The guide, a river dweller of indigenous ancestry, slipped the outboard into neutral to keep his boat and cargo of six tourists from interrupting the tumult in the water ahead. There, scores of black caiman—the largest alligator in Latin America, measuring up to five meters (16 feet)—churned the surface of the lake, thrusting their long snouts underwater to snag fish emerging from a nearby stream.

Such scenes are a daily occurrence in this sprawling swath of seasonally flooded Amazon rainforest called the Mamirauá Sustainable Development Reserve. But the astonishingly rich wildlife here is just one attraction. No less striking is the conservation model that is preserving these resources and ensuring livelihoods for the reserve’s 7,000 people—a mix of Amazon Indians, descendents of rubber tappers and migrants from the nation’s northeast living in 78 riverside communities.

Created in 1996 in the western state of Amazonas, Mamirauá was the first of Brazil’s 26 sustainable-development reserves. In protected areas of that type, local communities may engage in economic activities that are found through scientific research to be consistent with environmental conservation.

To be sure, Brazil’s 299 protected areas include a variety of land uses, ranging from state and national parks accessible to the public to areas restricted exclusively for biological research. A sustainable-development reserve isn’t the only type of protected area where locals are allowed to tap natural resources. In another type, the extractive reserve, locals may engage in such activities as rubber tapping and gathering nuts, wood oils and fruit. But unlike extractive reserves, the more rigorously overseen sustainable-development reserves must have management plans based on research authorized by Ibama, the enforcement arm of the Environment Ministry. In Mamirauá, this science-based management has shown impressive results that have influenced efforts elsewhere ranging from river-fish preservation to protecting seasonally flooded, or várzea, rainforest.

“The Mamirauá [reserve] is a historic and pioneering project that developed a sustainable management methodology for pirarucu [a large Amazon fish] that has been replicated elsewhere in South America,” says Virgílio Viana, former Environmental Secretary of Amazonas state and now director of the Sustainable Amazon Foundation (FAS), a nonprofit here. “Its methodology for doing managed forestry in flooded forests is also studied by other communities in Amazonas state. And Mamirauá has an eco-retreat that has become a model for minimum-impact ecotourism in Brazil, and which generates revenues for its riverside communities. In short, Mamirauá is an important component of environmental conservation in Amazonas State and other parts of South America.”

Mamirauá is remarkable in many respects, perhaps most importantly on account of the massive seasonal flooding that inundates its tropical woodlands over half the year—sometimes with as much as 10 meters (33 feet) of water. River dwellers not only build their wooden huts on high banks, but also on stilts. And in the flood season they keep chickens and even cattle on fenced rafts. Still, water levels in last year’s January-through-June flood season inundated the first floors of many huts, some of which have a second level for use during floods.

Thanks to its plentiful fish and fruits, Mamirauá is home to an unusual abundance of river birds, dolphins, reptiles and mammals—mainly monkeys and sloths, whose tree-climbing ability serves them well in the wet season. The area, designated in 1993 as a Ramsar Wetland of International Importance, also boasts a respected eco-resort, most of whose visitors come from the United States.

In the 1980s, Brazilian primatologist José Márcio Ayres discovered that a large white-haired, red-faced monkey endemic to the Mamirauá region, the white uakari (Cacajao calvus calvus), was in danger of extinction. Growing numbers of settlers were arriving and felling large quantities of valuable hardwood trees for sale to timber operators, shrinking the monkey’s habitat. Since the reserve’s creation, however, the population of the still-rare white uakari has grown as timber management improved.

Settlers were being lured to the region not just by timber, but by the up to three-meter-long (10-foot), 200-kilo (440-pound) pirarucu (Arapaima gigas), which is the largest scaled, freshwater fish in the world and is highly valued for its meat. The pirarucu is caught by net or harpoon when it surfaces for a split second every 10 to 15 minutes for air. With oxygen levels in the river water too low to sustain it, the fish has developed an ability to breathe air using modified swim bladders as lungs.

