Scientists want to know if Rio Grande contaminants are feminizing the endangered silvery minnow

After a soaking monsoon rainstorm, the Rio Grande through Albuquerque runs red. The next morning, as its waters again recede, spadefoot toads the size of quarters scamper atop the mud. Tiny fish wiggle into pools pressed by the river into the banks, and awkwardly-aloft ducks crash-land into the water. For a few hours, it’s easy to imagine this is a natural river, dependent only upon storm clouds and seasons for its ebbs and flows.

In fact, the Rio Grande is manipulated and managed, overused and oftentimes abused. Since the early 1990s, the conservation group American Rivers has repeatedly included the Rio Grande on its list of endangered rivers; in 2007, the group named it the world’s seventh most endangered river. Farmers and municipalities vie for water. During heavy rainstorms, urban runoff fouls its flows. Albuquerque’s wastewater treatment plant is the river’s sixth largest New Mexico tributary.

At the center of the debate over the river’s health is a 4-inch fish—the silvery minnow—whose survival is intricately linked to the water in which it lives.

In recent years, scientists have begun finding fish within the Rio Grande that are “


”—that is, male fish with egg cells within their testes. Now, biologists are embarking upon additional studies to learn how certain chemicals within water from wastewater treatment plants—which, during dry times, makes up a significant portion of the river’s flow—are affecting the Rio Grande’s native fish populations, including the endangered silvery minnow.

Already, the minnow can’t survive without help. Each year, biologists stock the river with hatchery-raised fish. Then, when the river dries during the summer months, salvage crews return to rescue minnows from shrinking pools of warm water.

It wasn’t always like this. Sixty years ago, the silvery minnow swam the length of the 1,850-mile-long

Rio Grande

and its tributary, the

Pecos River

. But as farming intensified and cities sprawled, water quality fluctuated and river levels dropped. Now, the fish is found only in pockets of a 173-mile stretch of the Middle Rio Grande, which, in turn, is divided by dams into three sections. To save the fish, the

US Fish and Wildlife Service

in 1994 listed it for protection under the Endangered Species Act, setting off a series of court battles, agency showdowns and political wranglings that proved much more is at stake than a tiny fish.

As biologists warned that the fish needed—no kidding!—water to survive, water managers, cities and irrigation districts panicked over their claims to the river’s water. Republican and Democratic lawmakers alike agreed, and everyone from former Sen. Pete Domenici, R-NM, to Gov. Bill Richardson argued that water meant for cities should not be used to protect an endangered species.

Since the late 1990s, the state’s Interstate Stream Commission, legally responsible for delivering water to Texas, has repeatedly clashed with the Fish and Wildlife Service, and disputed the federal agency’s minnow studies and flow recommendations.

Now, the commission says it’s time for the federal government to admit the species is improving and to lift certain protections for the minnow. At the end of June, the Attorney General’s Office and the commission’s director sent a letter to Fish and Wildlife, pointing out that all of the threats to the minnow’s survival are being addressed, and many have been reduced or are inapplicable.

Credits: Interstate Stream Commission

Federal officials and activists alike were surprised by the letter. For years, WildEarth Guardians Executive Director John Horning was in the thick of the silvery minnow debate.

(formerly Forest Guardians) filed suit against federal agencies for mismanagement, and also worked within a coalition to create a water reserve for the fish during dry times. In recent years, agencies and stakeholders have learned to better work together, Horning says, and there are opportunities that didn’t exist a decade ago. Perhaps more significantly, the past few summers have been relatively wet compared with those earlier in the decade.

“I still think the great threat to the health of the Rio Grande and to fish is water of sufficient quantity—well, fish need water,” Horning says. “And basically, the river gets sloppy seconds.”

As it turns out, those sloppy seconds may have serious environmental repercussions.

Evidence of contamination in the Rio Grande has been mounting over the last decade.

