Dolphin Day happens to be on April 14, so it’s time to talk about our friendly cetacean friends and their importance to our marine ecosystems.
Their name means “the fish with a womb”
Their name originally comes from the ancient Greek δελφίς (delphis), which roughly translates as “the fish with a womb.” The name itself reminds us that dolphins and other cetaceans are mammals that still need to breathe air.
They use sound to “see”
Another dolphin adaptation is echolocation, which evolved over the course of 50 million years using the melon, an organ of fatty tissue on its forehead that produces high-frequency clicks, according to a 2015 Smithsonian article by Danny Lewis.
Dolphin ears have also adapted to their marine environment. They receive sound through their throats, where it passes through a fat-filled cavity into the inner ear. The ear itself is isolated from the skull with air-filled sinus pockets, which gives them great directional hearing underwater.
In 2015, the Speak Dolphin research organization released findings that dolphin echolocation gives them three-dimensional information like depth. The next step is to find out just how much detail dolphins can see from echolocation.
Dolphins sleep one side at a time
Because they don’t breathe underwater, dolphins have evolved different sleep patterns that take these into account, according to Scientific American. One of their more amazing adaptations is their ability to sleep one side at a time, a sleep pattern called cat-napping. One half of the brain stays awake to maintain low-level alertness in case predators or obstacles appear. This side also signals when to rise to the surface — usually around two hours — so a sleeping dolphin can take a fresh breath of air, and then the process reverses, letting the active side rest.
They also have different ways of sleeping while swimming. In one of their deeper forms of sleep, dolphins simply float like a log on the water’s surface, which is why it’s called logging. In echelon swimming, young dolphins sleep while towed along in their mother’s slipstream. The mother is also usually asleep during this time — dolphin mothers don’t stop swimming for several weeks, in fact. Newborn dolphins lack the blubber needed to float easily, so falling asleep will mean that they will sink.
Dolphins beat humans in self-awareness
Bottlenose dolphins beat humans and chimpanzees when it comes to achieving self-awareness, showing signs of recognizing their reflections in a mirror as early as seven months of age, reported Rachel Morrison and Diana Reiss in a 2018 article published in PloS One. For comparison, most humans become self-aware by 12 to 15 months. This relates to dolphins’ early development of social awareness and advanced sensorimotor skills
They maintain different circles of friends
After self-awareness comes social awareness. Dolphins have names for each other. Specifically, male bottlenose dolphins have been recorded producing sounds and developing individual signature whistles within their first few months of life. They are known to keep their names for life, and their signature whistles help them identify their first-order alliances (friends) and second-order alliances (friends of friends).
Meanwhile, noise levels in the ocean have been going up, thanks to the many seafaring vessels that crisscross the waters, making it more difficult for dolphins to communicate.
They grieve their dead
The social ties between dolphins are strong enough that they have been observed exhibiting behaviors that resemble grief in humans. Dolphin mothers have been seen carrying their dead infants in their mouths or on their backs for around a week, and even adult males have been seen holding dead calves in their mouths.
Cetacean biologist Giovanni Bearzi and his colleagues have labeled this “post-mortem attentive behavior” and found a correlation between grief-like displays and brain size and complexity, according to a 2018 article in ScienceMag.com, written by Virginia Morrell.
Not all dolphins live in the ocean
While majority of dolphins live in ocean habitats — saltwater — there are a number of river dolphins that call inland rivers their home. These include the boto, or Amazon river dolphin, whom the native Amazonians consider as magical beings who take on human form and hide their blowholes under a hat, according to National Geographic.
There are also river dolphins in the Araguaia, Ganges, and Irrawaddy rivers. The Irrawaddy dolphin is down to 92 individuals in the Mekong river, as counted by the World Wildlife Fund. This decline is blamed on several factors, such as unrestricted hunting. The explosives used during the Vietnam War also caused audio trauma to their echolocation systems. More recently, the hydropower dam projects in the Irrawaddy and Mekong rivers disrupt the large fish migrations along the Mekong — the river dolphins’ food source.
It’s likely that the Irrawaddy river dolphin may go the way of the Chinese river dolphin or baiji, who have possibly been extinct since 2006, as reported by Nathan Thompson in a 2018 Al Jazeera article.
They deserve to be free
It is important to remember that dolphins are large-brained, cognitive animals. This accounts for their social nature, their communications with each other, and their complex relationships within their dolphin pods, other dolphins, and the rest of their marine habitats. They also transfer behaviors to succeeding generations — effectively a cultural transfer in their own cetacean way.
That said, they need their native habitats to flourish, and it bears repeating that dolphins need to live out in the open, not in dolphinariums or an enclosed facility like the upcoming Cebu Ocean Park. Some may claim that such facilities serve research purposes, but it is also well documented that dolphins in captivity behave differently than in the wild, as mentioned by Ocean Conservation Society President Maddalena Bearzi in a 2014 article for National Geographic Blogs.
Support dolphin conservation!
Instead of paying for dolphin shows and ocean parks, people who want to learn more about dolphins can instead donate to and participate in conservation programs. In the Philippines, we have the Marine Wildlife Watch of the Philippines, Coral Cay Conservation, and Marine Conservation Philippines, among others.
This appeared in Animal Scene magazine’s April 2019 issue.