A fresh look at river dolphins.

In the Amazon scientists are discovering how these ancient animals are adapting to an ever-changing environment

In January 1986 I visited the Amazonian rain forest for the first time. Jorge Reynolds, a Colombian electronic engineer who for more than two decades has been researching cardiac stimulation in animals, invited me to take part in an expedition to obtain electrocardiograms of river dolphins. (Reynolds has taken EKGs of animals as diverse as mosquitoes, electric eels, sea turtles, iguanas, dolphins, and whales.) During this and subsequent research trips, I became aware of the great research potential of these dolphins.

Two dolphin species--the boto and the tucuxi--share habitat in the Amazon and Orinoco rivers, the largest river system on the planet. The boto, as it is known in Brazil (Inia geoffrensis), better known by Colombian and Peruvian fishermen and rural people as bufeo colorado, or pink dolphin, belongs to the superfamily Platanistoidea, or river dolphins. They include four other dolphin species--the baiji of the Yangtze River in China; the two susus of India, Bangladesh, Nepal, Bhutan, and Pakistan; and the franciscana, the only one of the group that lives in the sea, off the coasts of Brazil, Uruguay, and Argentina. The tucuxi (Sotalia fluviatilis) belongs to the superfamily Delphinoidea, which includes all marine dolphins.

Besides being the largest river dolphin, the boto covers the widest geographical area, and can be found in Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, and Venezuela. The tucuxi inhabits the Amazon and Orinoco rivers, as well as the sea, and can be found in the Caribbean off the coast of Panama (recently, groups of these dolphins were sighted off the Nicaraguan coast), and also along South America's north and northeastern shores, from Colombia to Brazil.

Dolphin fossils indicate that river dolphins are older and more primitive than marine dolphins. Ancestors of the river dolphins existed from the Late Oligocene and Early Miocene epochs, about 20 to 25 million years ago; while marine dolphins are known to exist from the Late Miocene epoch, about 10 to 15 million years ago. Platanistoid dolphin fossils were found in marine deposits dating back to the Oligocene, Miocene, and Pliocene epochs, which indicates that the freshwater habitat is secondary and that the ancestors of modern river dolphins moved from the sea to the rivers. It has been suggested that the ancestors of the boto entered the Amazon River either from the Atlantic Ocean between 2 and 5 million years ago, or from the Pacific Ocean about 15 million years ago. The ancestors of the tucuxi entered the Amazon River at a much later date. Consequently, the species differ despite sharing the same environment. Botos had more time to adapt to freshwater than tucuxis and, therefore, experienced more anatomical changes that allow them to live in and use this environment perhaps more efficiently.

In 1956, American biologists James Layne and Ross Allen participated in an expedition to Leticia, Colombia, whose main objective was to capture live dolphins to be exhibited in the United States. Layne and Allen's observations (published in 1958), while limited, were the first published description of Amazon dolphins' ecology and behavior--and the first to examine the natural history of any river dolphin. Thirty years passed before the dolphins of this region again became of interest to scientists. And, it wasn't until last year that a multidisciplinary, long-term study of the biology, ecology, and behavior of the boto and tucuxi was begun. This research includes scientists from Colombia, Mexico, Peru, and the United States, and is sponsored by the United Nations Environment Programme (UNEP), the Monterrey Institute of Technology and Higher Studies (ITESM)--Guaymas Campus (Mexico), and the Colombian government, through the National Institute for Renewable Natural Resources and the Environment (INDERENA). The study is part of the UNEP-sponsored Action Plan for the Conservation of Marine Mammals in the Southeastern Pacific Ocean.

From our base of operation in Amacayacu National Park, in Colombia, at the mouth of Quebrada Matamata, our research area covers some seventy miles along the Amazon River, where it forms the border between Colombia and Peru, plus a small part of the border between Peru and Brazil. In order to find these dolphins, who are very elusive, we use a small outboard motor boat--only thirteen feet--which also allows us to navigate the different water systems of the Amazon--tributaries, lakes, as well as narrow channels. From March to December 1993, we spent over one thousand hours studying river dolphins, took a month-long census, and are now analyzing the data thus collected.

While we have found botos and tucuxis in practically all parts of the research area, we have identified four areas of higher concentration: the Loretoyacu River and Tarapoto-El Correo Lake region in Colombia; the Atacuari River, in Colombia and Peru; Caballo Cocha Lake and its channels in Peru; and Ramon Castilla in Peru and Brazil. Normally, we spent one or two days every week studying the dolphins in each of these areas. Through photoidentification--identifying the animals based on photographs that show their natural marks (scars), we were able to verify that some of these dolphins travel between the various areas. During our fieldwork we took more than ten thousand photos, whose detailed examination will provide information about the distribution, movements, social organization, behavior, and numbers of these dolphins.

