Scientist at Work Blog: Dinosaurs of the Rewa River

Dr. Lesley de Souza, research biologist at John G. Shedd Aquarium, writes from Guyana, where she studies the region?s rich aquatic wildlife, including the arapaima, one of the largest freshwater fishes in the world.

Dec. 24, 2012

Bouncing through the air away from Georgetown, everything below me turns to a sea of lush green forests undulating high and low across scattered Tepuis ? tabletop mountains found only on the Guiana Shield.? Majestic waterfalls charge down the sides of the Tepuis and merge into coffee colored rivers that wind their way through the forests and shimmer in the sun, the only breaks in the thick jungle.

In these dark waters, dinosaurs lurk ? dinosaurs with scales larger than poker chips.

I am on a five-passenger Cessna flying into the heart of Guyana?s Rupununi region. My destination is the Rewa River. My dinosaurs are one of the world?s largest and oldest freshwater fish, the endangered arapaima.

Arapaima (Arapaima gigas) can reach lengths of nearly 10 feet and weigh more than 440 pounds, earning them the moniker of ?dinosaur fish.? Arapaima are endemic to tropical South America, primarily found in the Amazon and Essequibo River drainages. The Rewa River, where I?m headed, is an isolated tributary of the Essequibo flowing north off the Guiana Shield.

Arapaima fishing once provided important income and sustenance for indigenous communities in Guyana. But their size, combined with their need to breathe air to survive, made arapaima extremely vulnerable to poachers. By 2000, overfishing and poaching nearly drove populations to extinction. Local conservation efforts helped the dinosaur fish survive, but they still became listed as endangered throughout their range in 2006.

Recently, the John G. Shedd Aquarium expanded its global conservation initiatives, and arapaima research became one of several ongoing applied field programs that work to sustain biodiversity and protect local livelihoods.

An important flagship species, the arapaima is in dire need of protection. Protecting them means conserving habitat with high biodiversity. But that is challenging when we still lack knowledge of their basic biology. Currently, there is no information on how much of the Rewa River is used by the arapaima. By tracking arapaima movement, we can contribute to management plans for future protected areas that the species needs.

As we descend, all I see for miles below is forest. My chest tightens as I imagine the airplane?s belly brushing against the tops of trees. Suddenly, I see a clearing and a field of grass. I emit a long exhale. We touch down and the plane wobbles down a grass runway lined with orange cones.

Amerindian men, women and children stand by, eager to observe the plane?s landing and curious about their new visitors. From the airstrip, I head to a landing on the Rupununi River with my field assistant Liz Smith. We prepare for the two-hour boat ride to the village of Rewa, located at the convergence of the Rupununi and Rewa Rivers.

The dynamic geologic history of the Precambrian-era Guiana Shield shaped the drainage patterns of this region?s rivers and influenced the evolution of its Neotropical fish. The landscape of fortress-like granite outcroppings, where jaguars often keep sentinel, demonstrates this vibrant history. For 200 miles, the Rewa meanders down the Guiana Shield?s north slope. Fractures in the basement layer of the Shield rift the river into a grand staircase of six major waterfalls and two minor cataracts.

No human populations live upstream of the river?s first 20 miles. The remoteness, isolation from humans, and conservation efforts by Rewa villagers help explain why the Rewa River contains the highest density of arapaima populations in Guyana.

View Larger Map of Rewa Here

As we navigate our way upriver, I witness the rich wildlife living amongst the arapaima.? Boisterous giant river otters swim through the dark waters, diving deep and reemerging to scold us for passing too close. Black and spectacled caiman bask confidently in the sun, as pairs of scarlet macaws cackle loudly overhead. The endangered giant South American river turtle (Podocnemis expansa) cautiously peeps its head up for air while its massive shell bobs just below the river?s surface.? Curving around the next bend in the river, I finally see my dinosaur, rising for air. The surface of the water breaks, and glinting red scales flash in the sun, disappearing as quickly as they arose; this is arapaima country.

As I watch the arapaima roll, I realize that finding them is the easy part. I imagine handling and performing surgery on such an enormous fish, and the serious challenges we will face. Being in the water, close to an incredibly powerful 300-pound arapaima, presents ample opportunity for broken bones, or worse.

We arrive in Rewa, and the villagers gather at the boat landing to greet us with large smiles. I am inspired by their passion to conserve regional wildlife and am excited to work closely with the Amerindians. My team is the first group of researchers to be based out of their community, and they seem intrigued. Within minutes, I am offered a glass of mango juice and I sit surrounded by guides and onlookers, who are equally eager to plot out the coming expedition.

Night falls, and I am overwhelmed by the number of stars I can see here ? as many as the grains of sand in the river. I lie in my hammock, small against the night sky, and try to imagine what it will be like to swim with the dinosaurs.

Critical to the success of this project is the partnership from:? Rewa Village, Ministry of Agriculture of Guyana, Ministry of Amerindian Affairs, Guyana EPA, University of Guyana, Karanambu Trust and Costa del Mar sunglasses.

Source: http://scientistatwork.blogs.nytimes.com/2013/01/22/dinosaurs-of-the-rewa-river/?partner=rss&emc=rss

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