In 2003, the state’s Environment Department and Department of Health reported that the majority of human wastewater contained antibiotic residues. In fact, up to 90 percent of pharmaceutical doses pass through humans or animals (such as those at dairies) and many antibiotics are not destroyed or removed by conventional wastewater treatment.

WildEarth Guardians Executive Director John Horning was involved for years in the silvery minnow debate.

In order to determine if poor water quality might be contributing to the decline of the silvery minnow, the Middle Rio Grande Endangered Species Act Collaborative Program had asked the Environment Department’s Surface Water Quality Bureau to monitor the Middle Rio Grande. That report was released last year. Although the most critical issue affecting the fish is the lack of adequate river flows to maintain its habitat, the state did find high levels of E coli in the river, as well as elevated levels of metals such as aluminum, copper and chromium. According to the report, water quality conditions exist that may affect the minnow’s reproduction and respiration, “further stressing the fish and reducing the likelihood for recovery.”

The state regularly monitors water quality in all rivers, surveying stretches on a rotating basis, according to Lynette Guevara, assessment coordinator for the Surface Water Quality Bureau. Currently, of the 370 miles of the Rio Grande surveyed, the state has noted “impairments” on 305 of those miles. These impairments range from aluminum levels and elevated temperatures to PCBs in fish tissues and widespread E coli contamination.

River contamination such as this is not a new phenomenon—but it is an evolving one.

The federal government began funding monitoring projects to learn how certain chemicals were affecting wildlife—including fish—in the late 1960s and ’70s, following Rachel Carson’s exposure in her book,

Silent Spring

, of the pesticide DDT’s impact on birds. A Fish and Wildlife Service marine biologist, Carson showed that


was causing birds to lay eggs with increasingly thin shells, and that certain bird populations were declining.

“That [monitoring] program lasted into the 1980s, and what they noticed was a lot of what are called ‘legacy’ pesticides decreased in fish—and that’s what folks were hoping to see,” Jo Ellen Hinck, a biologist with the US Geological Survey, who is based out of the Columbia Environmental Research Center in Missouri, says.

Legacy chemicals include DDT,


and mercury, which remain in the environment long after their use is discontinued.

Then, in the early 1990s, the issue of “

endocrine disrupters

” arose, and scientists realized they needed to do more than just measure the amount of contamination in tissue.

Endocrine disrupters include certain types of herbicides such as atrazine; the plastic compound bisphenol A; cadmium; DDT and other pesticides and insecticides still used today, including malathion; and a family of plasticizers known as phthalates.

These compounds affect the endocrine system, reproduction and fetal development, and scientists have learned that, even in very low doses, they can cause problems.

In the mid-1990s, the USGS began sampling fish in nine US river basins, including the Rio Grande, to learn about environmental contaminants. Only this time, scientists weren’t only measuring the amounts of chemicals or metals found within fish tissue. They also were looking for abnormalities in organs such as the liver, kidney, spleen, ovaries and testes.

“Scientists got better at creating chemicals where you didn’t have the accumulation in fish, and have that food chain accumulation—that led to, like, the thinning of bald eagle eggs,” Hinck says. “Those compounds can still have effects on the fish, but you can’t measure them because they don’t accumulate in the fish.”

What Hinck and her colleagues found was that many male smallmouth and largemouth bass had egg cells in their testes. “Intersex” fish showed up in all but one of the basins they studied—including in the Rio Grande. Endocrine disrupting compounds enter the fish’s body and mimic natural estrogens. (Like humans, fish also produce estrogens and androgens.)

Although Hinck says the Rio Grande results weren’t particularly alarming, taken with the data from the other large rivers studied, there is cause for concern.

“We became concerned with the incidents of ovotestes in male bass because it was becoming so prevalent,” she says. “Ovotestes” are gonads with both testicular and ovarian aspects.

In short, bass are not supposed to have eggs within their testicular tissue.

“Do we know what’s causing it? No,” she says. “But we do know that, if the majority of the fish have it, that seems anomalous to us.” Those findings have led them to take on additional studies, to try and learn what causes the reproductive disorders.

