Get Caught Up

Part 1: What are Cetaceans? An introduction to the whales, dolphins and porpoises

Whales, dolphins and porpoises make up a group of marine mammals known as cetaceans. Fossil evidence and the anatomy of contemporary cetaceans suggest that they are derived from the artiodactylids (a group including modern-day cattle and sheep) that adapted to life underwater. Like all mammals, cetaceans have a constant body temperature, have retained the need to breathe air, and they nurse their young with milk. Adaptations include the modification of forelimbs into flippers, the loss of hindlimbs and the development of blowholes, and tail flukes.

As in many animal groups, common names can be misleading, and cetaceans are most easily understood in their two groups: mysticetes (cetaceans with baleen) and odontocetes (toothed cetaceans). Baleen plates are made from modified hair and are arrayed vertically from the gums. They serve as a giant sieve to capture minute animal prey such as krill. The baleen whales, along with the sperm whale (an odontocete) are often referred to as the “Great Whales.” They are so named because they are the largest of the cetaceans, with the blue whale probably the largest animal that has ever existed on earth, at about 30 meters in length.

Odontocetes include the larger sperm whale and orca, beaked whales, pilot whales, the Arctic belugas and narwhals, porpoises, freshwater/river dolphins and several groups of oceanic dolphins. These species use their teeth to catch relatively large, often vertebrate prey. In addition to sight, they may use echolocation (reflected sound waves) to find their prey, particularly in conditions of low visibility.

Whales live throughout the world’s oceans, including in the Caribbean, but often travel over long distances. Migration is an adaptation seen in many groups of animals, including birds, butterflies and hoofed mammals. It is likely that all baleen whales except the Bryde’s whale, which is confined to the tropics and temperate regions, undergo some form of migration twice a year. In the most dramatic of these, when polar waters benefit from longer hours of summer sun and zooplankton (microscopic, floating animals) are abundant, whales travel to feed on this bounty. Full from a summer of feasting, they return to lower latitudes (the tropics) to calve and wait for the next summer when they will return to their feeding grounds. For some species, such as the grey and humpback whales, researchers have determined the exact locations for both wintering and summering grounds; for others, such as the fin whale, movements are poorly understood.