Aug. 20, 2017
Home / Articles / News / Features /  She-Fish?


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

August 25, 2010, 1:00 am

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 PBDEs, 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?”
Continue reading: Page 1 | Page 2 | Page 3 | Page 4 | Page 5 |


comments powered by Disqus


* indicates required
Choose your newsletter(s):

@SFReporter on Instagram