Biologists release hatchery-raised silvery minnows into the Rio Grande at Big Bend National park in 2008. This annual practice is part of an inter-agency effort to rekindle dwindling population levels.
Credits: Courtesy US Fish and Wildlife Services

Hinck points to a study released in 2007: Over the course of seven years, scientists with the University of New Brunswick dosed a remote Canadian lake with the hormones found in birth control pills, in order to determine how that synthetic estrogen affects wild fish populations. (The estrogen consumed by women taking birth control pills is excreted through urine and enters waterways via wastewater treatment systems, which are not equipped to remove many pharmaceuticals, including hormones.)

Everything from tadpoles to trout was “feminized.” And short-lived fathead minnows disappeared almost entirely because they could not reproduce. In their report within the Proceedings of the National Academies of Sciences of the United States, Dr. Karen Kidd and her colleagues wrote that their observations demonstrated that estrogens could, in fact, affect the sustainability of wild fish populations.

“[That’s] important because that study used environmentally-relevant concentrations of this hormone—they weren’t dosing those fish in unusually high concentrations,” Hinck says. “It was slightly higher than what you’re seeing in waters around the country.”

That has led USGS scientists to ask a number of questions: “If we do see these ovotestes in male fish, what does that mean for the population itself?” Hinck says. “Does that mean it is having an effect on the population to where they can’t reproduce as well? And, if so, what does that mean as far as ecosystem function in the future?”

Now, USGS is working with Fish and Wildlife to study the effects of flame retardants—polybrominated diphenyl ethers or


, which are found in everything from airplanes to children’s pajamas—on silvery minnows. They are currently in early stages of the study; within the next year or so, they will begin gathering data.

The USGS also is working with the US Bureau of Reclamation to study how chemicals found in wastewater effluent—including estrogenic compounds and endocrine disrupters—may be affecting

silvery minnows

. In the past, the US Environmental Protection Agency and the New Mexico Environment Department have detected endocrine-disrupting chemicals in the waters pouring out of wastewater treatment plants and into the Rio Grande.

But right now, no one is exactly sure how those chemicals may be affecting the fish’s ability to live and reproduce in the river.

Taken together, many of these studies reveal a link between water quantity and quality in the Rio Grande: The less water flowing between the banks of a river, the more concentrated contaminants become.

Water temperatures also rise when flows are low, and that can affect fish reproduction. Hinck herself learned this while working on a project on the

Gila River

as it stretches—and dries—downstream from Phoenix and Gila Bend, Ariz.

“What we found in the Gila River—an arid environment where you have pools rather than a flowing river throughout much of the year—we found that the reproductive biomarkers we were looking at, the hormones and some of the protein levels, ovarian and testicular development, was very unsynchronized in the fish, which is unusual,” Hinck says. “Typically, what we see is males and females being similar, that is, in similar stages of reproductive development. But downstream of Phoenix and Gila, where you have more of these pools and non-flowing water, they were just all over the board.”

They concluded that the unusual behavior might be due to a lack of water and higher temperatures that were disrupting spawning cues.

In a recent written communication with SFR, Joel Lusk, senior environmental contaminants biologist with Fish and Wildlife’s Ecological Services, explained that little is known about the effects of endocrine disrupters on the Rio Grande’s native fish, which include the silvery minnow. But Fish and Wildlife, along with other agencies, hopes to learn about those effects, through both laboratory and field studies, in the coming years.

The repercussions of water contamination on the silvery minnow is yet one more piece of the puzzle for the scientists charged with determining how to ensure the species’ survival.

Considering how much controversy has swirled around the silvery minnow since it was first listed for protection, it’s almost disconcerting to meet with the biologist overseeing the fish’s recovery.

First of all, a fisheries biologist can be hard to catch in the office. And, although he’s physically imposing—strikingly tall, blond and blue-eyed—Jason Remshardt is even-keeled and soft-spoken. He’s the kind of guy who doesn’t bother talking about agency clashes or politics. He talks about seines and flows, fish eggs and fieldwork.