From the 1970s to the mid 1980s, vessels capable of holding 50 to 80 tons of fish came from the western port city of Manaus to net pirarucu. Their crews also bought pirarucu from river dwellers moving into the region to supply them. Ayres persuaded the Amazonas state government in 1986 to set up the 2,000 square kilometer (772-square-mile) Mamirauá Ecological Station, a biological research center, to protect the white uakari and the pirarucu as well as other wildlife and the forest itself. Amazonas State authorities created the Mamirauá Sustainable Development Reserve ten years later, more than quadrupling the size of the protected area to 11,200 square kilometers (4,324 square miles), an area slightly smaller than the U.S. state of Connecticut.

Mamirauá is jointly administered by Amazonas State and the Mamirauá Sustainable Development Institute (IDSM), a research center that since 2001 has been a division of Brazil’s Science and Technology Ministry. The institute researches and monitors the use of sustainable development techniques, deploying 100 field workers who work in conjunction with residents of river communities. The institute has developed baseline studies on the behavior, habitats and reproductive capabilities not only of the pirarucu, but also the black caiman (Melanosuchus niger), the Amazon pink river dolphin (Inia geoffrensis), the Amazonian manatee (Trichechus inunguis) and various ornamental fish species. The black caiman is being harvested at Mamirauá on an experimental basis.

In 1996, when the Mamirauá reserve was created, Ibama banned the fishing of pirarucu in Amazonas State because of greatly depleted stocks. Three years later, river dwellers and Mamirauá Institute researchers presented Ibama with a plan for pirarucu fishing quotas aimed at sustainable harvesting of the fish during a two-month period in certain lakes. The plan, which Ibama approved, prohibited fishing for pirarucu in other lakes to allow for reproduction. Fishermen, using traditional knowledge, had already developed a way to count pirarucu to determine the best fishing spots in lakes connected to the region’s river system. When the fish surface for air, villagers can differentiate them by such features as size, color and markings.

Institute researchers standardized a method for dividing a lake into 2-hectare (4.9-acre) sections, and having a fisherman count all the pirarucu in that area before moving to the next one. Counts based on the fish sightings were judged to be accurate within 15%-20% as a result of follow-up research in which fish were actually netted. Researchers eventually determined village fishermen could catch 30% of the pirarucu from certain Mamirauá lakes two months a year and still allow stocks to grow.

After nine years of experimentation, these quotas have permitted the pirarucu, as well as fishermen’s profits, to recover. “The sustainable management practices which began being implemented at Mamirauá in 1999, allowed pirarucu stock to recover so much they now generate both food and income for river dwellers,” says Ellen Amaral, the institute’s coordinator of managed fishing. “In 1999, pirarucu stocks had become so depleted that only 46 villagers at Mamirauá were earning a livelihood from fishing. By 2009, 990 villagers were doing so.”

Carlos Eduardo Marinelli, an analyst at the Socio-Environmental Institute, among Brazil’s most respected green groups, applauds the success of Mamirauá’s managed fishing. Says Marinelli: “The Mamirauá reserve became a model for merging traditional knowledge and scientific methodology to sustainably manage a species.”

That system was so successful that in 2004, Ibama allowed pirarucu fishing using the Mamirauá method throughout Amazonas State. Then in 2008, Ibama issued a similar norm for the entire Amazon. Today, more than 100 communities in Amazonas State, including two regional cities, are using the pirarucu-management system. The institute also is implementing the system in partnership with Ipam, an Amazon environmental nonprofit, in the floodplains around the eastern Amazon port of Santarém.

Meanwhile, the system also has been adopted by Macuxi indigenous groups in Guyana to address overfishing of pirarucu in the 7,000-square-kilometer (2,703-square-mile) North Rupununi wetlands. “The Macuxi replicated the visual method of counting pirarucu, developed by Mamirauá river dwellers and the Mamirauá Institute, which is a very accurate and inexpensive way to determine how many pirarucu they can harvest each year,” says Graham Watkins, former senior wildlife biologist at Iwokrama, a Guyanese rainforest-research center.

