The general rule in maintaining marine mammals in captivity is to duplicate their natural environment as closely as possible. Most live in marine habitats, although some species migrate into freshwater; Baikal seals (Phoca sibirica) and five species of river dolphins have adapted completely to freshwater habitats. Manatee subspecies vary in the time they spend in freshwater, but the dugong (Dugong dugong) is completely marine.
Marine cetaceans should be kept in water with a salinity of 25–35 g/L, preferably using balanced sea salts. Water for captive marine cetaceans should be maintained as close to the pH of mid-ocean waters (8–8.3) as possible. Freshwater cetaceans and seals require water similar to that of their natural habitat. In the USA, the Marine Mammal Protection Act of 1972 specifies that coliform bacterial counts of water for captive marine mammals must be ≤1,000 MPN (most probable number/100 mL).
Marine mammals kept in the extremes of their temperature tolerance range are more susceptible to environmental and infectious disease. In general, cetaceans and pinnipeds are better adapted to cold than to heat, but species-specific tolerances differ. Inappropriately combining different species for display purposes can result in compromises that jeopardize the well-being of some species.
Good air quality, especially in indoor facilities (10–20 air changes/hr) is as important as good water quality. Photoperiods, light spectral and intensity requirements, sound tolerances, and flight distance requirements are not well established for any cetacean. Extremes in any of these factors should be considered detrimental in the absence of specific data.
Environmental requirements of pinnipeds are similar to those of cetaceans except that pinnipeds can “haul out” on land. Although captive pinnipeds can be kept in freshwater, saltwater pools that meet the specifications listed above for cetaceans are preferred. Most pinnipeds obtain their metabolic water requirements in food and do not require access to freshwater if provided fish with a high fat content. However, it is common practice to allow pinnipeds access to potable water.
Pools for captive pinnipeds should provide shelter from wind and some shade. Haul out requirements are different for each species, and some pinnipeds (eg, the Northern fur seal [Callorhinus ursinus]) require very specific timing of access to land (eg, only at the pupping season).
Sirenians are warm-water species with water requirements similar to those of cetaceans, although the most common sirenian in the USA, the Florida manatee (Trichechus manatus latirostris), migrates between marine and freshwater environments seasonally. Manatees do better in captivity if salinity is changed seasonally to match migration in the wild.
In captivity, the sea otter thrives best in a cold marine water system. Because the fur of the sea otter is its major protection against hypothermia, the water must be kept free of oils and organic material that could mat or damage the coat.
The polar bear naturally lives on arctic and subarctic ice. It has successfully adapted to subtropical climates in captivity but is more susceptible to dermatologic disease in warm climates. Polar bears traditionally have been provided with freshwater in captivity. Proper attention to filtration and water quality is beneficial.
Marine mammals must be restrained for thorough examinations. Trained cetaceans and pinnipeds can be taught behaviors to facilitate examination and collection of diagnostic samples. For these animals, the presence of familiar attendants is important.
For complex procedures or untrained animals, the safest approach to restraining a cetacean is to remove it from the water. Captive enclosures should allow water drainage so that cetaceans can be stranded without the use of nets. As the animal begins to lose buoyancy in the draining water, it should be positioned over thick foam pads to minimize struggling and injury. Nets are an alternative for corralling small cetaceans kept in sea pens or encountered in the wild; however, experienced personnel are required to minimize the risk of drowning or injury to the animal or staff. Netted cetaceans are placed on foam or specially designed stretchers or floats that can suspend the animal above water level.
Small cetaceans (dolphins) can often be restrained by the weight of three or four attendants—one person controls the peduncle of the tail fluke and the others apply weight to the animal’s body. The pectoral fins should be folded alongside the animal in a natural position to avoid permanent damage. In larger cetaceans (whales), the powerful tail fluke may be secured with mechanical restraints.
Capturing pinnipeds is generally easier on dry ground, although small animals can be captured in the water with end-release hoop nets. Larger animals should not be netted in water but should be coaxed or driven from the water or have the water drained from their pool. On land, hoop nets can be used on larger animals. Cargo nets, baffle boards, and “come-along” poles also can be helpful. Once captured, small seals can be restrained for some procedures by an experienced handler sitting on the seal’s back and holding the head. Larger pinnipeds or more complex procedures require an appropriately designed squeeze cage.
Sirenians are relatively docile; problems in restraint are generally due to their bulk and weight, and caution is recommended because they tend to roll. They can be handled in much the same way as cetaceans. Sea otters can be restrained like most other large mustelids. Hoop nets can be used to remove them from pools. Once they are out of the water, restraint bags, squeeze boxes, or other restraint devices for small wild carnivores can be used. Polar bears are large and dangerous, and manual restraint is not advised.
Physiologic adaptations to diving and marine environments make general anesthesia of cetaceans and pinnipeds difficult. Anesthetic drugs commonly used in other animals often have narrow margins of safety or cause unexpected reactions in marine mammals. Tranquilizers, sedatives, and anesthetics should be administered to marine mammals only by personnel experienced in their use. Specialized anesthetic machines and respirators (apneustic plateau) are required for cetaceans. Sirenians rarely require general anesthesia or tranquilization for treatment. Sea otters can be sedated with diazepam (0.2 mg/kg body wt) or tiletamine-zolazepam (1 mg/kg). A combination of fentanyl (0.22 mg/kg) and diazepam (0.07 mg/kg) has been successful for sample collection in wild sea otters. Narcotic recycling has been seen. Surgical anesthesia can be obtained with higher dosages of fentanyl-diazepam (0.33 mg/kg/0.11 mg/kg); tiletamine-zolazepam (2 mg/kg); or halothane, isoflurane, or sevoflurane, with or without nitrous oxide. Polar bears are routinely immobilized with etorphine, tiletamine-zolazepam with or without medetomidine, ketamine with xylazine, or a variety of other agents used IM. The required dose is highly dependent on the individual animal and environment.