Dolphin

What Exactly Are Dolphins?

Dolphins are fascinating aquatic mammals that have captured the imagination of humans for centuries. They belong to a group called Odontoceti, which includes other toothed whales like orcas and sperm whales. There are 40 extant species of dolphins, ranging in size from the diminutive 1.7m and 50kg to the imposing 9.5m and 10-tonne orcas.

Imagine a dolphin as a sleek, streamlined fish with a twist – it’s actually a mammal! Dolphins have flippers for swimming, conical teeth for catching prey, and a layer of fat (blubber) that keeps them warm in cold water. They’re widespread, from tropical species preferring warmer waters to those that thrive in colder climates.

But what do dolphins eat? Fish, squid, and occasionally large mammals like seals – it’s quite the varied diet! Males typically mate with multiple females annually, while females only mate every two to three years. Calves are born in spring and summer months, and mothers fast and nurse them for a relatively long period.

Now, let’s dive into their vocalizations. Dolphins produce various sounds including clicks and whistles. These aren’t just random noises; they’re essential for communication and navigation. They face threats from hunting, bycatch, habitat loss, and marine pollution – issues that affect not only dolphins but all aquatic life.

Interestingly, the name ‘dolphin’ comes from Greek δελφίς (delphís), meaning ‘a ‘fish’ with a womb.’ Meanwhile, the mahi-mahi fish is called the dolphinfish. In common usage, the term whale is used only for larger cetacean species, while smaller ones are considered dolphins.

There are six species of dolphins commonly thought of as whales: orca, melon-headed whale, pygmy killer whale, false killer whale, and two species of pilot whales. A group of dolphins is called a school or a pod – male dolphins are bulls, females are cows, and young ones are calves.

The Evolutionary Journey

Dolphins have evolved from land-dwelling mammals of the artiodactyl order (even-toed ungulates). They share this lineage with the Indohyus, an extinct chevrotain-like ungulate. Dolphins split from these ancestors approximately 48 million years ago and became fully aquatic by 5-10 million years later.

These marine mammals have torpedo-shaped bodies with non-flexible necks, limbs modified into flippers, a tail fin, and bulbous heads. Their skin is specialized for smooth movement through the water, lacking hair or glands except mammary glands. The thickness of their skin varies depending on species and age.

Blubber, found within the dermis and subcutis layer, helps regulate body temperature by constricting blood vessels when cold and releasing heat through thermal windows. Dolphins also use countercurrent heat exchange to conserve heat by transferring warm blood from the heart to cooler extremities.

Adaptations for Aquatic Life

Dolphins have unique locomotion structures, including two pectoral flippers, a dorsal fin for stability, and a fluke for propulsion. They are fast swimmers, with some species reaching speeds of up to 55.5 km/h (34.5 mph). Their fusing of the neck vertebrae decreases flexibility, while non-fused vertebrae in river dolphins allow for head turns up to 90°.

Dolphins swim by moving their fluke and rear body vertically, using flippers mainly for steering. Some species can porpoise out of water, increasing speed due to skeletal anatomy. Adaptations for diving include streamlined bodies, slowed heart rate, and re-routing blood to tolerate pressure.

Communication and Behavior

Dolphins have a network of blood vessels and nerve fibers in their dermis that extend to the epidermis, which enables them to sense vibrations and pressure changes. They generate sounds independently of respiration using recycled air and oil-filled organs. Echolocation provides orientation and information on an object’s shape and size.

The eyes are relatively small but retain good eyesight, with a field vision from side to side rather than binocular view. Most dolphins have adaptations allowing for clear vision and protection of their eyes. They lack olfactory lobes and nerve, suggesting a possible loss of smell, but some may still be able to taste.

Dolphins demonstrate advanced cognitive abilities such as teaching, learning, cooperation, scheming, and grieving. Their brain size is relatively large compared to body mass, indicating high intelligence. Self-awareness has been observed in dolphins, with some evidence supporting the idea that they possess this ability. However, results of mirror tests used to assess self-awareness are not universally accepted due to concerns over interpretation.

Dolphins are highly social animals that live in pods with varying sizes and structures. They establish strong bonds, helping injured or ill members, and display altruism towards other species. Dolphins communicate through various clicks, whistle-like sounds, touch, and posturing, exhibiting culture by teaching tools to young ones. They also engage in care-giving behaviors between fellows and different species.

Life Cycle and Sleep Patterns

Dolphins give birth to single calves born tail-first, becoming sexually active at a young age. Various species of dolphin engage in sexual behavior, including copulation with other species and aggression towards humans. The behavior of dolphins mainly spreads within generations rather than between parents and offspring.

Dolphins sleep with only one brain hemisphere in slow-wave sleep at a time, maintaining enough consciousness to breathe and watch for threats. Sleep patterns differ among species, with the Indus river dolphin sleeping in short bursts due to strong currents.

Feeding Methods

Dolphins have various feeding methods, including herding, corralling, and driving prey onto beaches. Some species whack fish with their flukes to stun them, while others use cooperative human-dolphin partnerships to catch fish. The behavior of dolphins mainly spreads within generations rather than between parents and offspring.

Communication

Dolphins communicate through a range of sounds including frequency modulated whistles, burst-pulsed sounds, and clicks. Signature whistles are unique to each individual and used for identification purposes. Dolphins have strong memories for these whistle sounds and can recognize them even after twenty years of separation.

Behavioral Patterns

In groups, dolphins tend to travel in pods with similar but not identical swimming patterns, using higher whistle rates to maintain contact and prevent losing pod members. Dolphins also frequently leap above the water surface, known as porpoising, which helps save energy while traveling. Dolphins show playful behavior such as carrying objects, playing with small animals, and interacting with other species like humans and humpback whales.

Health and Threats

Dolphins can tolerate extreme injuries such as shark bites, with rapid healing processes and minimal bleeding or injury from deep wounds. Some dolphin species are at risk of extinction due to pollution, collisions with boats, entanglement in fishing nets, and hunting practices.

Humans are also exposed to risks from dolphins, including mercury poisoning from dolphin meat, loud underwater noises from naval sonar and construction projects, and accidental by-catch in fishing nets. Dolphins are hunted for their meat and are susceptible to climate change impacts. Rising water temperatures cause range shifts, with some species moving to cooler waters or experiencing declines in populations.

Cultural Significance

Dolphins have played a significant role in human culture throughout history and religion, including in Greek myths where they were seen as helpers of humankind. Dolphins are also featured in ancient art and coins from Greece, where spotting them riding in a ship’s wake was considered a good omen.

Captivity Controversies

In addition to their cultural significance, dolphins have been associated with various deities and mythological figures, such as Poseidon, Arion, Dionysus, Aphrodite, Apollo, Ganga, Melikertes, Palaemon, Leucothea, Phalanthus, and the Makara. Dolphins are also depicted in heraldry, often as symbols of power and strength.

Dolphins have been kept in captivity since the 1960s, with many facilities opening around the world, including SeaWorld and Dolphin Bay. Various species are kept, but bottlenose dolphins are the most common due to their trainability and long lifespan in captivity.

Conclusion

The debate over keeping dolphins in captivity is a complex one. While some argue that it provides educational opportunities and entertainment, others believe it’s unethical given the high intelligence of these creatures and the potential for negative health impacts. As we continue to learn more about dolphins, our understanding of their needs and rights will undoubtedly evolve.

Condensed Infos to Dolphin

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