Endangered Amazon River Dolphins Threatened by Proposed Dams and Dredging

In Brazil alone, there are plans for 428 new dams over the next 30 years.

Amazon river dolphin in the Amazon river basin along Rio Negro, Brazil. Sylvain Cordier / Getty Images

While most of us are familiar with dolphins frolicking in the sea, Amazon River dolphins (Inia geoffrensis) call the Amazon and Orinoco river basins their home. Found in Brazil, Bolivia, Colombia, Ecuador, Peru, and Venezuela, these charismatically pink(ish) mammals are categorized as Endangered on the IUCN Red List.

Because of their broad range, which includes places as remote as backwaters, small lagoons, and even the rainforest, estimates of their population have been hard to gauge—but one thing is for sure. These aquatic mammals are in trouble, thanks to increasing anthropogenic threats. IUCN lists fishing, bycatch, intentional killing (fisheries use them for bait), and habitat destruction (mining, logging, and agricultural conversion). And add dams and dredging to the mix.

To get a better idea of how these threats are affecting the dolphins, researchers from the University of Exeter and the Peruvian conservation organization Pro Delphinus used satellite tags to track eight dolphins in the Peruvian Amazon. Their aim was to discover where the dolphins were in relation to fishing areas and proposed dams and dredging sites.

"The construction of dams, mainly in Brazil, is an expanding threat, with 175 dams operating or under construction in the Amazon basin, as well as at least 428 more planned over the next 30 years," note the authors in the study. (Downstream effects of dams on river dolphins have been previously observed.)

Additionally, the authors explain, a major project called the Amazon Waterway has been approved and is under contract for construction. The proposed waterway involves dredging sites across four main rivers of the Amazon basin and the expansion of ports to facilitate ship navigation across the Amazon, Ucayali, and Marañón Rivers.

"Knowledge of the ecology of the Amazon River dolphin, particularly its reliance on the diverse habitats available, is critical for improving the conservation prospects for this species," notes the study.

They found that on average, 89% of the dolphins’ home range was used for fishing.

Amazon river dolphin
Jose Luis Mena.

The dolphins were found to be an average of 150 miles (252 kilometers) from the nearest proposed dam and 77 miles (125 kilometers) from the nearest proposed dredging site.

While this may sound like safe-enough distances, the dolphins’ ranges spanned over 30 miles (50 kilometers) on average, and dams and dredging impact large stretches of river habitats.

And this was just the eight dolphins they were tracking, the authors point out that Amazon river dolphins live closer to the proposed sites than the ones from the study.

“It’s clear that the Amazon river dolphin is facing increasing threats from humans,” says Dr. Elizabeth Campbell, of the Centre for Ecology and Conservation on Exeter’s Penryn Campus in Cornwall.

“Fishing can deplete populations of the dolphins’ prey, and dolphins are also at risk from intentional killing and bycatch (accidental catching). Bycatch has been known to be a threat to these dolphins for the last 30 years, but there’s no real data on how many dolphins are caught per year.”

And the proposed dams and dredging are particularly concerning.

However, the study authors write that the "overlap of home ranges with anthropogenic threats highlights patterns that could help to identify priority areas for the conservation of river dolphins in Peru." They add that the Peruvian government has an opportunity to protect biodiversity.

“Peru has a chance to preserve its free-flowing rivers, keeping them a safe and healthy habitat for river dolphins and many other species,” Campbell said. “Given that many of these dams and dredging projects are still in the planning stage, we advise the government to consider the negative effects these activities have already had on river species elsewhere.”

The authors warn that it's not just Amazon River dolphins who will suffer. "In the case of dams and the Amazon Waterway, governments must consider explicitly the potential effects that dams will have at the basin scale and on freshwater species, as they will affect not only aquatic mammals but also the fisheries sector and food security"

"Without careful consideration," they conclude, "new dams will inevitably cause a decline in biodiversity and ecosystem services."

The study was published in the journal Oryx.