BioPark releases endangered Rio Grande silvery minnows

Fish who have never known the river graduated to the wild on Wednesday, when the Albuquerque BioPark and the U.S. Fish and Wildlife Service released 18,000 captive-spawned endangered Rio Grande silvery minnows.

Patrick Horley, the BioPark’s Aquatic Conservation Facility curator, scooped the minnows from a metal tank resting in a truck bed. Then he gently deposited the net of wriggling minnows into buckets full of muddy river water. BioPark and Fish and Wildlife staff dressed in waders carried the heavy buckets into the Rio Grande before tipping them slowly into the water and allowing the small, silver fish to swim away.

The operation was just one step in the effort to keep the species alive.

“It’s bittersweet,” Horley said. “Because we don’t know what their fate is, and we know what their fate is with us, but it’s also such an important part of what we do.”

The Rio Grande silvery minnow occupies 7% of its native range, living in just three sections of the river: the Albuquerque, Isleta and San Acacia reaches. It was first listed as endangered in 1994. Human intervention has been key to preventing the fish species’ extinction.

For more than 20 years, Fish and Wildlife, and the BioPark have been gathering minnow eggs in the spring, then releasing grown fish into the river in the fall.

In the early years, fish were not spawned in captivity. The eggs were raised to adulthood, then released. But the effort has grown more sophisticated, and now some of the wild eggs are used to breed more fish. The BioPark, along with state and federal officials, works with 13 other partners to conserve the fish.

The thousands of silvery minnows released this past week were all spawned at the BioPark. Most were spawned last year, and some were spawned this year.

The silvery minnow release turned out a crowd. BioPark staff were given a 15-minute warning over their walkie-talkies, in case they wanted to watch the spectacle. A dozen or so walked from the botanic garden to the muddy riverbank by the Central bridge. A cyclist crossing the bridge paused to watch from overhead.

Even though it was her day off, Trinity McCoy showed up to watch the release. She works with reptiles at the BioPark, but worked with the minnows previously. McCoy loves the fish so much she added a silvery minnow to the collection of tattoos on her arm.

“I think it’s a really cool project that benefits the whole river, and they’re really tiny and cute,” McCoy said.

McCoy’s black and white tattoo includes a stripe of color to show the minnow has been tagged. The BioPark tags every silvery minnow it raises with a line of latex paint injected below the skin. Tagging the fish allows other agencies to interpret trends in the fish population and get a sense of how successful the recovery effort is, Horley said.

As more and more buckets of fish were emptied in the river, the audience trickled away. When the final minnows were released, the remaining BioPark staff cheered.

Not all the BioPark’s silvery minnows get released. Typically 20,000 are kept over the winter to provide a brood stock for future years.

Soon, the BioPark, and Fish and Wildlife will collaborate on a second release, likely near the Alameda bridge. The release location is selected by Fish and Wildlife based on water conditions. That release will include roughly 19,000 fish. About half of those fish will be captive-spawned, while the rest will be from eggs gathered in the Rio Grande.

“It’s like graduation,” Horley said. “We’re sending them out to the real world. And we say, good luck. We hope the best for you.”

Cathy Cook covers the federal government for the Albuquerque Journal. Reach her via email at ccook@abqjournal.com.