Supervisory fish biologist for the minnows in Fish and Wildlife Service’s Fisheries Resource Office, Remshardt is just home from fieldwork on the Lower Rio Grande, where it flows along the border with Mexico. Just a few weeks earlier, when a 15- to 20-mile stretch dried near Socorro, salvage crews pulled minnows out of pools and relocated them to areas where they might survive.

Scientists have tried to understand since the mid 1990s how river drying affects the endangered fish.

“We spent most of the summer already doing salvage, which we do every summer. We had a good water year, good snowpack, but eventually that runs out, even in good years,” Remshardt says, pointing out that the river south of Socorro has dried a few times this summer.

“Now, we’re still trying to find out what the effects are,” he adds. “That’s the biggest question now: What does salvage and river drying mean for the minnow?”

Declining water levels threaten fish caught in shrinking pools during the summer months. Here, Yvette Paroz (US Bureau of Reclamation) and Jason Remshardt (Fish and Wildlife Services) use nets to search for silvery minnows.
Credits: Courtesy US Fish and Wildlife Services

As it is, the fish cannot survive on its own in the Middle Rio Grande. Not only do biologists try to save fish during summertime drying but, every year since 2001, they have released hundreds of thousands of hatchery-raised minnows into the Rio Grande.

Also, in accordance with the Fish and Wildlife Service’s road map for species recovery, state, federal and local agencies have invested in three “off-channel” facilities. Both the City of Albuquerque and the Interstate Stream Commission have built concrete refugiums where the fish are raised. In 2006, the US Bureau of Reclamation built a sanctuary in Albuquerque that theoretically will create, for the fish, habitat in the Bosque between the irrigation canal and the river during certain times of the year (the sanctuary was recently handed over to Fish and Wildlife, but has not actually been used yet). In addition, the Albuquerque Bernalillo County Water Utility Authority has built a fish passage structure for its new water diversion dam.

As part of Fish and Wildlife’s recovery plan, biologists also are trying to establish a second population of silvery minnows. That’s why, since 2008, Remshardt and his crews have been heading down to the Big Bend of Texas, using 1,000-gallon tanker trucks to dump several hundred thousand fish into the river there. So far, that project has been going well: They’ve documented the fish spawning and, this summer, caught larval and juvenile fish. Next year, they’re hoping to do a river-wide survey to determine how many fish are in the river, and how far they’ve expanded.

The official recovery plan says the fish must have three self-sustaining populations before it can be “downlisted” from endangered. But biologists remain unsure where that third population might be re-introduced: Given the prevalence of dams along the Rio Grande, it’s hard to imagine where a third population might take hold.

So, after a decade of recovery work and collaboration among federal, state and local agencies, and millions of dollars spent, how is the minnow doing?

“All indications are we’ve sort of bounced back from what most folks would say was the low period—2003, 2004—when catch rates were at the lowest,” Remshardt says.

At that point, there were basically no fish in Albuquerque and only a few fish in the Isleta Reach to the south. The few fish biologists were finding lived in what’s called the San Acacia Reach between the Sevilleta National Wildlife Refuge and Elephant Butte Reservoir.

“And now, we see fish at almost all the monitoring sites, year-round,” Remshardt says, noting that while Fish and Wildlife has increased and honed its ability to raise and stock fish, biologists are also seeing fish reproducing and surviving in the river.

That said, it only takes one bad year to blow the fish’s recovery. The minnow’s lifespan is maybe two or three years in the wild. In many cases, the fish live only one year. To survive, the minnows must reproduce each year:

“Every year, you have to have a successful number of fish reproduce to replace the ones that are lost,” Remshardt says. “So it’s a struggle to make sure you get that done every year.”

And there are two main issues that still have yet to be resolved: river intermittency and fish passage.

Because stretches of the river are divided by dams, it’s impossible for the fish to move on their own into safe waters when flows dwindle or disappear.

“Those are the two big ones we need to get answers to, or work around, before we can even talk about making this population self-sustaining,” Remshardt says.

