Management of Marine Mammals

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.