Over 150 Dolphins Die in Lake Within a Week: 'Staggering'

Some 153 dolphins have died in a single week in a Brazilian lake, 10 percent of the lake's entire dolphin population.

The Lake Tefé dead were made up of 130 pink dolphins and 23 tucuxi dolphins, both of which have declining populations and are listed as "endangered" on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.

Lake Tefé's water temperatures soared to a staggering 102.38 F during the last week of September, when the dolphins were found dead in these huge numbers, alongside hundreds of dead fish, according to a statement from the Mamirau Institute for Sustainable Development (IDSM) and environmental group WWF-Brasil. The average water temperature of the lake is usually around 89.6 F, but has spiked massively due to intense drought.

"What is happening at Lake Tefé is appalling. The impact of the loss of these animals is enormous and affects the entire local ecosystem", Mariana Paschoalini Frias, conservation analyst at WWF-Brazil, said in a statement.

Pink river dolphins, also known as Amazon river dolphins, are the largest species of river dolphin, reaching up to 8.2 feet long. These dolphins gain their characteristic pink color from repeated abrasion of the skin during aggressive interactions with others of their species.

"Scientists are working now to try to understand the problem specifically, however we know in mammals that high temperatures stress out the animals' physiology by bringing them out of what's called their 'thermal neutral zone'. This is the set point of the body where metabolism has to rise to keep the animals' body temperature constant," Jason Bruck, an assistant professor of biology at Stephen F. Austin State University, told Newsweek.

"At some point these animals are just not adapted to swim in 102 F waters."

The water in Lake Tefé was tested by local environmental consultancy Aqua Viridi, who found a large amount of algae Euglena sanguinea. This algae makes a toxin that often kills fish. However, necropsies on the dolphins did not reveal that the algae or its toxins caused their death, nor did viral or bacterial pathogens, meaning that the driver of the mass death is likely the abnormally warm water temperatures.

"The river dolphins were in shallow waters that with sunlight and little or no rainfall made water temperatures become very hot," Patricia Charvet, a professor of aquatic biology at the Universidade Federal do Ceará in Brazil, told Newsweek.

"By being aquatic mammals, water helps keep their body temperatures within their physiological tolerance levels. Most aquatic fauna from the Amazon Region tolerates higher water temperatures when compared, for example, to aquatic animals from temperate regions. Anyway, there are limits in terms of water temperature they can endure, even for these tropical organisms.

"Sometimes strandings in closed lakes can do this (water levels go down and the connection with the main river channel is lost, leading to shallow lakes with overheated waters)."

The extreme drought in the region has also led to dramatic declines in water levels, which is devastating for communities that use the waterways as major routes of transport: the city of Manaus, the capital of the state of Amazonas at the junction of the Amazon and Negro rivers, reached its lowest water levels in 121 years on Tuesday.

"The Amazon Region is facing one of its worst droughts in history due to an extremely strong El Niño phenomenon," Charvet said. "Around May-June this year, weather experts started alerting that waters from the Pacific Ocean were becoming abnormally hot (much warmer than expected) and warned that they were probably looking at one of the strongest El Niño events ever recorded. Now, the El Niño is causing extreme droughts in the mid to west Amazon Region (mainly Manaus and westwards)."

Conservation efforts at Lake Tefé are attempting to prevent further dolphin casualties from the heat, physically blocking off of the hottest regions of lake and moving the remaining dolphin to deeper, cooler waters.

"We formed a huge coalition to help collect carcasses, monitor live animals in critical areas of low depth and high temperatures, collect and send biological and water samples for analysis. An entire effort to get to the root causes of this unprecedented event," Frias said.

"In our studies on Amazonian dolphins, we found that they suffer from various pressures, such as predatory fishing, mercury contamination and the impact of hydroelectric plants. But these events in Tefé show that more research needs to be carried out on how they will be affected by constant climate change."

However, with continued climate change, the dolphins will remain at risk of similar events like this happening again.

"In the long run the deaths of these river dolphins is associated with climate change. Unfortunately, the changes we are causing throughout the world will likely impact more specific environments/ecosystems, altering rainfall and hydrologic water balance. Indirectly, deforestation is also contributing to temperature increases (land, air and water) in the Amazon Region but the overall scenario is an extreme drought caused by little or no rainfall associated with the El Niño phenomenon," Charvet said.

"Perhaps it's time for some faster changes regarding climate change prevention to avoid other deaths."

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