The spectacled caiman and its much bigger cousin, the black caiman, the largest predator in the Amazon, are evidently on the rebound in Mamirauá. It is the job of this young biologist to help make sure that their return is permanent.

Sitting on the porch of his little floating house, a troupe of monkeys swinging through the trees on the riverbank, da Silveira describes how it is to work in practically virgin scientific territory.

Until recently, about all the outside world knew about these top predators was contained in accounts of missionaries and explorers. But local people knew a great deal about caimans, because they hunted them. The market for luxury shoes and handbags had put a price on the heads of these alligator look-alikes, and in many places, caimans were all but wiped out. "We almost lost a big one before we got to know anything about them," said da Silveira.

Then, in the 1960s, the international community adopted a set of tough restrictions on the trade in caiman skins, giving the animals a reprieve. Today, some hunting continues, but the objective is meat, not skins. It's not a popular occupation, venturing out at night to tangle with a beast nearly as long as the tippy canoes. The local people themselves don't eat caimans, but salt the meat for sale to middlemen, who in turn pass it off as fish.

As a scientist, da Silveira does not condemn the hunters. In fact, he hires them as guides and plies them for information on where the caimans breed, lay their eggs and hunt for food. "Their role in my research is fundamental," he says, and in any event, "hunting is a reality."

Da Silveira's goal is not only to protect the caimans, but also the livelihood of the people who use them. The same is true for much of the work being carried out by 10 other researchers working in Mamirauá. Although good scientific data on an animal's biological needs and its place in the environment is essential in any effort to protect biodiversity, it is particularly important when the objective is something less than total protection, as is the case in Mamirauá. Only with this information in hand can scientists and community members carry out a management plan that will ensure an animal's long-term contribution both to the ecosystem and the local economy.