The baiji, for example, is considered functionally extinct by IUCN, with the last sighting in 2004, due to heavy pollution to the Yangtze River.

The tube in the head, through which this kind fish takes its breath and spitting water, located in front of the brain and ends outwardly in a simple hole, but inside it is divided by a downward bony septum, as if it were two nostrils; but underneath it opens up again in the mouth in a void.

Aristotle, however, could already see many physiological and anatomical similarities with the terrestrial vertebrates, such as blood (circulation), lungs, uterus, and fin anatomy.

[citation needed] His detailed descriptions were assimilated by the Romans, but mixed with a more accurate knowledge of the dolphins, as mentioned by Pliny the Elder in his Natural history.

The harbor porpoise is one of the most accessible species for early cetologists, because it could be seen very close to land, inhabiting shallow coastal areas of Europe.

[17][24] Toothed whales have also evolved the ability to store large amounts of wax esters in their adipose tissue as an addition to or in complete replacement of other fats in their blubber.

They swim by moving their tail fin and lower body up and down, propelling themselves through vertical movement, while their flippers are mainly used for steering.

They do, however, lack short wavelength-sensitive visual pigments in their cone cells, indicating a more limited capacity for colour vision than most mammals.

[31] The ear is acoustically isolated from the skull by air-filled sinus pockets, which allow for greater directional hearing underwater.

[43] Allometric analysis indicates that mammalian brain size scales around the two-thirds or three-quarters exponent of the body mass.

In Shark Bay, a population of Indo-Pacific bottlenose dolphins put sponges on their beak to protect them from abrasions and sting ray barbs while foraging in the seafloor.

Males make a lot of slow clicks in breeding grounds (74% of the time), both near the surface and at depth, which suggests they are primarily mating signals.

[24][62] One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball.

[60]: 43–55  A study in the Galápagos found that squid from the genera Histioteuthis (62%), Ancistrocheirus (16%), and Octopoteuthis (7%) weighing between 12 and 650 grams (0.026 and 1.433 lb) were the most commonly taken.

Older females, though unable to have their own children, play a key role in the rearing of other calves in the pod, and in this sense, given the costs of pregnancy especially at an advanced age, extended menopause is advantageous.

[80] [81][82][83] Ambergris, a solid, waxy, flammable substance produced in the digestive system of sperm whales, was also sought as a fixative in perfumery.

As the scope and size of the fleet increased, so did the rig of the vessels change, as brigs, schooners, and finally ships and barks were introduced.

In the 19th-century stubby, square-rigged ships (and later barks) dominated the fleet, being sent to the Pacific (the first being the British whaleship Emilia, in 1788),[84] the Indian Ocean (1780s), and as far away as the Japan grounds (1820) and the coast of Arabia (1820s), as well as Australia (1790s) and New Zealand (1790s).

Though a properly harpooned sperm whale generally exhibited a fairly consistent pattern of trying to flee underwater to the point of exhaustion (at which point it would surface and offer no further resistance), it was not uncommon for bull whales to become enraged and turn to attack pursuing whaleboats on the surface, particularly if it had already been wounded by repeated harpooning attempts.

A commonly reported tactic was for the whale to invert itself and violently thrash the surface of the water with its fluke, flipping and crushing nearby boats.

[87] However, the recovery from the whaling years is a slow process, particularly in the South Pacific, where the toll on males of breeding age was severe.

The killing of the animals used to be done by slitting their throats, but the Japanese government banned this method, and now dolphins may officially only be killed by driving a metal pin into the neck of the dolphin, which causes them to die within seconds according to a memo from Senzo Uchida, the executive secretary of the Japan Cetacean Conference on Zoological Gardens and Aquariums.

[95] A veterinary team's analysis of a 2011 video footage of Japanese hunters killing striped dolphins using this method suggested that, in one case, death took over four minutes.

The most circulated footage is probably that of the drive and subsequent capture and slaughter process taken in Futo, Japan, in October 1999, shot by the Japanese animal welfare organization Elsa Nature Conservancy.

[107][108] Many organizations are dedicated to protecting certain species that do not fall under any international treaty, such as CIRVA (Committee for the Recovery of the Vaquita),[109] and the Wuhan Institute of Hydrobiology (for the Yangtze finless porpoise).

Bottlenose dolphins are the most common species kept in dolphinariums, as they are relatively easy to train, have a long lifespan in captivity, and have a friendly appearance.

In August 1989, a dominant female orca, Kandu V, tried to rake a newcomer whale, Corky II, with her mouth during a live show, and smashed her head into a wall.

[116] In February 2010, an experienced female trainer at SeaWorld Orlando, Dawn Brancheau, was killed by orca Tilikum shortly after a show in Shamu Stadium.

[122] In the aftermath of the release of the film, Martina McBride, 38 Special, REO Speedwagon, Cheap Trick, Heart, Trisha Yearwood, and Willie Nelson cancelled scheduled concerts at SeaWorld parks.

[123] SeaWorld disputes the accuracy of the film, and in December 2013 released an ad countering the allegations and emphasizing its contributions to the study of cetaceans and their conservation.