Special Issue Survey of Cetaceans in Captive Care

2. Whales, Dolphins, and Porpoises: Presentation of the Cetaceans 293Maintaining the water temperature in captivity atthe same level as the original habitat is critical.Although marine mammals have efficient waysof regulating temperature, exposing the animal toexcessive heat is as life threatening as excessivecold (Geraci, 1986b). They can tolerate and adaptto some variation, but they should not be exposedto drastic and sudden changes to maintain a balancedenergy budget. It is important to keep ananimal wet, especially the flippers and flukes,during transportation, to prevent overheating.Odontocetes have teeth, which they use tograsp prey or for social interactions. In some species,the teeth are barely apparent, or their numberis greatly reduced, as in the narwhal or beakedwhales. Odontocetes do not chew their food, butsome dolphins behead fish by smashing or shaking.Other cetaceans swallow their fish whole, headsfirst. They eat a wide variety of fish, squid, andcrustacean; and some larger whales, such as killerwhales in the wild feed on other marine mammalsand birds (see Chapter 7 for details). The smallestspecies of odontocete, the harbour porpoise,requires a daily portion of food estimated to be upto 13% of its body weight in winter (Evans, 1987),whereas the bottlenose dolphin may need between3 and 6.5% of body mass per day (Barros & Odell,1990), depending on the type of food, the watertemperature, season, activity, and if females arepregnant or nursing (Reddy et al., 1994; Kasteleinet al., 2003). In contrast, the baleen whales haveplates of keratin, hanging from the palate, insteadof teeth. These plates filter zooplankton, fish, andsquid from the water into the mouth (Evans, 1987).Because Baleen whales require such a specializeddiet and such large quantities of food, they rarelyhave been kept in captivity (Stewart, 2001).Pelagic marine species live in a salty environmentthat is four times more concentrated thanbody fluids. The anatomy and physiology of cetaceansare aimed at reducing water loss. This canbe observed in the small amounts of water lostduring respiration and in the production of concentratedmilk, faeces, and urine. Salt and waterbalance is achieved mainly through food, whichprovides water directly available or derived fromthe oxidation of fat. The fattier the fish eaten, themore water is available to the cetacean. As a result,a prolonged fast in a sick animal can quickly leadto dehydration (Geraci, 1986a).Cetaceans are voluntary breathers, meaningthat their breathing is under conscious control;the blowhole is normally closed. Thisis different from humans whose breathing isinvoluntary and a reflex. During sleep periods,dolphins rest each hemisphere of their brainseparately while the other hemisphere is activelykeeping the animal in motion and controlingbreathing. All cetacean species studied have beenshown to exhibit unihemispheric slow-wave sleep(Mukhametov et al., 1977; Mukhametov, 1987,1988; Mukhametov & Lyamin, 1994; Lyaminet al., 2002; Ridgway, 2002) or signs of this sleepstate behaviourally (Lyamin et al., 1998, 2000;Sekiguchi & Koshima, 2003). During respiration,a cetacean exchanges about 80% of the aircontained in their lungs as opposed to 17% forhumans. Exhaling and inhaling usually takes lessthan one second.Some cetaceans can hold their breath fromseveral minutes to more than an hour. Bottlenosewhales have been recorded under water for aslong as 80 min, and sperm whales at depth of3,195 m (Leatherwood & Reeves, 1983; Evans,1987; Klinowska, 1991; Hooker & Baird, 1999).Many of the smaller whales and dolphins can diveto several hundred meters for up to 10 min. Thenecessity to dive at great depths and to hold theirbreath for long periods of time has brought aboutanatomical and physiological adaptations. Theseinclude the compressible rib cage and lungs, aslower heartbeat while diving, a shunting of theblood away from limbs and toward the heart andbrain, and a high content of oxygen-binding protein—themyoglobin—which prevents musclesfrom oxygen deficiencies (Geraci, 1986a). In captivity,only shallow depths are available comparedwith great depths in the wild. Yet, it is importantto provide animals with habitats as large and deepas possible to encourage diving and rapid swimming.Adaptations of the epidermis reduce turbulence,and the streamlined shape of their bodiesallows dolphins to swim fast. Recent studies havedemonstrated that realistic maximum swimmingspeeds for dolphins are lower than previouslyreported, which were based on sparse data andimprecise measurement techniques. Bottlenosedolphins, false killer whales, and short-beakedcommon dolphins have reached maximum speedsbetween 28.8 and 29.5 km/h, and long-beakedcommon dolphins can attain the speed of 24.1 km/h (Rohr et al., 2002; Anonymous, 2003). Cruisingspeed of bottlenose dolphins is on average 6 km/h(Anonymous, 2003).Cetaceans become sexually mature at differentages, depending on their species, but individualsseem to reach sexual maturity when they obtaina certain size, rather than a certain age. Gestationperiod varies from 7 to 12 months for dolphinsand up to 18 for larger species such as the killerwhale (Schroeder, 1995). Calving intervals varyfrom one to six years. Gestation, calving interval,and life spans are longer for larger species. Theharbour porpoise, for example, is expected to livefor up to 24 years (Read, 1999), the bottlenose