Special Issue Survey of Cetaceans in Captive Care

Aquatic Mammals 2005, 31(3), 288-310, DOI 10.1578/AM.31.3.2005.2882. Whales, Dolphins, and Porpoises:Presentation of the CetaceansWhales, dolphins, and porpoises live their entirelives in the water, and in the process of adaptingto this environment, became the most specialisedmammals. From the small vaquita (Phocoenasinus) to the giant blue whale (Balaenoptera musculus),cetaceans have adapted to the aquatic environmentin very different ways yet have retainedmany common anatomical and behaviouralcharacteristics.This overview of the taxonomy, biology, andbehaviour of cetaceans may help the reader tobecome familiar with aspects of the animals thatare relevant to the design of their habitat.IntroductionWhales, dolphins, and porpoises are marine mammalsbelonging to the order Cetacea. Other marinemammals belong to two other orders: the Sirenia,which includes the manatees (Trichechus sp.) andthe dugong (Dugong dugon), and the very largemammalian order Carnivora, which includes thesuborder Pinnipedia—seals (Phocidae family), sealions (Otariidae family), and walrus (Odobenidaefamily)—and the suborder Fissipedia, or landbasedcarnivores, with the two families Mustelidaeand Ursidae, which include the sea otter (Enhydralutris) and the polar bear (Ursus maritimus). Thesirenians are the only other marine mammals,besides cetaceans, to live their entire life in thewater.The order Cetacea is subdivided into two suborders:(1) Mysticeti or baleen whales and (2)Odontoceti or toothed whales. There are presently14 known species of mysticetes and 72 knownspecies of odontocetes (Rice, 1998; Anonymous,2001; Beasley et al., 2005).Despite their streamlined, fusiform body shape,cetaceans retain all the key characteristics ofmammals: they are warm-blooded, breathe airwith lungs, bear live young, nurse their young,and some even have traces of hair.Most species kept in captivity are from the suborderOdontoceti. Apart from two stranded graywhale calves (Stewart, 2001), no baleen whale hasbeen kept in captivity for a long period of time dueto its large size.The ancestor of all cetaceans is a small landmammal, Mesonyx, a quadrupedal animal thatgave rise to the modern ungulates. Around 50million years ago, this animal started colonisingcoastal fringes, swamps, and possibly the warmwaters of the ancient Tethys Sea, later evolving intothe cetacean ancestors, the suborder Archaeoceti.Between 38 and 25 million years ago, theydiverged into the ancestors of the odontocetes andthe mysticetes (Evans, 1987). The Delphinidaefamily is a relatively modern group, the largest andthe most diverse among cetaceans, comprising thesmall Commerson’s dolphin (Cephalorhynchuscommersonii), the bottlenose dolphin (Tursiopstruncatus), the large pilot whales (Globicephalasp.) and the killer whale (Orcinus orca). It isthe cetacean family most widely represented inoceanaria.TaxonomyTables 2.1 and 2.2 present the taxonomy of the twocetacean suborders. The classification and namesfollow Rice (1998) and Anonymous (2001).Cetacean Biology and BehaviourAnatomy, Physiology, and Life HistoryCetaceans developed some unique adaptations tolive a completely aquatic life. Their body is streamlinedand hydrodynamic to minimise resistance inthe water. Nostrils migrated to the top of the headto allow rapid air exchange while briefly surfacing.They exit the head as one external blowholein odontocetes and two blowholes in mysticetes.Forelimbs have been reduced to paddle-like “flippers”that are used mainly for steering. The hindlimbs evolved into boneless horizontal tail flukes,which provide powerful propulsion. Unlike thefish tail, which has a side-to-side movement, thetail flukes of a cetacean have an up-down motion.Most species have a dorsal fin that serves as a stabilizerand/or plays a social role (Geraci, 1986a;Evans, 1987).Being warm-blooded, cetaceans use a lot ofenergy to maintain a stable body temperature inwater where the heat exchange is 25 times fasterthan in the air. Instead of an insulating coat offur or hair, which would impede swimming inthe water, they developed an insulating layer offat called blubber. Not all cetaceans lack hair,but most are vestigial and scarce. Hair is presentat birth in some species, but quickly disappears,© 2005 EAAM