Fishing, dams and dredging close in on Peru’s river dolphins, study shows

Amazon river dolphins navigate the complex waterways of the forest, their pods spread across the Amazon Basin in six different countries. The routes of these large, pink mammals are naturally blocked by land, waterfalls and stretches of shallow water, but increasingly something else is in the way: human activity.

According to a recent study published in the journal Oryx, Amazon river dolphins (Inia geoffrensis) in Peru are threatened by fishing activity as well as the proposed construction of dams and dredging operations.

“It’s clear that the Amazon river dolphin is facing increasing threats from humans,” lead author Elizabeth Campbell, of the Centre for Ecology and Conservation at the University of Exeter, U.K., said in a statement.

Researchers from Exeter and Peruvian conservation organization Pro Delphinus fitted satellite tags on eight dolphins in the Peruvian Amazon to track their movements in relation to fishing areas, dams and dredging sites.

The findings revealed that an overwhelming 89% of the dolphins’ home range is subject to fishing activity. Fishing not only depletes the dolphins’ food sources but also subjects them to intentional killing and accidental capture, known as bycatch.

The Amazon river dolphin is currently classified as endangered on the IUCN Red List. Actions that further threaten these large mammals could have dire consequences for the entire aquatic ecosystem.

“As they are at the top of the food chain and are piscivorous, the pink dolphin basically controls fish populations, as they eat the weakest fish,” Miriam Marmontel, who heads the Amazonian aquatic mammals research group at the Mamirauá Institute in Brazil and was not involved in this latest study, told Mongabay. “In a way, they clean up the environment for the rest of the biota.”

The authors stressed the need to expand river dolphin tracking programs to cover multiple seasons, track more female dolphins in study areas, and increase the number of tracked individuals in other regions. Prior to being declared endangered in 2018, the river dolphin was categorized by the IUCN as data deficient because of limited information on its population, ecology and threats. This was in part due to the difficulty of catching, tagging and tracking dolphins in the Amazon.

Last year, another group of researchers fitted some Amazon river dolphin with radio transmitters in the Amanã Sustainable Development Reserve in the Brazilian state of Amazonas. The researchers were able to map the dolphins preferred zones and identify priority regions for species protection. Hydroelectric dams, fishing, and contamination from mining are the biggest threats to the species across this range.

The construction of dams, particularly in Brazil, poses a growing threat to the river dolphins and other aquatic wildlife of the Amazon Basin. There are 175 dams either in operation or under construction in the basin, with an additional 428 planned over the next 30 years.

The research team observed that the dolphins in the study were, on average, located roughly 252 kilometers (157 miles) from the nearest proposed dam and 125 km (78 mi) from the closest proposed dredging site.

Although these distances may seem substantial, the dolphins’ ranges typically span over 50 km (30 mi), and the construction of dams and dredging can have far-reaching impacts on large stretches of their river habitats. Furthermore, the study indicated that many Amazon river dolphins inhabit regions even closer to the proposed sites than the individuals tracked in this study.

Another looming threat is the construction of the Amazon Waterway, which aims to improve navigability for cargo freighters along 2,687 km (1670 mi) and four rivers of the Peruvian Amazon: the Huallaga, Marañón, Ucayali and Amazonas. The project, which has been approved and is already under contract, involves dredging sites along the four main rivers in the basin, including expanding several ports to facilitate heavier ship traffic.

Indigenous and local communities and environmental groups have objected to the Amazon Waterway project, saying its impact assessments aren’t scientifically robust. After construction of the waterway, regular dredging will be required to keep the passages navigable for larger vessels.

Dredging has been correlated with higher stress levels and lower testosterone in the Yangtze finless porpoise (Neophocaena asiaeorientalis), the last remaining freshwater cetacean in China following the disappearance of the baiji (Lipotes vexillifer) — an extinction attributed to dams. Once complete, the waterway could also “lead to collisions with dolphins and an increase in underwater noise,” the Peruvian study said.

Campbell called on the Peruvian government to consider the detrimental effects that similar hydroelectric activities have had on river species elsewhere, urging caution in the planning stages of dams and dredging projects.

“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,” Campbell said.

“Peru has a chance to preserve its free-flowing rivers, keeping them a safe and healthy habitat for river dolphins and many other species.”

Citations:

Campbell, E., Alfaro-Shigueto, J., Mangel, J. C., Mena, J. L., Thurstan, R. H., Godley, B. J., & March, D. (2023). Satellite-monitored movements of the Amazon River dolphin and considerations for their conservation. Oryx, 1-11. doi:10.1017/S0030605322001557

Nabi, G., Hao, Y., McLaughlin, R. W., & Wang, D. (2018). The possible effects of high vessel traffic on the physiological parameters of the critically endangered Yangtze finless porpoise (Neophocaena asiaeorientalis ssp. asiaeorientalis). Frontiers in Physiology, 9. doi:10.3389/fphys.2018.01665

Banner image of Amazon river dolphin in Peru courtesy of  Jose Luis Mena.

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