Under the relentless Amazon sun, researchers aboard the boat Comandante Gomes 3 squint so as not to miss the few seconds in which the dolphins (pink dolphin) and tucuxis (grey dolphin) emerge from the muddy waters to breathe.
The strenuous work of the Amazon Dolphin expedition, carried out for three weeks along 1,200 km along the Solimões, Purus and Japurá rivers, aims to answer a dramatic question: after years of large-scale hunting, Amazon dolphins are still threatened with extinction ?
The most worrying situation is that of the boto. Starting in the early 2000s, an Inpa (National Institute for Amazonian Research) monitoring led by biologist Vera da Silva began to notice a sharp decline in the species population in the Sustainable Development Reserve (RDS) Mamirauá (530 km from Manaus ).
Next, Inpa concluded that the population of the dolphin in Mamirauá had been falling by half every ten years. The discovery placed him on the International Union for the Conservation of Nature and Natural Resources (IUCN) red list of endangered animals in 2018.
Two years later, the tucuxi, who usually die after being trapped in fishing nets, received the same classification. Today, all river dolphin species in the world are threatened, and one of them, the baiji, has become extinct in China.
With the boto, the reason for the abrupt reduction was the popularization of its use as bait for fishing piracatinga, also known as water vulture. To be caught, this species of scavenger fish is lured into an enclosure by the fat of the butchered porpoise, a frenzy similar to a piranha attack. Alligators are also often used in the activity, but with a lower ecological impact.
“Piracatinga fishing is the most glaring threat, the one we have to deal with more quickly,” says the expedition’s chief researcher, Sannie Brum, 38, from Rio de Janeiro.
“The declines have been observed in very specific areas, but as they are emerging, unresolved and escalating threats, they were classified as an extinction threat by the IUCN”, says the biologist.
Fishing for Amazon dolphins is already prohibited, but this legal protection alone was not enough. Therefore, in 2015, the federal government decreed, for five years, a moratorium on fishing and the sale of piracatinga.
The suspension of this activity was renewed twice for periods of one year and now ends on July 1, 2022. The decision is up to the federal government, via the Ministry of Agriculture.
The consumption of piracatinga is rare among riverside dwellers, but its meat is highly appreciated in Colombia, which opened the market for this fish some 20 years ago. Since 2017, however, the neighboring country has suspended marketing for an indefinite period, after surveys have detected a high concentration of mercury in meat.
In Brazil, it is common for piracatinga to be sold “disguised” as a douradinha filet or pirarucu, deceiving the consumer.
According to a report by the Ministry of Agriculture, based on figures provided by the state government, Amazonas produced about 4,500 tons/year between 2011 and 2014. Fishing occurs mainly in the Solimões River.
Statistical blackout
The problem is that, during the term of the moratorium, there has been no effective monitoring of the population trend. In 2016, Cepam (National Center for Research and Conservation of Amazonian Biodiversity), of ICMBio (Chico Mendes Institute for Biodiversity Conservation), carried out a first expedition along the Solimões and Purus rivers. The project provided for another five counts annually, until 2020, but there were no more resources for travel.
Monitoring was only resumed in October, thanks to a partnership between Inpa and the NGO Sea Shepherd Brazil, which initially decided to sponsor six semiannual monitoring trips, with the same itinerary as in 2016. The first expedition, accompanied by the report from sheet, was completed last Saturday (23).
“When we embrace a cause, we stay for a long time,” says Nathalie Gil, who leads the campaign at Sea Shepherd, funded through donations. “We created this model of thinking in three years, but we want to stay much longer. It starts with research and who knows, in the future, it even becomes an inspection.”
According to Brum, there is no way to assess the population of dolphins and tucuxis only with the 2016 expeditions and the recently completed one. In meetings with the ministry, the scientist, as a representative of Inpa, defended the renewal of the ban for another six years, the time necessary for a conclusive evaluation.
The reason is the slow life cycle of botos. They only reach sexual maturity after ten years. Gestation lasts from 12 to 13 months, and only one offspring is born at a time, which is under the care of the mother for three years.
Despite this positioning by Inpa, the ministry is against the moratorium and defends the “sustainable” resumption of piracatinga fishing, although it avoids talking about deadlines.
“The trigger for the adoption of the moratorium was the use of wild species, including the emblematic boto, as bait for the capture of piracatinga. However, it is also worth mentioning that the moratorium brought a great restriction on the income options of riverine communities, because, in some areas, there are reports that the piracatinga component, in the total weight captured, reached 35%”, says the folder, in a note.
Brum denies that fish is so important to the local economy. “In conversations we have had with fishermen since the ban in our study area, especially in the Middle Solimões, fishers do not point out to us the ban as a serious restriction on their income.”
Whale Method
To calculate the porpoises and tucuxis, the Inpa researchers use a method created for whales, adapted to Amazonian conditions and to river dolphins. This is an estimate: as cetaceans move and are only seen when they come up to breathe, it is not possible to count them all.
To measure population density, biologists then divide the distance traveled into transects, a unit used to count both plants and animals. In the case of Amazonian dolphins, a new transect is created every 2 km traveled.
The tucuxis (gray), which usually swim in groups, are more visible than the pink dolphins, with a more solitary behavior. Therefore, when calculating the density, the researchers estimate that, on average, they see 70% of the tucuxis in a given transect. For pink dolphins, the percentage drops to 40%.
In the field, the work involves six researchers, divided into two groups, posted on platforms at the bow and stern of the boat. Each team has two porpoise watchers and a note taker.
In general, there are six hours of work, in the morning and in the afternoon, in intense heat. Over the 19 days of counting, around 1,400 botos and 3,200 tucuxis were sighted. The conclusions regarding the numbers, however, will only be reached after the six planned trips.
In the 2016 count, which will serve as a basis for monitoring population dynamics, the Purus River was the place with the highest density – and not just porpoises in the Amazon. No species of cetacean in the world has recorded density as high as that of the Purus River, according to researcher Sannie Brum. She cites two reasons: the high fishiness and managed fishing in the RDS Piagaçu-Purus.
On the other hand, the density of porpoises decreased drastically in the region of Manacapuru (100 km from Manaus), where there was intense fishing for piracatinga. It was there that the expedition caught the only point of this activity during the trip, a sign that the moratorium has eased but has not ended the practice.
If the boto goes extinct, the Amazon will lose one of its most original inhabitants. While the tucuxi, a relative of the sea dolphins, entered the mouth of the Amazon River “only” 2.5 million years ago, the dolphin has been in the Amazon region since the current forest was a large lake, about 30 million years ago .
This long time of adaptive evolution resulted in unique features. One of the most important is in the head. The very pronounced “melon” indicates a sophisticated echolocation that allows you to navigate through the flooded forest and find fish in murky waters.
Unlike other dolphins, porpoises do not have fused neck vertebrae. As a result, they are more flexible, even folding into a “U” shape.
Another exclusivity is teething. In addition to the conical teeth, common to all dolphins, there are also incisors at the back of the mouth, which are used to chew tougher species of catfish. “It’s a very, very adapted species for the Amazon”, says Brum.​
The reporter traveled at the invitation of Sea Shepherd Brazil.
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