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What is a marine mammal? As the name suggests, marine mammals are not fishes spending all or part of their life underwater.
Just like terrestrial mammals, they are warm-blooded animals who breathe the air through their lungs and give birth to well formed newborns. Calves are suckled by their mothers by means of the milk secreted by their mammary glands, which is where the term “mammal” comes from (from mammalian=mamma).Marine mammals include various species: dolphins, porpoises, whales, seals, sea lions, manatees, dugongs as well as polar bears and otters.
The order comprising most species is that of cetaceans: it accounts for more than 80 species including whales, rorqual whales, dolphins, porpoises and so on. Seals, sea lions, walruses and sea elephants belong to the order of the Carnivorous, a suborder of the Pinnipeds. The order of Sirenoids includes dugongs and manatees.
The dolphins of Palablu belong to the species scientifically called Tursiops truncates, or Bottlenose Dolphins (Montagu, 1821). Bottlenose dolphins are among the best known and investigated species of the Cetaceans. Found almost in all seas, from tropical to temperate waters, they do not populate particularly cold-watered seas. They can also be easily spotted in the Mediterranean Sea. Some groups live closed to the shore and are substantially non-migratory; some others reside in open water and may move widely.
Bottlenose Dolphins are medium to small in size: their length can vary from 2.5 to 3.8 metres, and their weight can fluctuate between 180 and 300 kg. A newborn dolphin is almost one metre long. Such varying parameters indicate that the size as well other morphological characters of this species vary according to the geographical area they populate and how distant from the shore they reside.
Bottlenose Dolphins are stocky and powerful, with a short rostrum that is clearly defined in comparison with the rest of their muzzle. The melon, i.e. the dolphin’s forehead, is well developed.The dorsal fin, located in the middle of the body, is high and falcate (curving slightly to the back): its function is to stabilize the dolphin’s swimming. Pectoral fins are short and thin and allow rotation of the body. The caudal fin, typically half-moon-shaped, serves as a propulsor: an upwards movement generates the push when swimming. The dorsal and caudal fins have no bone structure: they are made of a skin duplication stiffened by connective tissue and collagen fibres. Pectoral fins are the equivalent of the forelimbs of terrestrial mammals which developed and transformed into fins to adapt to the water environment. They are formed by all bone structures that are typical of the forelimbs of the other mammals.
The colouration pattern is usually uniform: dark grey on the back, shading towards a lighter grey on the abdomen, which, in some cases, can also be snow-white.
These animals can go as deep as 600 metres, without breathing for up to 10 minutes. The Bottlenose Dolphin is very powerful and can reach a speed of 30 km/h; it is very agile and, when necessary, it can reach maximum peaks of 50 km/h.
Bottlenose Dolphins eat a rich variety of preys and use several hunting techniques, some of which require complex cooperation and organization schemes. They eat mostly fish (grey mullets, eels, anchovies, sardines, mackerels, herrings, mullets, etc.), but also squids, cuttlefishes, octopuses, and if necessary, crustaceans and other invertebrates of benthos. Their teeth, 20 to 26 per half-jaw, are small and cone-shaped and are not used to chew. Tursiops swallow their prays whole. Teeth can reveal information about the age of the dolphin: by analyzing and counting the layers of dentine that deposit according to annual rhythms.
Dolphins do not experience the Rem sleeping phase (i.e. the dreaming phase), they only sleep “lightly”. They do not really sleep, but rather they “rest”. When resting, dolphins alternate their brain’s hemispheres, maintaining active only one at a time: this is how breathing is guaranteed, i.e. the active hemisphere is responsible for the impulse to reach the surface and avoid the risk of drowning. Moreover, the active hemisphere allows the dolphin to be awake enough to perceive any predators or dangerous coming.
Cetaceans have their genitals located in the abdominal cavity, into pouches that are not visible externally. It is often difficult to recognise a male from a female unless the genital region can be observed from close up. In fact, the only external evidence to determine a dolphin’s gender is the different distance between the anal and genital slit: in males the genital and anal slits are clearly distinct and separate; in females, they are much closer and one seems like the continuation of the other, with 2 tiny mammal slits to the side.
