Dr. Erika Sullivan
My recent move to South Australia has allowed me to explore its natural wonders below ocean waters. My first adventure started steps from my flat in Holdfast Bay. A company called Temptation Tours promoted swimming with wild dolphins in their natural habitat. Being conscious of the effects of human behaviour on species survival, they assured me that their actions as a tour company were regulated, had no adverse effects on wild populations, and that these dolphins were naturally curious. So a coworker and I signed up and were ready to find Flipper!
The morning we were scheduled to go, it rained and our tour was cancelled. The company assured us visibility was important for a positive experience. We rescheduled the following week, graced with sunny skies and near-perfect visibility. The large catamaran filled with locals and tourists set sail in search of dolphins! Swimmers geared up in wetsuits, masks, and snorkels, while observers watched from the boat. Swimmers jumped in the water, hanging onto ropes with buoys being towed off the boat’s stern as dolphin pods swam past. We were lucky to encounter a type of dolphin known as the Common dolphin. We also found the more popular Bottlenose dolphin, like the one playing Flipper in the 1964 television series. It was exhilarating being under water as pods swam by with speed and curiosity. Hearing them echolocating, or what appeared as them talking about us, was fascinating to witness. This experience as a veterinarian led me to enrol in a Marine Veterinary Wildlife Course furthering my knowledge on cetacean physiology, anesthesia, therapeutics and rescue.
The Common Dolphin
The Common Dolphin contains two species within the genus Delphinus. Cetologists include the short-beaked common dolphin (Delphinus delphis) and the long-beaked common dolphin (Delphinus capensis). Genetic studies in the 1990s suggested including a third species, the Arabian common dolphin (Delphinus tropicalis), however taxonomists classify this as a regional variety; a subspecies of the long-beaked common dolphin. Despite having common in its name, they are not as common as other dolphin types.
Common dolphins are identified by their unusual colour pattern. They have dark backs and white underbellies, with sides that look like an hourglass pattern coloured yellow or gold in the front and grey in the rear. They are a medium-size dolphin approximately 2 meters long and weigh between 80 - 200 kg. Males are longer and heavier than females. Their beaks are long containing 60 small, sharp, interlocking teeth on each side of their jaw, which they use to eat squid and fish.
The Common dolphin is widely distributed in warm-temperate and tropical waters. Long-beaked varieties prefer shallow, warm coastal waters, while short-beaked varieties live along shelf edges in seamounts and escarpments. They can dive 200 metres deep and live in pods of hundreds to thousands. They are fast swimmers, reaching speeds of 60 km/hr and perform acrobatics for fun. Within their pod they display altruistic behaviours to support injured members. Occasionally they are found interacting with other species like pilot whales, or bow-riding on baleen whales and boats.
The Bottlenose Dolphin
Bottlenose dolphins are the most common member of oceanic dolphins. Within the genus Tursiops, species include the common bottlenose dolphin (Tursiops truncatus), the Indo-Pacific bottlenose dolphin (Tursiops aduncus), and the Burrunan bottlenose dolphin (Tursiops australis). They can hybridize with other species like Risso’s dolphin, or false-killer whales creating a hybrid known as the Wolphin. Living in pods up to 1000 members they inhabit warm temperate oceans worldwide. They eat fish, crustaceans, and squid, using their cone-like teeth to grasp, but not chew, their food. Dolphins use echolocation, emitting clicking sounds and listening for a return in echos, to determine the location and size of nearby items, including prey.
Bottlenose dolphins are grey, varying from dark grey on the dorsal fin to light grey on the underside. Adults are 2 to 4 meters long and weigh between 150 to 650 kilograms; however, size varies with habitat, with dolphins in warm shallow waters being smaller than those in cool pelagic waters. About 20% of their bodyweight is blubber. Their vision is good above and below water, but olfaction is poor since their blowhole is closed underwater, opening only for breathing at the surface. They live on average 20 to 40 years.
Communication through burst-pulsed sounds, whistles, and body language is how bottlenose dolphins communicate with their pod, indicating nearby food or danger. They lack vocal cords so sound is emitted via six air sacs near the blowhole. Intelligence is demonstrated by willingness to use tools, like when they place marine sponges over their face, protecting it while searching for food on sandy sea bottoms. “Strand feeding” is a technique used by pods where they create a wave projecting fish onto sandy banks, after which they follow, temporarily stranding themselves to eat their catch before flopping back into the water. Their curiosity and intelligence is the reason so many Bottlenose dolphins end up in captivity, performing at aquariums and on television.
Dolphins have genital slits on their underside, with females having mammary slits facilitating sexing. Males fight for rank and access to females during the mating season. Gestation averages 12 months with births occurring in warm shallow waters. Calfs are dependent on their mothers for up to 8 years and continue associating with them for years, making it necessary when treating stranded juveniles to reunite them with the dam to facilitate survival. Pod compositions vary based on sex, age, reproduction, and familial relations.
Dolphins face threats to survival from humans. Metal pollutants in water, hunting for use as shark bait, and extensive human activity in the Mediterranean Sea pose significant risk. Shark attacks and entrapment in fishing nets cause death. Boycotting tuna products for this reason lead to “dolphin-safe” labeling methods to prevent dolphin endangerment. The Convention on the Conservation of Migratory Species of Wild Animals is an intergovernmental treaty aiming to conserve migratory wildlife species. Appendix I strives to protect migratory species threatened with extinction and restore places where they live. Appendix II lists species that benefit from international co-operation for conservation. The short-beaked Common dolphin is listed globally on Appendix II, while the Mediterranean population is listed on Appendix I. By increasing global awareness, conservation efforts, and respect for our oceans, and encouraging dolphin-friendly tourist operations, only then will dolphins be preserved for future generations.