In accordance with Title IV of the Marine Mammal Protection Act (MMPA) to provide guidance on stranded marine mammals, current methods employed for euthanasia were evaluated. Many methods will accomplish death, however, only a few are considered humane by published guidelines.1,3,4,6 A humane death is described as one that results in rapid unconsciousness followed by cardiac and respiratory arrest.1 The most common forms of acceptable humane euthanasia in marine mammals are ballistics or injectable drugs.
Both of these techniques have inherent concerns. Ballistic weapons can cause injury to surrounding personnel and other animals if not done correctly. The most humane death by ballistic weapons occurs when the brain is destroyed instantaneously. However, there are unique anatomic considerations in cetaceans that make the use of ballistics challenging. The skin, blubber, and muscle that make up the forehead (melon) absorb kinetic energy from a projectile decreasing impact. The anterior surface of the cetacean skull is concave with extensive sinuses, contributing to the likelihood of bullet deflection. In addition, extensive muscle on the nuchal, parietal, and occipital regions of the skull makes occipital shooting ineffective.2 Use of ballistics in mass strandings can be distressful to the surviving animals. Exposure to the noise, visual destruction, agonal vocalizations, and release of pheromones by a frightened animal can exacerbate anxiety and fear in the conscious animals.6 The use of ballistics should be reserved for species with determined projectile methods and for highly trained personnel.
Injectable agents used for euthanasia are presently considered among the most humane.9 The injectable agents commonly selected are controlled drugs and there are concerns that these drugs may enter the environment from the remains of the animal. There are administration challenges of injectable drugs due to the large size of many marine mammals necessitating large volumes of drug, coupled with difficulty obtaining venous access. The preferred injectable agents for use in marine mammals are pentobarbital and etorphine. These agents have been used successfully in very large stranded whales despite the above mentioned challenges.7,8,10 Preferred routes of administration are intravascular, intramuscular, intrahepatic, or intraperitoneal.1,5 Barbiturates (pentobarbital) cause rapid unconsciousness followed by respiratory and cardiac arrest, and cause minimal distress to the animal, making this the preferred class of drug for euthanasia in all species.1,4,6 Most countries limit the use of this drug to people who are appropriately licensed (e.g., individuals registered with the United States Drug Enforcement Agency). A dose of 10 mg/kg will induce a level of anesthesia, and in cetaceans a period of apnea long enough to usually cause hypoxia and death without consciousness.10 A dose of 60–200 mg/kg is recommended to perform euthanasia.
Etorphine is an intramuscular alternative.9 This drug is an ultra-potent opioid and is considered up to 10,000 times more potent than morphine sulfate. This poses risk to personnel handling this drug, especially at the doses needed for euthanasia. This drug is tightly regulated in the United States and relatively few people are approved to obtain and use this drug. Immobilon® (etorphine and acepromazine) is manufactured, and more commonly used in Europe. The approximated volume of Immobilon® needed is 0.5 ml/1.5 m in dolphins and porpoises, and 4 ml/1.5 m in whales.9 The use of other injectable anesthetic agents that anesthetize a marine mammal to a level of unconsciousness may be followed by an alternative method of euthanasia (e.g., smaller doses of euthanasia drugs, exsanguination) and still be considered humane when unconsciousness is achieved quickly and painlessly.
It is imperative that death be verified. The absence of a heartbeat is the only reliable confirmation of death in mammals. If there is any doubt about confirmation of death, a secondary physical means of euthanasia should be performed to ensure death.4 Several physical methods are bilateral thoracotomy, lancing the major vessels, exsanguination, and gunshot through the heart or brain.
This work is supported by the National Marine Fisheries Service.
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