By: Margaret Zhou, Partnerships Manager
Nathan Lujan began his career studying South America’s ancient rivers. Now he’s racing against time to document the continent’s fish species before they’re lost. This is a special River Guardians feature for World Fish Migration Day 2016.
A life exploring America’s rivers
In 2005, fish biologist Dr. Nathan Lujan was leading a scientific expedition to Venezuela. He was there to collect specimens and data from various river habitats – shallow water, deep water, rapid currents, slow-moving ones. After one particularly productive day, his team returned with buckets full of fish specimens just as the weather took a sudden turn for the worse.
As storm fronts rolled in from two directions, Dr. Lujan and his colleagues worked quickly to process their specimens before they began to rot. Then Dr. Lujan looked up and saw the team’s cook advancing on them; she was distressed and hallucinating that her chronically ill mother was crying out for her.
As Lujan watched, she ran down to the river to try to drown herself. Amidst the downpour, Dr. Lujan raced after her, pulled her back into the camp, and restrained her in her hammock to prevent further self-harm, before rushing back to finish his work.
Dr. Lujan says now, “These are the kinds of things you’re not trained to deal with as a scientist, but that you encounter sometimes while doing field work in the tropics.”
As he recounted the story to me, a smile seeped into his otherwise levelheaded tone. Dr. Lujan is not one for exaggeration, but he did appreciate re-telling that story for its Shakespearian quality.
Discovering ancient rivers
Dr. Lujan has been studying the evolutionary biology of tropical fish for 21 years – pretty much since he was capable of academically studying anything. In college, he completed not one but two undergraduate theses on fish ecology.
His research aims to understand the biological rules that govern fish communities, evolution and diversity. Specifically, he focuses on fish primary consumers – fish at the bottom of the food chain – because of their role in setting the foundation for riverine food webs.
I had to ask: “Why fish?” His answer makes it clear that his obsession with fish is actually rooted in his love for rivers.
Dr. Lujan grew up in Nashville, Tennessee, where he spent his childhood exploring the rivers, creeks, and streams around his home. He was amazed by the beauty and otherworldliness of these natural ecosystems. Deciding that he wanted to spend his life exploring rivers, he figured that there was no better way to do that than as a biologist.
Lujan first worked for the Tennessee Valley Authority as an ecologist and biologist who used metrics of fish and insect community composition to monitor and protect the river valley. But a desire to investigate rivers around the world led him to tropical South America.
While working toward a PhD in Evolutionary Biology, Dr. Lujan began visiting the Guiana Shield – a geologically ancient highland area that spans Venezuela, Guyana, Suriname and French Guiana. He’s revisited this area on at least nine more expeditions since then. And what he’s found is incredible: For 60 to 70 million years, up until two to five million years ago, an ancient river drained the southern side of the Guiana Shield. This river, called the Proto-Berbice, united many rivers that are currently tributaries to the Negro, Orinoco, Branco, Essequibo, and other river basins that now flow in different directions.
Dr. Lujan’s research has expanded our understanding of the historical linkages of that ancient river and of the extent to which the Guiana Shield highlands were an early incubation chamber for South American fish diversity. Many fish lineages that are widespread in South America today have their origins in the Guiana Shield’s ancient waterways.
What fish DNA can tell us about rivers
To better understand the fish he’s studying, Dr. Lujan turned to DNA analysis. He uses DNA sequencing tools – originally developed for the human genome project – and applies them to fish. It’s a cutting-edge way of analyzing population structure and evolution based on genetic evidence; scientists in the not-so-distant past had to rely on how fish looked from the outside – their morphology.
Dr. Lujan has recently applied these tools to a biodiversity survey of the lower Xingu River in Brazil, on an area called the Volta Grande. The so-called “Big Bend” of the river is a 160-kilometer-long horseshoe curve that forms a maze of rapids and channels. He went there to test for the existence of new species that look like other species, or “cryptic populations,” that may not be detectable through morphology alone.
For the study, Dr. Lujan and his colleagues collected large numbers of one silvery fish species that can be found on sandy beaches at night, where the species goes to feed and spawn.
Though the fish were morphologically identical, the genetic data indicated there were two separate, reproductively isolated populations. Dr. Lujan’s colleague, Dr. Mark Sabaj Perez, then realized that all the individuals in population 1 were collected in dry season expeditions, whereas population 2 was only collected in a high water season.
To the scientists, that meant that the two populations were differentiated by the season in which they spawn. One population moves into the sand beach habitat at low water and spawns during the dry season. The other population waits to occupy sandy areas that are only submerged when the water level is higher.
These findings are just one small example of the highly delicate balance at play in a natural world full of complexities that we cannot perceive with the naked eye alone. Any disruption to the balance, no matter how minor it may seem to us, may mean the difference between life and death for an entire species, and perhaps an ecosystem.
From the Guiana Shield to Belo Monte
I asked Dr. Lujan about the biggest threats to South American rivers today. His answer was unequivocal: gold mining and dams.
In a 2012 study that sought to quantify the impacts of mining in the Andes Mountains, Dr. Lujan and his colleagues measured the algal, macroinvertebrate, and fish abundance and diversity along the Inambari River in southern Peru. They collected samples along a gradient, from 4,200 meters above sea level in the Andes to 200 meters above sea level, where the Inambari enters the Amazon basin.
