What a difference a year makes.
This time last year, people working to protect the endangered Rio Grande silvery minnow were guardedly optimistic about the little fish. A heavy 2017 winter snowpack led to a large spring runoff that allowed water managers along the middle Rio Grande in New Mexico to “overbank” water into the bosque – a riparian woodland – that borders the river. All those miles of flooded nooks and crannies among the cottonwoods are prime fish spawning grounds, and the minnows made use of them for several months.
But this year, a nearly nonexistent snowpack across New Mexico has meant nearly no spring runoff – certainly not enough to create the overbanking conditions that the silvery minnow prefers for spawning. In fact, nearly 20 miles of the Rio Grande have already dried in New Mexico between Bosque del Apache and Socorro. The comparison in runoff between 2018 and 2017 “has been the biggest difference between two years that we have seen,” said Mary Carlson, a spokesperson at the Bureau of Reclamation.
The dramatic swing is an unpleasant surprise following the previous year’s abundance.
“Last year was a really, really good year,” said Thomas Archdeacon, a fish biologist with the U.S. Fish and Wildlife Service who studies and monitors the silvery minnow. The 2017 flooding created a huge bump in the endangered fish’s population.
“The fear is that many, if not most, of those fish will perish,” said Kathy Lang, curator of the Silvery Minnow Refugium breeding program at the Albuquerque BioPark. “That is our biggest concern.”
And so crews are out in the drying sections of the Rio Grande, searching for silvery minnows in pools and puddles in the riverbed. Archdeacon said he has collected about 61,000 minnows so far this spring to be transported upstream to areas he hopes will have perennial water flows.
It’s part of an intricate plan to keep these tiny fish in a river that has changed dramatically around them in the past century. The changes come from a trio of Ds: dams, diversions and droughts.
Historically, schools of minnows have swum up and down the river as the waters rose and ebbed throughout the year. But at the start of the 20th century, dams began to block the fish’s ability to travel the length of the Rio Grande and migrate away from dry stretches. Dams also keep the fish from breeding with other fish farther up or downstream, hampering genetic diversity. Those dams and their reservoirs were designed to mitigate annual spring floods and to manage and divert river water for farming in the Rio Grande Valley. They benefit farmers and people who live along the river – but they make life difficult for the minnow.
Add regular droughts to the mix and it often becomes difficult for the silvery minnow to live in the main branch of the river at all.
Efforts to save the minnow help more than just the minnow itself. This little fish has become what Archdeacon calls an “umbrella” species because actions taken to save it also help protect the lives and needs of other plants and animals along the middle Rio Grande.
The current 15-year plan for saving the silvery minnow involves capturing eggs and raising them to be released in coming years; transporting fish to wet stretches of river; building fish passages around dams; and juggling water between rights holders along the river to keep the Rio Grande wet when the fish needs to spawn. As noted, the first and second parts of the plan are already underway, and water managers are now planning up to four small water pulses to be released from upstream reservoirs specifically for the fish. It is hoped the extra water will allow the minnows in the river to spawn. Biologists will then collect as many of the eggs as they can, to be used in the captive breeding program.
“This particular operation is being done for the minnow,” said Carlson, “though it’s beneficial to the entire ecosystem.”
Many of the plants and animals along the Rio Grande evolved alongside the river’s annual ebb and flow. So this year’s pulses of water – though small – will help the silvery minnow as well as other bosque natives, such as the endangered southwestern willow flycatcher, the yellow-billed cuckoo and the cottonwood trees themselves, all of which benefit from spring runoff.
Meanwhile, teams are out in the low water collecting fish.
Lang said that most years she asks her collection crews if they got any eggs, but “this year I ask, ‘Did you get any water?’” However, she noted one upside to low water in the river: It’s easier to find and collect fish and eggs as they pool in what little water remains. During last year’s overbanking, when the fish bred among the flooded trees and bushes, “We ended up collecting a grand total of 10 eggs,” she said. This year, Lang believes it would be great to collect 100,000–200,000. “I don’t know how probable” that is, she said, “but it is possible.”
Also, Archdeacon added, “there are just tons of [wild] 2017 fish out there.” All of these fish and eggs from last year are important because the minnow only lives 2–3 years in the wild, and just a couple of years of serious drought could wipe out that population. Archdeacon said that if the snowpack fails again next year, that population “is going to crash,” which is why a breeding program is so important.
Even so, it requires new fish and eggs to keep its own population up and the genetic pool diverse. So, as much as possible, the breeding program uses fish and eggs captured from the wild rather than ones from hatcheries. “Those are the fish that survived river conditions,” said Lang. “We want their offspring to continue.”
But what happens if they don’t continue? What happens if the silvery minnow disappears from the Rio Grande? Jen Pelz, a program director at WildEarth Guardians, said the river would change dramatically if it lost its “umbrella” protector. “Worst-case scenario? The river only operates from March to October as a way to transport water downstream,” for irrigation and water rights management, she said. “And I think that’s a really sad place for our river to end up.”
Correction: This story has been corrected to reflect that the fish collected from dry stretches of the river are not going into the breeding program, but are transported upriver to wet stretches.