Written by Ben Goldfarb
The brave humpback chub has successfully withstood dams and invasive species, but climate change and reduced river flows pose new threats to them.
In the annual Spring Survey conducted by the U.S. Fish and Wildlife Service, the bony tailfish under the Little Colorado River Waterfall swim past the bluehead sucker. The Little Colorado River is a tributary of the Colorado River in Arizona. The bony tail fish is difficult to find, usually living in muddy waters, and needs to be lured by fish food in small net bags. Photo by David Herasimtschuk / Freshwaters Illustrated
The Colorado River is known as the most industrious river in the Western United States. Recently, it has been earning overtime pay.
The Colorado River is an important source of water in the United States, known as the "lifeline of the Southwest", and provides drinking water to 40 million residents in seven states every day. The Grand Canyon is a magnificent part of the basin and a popular tourist area, welcoming more than 6 million visitors a year.
The Colorado River Basin is also home to many non-human beings, especially the peculiar and tenacious fish that roam its turbid deep waters. It is home to stout bonetails, razor-backed lipfish and pointed leaf-lipped fish. The pointed leaf-lip fish was a ferocious predator, about 1.8 meters long, and early anglers had to tie the fishing line to the truck bumper to pull it ashore. The lower Colorado River region has the highest proportion of endemic fish in North America, with 6 of the 8 native fish species not present anywhere else on the planet.
In the unique ecosystem of the Colorado River, the bony tailfish is the most thoroughly studied fish. It is a member of the Minoan family, with a silvery body, about 30 cm long, a large orange fin, and a fleshy ridge-like protrusion on the back.
"They're a unique part of the Grand Canyon, like rocks, springs, and everything else that makes this place special," said brian Healy, a fish biologist at Grand Canyon National Park. "They've evolved here for millions of years." In the 19th century, a gold prospector in the canyon reported that you could "pull them out by the tail, twice at a time."
However, the bony tailfish did not fare well in the 20th century. On the one hand, fisheries managers began to farm non-native trout and perch and encouraged fishermen to kill bulbophyllum and other "junk fish" because they believed that these fish lacked the value of the fish. On the other hand, the government began building large federal dams, such as the Largest Hoover Dam in the United States, which destroyed the turbulent, rocky sections of the river on which the bony tail fish depended. In 1967, the government declared the bony tailfish as endangered.
The bony tail fish swim under the waterfalls of the Little Colorado River. Photo by David Herasimtschuk / Freshwaters Illustrated
During the annual survey of the dorsal carp, randy van haverbeke, a biologist at the U.S. Fish and Wildlife Service, measured the weight of the dorsal carp, after which he released a net full of dorsal calodons back to the Little Colorado River. Biologists and photographers use the same bait to lure the bony tailfish to appear. Photo by David Herasimtschuk / Freshwaters Illustrated
In recent years, the population of bony tail fish has begun to rise again, thanks in part to conservation measures, such as the transfer of fish to high-yielding tributaries that have not been damaged by dams. There are now about 12,000 adult bony tailfish living in the Grand Canyon, and thousands more are scattered in four populations upstream.
In a 2018 study, the U.S. Fish and Wildlife Service found that the situation of the bony tailfish has improved considerably enough to downgrade from an endangered species to a threatened species, suggesting that they are no longer at risk of extinction.
After three years of review, on 15 October, the bony tail fish was finally identified as a threatened species. The U.S. Fish and Wildlife Service has also proposed the same initiative for the razor-backed butterfish, which has been listed as endangered since 1991. These rulings show that the threatened ecosystem of the Colorado River is moving in the right direction, with decades of research and conservation work being recognized.
However, the future of the bony tail is not safe. The federal government recently declared the Colorado Basin the first-ever water shortage crisis, triggering water cuts in some states, such as Arizona. Other states, such as Utah, are exploring the possibility of increasing water use. According to one projection, climate change could cut the flow of the Colorado River in half by the end of the century.
"For the bony tail fish, their future is not promising," said Taylor Mckinnon, a senior public lands activist at the center for biodiversity, a nonprofit organization. "I don't believe they're out of danger at all."
How dams threaten the survival of the bony tailfish
Before human intervention, the Colorado River was prone to violent fluctuations, from torrential torrents in the spring to trickles in the summer. About 65 million tons of sediment (liquefied material from western mountains and deserts) flow through the Grand Canyon each year. Many scientists believe that the dorsal bony tailfish evolved a dorsal bulge in order to survive in this unstable environment. Some believe that these bumps act as keel-like stabilizers, allowing them to withstand spring floods. Others speculate that such a structure makes it difficult for predators to swallow by the sharp-headed leaf-lipped fish.
Beginning in the 1930s, the dam changed the river. Dams have sprung up to control flooding, storage and hydroelectric power, and huge concrete walls have divided the Colorado River into slow-flowing reservoirs that are no longer suitable for the growth of the bony tail fish, which prefer turbulent currents and lay their eggs on rocks at the bottom of the river. The Hoover Dam and the Fire Canyon Dam in Utah, which span the Nevada and Arizona borders, destroyed nearby populations of bony tailfish.
