By Nadim Parves and Md. Rasel Mia, Wildlife Conservation Society (WCS) Bangladesh
Kuakata, Bangladesh - May 25, 2022 - Imagine discovering a whale in Bangladesh that looks like a shark and is smaller than most dolphins. That is exactly what happened when a member of the Kuakata Dolphin Conservation Committee posted a photograph of a Dwarf sperm whale that stranded on the beach near Kuakata. Known to scientists as Kogia sima, the whale was initially found alive. Local people heroically tried to push it back out to sea, but the whale floated back with the incoming tide before it died about two hours later. Although tragic for the whale, the photographs were exciting for wildlife conservationists. They were first confirmed record of this wildlife species occurring in Bangladesh.
Volunteer members of the Kuakata Dolphin Conservation Committee, who had attended a basic training on responding to cetacean (the scientific grouping of whales, dolphins, and porpoises) mortalities, conducted by the Wildlife Conservation Society (WCS) in November 2021, enthusiastically shared more detailed photographs. While looking through these photographs, we were taken by surprise. The whale looked almost like a shark with a square head, forward jutting snout, and a white band that looked like fake gills. This is by design, not coincidence. The Dwarf sperm whale exhibits these features to fool predators, such as killer whales and large sharks, into thinking that it is a shark. Besides fake gills, Dwarf sperm whales have another unique characteristic among cetaceans. The whale has a small sac hanging off its intestines filled with a reddish-brown liquid that it releases into the water to hide from predators. This is like the inky black fluid released by octopuses when they are frightened. As the world’s smallest whale, Dwarf sperm whales cannot depend on their size to scare off predators.
The Dwarf sperm whale is one of more than 90 species of cetaceans. Cetaceans are air-breathing mammals that spend their entire life in water. Just like humans, female cetaceans normally give birth to a single baby or calf that feeds on mothers’ milk before becoming independent. Dolphins, porpoises, and a few ‘toothed’ whales, like Dwarf sperm whales, have sharp teeth to catch slippery prey which they suck into their mouth. Like all cetaceans, they do not chew their prey but swallow them whole.
All cetaceans have a strong tail fin or flukes that they move up and down to propel themselves forward, two side fins for maneuvering, and most have a dorsal fin for balance and regulating body temperature. The shape of their fins, head, beak or rostrum, body, along with coloration are used to distinguish between species. Dwarf sperm whales are easily confused with closely related Pygmy sperm whales, also known as Kogia breviceps. However, the relatively large triangular dorsal fin, located about halfway from the tip of its snout to its tail flukes, and small size allowed us to positively identify the cetacean that stranded in Kuakata as a Dwarf sperm whale.
This record in Bangladesh is particularly important because very little is known about Dwarf sperm whales, which live in the deep sea. Although, the species was never seen during more than a decade of WCS surveys conducted in waters offshore of Bangladesh, Dwarf sperm whales may be more abundant than we suspect since they are typically only seen lying motionless on the surface when the water surface is completely calm. While we do not have any information about the cause of death of the Dwarf sperm whale that stranded in Kuakata, there is growing evidence from other areas of the world suggesting that both Kogia species are particularly vulnerable to swallowing plastic debris, which they mistake for their squid, octopus, and cuttlefish prey. Plastic debris can block their digestive system, causing them to starve to death. One astounding discovery was that the Dwarf sperm whale was pregnant with two calves. This is extremely rare among cetaceans that typically only give birth to a single offspring at a time.
Members of the Kuakata Dolphin Conservation Committee, along with officers from the Forest Department, Bangladesh Fisheries Development Corporation, and members of the public who assisted them, acted as exemplary Ocean Guardians. They attempted to return the whale to sea and contacted experts to advise them about what to do. They deserve full credit for the discovery of a new wildlife species never documented before in Bangladesh.
Figure 1 caption: The white band on the side of the head on Dwarf sperm whales is a false gill that helps them to look like a shark for scaring away predators. Photo © Asaduzzaman Miraj
Figure 2 caption: Despite the great effort made by members of the Kuakata Dolphin Conservation Committee to return the stranded Dwarf sperm whale back to sea, the pregnant female died. Photo © Asaduzzaman Miraj
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