What do pink dolphins eat in the Amazon?

The same research describes how a boto hunts. It uses a wide range of habitats: 60% of the prey species it eats are mid-water fish and 33% live near the bottom, and about 49% of prey species are solitary while 42% form shoals.² In other words, the boto does not specialise in shoals that it can herd. It takes fish where it finds them, in the open water, at the bottom and in the shelter of the flooded forest.

Timing matters too. The Mamirauá chapter reports that both Amazon dolphins catch mostly day-active fish, between 65% and 75% of prey species, and that more than 35% of what they eat is carnivorous fish.¹² That means the dolphin's own prey are often hunters too. It also means a boto is a predator several steps up the food chain, and the IUCN flags mercury and other pollutants as a concern for dolphins in the Amazon.¹³

To find the fish in water that is brown or black, the boto uses sound. Both Amazon river dolphins have biosonar to locate prey and to get their bearings under water.⁴ The jaw does the rest once a fish is caught: the front of each half carries 18 pairs of conical teeth and the rear 10 pairs of molar-like ones, 28 in all.¹⁴ A mouth with both kinds can hold a slippery fish and crush hard prey.

A nursing mother needs plenty of food, and the river calendar helps her. ICMBio reports that births are timed with the falling river, when the fish are crowded into less water.²⁵ The IUCN adds that nursing females choose lakes, probably for the weak current, the supply of small fish and protection for a calf against predators such as large sharks.²⁶ A lake in the dry season is a larder and a nursery at the same time. At the other end of the cycle, the animals pull out of the lakes and shallows as the water drops, possibly to avoid stranding.²⁷ That movement puts them back in the main channel, where most adult males spend their time.²⁸ If you want to know what pink dolphins eat at any given time, the key question is where in the river they are, because the menu follows the water.

Feeding is where the diet question meets tourism. In Novo Airão, on the Rio Negro, contact began in 1997 at a floating restaurant when the owner's daughter began to feed a visiting boto, and about 15 animals came every day to take fish portions that visitors bought for BRL 15.^7,15 Researchers pointed to problems: the animals may get more food than they need, swallow plastic and other items dropped into the river, or injure themselves on the platform's edge.¹⁶

Some visitors make it worse. ICMBio's account says that some tourists offer food that is not part of the natural diet, such as snacks and pieces of bread, or hold the dolphins out of the water for a photograph.⁵ An INPA researcher said that when around 80 tourists crowd a platform the dolphins change their natural behaviour and become more aggressive with each other over the food.^22,17 The IUCN's warning is brief: feeding by people can make dolphins ill and puts them at greater risk from passing vessels.¹⁸

The rules are patchy. Brazilian law does not specifically forbid feeding wild animals in protected units, though a few units add their own bans, and a decree of 2008 forbids intentionally harassing cetaceans.^21,34 ICMBio adds that Amazonas already has its own instruction regulating tourism with botos.²³ The safest rule for a traveller is also the simplest: do not feed them, and do not book a stop that sells fish for the purpose.