Rescuing Rio de Janeiro’s dolphins from extinction

First of all, just 60 kilometers from the city of Rio de Janeiro, dozens of gray dolphins (Sotalia guianensis) cautiously pass by the boat and surface to breathe.

Leonardo Flach stands on the bow taking photos and later identifies individuals by their dorsal fins.

After all, the view of Sepetiba Bay is picturesque, with its clear sea and mountains covered in forest around it, but the water is far from crystal clear.

“Here in Brazil, [the gray dolphin] is one of the most common species in estuaries and bays, but also one of the most threatened,” says Flach, a biologist and co-founder of the NGO Instituto Boto Cinza.

He has been studying these marine mammals in Sepetiba Bay since the 1990s to understand the dangers they face and to find solutions to protect them.

One of the main threats to these dolphins is chemical pollution in the sea.

Flach was part of a study published in March that found high concentrations of toxins in gray dolphins in Sepetiba Bay over a 12-year period.

This is the result of dredging, industrial pollution and raw sewage.

Flach says that almost 80% of the region’s sewage is discharged into the bay untreated, polluting the sea with pathogens and pharmaceuticals excreted in urine.

“Our gray dolphins, which live in semi-enclosed bays, are among the most polluted in the world,” explains Mariana Alonso, a professor at the Institute of Biophysics at the Federal University of Rio de Janeiro.

Exposure to these chemicals has been linked to hormonal changes and problems in the reproductive and immune systems of the gray dolphins, leading to greater susceptibility to infectious diseases, according to the study’s researchers.

The outbreak of the virus among the gray dolphins from November 2017 to March 2018 was fatal: at least 277 dolphins died,

killing almost a quarter of the Sepetiba Bay population and 6% of the dolphins in the neighboring Ilha Grande Bay.

“This virus was far more lethal because it struck a population whose health was already compromised,” says Flach.

Gray dolphins are particularly vulnerable to polluted water because they exhibit a behavior known as “site fidelity” and rarely leave their natal habitat.

This means that however dirty the water becomes, the animals remain there despite the impact on their health.

After all, Guanabara Bay has a total water surface area of 328 square kilometers and is one of the most densely populated areas of South America, with around 11 million people.

It is also surrounded by the second-largest industrial concentration, with about 10,000 industries,

including chemical plants, as well as 16 oil terminals and 12 shipyards.

Development in Guanabara

A 2017 study described development in Guanabara as “uncontrolled, unsustainable or unplanned.”

Gray dolphins in Guanabara Bay face constant daily threats from industrial toxins,

raw sewage and ship noise that interferes with dolphin sonar.

This combination causes chronic stress that affects the dolphins’ immune and reproductive systems, explains Rafael Carvalho, a biologist at the Center for Aquatic Mammals and Bioindicators (MAQUA) at the State University of Rio de Janeiro.

Females in the bay have been observed to be sterile even though they reached sexual maturity years ago, which means they may have fertility problems, Carvalho said.

For those that do manage to reproduce, he says, the chances of their offspring surviving are “very low.”

“These chemical elements characterize the health of these animals,” Carvalho said. “That is why the population decline in recent years has been huge.”

Cleaning Guanabara Bay and reducing daily pollution is a huge undertaking and requires a multifaceted solution.

But progress is being made.

Águas do Rio, the water and sewage services company of Rio de Janeiro, has implemented a series of infrastructure and technological developments in Guanabara Bay over the past two years to prevent 82 million liters of sewage from being dumped into the sea, the company said in a statement to Mongabay.

MAQUA researchers found that a reserve created in the northern part of the bay in 1984 was a refuge for gray dolphins, highlighting the importance of protected areas and the need to create more.

One way to understand the dangers facing the dolphins is to examine their carcasses to determine what killed them and where they were before they died.

But to clarify the current public health situation, researchers need to examine live samples.

In Sepetiba Bay, Flach mounts his camera and balances a small spear-gun-like device on his body.

He sights a group of dolphins, aims and fires a small dart into the group, creating a commotion when it hits one.

With a shout of triumph, Flach leans over the boat and pulls the dart out of the water, removing the blubber and skin from the tip.

The biopsy causes some discomfort, but it is not harmful, Flach says.

For researchers, this piece of flesh is a valuable source of information for determining the dolphin’s sex and measuring toxic and pathogenic concentrations in its skin.

Research to protect the gray dolphin

Flach places the sample in a test tube and the contents are sent to researchers at the Federal University of Rio de Janeiro for analysis.

Another way to monitor the dolphin population is through photographs.

In his Sepetiba Bay office, Flach has thousands of photos of gray dolphins with their dorsal fins breaking the surface of the water.

Each fin is unique, like a human fingerprint, and the photos make it possible to track the dolphin population, also recording animals caught in fishing nets and drowned.

After all, bycatch — when marine animals such as dolphins or turtles are accidentally captured in fishing nets — is another threat to gray dolphins, killing up to eight cetaceans per month in Rio de Janeiro.

Source: brasil.mongabay.com

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