MANCHESTER, Tenn. (CN) – The pond lies in the Tennessee barrens, a flat region of the Volunteer State that stretches across five counties and is home to cattle farming and the Bonnaroo Music and Arts Festival. It sits below a highway carrying 18-wheelers, bordered by willow trees and a grove of bamboo. About the size of two backyard pools placed end-to-end, the pond is easy to miss.
On Tuesday, after weeks of waiting, a group of biologists and conservationists returned about 400 endangered Barrens topminnows to one of their last remaining homes in the world: the Summitville Mountain Spring near Manchester, Tennessee.
The pond is fed by an underground stream that comes out of a rock face. On the other side, a concrete escarpment gives the pond a two-foot drop off before the water trickles under the highway, past a field of grazing cattle, and flows into West Fork Hickory Creek.
That concrete drop-off is key – it’s what separates the colorful Barrens topminnows in that pond from the invasive western mosquitofish lurking downstream.
Originally, the western mosquitofish was introduced to the barrens to eat mosquito larvae, like it has been introduced the world over. But the mosquitofish attack the topminnow, eat their young and prevent them from reproducing. Once mosquitofish move into an area, it’s only a matter of time before the Barrens topminnows there cease to exist.
But this pond is far from perfect. Four times in the last decade and a half, rescue teams needed to snatch the topminnow from this location as drought descends and the pond dries up.
The Tennessee Wildlife Resource Agency keeps an eye on the pool. If the water level drops, it calls the Tennessee Aquarium in Chattanooga and Conservation Fisheries in Knoxville to rescue as many Barrens topminnow as they can.
On Oct. 3, with a drought looming, a rescue team had brought a 10-foot seine net and pulled fish from the pond. Tennessee Aquarium took 200 and Conservation Fisheries took another 200.
When the U.S. Fish and Wildlife Service placed the Barrens topminnow on the endangered species list last month, 200 of the fish were not swimming in the wild. They were kept in two, black 140-gallon vats in the Tennessee Aquariums’ quarantine facility in Chattanooga, next to a few saltwater rays and near a 38,000-gallon saltwater tank holding a couple of sandbar sharks.
On Tuesday morning, aquarists at the Tennessee Aquarium loaded the fish in three water-filled plastic bags, and lifted a cooler into the back of the pickup truck belonging to Matt Hamilton, the aquarium’s curator of fishes.
After Hamilton made the hour-and-a-half drive to Manchester from Chattanooga, representatives from the Tennessee Wildlife Resources Agency and the U.S. Fish and Wildlife service were already there, along with Conservation Fisheries.
Speaking by phone a few days before the drop, Pat Rakes, co-director of the Knoxville-based Conservation Fisheries, said the Tennessee River watershed is one of the most biologically diverse waters in the world.
“If you look at anything, salamanders, mussels, crayfish, any of them, the Tennessee watershed is one of the most diverse in temperate latitudes,” Rakes said.
When he came to the University of Tennessee back in the 80s, Rakes’ professor suggested he study the Barrens topminnow.
The fish wasn’t initially added to the endangered species list after it was proposed in 1977 because, Rakes said, the Fish and Wildlife Service held hearings on the species and “basically got ran out or tarred and feathered at those hearings so they decided to hold off for a while.”
The habitat of the Barrens topminnow has shrunk to only five locations where mosquitofish are absent, according to last month’s federal rule listing the species as endangered. But the fish face challenges to survival in all of them.
Hamilton has worked on recovery efforts for more than two decades. When he first got involved, those efforts entailed collecting as many diverse genetic strands of the fish as possible, to ensure the species doesn’t plunge into a genetic slump and die out. The FWS and TWRA approached landowners asking if they could place Barrens topminnow on their land.
Over the years, groups like the Tennessee Aquarium and Conversation Fisheries attempted to plant Barrens topminnow in 30 locations across the barrens, but that plan to propagate the fish across its historic range didn’t work.
The conservationists last rescued Barrens topminnow from the Manchester pond in 2016. With the region gripped by drought, Hamilton said, the pond shrunk to a puddle. Some of the topminnows were rescued and the rest lying inside were given up to predators – birds, raccoons and perhaps the neighborhood cat.
At the pond on Tuesday, the conservationists placed five bags in the water at the pond’s edge, opened them and let them sit to let the water temperature equilibrate.
Looking into the water, they saw fish already there. Despite the drought, the remaining topminnow had survived this time.
After a few minutes, Rakes grabbed a travel mug and started pouring pond water into each of the five open bags.
This was to ensure that the water in the bags matched the pH level of the pond water, for instance, to ease the transition.
In one of the five bags, full-grown topminnows bumped up against the plastic wall. Their spotted bodies are the color of the dull leaves at the bottom of the pond. The tips of their fins shine a sky blue. In the spring, the males will burst into a bright color.
According to Rakes, the only thing that can be done to ensure the topminnow’s future is genetic engineering similar to what was used to control the Zika virus, something that would eradicate the western mosquitofish from the barrens.
Rakes’ assessment of the topminnow is dire. Soon, it might cease to live in the wild and be kept in aquariums, he said.
But its addition to the endangered species list helps because it brings federal money. For instance, it could free up funding to get a pump and a well that would ensure the pond does not run dry.
In the coming years, however, the FWS believes climate change may pose a threat to the Barrens topminnow.
“In the broader southeastern United States, variability in weather is expected to increase over the next century, resulting in more extreme dry and wet years,” the agency’s rule said.
Hamilton hopes that more members of the Association of Zoos and Aquariums will take topminnows and have breeding stock of their own.
Currently, TWRA plans on contracting with Tennessee Aquarium to have it write the propagation plan for the fish.
One by one, Rakes, and then Adam Johnson, an aquarist at the Tennessee Aquarium, took turns slowly tipping out the bags and letting the fish flow into the pond.
“They’re going to dive into cover,” Rakes explained as he slowly tipped the first bag into the pond.
On the last bag, some of the young topminnows got stuck in some of the folds of plastic. Johnson coaxed them out.
“The fish are back,” Hamilton announced.
The humans left the pond, stirring the mud at the bottom. Leaves slowly swirled on the surface.
A small fish – about an inch or so long, and one that could have been mistaken for a tadpole – darted up to the surface.
It paused, and then sped off.