A bulbophyllum swims in the rushing little Colorado River. In fast-flowing waters, their bulging backs help increase stability. Photo by Jeremy Monroe / Freshwaters Illustrated
Within the protection of Grand Canyon National Park, the bony tailfish survives. But even there, the fish are still heavily affected by the dam. In 1963, the government completed construction of the Glen Canyon Dam in Arizona, located upstream of the Grand Canyon, forming the massive Lake Powell. This lake altered the canyon below, adversely affecting the bony tailfish. Bulbophyllum can only grow and spawn in warm water (at least 15.6°c), but the water flowing through the Glen Canyon Dam comes from deep in Lake Powell, which is about 11°c lower than natural rivers. Cold currents delay spawning, hinder the growth of bony tailfish, and make juveniles more vulnerable to attacks by hungry trout.
The dam also intercepts sediment from rivers. Bulbophyllum used to hide in calm backwater behind canyon sandbars that formed and moved with sediment deposited by rivers during floods. But Lake Powell intercepted flooding, intercepted silt, wiped out beaches and sandbars, and deprived the bonytail of its key habitat.
Over time , the bony tailfish split into five small , separate populations. The largest group gathers around the Little Colorado River, a tributary that meets the main stream of the Colorado River at the Grand Canyon. Four smaller populations have also survived in the upper Colorado and the Green River in Utah. But these isolated populations continue to decline. By 2002, only about 10,000 heads remained in the wild.
Establishment of new populations
In the early 2000s, biologists at the U.S. Fish and Wildlife Service and other agencies began to push more aggressively for the recovery of the bony tailfish. In 2003, the department began using helicopters to transfer the small Colorado River's bony tailfish to tributaries of the Grand Canyon, hoping to build new populations that would prevent them from becoming extinct. Relocated bulbophyllums now thrive in the upper reaches of the Little Colorado River, Havasu Creek and Bright Angel Creek, warm, unduttled tributaries that provide them with good conditions for growth.
"If they can reach adulthood faster, they could theoretically better fend off predators and contribute to populations at a higher rate," said Mike Pillow, a biologist at the Arizona Wildlife Service. "We think the resettlement is a good start."
The government has also made adjustments to the operation of the Glen Canyon Dam. Beginning in 1996, the Reclamation Bureau, which manages the dam, began conducting "high-flow experiments" from time to time to simulate flooding. The sudden current and the sediment it left behind were meant to build more camping beaches for boatmen, but unexpectedly formed new sandbars and backwaters, which benefited the bony tailfish.
Perhaps the biggest push comes from an unexpected ally: climate change. The Colorado River has been plagued by drought since 2000, a disaster triggered by climate change that has reduced river flow by nearly 20 percent. But the waters of Lake Powell warmed as a result. What's more, Lake Mead behind the Hoover Dam has also begun to shrink, and now accounts for only 34 percent of its capacity. Sandbars and whirlpools re-emerged, and exposed rapids prevented invading predators from going upstream, creating a refuge for native fish.
A bigger threat is coming
The downgrading of the bonytail is certainly good news, but it does not mean that the road ahead is bright.
On the one hand, north of the Grand Canyon, the bony tailfish are still struggling with their predicament. A school of fish living in Colorado's Black Rock Canyon has only 450 adult fish — probably half of what it was 20 years ago. Other populations have stabilized but failed to increase.
Greedy invasive fish such as the Bilgos, Pike, and Smallmouth bass dominate the upper reaches, preying on small bulbophyllums. As climate change warms rivers further, these invasive species are likely to continue to expand their territory.
In the Grand Canyon, the historical stronghold of the bony tail fish, the number of exotic brown trout and blue-green scaled gill sunfish has begun to increase. Warm water that favors the survival of the dorsal bony tail may also eventually help more aggressive predators arrive. Heily of Grand Canyon National Park said: "If we have to go through more drought years in the future, then the likelihood of warm water non-native fish crossing the dam and spawning in the park will be higher." ”
Van haverbeke released a bony tailfish back into the Little Colorado River. Photo by Jeremy Monroe / Freshwaters Illustrated
The colorado River's warm, dry climate makes the future of the bony tail fish uncertain.
Jack Schmidt, a river scientist at Logan Utah State University, said that to ensure a bright future for the bony tailfish, lawyers, engineers and politicians must work with fish biologists and other researchers to find a solution early.
In the past, the well-being of the finned inhabitants of the Colorado River has been deferred, but future solutions must include measures to promote their survival, Schmidt said.
"All major policy decisions and major negotiations in the future will have a significant impact on the ecosystem of the watershed," Schmidt said.
This means that we may want to maintain a suitable water temperature by controlling dam discharge, or design a more stable water flow to promote the growth of aquatic insects. But as climate change exacerbates Colorado's growing water scarcity, these actions may be difficult to accept.
"We're trying to strike a balance between electricity, water, recreation, and fish habitat," said Mark McKinstry, a biologist at the Reclamation Bureau. "When this balance is tilted, other uses are affected."
(Translator: Strange Flowers Blossom)