The U.S.-based Wildlife Conservation Society has adapted Mamirauá methods for use in various South American countries. In 2003, WCS together with researchers at the Amazonas Federal University (Ufam) and Instituto Piagaçu (IPI), a Brazilian research institute, began using Mamirauá models to manage pirarucu at the 10,080-square-kilometer (3,892-square-mile) IPI-run, Piagaçu-Purus Sustainable Development Reserve in Amazonas State, home to 5,500 river dwellers. Pirarucu populations there have since grown considerably.

WCS researchers have drawn on Mamirauá pirarucu-counting techniques to develop their own system of quotas for the hunting of collared peccaries (Pecari tajacu) in a Peruvian reserve and the annual shearing of wool from vicuña (Vicugna vicugna Molina) in a protected area in Bolivia. Says the WCS’s Avecita Chicchón: “The Wildlife Conservation Society successfully replicated and retailored the Mamirauá approach in other South American countries because it said, ‘It’s fine to use wildlife if you do so with a management plan that allows you to harvest it for a long, long time.’ ”

Mamirauá also has helped develop a forestry model for seasonally flooded woodlands. Today, 32 of the reserve’s 78 communities are using the timber practices, which involve Ibama approval of a forestry-management plan and the cutting of a far smaller number and far greater variety of trees than in the past.

In Mamirauá, the advent of managed forestry in 1999 meant each community had to quit supplying logging companies and submit a tree inventory and forest-management plan to Ibama. The plan divides the area to be cut into 25 sections and allows the communities to cut in only one section a year. The communities practice the lowest-impact of the three types of managed forestry authorized by Ibama. They can cut only 25 cubic meters of wood (about three trees) per hectare (2.47 acres), and the timber must be a mix of up to 42 commercial species, not just the most valuable ones.

Mamirauá communities also do low-impact farming as well as sustainable artisanry that includes the production of fiber carpets, seed-strungs jewelry and wooden sculptures. At the same time, they derive income from ecotourism, though visits total about 550 a year due to the difficulty and cost of reaching the region. Getting there involves a two-hour plane ride from Manaus, the capital of Amazonas State, to the port of Tefé, home of the Mamirauá Institute, and a 90-minute motorboat ride to the Uakari Floating Lodge. The lodge, which has no telephone or Internet connections, accommodates up to 20 guests in five double-suite bungalows which, like the lodge’s communal area, float on thick logs at a riverbend near a large lake teeming with wildlife. During the dry season, guests can take forest walks, explore the rivers and lake by canoe or motorboat and visit local communities. In the wet season, all forest exploration is done by boat, as the rainforest is flooded.

The lodge runs on solar power; inorganic trash is sent to Tefé for recycling; organic waste goes through a portable septic system; and sludge is buried in the forest. Visitors are not allowed to feed wild animals, even fish.

“I have stayed at other eco-resorts where monkeys are used to being fed bananas when they appear at guests’ verandas, and where dolphins have become accustomed to being fed fish by tourists at docks,” says Carlos Heitor de Faria, a Brazilian who stayed at the Uakari Floating Lodge in 2008. “At Mamirauá, wild animals don’t approach the lodge or bungalows because the practice of feeding them is rigorously banned. It’s the first thing lodge officials tell us. So, you have to go looking for the animals, rather than vice versa.”

Ecotourism at Mamirauá generates R$650,000 (US$371,000) annually, most of which is used for supplies, maintenance and pay for the 60 employees. About half of the R$30,000 ($17,000) in net profit is used for monitoring against poaching in the area around the lodge and the seven nearby riverside communities. The monitors, like the cooks, handymen and guides, are all locals. The remaining half of the profits are shared among the seven communities, which spend it on local projects, such as rainwater-collection systems.

Says Francisco Alves, a leader of one of the seven communities linked to the lodge: “About 75% of the young men leave the community and go to Tefé to get low-paying jobs, doing handyman and maintenance work. But a considerable number of them miss the sense of community and return home. And some bring wives with them. So the size of the communities doesn’t change too much.”