On one of these trips we learned the limits of our close-up examination. Although dolphins may appear delicate and gentle, they can become aggressive and are very powerful in the water. We were following a couple pairs of adult botos as they were trying to mate. Suddenly, after we had been following them for some thirty minutes at a distance of over forty to sixty yards, one of the dolphins changed direction quickly, coming directly toward our small boat. It forcefully struck the water twice with its tail very close to the boat's bow, then jumped up almost completely out of the water, drenching us as it fell hard on the water's surface, then continued on its way. We all remained silent, wet, and although not speaking about the matter, understood the message clearly: Don't bother us!

While botos and tucuxis are equally numerous and both are seen near the shore, only botos penetrate underwater vegetation. We believe that in many instances they do so for feeding. Unlike other dolphins, the cervical neck vertebrae of the boto's spine are not joined, which permits the dolphin to move its head freely to either side--an important anatomic adaptation allowing it to swim among immersed tree roots and stalks.

The boto, measuring almost eight feet and weighing about 350 pounds (males are larger than females), also appears to be less hydrodynamic than the tucuxi. Several characteristics of the boto make it unique among dolphins. First, of all the river dolphins, only the boto has tiny sensorial hairs on the back of its large, wide beak. These hairs probably perform a tactile function and help dolphins to find fishes and invertebrates for food on the river-bed. Second, its tooth structure consists of two types of teeth: about half of the teeth from the end of the beak to the rear are conical, while the remaining teeth are of molar shape. These molars allow dolphins to seize and grind hard-scaled fish. The teeth of all other sixty-six toothed whale, dolphin, and porpoise species are conical. The boto's flippers consist of six fingers each (a condition shared only by the vaquita or Gulf of California harbor porpoise), while all other marine mammals have five fingers. The boto's flippers are wide and oar shaped, giving it great mobility as it swims. The pink color of the boto, unique among mammals, is due to the fact that its blood moves through very shallow subcutaneous vessels. However, not all botos are pink. Although most adults have this coloration, we have also observed pink calves and juveniles. Many factors probably affect the dolphin's coloration, such as maturity, sex, geographic location, genetic differences, and the water's transparency and temperature.

Although the tucuxi is smaller and more slender than the boto, females are larger than males. The freshwater variety grows up to five feet, about one foot smaller than the marine version of this species, and weighs nearly 110 pounds. One of the more visible characteristics that distinguish the tucuxi from the boto, when both are seen in the water, is its large, hook-shaped, well-defined dorsal fin. Its coloring pattern generally includes a light gray back, lighter gray or almost white flanks, and a pink or cream-colored ventral region.

Like other animals living in rivers--such as fishes and invertebrates--river dolphins form smaller groups, or pods, than their counterparts in the sea. While we have seen groups of up to six individuals (on one occasion we saw a group of thirteen), botos generally can be seen alone or in pairs. Many times these pairs consist of a female with her offspring. However, it is common to find several groups in feeding areas where up to twenty-five dolphins can meet. While the tucuxi is more commonly found in groups smaller than six individuals, we have sighted groups of up to twenty. More than fifty of these dolphins may gather when feeding. By contrast, at sea, dolphins may gather in groups of hundreds or even thousands of individuals.

As we discover more about these ancient species--their behavior, ecology, and adaptations--we realize that they can be ideal indicators for monitoring their freshwater ecosystems. In 1986 this same conclusion was reached by scientists attending a meeting in the People's Republic of China to discuss the problems of river dolphins worldwide. While most of the Amazonian dolphin populations appear stable, strategies must soon be developed to ensure their long-term survival.

As we try to ensure the viability of the Amazonian ecosystems for all their inhabitants, the most comprehensive conservation strategies and scientific research projects might well borrow an idea from nature. Just as river dolphins know no national borders, so our efforts to study and preserve these species will be most successful when they are pan-national and cooperative. Clearly, the fate of the boto and tucuxi is closely linked to the fate of the environment as a whole.

Of Dolphins, Men, and Myths

Dolphins, particularly pink dolphins, have long been important in the mythology of Amazonian peoples. According to one legend, during the festivities that are part of a girl's coming of age, dolphins would transform themselves--taking on human shapes and leaving the river. Since they could still be recognized, they'd wear large black hats to help disguise their blow-holes and prominent foreheads. Entering the hose where the party was being held (being careful not to drink alcohol because they would immediately be turned back into dolphins and die outside of the water), the dolphin-men would seize the girl and carry her away forever to their underwater cities.

Omar Vidal, a Colombian marine biologist, is a senior researcher for the study of Amazonian dolphins and a professor at the Monterrey Institute of Technology and Higher Studies--Guaymas Campus.