Along the upper slopes, they found mostly natural intact ecological gradients. It was a different story in the lower part of the river.
Andean rivers carry a great deal of sediment naturally, but that sediment drops out of the system quickly and isn’t as fine as the sediments produced by mining. In the lower, heavily-mined reaches of the Inambari River, there were almost no catfish and no macroinvertebrates. Their habitats had been eliminated by mining. Life was extinguished.
When it comes to dams, Dr. Lujan says, one of the first major concerns is the blockage of migratory fish routes. At least one species of South American tropical river catfish migrates up to 8,000 km from headwaters to lowlands. These migrating fish need rivers free of blockages the whole way.
Rapidly flowing rivers also serve as incubation chambers for new species of fish to evolve. Microhabitats that exist as separate places along a rapidly flowing river are similar to islands in the ocean, Dr. Lujan says. Just as islands promote biodiversity, so do the habitats that exist in the rapids.
“When you build a dam in these areas, you fundamentally alter the ecology of rapids habitats. You turn what was once a shallow, fast-flowing habitat into a slow-flowing, deep water habitat,” Dr. Lujan says.
Dr. Lujan hopes that advocates will use his research on South American rivers in and around the Amazon basin to identify the impacts of large dams like Belo Monte. That, however, takes time. Still in its first few months of operation, Belo Monte is a “serious threat” according to Dr. Lujan, but we won’t know how serious until after we can measure its impact on river biodiversity against the record of biodiversity before the dam.
Dr. Lujan explains the science behind the dam’s impacts with little emotion. But when I ask “What gives you hope?” he sighs.
“In general, it’s hard to maintain hope. It can be very depressing to go to these beautiful ecosystems and see the pace at which they’re being altered by human activity.
“I share a blind hope with many conservationists that technology will soon reach the point where we won’t need hydroelectric power as much anymore, so the pressure to expand hydroelectric dams will be reduced.”
Dr. Lujan also noted that he’s found hope in several surveys he had done for the Inter-American Development Bank, the Inter-American Investment Corporation, and dam building companies on the potential impacts of proposed dam projects.
One of these projects involved an international dam building company considering the construction of a hydroelectric plant at Amaila Falls on the Kuribrong River in west central Guyana. In his pre-impoundment survey, Dr. Lujan discovered a new species, Characidium amaila, that was found only in rapids habitats around the impact area of the proposed dam. The bank and dam company then agreed to change the dam design to minimize impacts to the species’ habitat.
Ultimately, for other financial and logistical reasons, the Amaila Falls Dam was not built. But, Dr. Lujan was impressed by the environmental policy units of the Inter-American Development Bank and their desire to ensure that the project would have minimal impact on biodiversity.
Yet, when asked how feasible it is for projects to live up to their environmental standards, he replied that it ultimately depends on the degree to which the financial institutions backing the projects institutionalize compliance with environmental standards. That’s where the role of civil society comes in.
“With social pressure and the work of organizations like International Rivers, hopefully pressure can be brought to bear on all major international lenders to ensure that they abide by the same high standards of environmental safeguards.”
Over the past five years, Dr. Lujan has worked closely with International Rivers to make the case for the protection of South America’s great rivers.
A snapshot of biodiversity
Dr. Lujan says that his most valuable work has been to describe species and highlight biodiversity through science and photography. By studying how some fish species have evolved, he’s had a glimpse into the history of rivers as far back as millions of years.
As a river scientist, he’s documented his travels in photos and videos, published numerous articles and books, traveled around the world to share his research, and even given aquarium fish hobbyists some tools to help care for the original ecosystems of the exotic fish species they love. Non-scientists who find his work are amazed by the underwater beauty captured in his photos, so rarely seen by most of us.
Yet, Dr. Lujan’s work, like the work of many conservation biologists, often involves removing these beautiful fish from their natural habitats.
When asked how he feels about that, Dr. Lujan recognizes my concern. He explains that once the fish are captured, before they are processed for their tissues, they’re euthanized so that they have a painless death. The fish are then preserved, packaged, and sent to natural history museums. What he says next, though, hits home.
“When you go into these habitats, you see such large-scale habitat destruction by mining or dams occurring at a much faster rate than scientists can assess the biodiversity. You recognize what we’re up against as scientists trying to understand these ecosystems.
“So in that sense, I feel a great deal of urgency to provide as thorough as possible a record of the biodiversity of these ecosystems – before they’re destroyed and that knowledge is lost.
“The rate of development of tropical rivers today is beyond my capacity to affect as a scientist. We can only hope that future generations will elevate the value of natural ecosystems beyond just servicing hydroelectric needs. If that awakening occurs, they will need the specimens, data and tools we’re generating now for conservation, to understand how these ecosystems function in a natural state.
“We’re generating a snapshot of biodiversity as it exists in a single place and point in time. These specimens and data will be available for hundreds of years as a permanent record of biodiversity in those areas – that snapshot will hopefully always be on the shelf for future generations, to serve as a guide to the long-term conservation of these ecosystems.”