Originally published 2021-09-19.
In February 2019, local fishermen on Marajó Island in northern Brazil found the carcass of a young humpback whale lying in a mangrove forest near Araruna Beach, outside the town of Soure. The calf, roughly 8 metres (about 26 feet) long, was around 15 metres from the shoreline. The photos went viral as a "whale in the Amazon rainforest" mystery, but the setting was actually coastal mangrove at the mouth of the Amazon River, and researchers quickly identified the most likely explanation: unusually high tides carried the body inland.
The story resurfaced online in 2021 as if it were new. Here is what really happened, why a humpback was there at all, and which popular theories about stranded whales hold up.
Where the whale was found
Marajó is a vast island, roughly the size of Switzerland, sitting where the Amazon and Pará rivers meet the Atlantic Ocean. Its coastline is fringed with mangroves, salt-tolerant trees that grow in the tidal zone and are flooded and drained by the sea every day.
That detail changes the picture entirely. A whale deep inside a dense inland jungle would be inexplicable. A whale lying among coastal mangroves a short distance from the beach, in an area the sea floods twice daily, is surprising but understandable.
The fishermen alerted Bicho D'água, a local nonprofit marine research and conservation group, whose team went to examine and document the carcass. The group shared images of the find on social media:
A post shared by Bicho D'água (@bicho_dagua)
How it most likely got there
Researchers from Bicho D'água told reporters that the calf had probably died at sea several days before it was found, possibly after becoming separated from its mother. Without her milk, a young calf can quickly starve.
At that time of year, tides in the area rose by nearly 4 metres (about 13 feet) twice a day and flooded the mangroves. As a dead whale decomposes, gases build up inside its body and make it float. The researchers' explanation was that a combination of a buoyant carcass and an exceptionally high tide pushed the body over the beach and into the trees, where it was left behind as the water retreated.
The Federal University of Pará's pathology laboratory carried out a necropsy to look for the cause of death. Detailed results were not widely publicised, so the exact cause remains unconfirmed in public reporting.
Why a humpback was off northern Brazil in February
This is the genuinely puzzling part. Humpback whales that breed off Brazil normally do so during the southern winter, roughly July to November, mainly around the Abrolhos Bank off the state of Bahia, far to the south of Marajó. In February those whales would usually be feeding thousands of kilometres away in the cold waters near South Georgia and the Antarctic.
Finding a calf near the equator at that point in the year was therefore unusual. Researchers suggested it might have come from a different population, possibly one from the North Atlantic, and DNA testing was planned to check its origin.
Humpbacks are famous travellers. Individuals have been recorded swimming as far as 8,000 kilometres in one direction between feeding and breeding grounds, one of the longest migrations of any mammal.
A conservation success story, with caveats
Humpbacks were hunted heavily during the commercial whaling era, and the global population fell to an estimated 5,000 or so by the 1960s. The International Whaling Commission banned commercial humpback hunting in 1966.
Some older accounts still describe the species as endangered, but that is now out of date at the global level. The IUCN Red List classifies the humpback as Least Concern, with an estimated population of around 135,000 and an increasing trend. Several countries, including the United States, Canada and Australia, have eased their protection categories as populations recovered.
Recovery is uneven, though. The small, isolated population in the Arabian Sea numbers only around 80 animals and is considered endangered. Ship strikes, entanglement in fishing gear, noise and changes to prey caused by warming oceans remain serious threats everywhere.
Why whales strand: what the evidence says
Strandings have many causes, and scientists usually examine each case individually. The best-supported explanations include:
- Illness, injury and starvation. Sick, injured or orphaned animals often weaken and drift ashore, alive or dead. A calf separated from its mother, as suspected here, fits this category.
- Human impacts. Collisions with ships and entanglement in nets and ropes are leading causes of death for large whales in busy waters.
- Military sonar. Intense naval sonar has been linked to mass strandings, most strongly in deep-diving beaked whales, which can suffer injuries similar to decompression sickness after surfacing too quickly in panic.
- Geography and tides. Shallow, gently sloping coasts and large tidal ranges can trap animals or deposit carcasses well above the usual waterline.
Some researchers are also investigating whether solar storms, which disturb Earth's magnetic field, might confuse whales that may use magnetic cues to navigate. The idea is intriguing but still under study and far from proven.
Claims that whales simply "die of stress" when separated from their group are harder to support in that simple form. Stress can play a part in a weakened animal's decline, but scientists rarely name it as a sole cause.
What to do if you find a stranded whale
If you come across a stranded whale or dolphin, alive or dead, keep a safe distance and contact local authorities, a coastguard or a marine rescue network straight away. Large animals can move suddenly, and carcasses can carry diseases or even burst as gases build up. Avoid touching the animal, keep dogs away, and note the location, time and photos for responders.
The Marajó whale is a reminder that viral mysteries often have grounded explanations. Here, the real story involved tides, mangroves and an unusual migration, and it is arguably more interesting than the myth of a whale lost in the jungle.
Sources: CNN, 26 February 2019; photos by Bicho D'água; Wikipedia: Humpback whale; originally reported via IFL Science.
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