The team of experts at the Albuquerque Biological Park said Monday the release will be a big step toward ensuring the survival of the rare Rio Grande silvery minnow, which was listed as endangered in 1994 due to its plummeting population.
The minnow used to be abundant in the Rio Grande and some of its tributaries from northern New Mexico down to the Gulf of Mexico. Due to pressures on the river and changes in habitat, the minnow today only occupies about 5 percent of its historic range - a stretch of the Rio Grande in central New Mexico.
Between 400,000 and 500,000 minnows were being taken from the breeding facility at the biopark and a fish hatchery in southeastern New Mexico to the Big Bend area. The fish were riding in special tanks in trucks equipped with monitors and oxygen.
"For us, it's historic," said Chris Altenbach, the biopark's curator of fishes. "For us, this is what we're interested in seeing, that the fish do well."
Once the minnows get to Big Bend, they will be placed in holding pens in the river so they can acclimate. There are two release sites within the park's boundaries as well as one upstream and one downstream.
Biologists expect to open the pens and let the minnows explore more of their new home on Wednesday.
"We're not just dumping them straight into the river," said Jason Remshardt, the U.S. Fish and Wildlife Service's lead biologist for the minnow. "When you first stock fish, especially when they've been on the truck for 12 hours, they're a little stressed. Their first instinct is to swim down river as fast as they can."
Remshardt said this week's work has been in the planning stages for years. As part of the minnow's recovery plan, the Fish and Wildlife Service hopes to establish at least three stable populations - including the one in central New Mexico.
"To have a chance at making it, we have to have multiple populations and the more we have, the less pressure it puts on any one by itself," Remshardt said.
Aimee Roberson, a Fish and Wildlife Service biologist in Alpine, Texas, said the goal of the reintroduction is to one day be able to downlist the minnow and eventually remove it from the threatened and endangered species list altogether.
The minnows that will be released in Big Bend will be considered a nonessential, experimental population, meaning they will not have the same Endangered Species Act protections as those in the Middle Rio Grande.
The Fish and Wildlife Service said the experimental designation ensures that the daily activities of private landowners and water users will not be affected by the reintroduction.