Death comes to the Amazon

 Death comes to the Nile Amazon

Amazon River Dolphin (modified from Scientific American).

Hot temperatures are again hitting the Amazon River and its tributaries. In 2023, temperature spikes in and around Lago Tefé killed hundreds of river dolphins. Tefé is located in the heart of Amazonas, approximately 400 miles up the Amazon River from Manaus, the capital of the region. As a whole, the region is sparsely populated, as Manaus is one of the two cities that have a large population of over 1 million. 

Once again, temperatures are rising, and combined with regional droughts, this has created another deadly zone. In November, the lake's waters reached 41 degrees Celsius (105.8 degrees Fahrenheit). David Hannah said, "Drought conditions often coincide with high atmospheric temperatures, and such trends will become more intense and frequent with climate change." Additionally, droughts have lowered the lake levels, leading to new problems. The issue extends beyond just one lake to the entire region. Researchers found that in 2023, half of the surveyed lakes had temperatures above 37 °C.

The Amazon River Dolphin (also known as Pink River Dolphin or Boto), Inia geoffrensis, lives in the freshwater rivers and tributaries of the Amazon and Orinoco river basins in South America (Brazil, Venezuela, and Colombia). In Amazonian folklore, the boto is said to have mystical powers and to transform into a handsome man at night. Many local myths and stories feature this dolphin.

Notable for their pink coloration, which can range from gray to bright pink and becomes more vivid with age. Males are typically pinker than females. They have a long beak and a flexible neck. Adults can reach lengths of up to 8 feet (2.5 meters) and weigh as much as 450 pounds (204 kg). In the wild, they live 15–30 years, although their lifespan is much shorter due to increasing threats.

These intelligent animals are primarily solitary or found in small groups. However, large gatherings can occur when food is abundant. They are carnivores that feed on fish, crustaceans, and occasionally small turtles.

Females typically give birth to a single calf after a gestation period of 11-15 months. Calves are born during the rainy season when rivers flood, providing more space and food.

Besides habitat destruction, the leading cause of biodiversity loss, dolphins are sometimes hunted for use as bait in fisheries. Mercury pollution from gold mining also affects their health. Efforts to protect the species include establishing protected areas, promoting environmental education, and conducting research projects to better understand their population and needs.

These dolphins stand out among their peers in a few ways. Amazon River Dolphins have unfused vertebrae in their necks, allowing them to turn their heads left and right. This helps them navigate through complex flooded forests. Their extended, narrow beaks are lined with up to 140 teeth, designed to catch various prey in murky waters or among branches and roots. The pink coloration is unique and can become brighter with age, abrasions, or excitement. The color results partly from capillaries near the skin and increased blood flow during physical activity. Their wider beaks deliver exceptional agility for precise movement through submerged vegetation and debris. Their dorsal fin is low and ridge-like, helping them avoid entanglement in branches and making navigation through shallow, obstacle-filled waters easier.

Hunting in Muddy waters:

Amazon River Dolphins have highly developed echolocation, which is essential for hunting and navigating in the dark, muddy waters. They use a wide range of vocalizations, including clicks and whistles, for both navigation and social interaction. Their rounded forehead (melon) helps with this. Their long beaks, equipped with vibrissae (whisker-like hairs), enhance their sense of touch in the muddy riverbeds.

Other dolphins that live in, or at least, venture into freshwater zones of the planet include the La Plata Dolphin, Pontoporia blainvillei, found in estuaries in Argentina, southern Brazil, and Uruguay, the Ganges River Dolphin, Platanista gangetica in Nepal, Indian, and Bangladesh, the Indus River Dolphin, Platanista gangetica minor, usually listed as a subspecies of the Ganges dolphin, in the Indus River of Pakistan, and the Yangtze River Dolphin, Lipotes vexillifer, in China, which may be extinct. There are also two closely related species to the Amazon River Dolphin: Inia araguaiaensis, the Araguaian River Dolphin, and Inia boliviensis, the Bolivian River Dolphin; these are sometimes considered subspecies rather than full species. The map (figure 2) uses slightly different names for full and subspecies. 

Some river dolphins are closely related, specifically the subspecies in southern Asia and the South American species. However, overall, they are paraphyletic, with the Ganges species being far removed from, for example, the Amazon species, having presumably evolved from marine species in that region. They retain similar features due to convergent evolution in comparable habitats. (Figure 2).

 Figure 2. Relationships among River Dolphins (from Nikaido et al. 2001) with estimates of branching dates (in millions of years ago) using the relaxed molecular clock based on DNA flanking a region called SINE (short interspersed Nuclear Elements). The relaxed molecular clock allows different estimates on different branches. Times estimated from fossils are in parentheses.

Figure 3. Distribution of River Dolphins 

(stolen/mod from Hamilton et al. 2001).

Let me paraphrase the beginning of others’ messages of dread:

The sixth extinction is upon us…

EO Wilson

 &

The climate emergency is here…

Ayan Fleischmann.

 

Yes, we are in it. Human-wrought climate change is wreaking havoc on the planet, and today the Amazon rainforest, the world’s richest and most varied biological reservoir, is in the crosshairs.

 

Sources and Further Readings:

David Hannah, quoted above, is Professor of Hydrology and UNESCO Chair in Water Sciences at the University of Birmingham.

Hamilton, Healy & Caballero, Susana & Collins, Allen & Brownell, Robert. 2001. Evolution of river dolphins. Proceedings. Biological sciences / The Royal Society. 268. 549-56.

 

Nikaido, Masato & Matsuno, Fumio & Hamilton, Healy & Brownell, Robert & Cao, Ying & Wang, Ding & Zuoyan, Zhu & Shedlock, Andrew & Fordyce, Robert & Hasegawa, Masami & Okada, Norihiro. 2001. Retroposon Analysis of Major Cetacean Lineages: The Monophyly of Toothed Whales and the Paraphyly of River Dolphins. Proceedings of the National Academy of Sciences. 98. 7384-7389.