Whales, dolphins, and porpoises are categorized taxonomically as within the order Cetacea. As mammals, cetaceans breathe air, give birth to live young, and nurse their offspring. They are also highly intelligent and social animals. There are over 80 extant species of cetaceans, categorized into two suborders: the toothed whales (odontocetes) and baleen whales (mysticetes). Sperm whales, orcas, beaked whales, belugas, narwhals, porpoises, and dolphins are odontocetes, of which there are about 70 known species. Baleen whales, also known as mysticetes, are comprised of 14 species - blue, fin, sei, Brydes, gray, bowhead, humpback and minke whales among them.

Odontocetes use their teeth to catch their prey, whereas mysticetes use their baleen plates to filter vast quantities of water, straining out their prey. Mysticetes are much larger than odontocetes and are considered the "great whales" - although the largest of the toothed whales, the sperm whale (made famous by Herman Melville in Moby Dick), is also considered a great whale.

The hunting and killing of cetaceans by humans is termed "whaling" and occurs on both odontocetes and mysticetes in several countries. Whales, dolphins and porpoises are hunted and killed for the sale of their meat and parts, to reduce competition for fish, and by aboriginal subsistence communities for their meat and other parts. Odontocetes are whaled in some communities for their teeth, which are used as currency. Some cetaceans are also captured live for sale to aquariums.

Generally whaling can be split into two types - whaling on great whales and that on small cetaceans, such as the infamous drive hunts in Japan and the Faroe Islands. Since 1946, whaling on the great whales has, for the most part, been overseen by the International Whaling Commission (IWC) under the International Convention for the Regulation of Whaling (ICRW). While the ICRW includes definitions for some odontocetes and includes references to toothed whales in its Schedule (the set of adopted rules and definitions), the IWC has largely concentrated its work on the baleen whales and the sperm whale in terms of setting whaling quotas and other whaling requirements. The IWC Scientific Committee, however, routinely works on issues relating to all cetaceans.

The Animal Welfare Institute believes all whaling to be inherently cruel. Even the most advanced whaling methods cannot render the animals insensitive to pain prior to slaughter, as is the norm for domestic food animals. Modern whaling on great whales and sperm whales involves the use of harpoons fired into large, moving targets from moving platforms on a shifting sea, often under extreme weather conditions. The harpoons are usually fitted with penthrite grenades which are supposed to penetrate to about 12 inches and then explode, releasing claw-like protrusions to rip into the flesh. Death can come by trauma, laceration or brain wave shock.

After harpooning, the animal is then typically hauled - alive or dead - to the catcher ship using a line attached to the harpoon, with the claws biting into the flesh, blubber or organ for purchase. For animals who have not been stunned or killed, the pain and distress during hauling is excruciating. Rifles may also be used as primary or secondary killing methods, often adding to the suffering of the animals.

The likelihood of obtaining a clean, accurate strike resulting in a swift death is extremely low and animals can take hours to die, especially when harpooners do not target the head area as in the Japanese hunts. Even if a clean strike is thought to have been achieved, actually measuring efficacy is also problematic. The IWC provides criteria for determining death and under the criteria, a whale can be considered insensible and/or dead when, upon visual observation - usually by the whaler - it displays relaxation of the lower jaw and no flipper movement, or sinks without active movement. Reputable scientific experts in the field have questioned the validity of these criteria and are in agreement that these are not fool proof measures of insensitivity and death.

From a purely physiological standpoint, there are significant differences in the mass, length, and organ placement of whale species targeted by whalers. Unlike farm animals in conventional production who have been bred for consistency in size and weight, individual whales even within species might differ in length by 10 to 20 feet. While an exploding penthrite grenade harpoon might achieve a successful kill on a 25-foot minke whale, the same harpoon has little chance of rendering a 60-foot fin whale dead or unconscious with a single shot.

Some work has been done outside and within the IWC to improve whale killing methods, although there is a very long way to go. It is critically important that all who hunt and kill whales are amenable to making improvements to reduce the whales’ pain and suffering. Most recently AWI participated in a workshop on whale welfare and ethics comprising international experts in animal welfare science, policy, legislation and ethics held in March 2011. The report is available here. The conclusions and recommendations from the workshop were subsequently discussed at IWC63 in July 2011, and further progress is expected in the future.