But when it comes to water, the fish is not at the top of everyone’s priority list.

The Las Lunas refugium is one of several sites where biologists raise silvery minnows in captivity for introduction into the wild.
Credits: Interstate Stream Commission

For the Fish and Wildlife Service, the mandate is to enforce the federal

Endangered Species Act

by recommending river flows for fish habitat and working to boost populations. But the New Mexico Interstate Stream Commission has its own obligations—to the citizens of New Mexico.

Its role is to protect, serve, investigate and develop the waters of the state—both interstate and intrastate streams—and to comply with interstate compacts, or agreements, that deliver water to downstream states. According to its director, Estevan López, the commission also must ensure that New Mexico receives the full benefit of those agreements.

In the case of the minnow, he says, when Fish and Wildlife established minimum flow requirements, it could have affected the commission’s ability to meet compact obligations with Texas.

“We really got involved in a serious way about trying to make sure that whatever requirements are established for maintaining the fish are things we think are doable,” he says. “Secondarily, one of our statutory charges is to protect the waters of the state, and so we look at it from the perspective of protecting existing and planned future uses [of water] by the citizens of the state.” He points out that, in the past decade, the commission has spent approximately $10 million on work related to the silvery minnow.

By requesting that Fish and Wildlife downlist the minnow from endangered to threatened, as it did in June, López says the commission is acknowledging the work biologists, agencies and stakeholders have accomplished through the Middle Rio Grande Endangered Species Collaborative Program.

“It probably wouldn’t change anything immediately for us,” he says. “I think more than anything it would be recognition that we’re on the right path.”

He adds that the commission submitted its request to Fish and Wildlife as part of a status review of the fish—not because it plans to pursue litigation or step back from its role within the collaborative program.

That said, López thinks water managers should have more flexibility—to learn from how the fish is responding to recovery work by biologists—and to adapt to conditions, rather than having to follow Fish and Wildlife’s requirements at all costs.

The commission also hires its own biologists—from private consulting firms—to carry out fish studies.

“I don’t know if I would want to characterize it as contradicting the studies of the Fish and Wildlife Service but, rather, I think we’ve refined the questions that we’re asking, and we’re doing a better job of really understanding the answers to those questions as we shape them better,” López says.

From his perspective, for instance, the issue of river flows is not clear-cut.

“Clearly, if we had the luxury of having water in the entire length of the river every year, that would be great, but I think that, even under pre-development conditions, there were years when you had drying,” he says. “I think we have to recognize that’s the sort of environment the fish evolved in and take other actions that will allow it to rebound when there is drying.”

He points out that the minnow’s increased numbers within the past few years show there is probably more management flexibility than people had considered in the past. As a result of the collaborative program, the fish is doing much better than it was a decade ago, he says. But perhaps it’s time for a change in mind-set.

It’s difficult for most people to care a whole lot about almost any species of fish—never mind a 4-inch-long minnow. Even Remshardt acknowledges that.

“It’s not the minnow itself, but what the minnow represents: the river,” he says.

The minnow began as a native species on the brink of extinction. It’s become a key reason there’s water in the river.

Interstate Stream Commission Director Estevan López says his agency has to ensure it meets the state’s water obligations to other states and New Mexico’s citizens.

It doesn’t take much to notice the difference between stretches where the minnow is protected—where there are cottonwoods, birds and other wildlife—and, say, the river as it flows through El Paso, Texas.

“There, the Rio Grande is a trapezoid concrete ditch—where there is no biological protection—and that’s sort of what you end up with, where they channelized it and tried to move it away from the city as quickly as possible,” he says. “It’s just a conveyance channel for more irrigation water.”

The minnow has its own benefits to the ecosystem, he says, and its own reason to exist.

Like the state, Fish and Wildlife also hopes to someday remove the fish from protection under the Endangered Species Act.

“Everybody wants to see the fish delisted,” he says. “It’s just that we want to see it delisted because it’s surviving.”  SFR

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