” Bosque restoration efforts on behalf of the tiny fish also benefit other species that use the environment, such as the endangered southwestern willow flycatcher, the yellow-billed cuckoo and the cottonwoods that dominate the forest.

“So many of the animals and plants in this basin are adapted to – and function well with – a natural hydrograph of snowmelt runoff,” said Joel Lusk, senior biologist with the U.S. Fish and Wildlife Service. “It’s not just the minnow.”

In December, the U.S. Fish and Wildlife Service released its latest plan for saving the silvery minnow. Called a biological opinion, it sets out population goals and lays out the groundwork for preserving the fish for the next 15 years. The plan calls for: capturing eggs and raising fish to be released in bad, dry years; transporting fish from drying stretches of river to wet ones; modifying river flows to minimize dry stretches; and building fish passages around key dams. The biological opinion affects the work of 16 federal, state and tribal agencies.

“It’s a different approach,” said Donnelly from the Bureau of Reclamation. Many of the biological opinion’s recovery efforts also appeared in the previous plan started in 2003. But the current plan involves less juggling of river and irrigation flows to keep fish habitat wet.

Not everyone thinks the new plan does enough. “We’re not really talking about biological recovery,” said Jen Pelz, the wild rivers program director for Wild Earth Guardians. “This 15-year biological opinion is mostly insuring that the species doesn’t go extinct.” In 1999, Wild Earth Guardians sued the Bureau of Reclamation and the Corps of Engineers for not doing enough to protect the silvery minnow.

But for now, the river is up, storms keep dumping rain and snow in the highlands and there are silvery minnows spawning in the Rio Grande.

“I think there’s no doubt that it will be a good year for the river’s health and the silvery minnow,” said Pelz. But she’s apprehensive about the future. “One really great year, or a couple pretty good years, can be followed by a number of dry years.”

Dry years are hard on the Rio Grande – and even harder on the silvery minnow.

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