dezembro, 17 2024

By Ana Barbour, special for WWF-Brazil 

The degradation of rivers and overfishing harm the natural conditions for river dolphins to feed, leading to a decrease in the number of fish. To cope with this challenge, river dolphins often resort to the gillnets (fixed fishing nets) used by riverside communities, who rely on fishing as their main source of income and sustenance. Unfortunately, in this situation, the dolphins can become tangled in the fishing nets and, unable to reach the surface to breathe, drown. There are also instances where fishermen, frustrated by the damage caused when dolphins tear through the gillnets to reach the fish, retaliate by killing the animals. This reality poses a significant challenge for the conservation of river dolphins and the survival of many families in the Amazon region. 

To address the issue and promote harmonious coexistence between these animals and humans, WWF-Brazil, in partnership with the Society for Research and Protection of the Environment (Sapopema), tested a groundbreaking piece of equipment called a pinger from June 2023 to June 2024. This device, installed on fishing nets, emits high-frequency sound waves that overlap with the communication range of the species, serving as a warning not to approach. “These devices have been used in rivers in Cambodia, Indonesia, and India since 2021, and they have shown great results in reducing entanglements and bycatch (death by drowning due to an inability to surface for air), while also increasing the number of fish caught,” explains Mariana Paschoalini Frias, conservation analyst at WWF-Brazil. 

The experiment was conducted in the community of Prainha I, located in Pará, in the Lower National Forest of the Tapajós River, where conflicts with the pink river dolphin (Inia geoffrensis) and accidental entanglements of the tucuxi (Sotalia fluviatilis) are frequent. “Since 2014, we have conducted three population estimates of Amazonian river dolphins in the Tapajós River, and we found that both populations are in decline,” says Neriane Nascimento, a biologist at Sapopema. She notes several threats to the species, including conflicts with fishing, contamination of rivers by mercury from illegal gold mining, deforestation, and hydroelectric dams, which isolate and harm the animals' feeding and reproduction. “In our concern for environmental conservation, we are also mindful of the people living in these territories. If the environment is degraded, they are the first to suffer,” adds Neriane. 

Listening, Training, Practice, and Results 

At the beginning of the project, the community of Prainha I had a very negative perception of the river dolphins. As local fisherman Dionísio Farias reported, “Hundreds of people want to get rid of the animals because they cause a lot of damage. The river dolphins get into the fishing nets, rip them open, and take the fish. Sometimes we go hungry.” 

In this scenario, the first step was to hold a workshop on conflict resolution and coexistence strategies to raise awareness among residents about the presence of river dolphins, the threats to their survival, and their relevance to the health of the river, the forest, and the community. “Now I recognize that the dolphin is important for the river. Wherever it is, we know there are fish. All the residents are very hopeful that this project will be successful because we want to fish without harming the river dolphins,” said fisherwoman Juliana Sousa after the training. As part of the workshop, the pinger was introduced as a possible solution for reducing damage to fishing nets and improving fishing productivity. “We demonstrated how the device works and the correct way to install it on the gillnets, as the fishermen themselves handled the equipment throughout the project,” recalls Mariana Frias. 

In the first phase of testing, the dolphins moved away from the gillnets, resulting in a 40% success rate in reducing damage to the fishing nets and a threefold increase in the amount of fish caught, positively impacting families' income and food supply. However, in the second phase, this result decreased, indicating that the dolphins began to adapt to the noise and sought ways to approach the gillnets again. “They avoided the pinger by diving deeper or swimming on the surface with their heads above water,” says Dionísio Farias. 

According to Mariana Frias, this behavioral change, observed only in the Amazon river dolphin, is explained by the fact that the tucuxi does not stay in shallow areas, preferring the central channel of the river. “The tucuxi has difficulty escaping from fishing nets. So, when it passes near one, it immediately detects the pinger's signal and knows how to avoid it. As a result, there has been a noticeable reduction in the number of tucuxis observed near fishing areas.” The Amazon river dolphin is unique in that it can swim backward and touch the tip of its tail fin with its beak, forming a circle. “It learned this by navigating through the flooded forest, which helps it fish using the nets, often without getting tangled. This is an important evolutionary skill that has also aided its adaptation to the numerous fishing nets along the rivers,” she explains. 

Despite this difficulty, the conservation analyst considers the results positive. In addition to keeping the animals away, the pingers provided valuable knowledge about the species. During the project, there were also no incidents of river dolphins becoming tangled in the fishing nets. Another significant advance was the marked change in the community's negative perception of river dolphins and an increased understanding of the need for coexistence. "However, we know that we need to improve. To do this, we must better adapt the method to the techniques used by fishermen. We also want to expand the project to reach more fishermen in the same community and in surrounding areas, with larger-scale and long-term experiments," emphasizes Mariana. 

Neriane also emphasizes the need to establish a fishing agreement in the region. "Over the years, the community has faced pressure from commercial fishing, which is depleting fishing resources. This affects the entire ecosystem: the fish, the river dolphin, and the fishermen," she concludes.