Number of Guiana Dolphins Living in Rio’s Guanabara Bay is Lowest in History

RIO DE JANEIRO, BRAZIL – The current number of Guiana Dolphins (called “boto cinza” in Portuguese), endangered for decades in Rio de Janeiro, is the lowest ever recorded.

In the 1980s the cetaceans’ population totaled 400, but today there are 29, with only four calves. In the last five years, 16 have died, seven of them newly born.

“The animals reproduce, but many calves don’t survive,” alerts José Lailson Brito Junior, coordinator of the Maqua Project and professor at the State University of Rio de Janeiro (UERJ).

According to the researcher who has been monitoring the life of the Guiana Dolphins in Guanabara Bay since the 1990s, three types of pollutants influence the species’ mortality rate.

The combinations of pesticides, polychlorinated biphenyl (oil found in capacitors and energy transformers), and polycyclic aromatic hydrocarbon (present in fuels, crude oil and coal) that reach the marine environment through leaks are the most critical for biodiversity.

In the case of calves, contamination occurs through nursing. As the Guiana Dolphins are at the top of the food chain, they show a high concentration of contaminants.

“Every mammalian calf does not yet have a very well developed immune system and during nursing, the calf receives a very high dose of these pollutants in a short time through milk,” explains Lailson, who has also found evidence of miscarriage.

The Guanabara Bay Guiana Dolphin population is considered the most endangered on the Brazilian coast. The concern increases even more due to the number of ships that anchor in the region.

In December, O Globo newspaper showed that the bay has 15 anchorage areas and harbors some 250 medium and large ships a month.

However, even when stationary, the ships keep their engines running and form a curtain of noise pollution, with very loud underwater sounds, damaging the bio-sonar system of these cetaceans.