Dream

I was swimming in an outdoor pool with full grown porpoises. The story told to me was that had been accidentally packed in patio furniture that was shipped from overseas. They arrived looking like one inch frogs but they grew and grew.

Porpoises, as opposed to their dolphin counterparts, don't thrive in captivity, and it is very difficult to maintain a porpoise.

Life cycle

Porpoises are fully aquatic creatures. Females deliver a single calf after a gestation period lasting about a year. Calving takes place entirely under water, with the foetus positioned for tail-first delivery to help prevent drowning. Females have mammary glands, but the shape of a newborn calf's mouth does not allow it to obtain a seal around the nipple— instead of the calf sucking milk, the mother squirts milk into the calf's mouth.[24] This milk contains high amounts of fat, which aids in the development of blubber; it contains so much fat that it has the consistency of toothpaste. The calves are weaned at about 11 months of age. Males play no part in rearing calves. The calf is dependent for one to two years, and maturity occurs after seven to ten years, all varying between species. This mode of reproduction produces few offspring, but increases the probability of each one surviving.[10]
Diet

Porpoises eat a wide variety of creatures.

Recently discovered hybrids between male harbour porpoises and female Dall's porpoises indicate the two species may actually be members of the same genus.[5]


Porpoises have a bulbous head, no external ear flaps, a non-flexible neck, a torpedo shaped body, limbs modified into flippers, and a tail fin. Their skull has small eye orbits, small, blunt snouts, and eyes placed on the sides of the head. Porpoises range in size from the 1.4 metres (4.6 ft) and 54 kilograms (119 lb) Vaquita[6] to the 2.3 metres (7.5 ft) and 220 kilograms (490 lb) Dall's porpoise.[7] Overall, they tend to be dwarfed by other cetaceans. Almost all species have female-biased sexual dimorphism, with the females being larger than the males,[8][9] although those physical differences are generally small; one exception is Dall's porpoise.[10][11]

Odontocetes possess teeth with cementum cells overlying dentine cells. Unlike human teeth, which are composed mostly of enamel on the portion of the tooth outside of the gum, whale teeth have cementum outside the gum. Porpoises, like other odontocetes, possess only one blowhole.[9] Breathing involves expelling stale air from the blowhole, forming an upward, steamy spout, followed by inhaling fresh air into the lungs.[9][12] All porpoises have a thick layer of blubber. This blubber can help with insulation from the harsh underwater climate, protection to some extent as predators would have a hard time getting through a thick layer of fat, and energy for leaner times. Calves are born with only a thin layer of blubber, but some species compensate for this with a covering of fine, downy hair known as lanugo.[9][13]

Porpoises have a two-chambered stomach that is similar in structure to those of terrestrial carnivores. They have fundic and pyloric chambers.[14]
Locomotion

Porpoises have two flippers on the front, and a tail fin. Although porpoises do not possess fully developed hind limbs, they possess discrete rudimentary appendages, which may contain feet and digits. Their flippers, for example, contain four digits. Porpoises are fast swimmers in comparison to seals, which typically cruise at 5–15 kn, or 9–28 kilometres per hour (5.6–17.4 mph); Dall's porpoise, in comparison, can travel at speeds up to 74 kilometres per hour (46 mph).[15] The fusing of the neck vertebrae, while increasing stability when swimming at high speeds, decreases flexibility, making it impossible for them to turn their head.[16] When swimming, they move their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering. Flipper movement is continuous. Some species log out of the water, which may allow then to travel faster, and sometimes they porpoise out of the water, meaning jump out of the water. Their skeletal anatomy allows them to be fast swimmers. They have a very well defined and triangular dorsal fin, allowing them to steer better in the water. Unlike their dolphin counterparts, they are adapted for coastal shores, bays, and estuaries.[9][13]
Senses
Biosonar by cetaceans

The porpoise ear has specific adaptations to the marine environment. In humans, the middle ear works as an impedance equaliser between the outside air's low impedance and the cochlear fluid's high impedance. In whales, and other marine mammals, there is no great difference between the outer and inner environments. Instead of sound passing through the outer ear to the middle ear, porpoises receive sound through the throat, from which it passes through a low-impedance fat-filled cavity to the inner ear.[17] The porpoise ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.[18] Odontocetes send out high frequency clicks from an organ known as a melon. This melon consists of fat, and the skull of any such creature containing a melon will have a large depression. The large bulge on top of the porpoises head is caused by the melon.[9][19][20][21]

The porpoise eye is relatively small for its size, yet they do retain a good degree of eyesight. As well as this, the eyes of a porpoise are placed on the sides of its head, so their vision consists of two fields, rather than a binocular view like humans have. When porpoises surface, their lens and cornea correct the nearsightedness that results from the refraction of light; their eyes contain both rod and cone cells, meaning they can see in both dim and bright light. Porpoises do, however, lack short wavelength sensitive visual pigments in their cone cells indicating a more limited capacity for colour vision than most mammals.[22] Most porpoises have slightly flattened eyeballs, enlarged pupils (which shrink as they surface to prevent damage), slightly flattened corneas and a tapetum lucidum; these adaptations allow for large amounts of light to pass through the eye and, therefore, they are able to form a very clear image of the surrounding area.[19]

The olfactory lobes are absent in porpoises, suggesting that they have no sense of smell.[19]

Porpoises are not thought to have a good sense of taste, as their taste buds are atrophied or missing altogether. However, some have preferences between different kinds of fish, indicating some sort of attachment to taste.[19]
Sleep
Further information: Unihemispheric slow-wave sleep

Unlike most animals, porpoises are conscious breathers. All mammals sleep, but porpoises cannot afford to become unconscious for long because they may drown. While knowledge of sleep in wild cetaceans is limited, porpoises in captivity have been recorded to sleep with one side of their brain at a time, so that they may swim, breathe consciously, and avoid both predators and social contact during their period of rest.[23]