Note from Con Slobodchikoff: This is a guest post by Randall Johnson, who has been a frequent contributor to the Reconnect With Nature Blog and the Dog Behavior Blog.
Not long ago, I received an e-mail from a friend of mine who has dedicated almost 30 years of her life to protecting a large tract of the Amazon rainforest outside of Iquitos, Peru. She told me that in the early part of May, six pink river dolphins, or 'botos', Inia geoffrensis, had been found dead on the Ucayali River and evidence suggested they had been victims of commercial fishermen who had recently passed through area. Having spent a lot of time in that region in the early '90s, I felt a twinge of sadness and regret because I remember how that part of the forest used to be relatively unspoiled.
LAGOA DA PRATA BOTOS (Photo Credit: Randall Johnson) Photographed in a clearwater lake in Brazil, this boto, Inia geoffrensis, displays its long beak, small eye, a paddle-shaped flipper, and dorsal ridge. Because their cervical vertebrae are not fused together, as in marine dolphins, botos can bend their necks to an angle of 90° to its body, downward or sideways, and some of this flexibility can be inferred by the neck folds. Although their eyes appear small, in the skull they are just as big as those of marine dolphins and their eyesight is surprisingly good, with aquarium-held animals having proved capable of recognizing people by vision alone. In murky waters, however, they rely on a highly-developed echolocation system to navigate and find food and there is some evidence that they may be capable of stunning prey fish by using sonic bursts produced by their melon, a separate organ on their foreheads (visible in the photo), the shape of which can be altered at will.
LAGOA DA PRATA BOTOS (Photo Credit: Randall Johnson) Also known as the "pink dolphin", botos that spend a lot of time in clearwater lakes or tributaries tend to be uniformly gray, which is thought to be the skin's reaction to more constant exposure to sunlight. In murkier waters, adults often display some degree of pink coloration, ranging from completely pink to pink swashes and patches, with the rest of the body a medium to light gray. The boto pair in the photo, identified as male and female, typifies that most Inia sighted in the wild are single individuals or pairs, usually mother and calf. Although little is known about the social lives of these animals, their social organization seems to be intricately linked to the seasonal rising and falling of the water level, with dolphins dispersing during the high water, or flood, season and regrouping during the low-water, or dry, season. Coordinated fishing has been reported, sometimes involving tuxuxi dolphins and giant river otters, and the author of this post has also documented that botos practice food-sharing.
This latest report of river dolphin deaths may seem insignificant at first glance, but it drove home the point that the world's freshwater dolphins are the most endangered cetaceans, with their populations in decline, mostly as a result of human activities and impacts on their habitats. In fact, one species, the baiji, or Yangtze River dolphin, was declared 'functionally extinct' when an international team of researchers failed to find a single dolphin during a 2006 survey expedition.
At about the same time, an ambitious two-year-long river dolphin census was getting underway in South America, involving 13 rivers and covering five nations and 3,600 km of rivers. Led by Fernando Trujillo, scientific director of the Omacha Foundation (Colombia) and financed by WWF Switzerland and WWF LAC's Freshwater Program, the census recorded 3,188 botos and tucuxi dolphins, Sotalia fluviatilis.
"This census gives us a baseline population for these species and gives us an insight into the state of the ecosystems they inhabit," said Trujillo. "These results also provide the foundation for designing an evaluation and monitoring program for South American river dolphins."
A new method for surveying river dolphins, developed for the purpose of this census, was certified by whale experts from the International Union for the Conservation of Nature (IUCN) and eighteen professionals were trained in it before getting started.
The survey confirmed the major threats faced by these dolphins: pollution from farming, industry, and mining; hydroelectric development; boat traffic and disturbance; prey depletion due to over-fishing; and incidental mortality in fishing nets.
A relatively new and particularly serious threat was also identified: in parts of Peru and Brazil, botos are being deliberately killed and their decomposing carcasses are used as bait to attract a variety of catfish (mota fish), making it easier to catch this commercially valuable species. For instance, between 800 and 1,200 pounds of mota fish came be captured in two hours using a two-meter long boto.
This practice is growing at an alarming rate and hundreds of dolphins are being killed each year in Peru and Brazil for mota fisheries alone. It now represents a serious threat that needs to be addressed to prevent unrecoverable damage to the affected dolphin populations.
In the past, Amazon River dolphins were protected by a body of legends and beliefs that accredited them with magic powers. There is, for instance, a widespread belief that the boto is a shape shifter, or encantado, who transforms into an irresistibly handsome young man and seduces young women. [Children born with certain birth defects are believed to be the offspring of a boto and women who conceive while their husbands are away can blame the dolphin.]
Many locals don't kill or eat dolphins because they are believed to carry the souls of the dead. In other locations, dolphins aren't killed because to do so would bring bad luck or misfortune.
And the tucuxi dolphin is thought to be a kind of "brujo", or wizard, which is either feared or revered, depending on the tributary. [I know this to be true based on personal conversations I had in Peru.]
However, commercial fishermen come from areas that don't share these beliefs. Their bottom line is profit-driven, so they aren't deterred by the dolphins' legendary powers.
Sadly, even local fishermen are now killing botos because they see them as competitors for a diminishing supply of fish, even though there is only a small degree of overlap between the species of fish eaten by dolphins and the species of fish eaten by humans.
According to the IUCN's 2008 Red List, we are facing an "extinction crisis", with almost one in four [mammals] at risk of disappearing forever. The study showed that at least 1,141 of the 5,487 known mammals on Earth are known to be threatened with extinction and the world's remaining river dolphins are prominently featured among them.
Given that they are top predators in their ecosystems, river dolphins are not only visible indicators of the overall health of the rivers in which they live, but they are essential to maintaining the delicate balance of the entire ecosystem. Removing top predators---something our species is quite adept as doing--can set off the eventual collapse of the ecosystem they occupy with disastrous results that ultimately affect human populations. How many times do we need to learn this lesson before it finally sinks in?