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Marine Mammals

Marine Mammals

What comes to mind when the subject of marine mammals is introduced? Most people probably only think of a few species of dolphins, whales, or seals. But there are over one hundred species grouped into three orders: cetaceans, sirenians, and carnivores.

Marine mammals commonly are defined as mammals that require the ocean for most or all of their needs. Yet some scientists disagree on where to draw the line between terrestrial and marine mammals. Some regard a few species of bats and even the Arctic fox as marine mammals because they depend on food from the sea. Regardless of these more inclusive definitions, all true marine mammals have adapted to life in the water in wonderful ways.


Cetaceanswhales, dolphins, and porpoisesspend their entire lives in water. Cetaceans are divided into two types: mysticetes and odontocetes.


Mysticetes, such as humpback, right, minke, and gray whales, have baleen instead of teeth that are used for filtering small fish and invertebrates from sea water. Blue whales, the largest of all animals on Earth, at up to 27 meters (90 feet) long, are included in this group. Most baleen whales make yearly migrations, feeding during the summer in colder water and traveling up to thousands of miles in warmer and shallower areas to mate and give birth 1 year after mating. Baleen whales also have a thick layer of blubber, which is used both for insulation in cold water and energy storage during migration and winter fasting.


The rest of the whales, as well as all dolphins and porpoises, are grouped together as odontocetes because they have teeth. Sperm whales, the largest odontocetes at up to 18 meters (60 feet) long, dive to as deep as 1.6 kilometers (1 mile), where they feed on deep-water fishes and squid. Most females of both sperm and pilot whales stay with their mothers their entire lives; but the males more often leave and form all-male groups. In sperm whales, they even live alone as "bachelors," only meeting up with other whales for breeding.

Although called a whale because of its size, the killer whale (Orcinus orca ) is actually the largest member of the dolphin (Dephinidae) family. Killer whales, also often called orcas, have been studied most extensively in the Puget Sound off Washington state and British Columbia, where they are divided into two types: residents and transients.

Resident orcas eat fish and spend their lives in specific regions. Male and female offspring stay with their mothers their entire lives. Transient orcas eat primarily marine mammals, but even birds, turtles, or sharks are eaten on occasion. Transient orcas move between areas much more frequently; consequently, their family units are not as stable as the residents' units.

The smaller dolphins feed on a wide variety of organisms. Some, such as the pan-tropical spotted dolphin or the common dolphin, feed in the deep waters of the open ocean and are not seen by humans as often as the many species that come close to shore. Spinner dolphins have different forms: some live only in the deep ocean like those mentioned above, whereas others feed in deep water at night but rest in shallow bays during the daytime. Several dolphins, called river dolphins, live only in fresh water. Dusky dolphins of the southern hemisphere cooperate to herd schooling fish, to feed on them more successfully.

Bottlenose dolphins are very common in the wild and can be found close to shore almost anywhere except in Arctic and Antarctic waters. These dolphins feed on a wide variety of prey, mostly fishes, and many have adapted to living in areas close to humans. Flipper was a trained bottlenose dolphin that starred in a movie and a television show in the 1960s.

Porpoises are similar to dolphins, but tend to occur more often in colder waters. They also have different teeth, dorsal fin shape, and skull structure from those of true dolphins. The vaquita, or Gulf of California harbor porpoise, is endangered due to many individuals being killed in gill nets .


Manatees and dugongs are included in the order Sirenia. They are the only herbivores among marine mammals, feeding on sea grasses in tropical waters. They are slow-moving coastal animals, which is unfortunate for many manatees that often are struck by boats, being killed or severely injured. Because of their slow movements and inshore habitats, manatees often are kept successfully in large commercial aquaria.


The order Carnivora, of which cats and dogs are members, includes the pinnipeds (seals, sea lions, and walruses); sea and marine otters; and polar bears. All pinnipeds spend part of their time on land or ice but feed in the sea. Most mate on land or ice, and all need to be out of the water to give birth. The newborn pups are nursed anywhere from 3 days to 3 years, depending on species, and are mostly independent afterwards.

True seals, such as harbor seals, harp seals, or elephant seals, have thick blubber layers for insulation and have a strange way of getting around on land. They have to wiggle forward like an inchworm because their front flippers do not reach the ground. Despite their clumsiness on land, they are excellent swimmers. True seals have shorter infant care than the other pinnipeds.

Fur seals and sea lions have thinner blubber layers, and rely more on hair for insulation. They can walk on all four flippers, but generally do not dive as deep as the true seals. California sea lions are commonly trained to clap and play with balls in aquaria. Walrus, known for their long ivory tusks, occur only in the Arctic Ocean. They are also common entertainers in aquaria.

Sea otters and marine otters, both of the Pacific coast of the Americas, have the thickest fur of all marine mammals, and spend much of their time keeping it clean. Sea otters use their paws to gather shellfish to eat, and may even use rocks to crack open the shells. Marine otters cannot use their paws the way that sea otters do, and instead just grab prey with their mouths.

Although they do not spend as much time in the water as other marine mammals, polar bears are well adapted to life in the water. They swim with large paddle-shaped fore and hind feet, and feed on fishes in the water and seals on land or ice. Occasionally, they will even eat white whales and have been known to attack humans when threatened or approached too closely.

The Human Connection to Marine Mammals

Humans have had a long history of interaction with marine mammals, primarily with humans as hunters and marine mammals as prey. By the middle of the twentieth century, large-scale, unregulated whaling led to severe depletion of some populations. Within the last half century, recognition of this fact, combined with insights into the intelligence of marine mammals, has led to the emergence of protection and appreciation as the primary interactions between humans and marine mammals.

Aboriginal hunters of many coastal groups have long exploited whales, seals, sea lions, and other marine mammals for subsistence (survival) and, in the case of seals, fur. The effect of Native hunters on population levels was almost always small, unlike for some terrestrial mammals, because hunting large mammals on the open ocean is hard and dangerous, and an enormous amount of meat can be harvested from a single kill. Shore-dwelling seals are more susceptible to local extirpation, but even that was rare in the absence of commercial (rather than subsistence) hunting. Unregulated commercial hunting, however, can and has led to widespread decline in marine mammal populations. For example, fur seals were driven close to extinction in the 1800s by overhunting.

In colonial times, oil rendered from whale fat (blubber) was the main product that drove commercial whaling. Before the development of petroleumbased fuels, whale oil was widely used in lamps. Commercial whaling in the American colonies and elsewhere depleted coastal whale populations early on. Larger whaling ships and longer voyages further out to sea were the pattern in the 1800s, until exploitation of fossil fuels largely ended commercial whaling for oil.

Whaling for meat continued to be a commercially profitable enterprise, however, and the development of sea-based "factory ships" for processing whales led to continued decline in the numbers of whales. Recognizing the serious depletion of whale populations, the International Whaling Commission (IWC) was founded by international agreement in 1946 to regulate the whaling industry. In 1983, the IWC decreed a moratorium on all commercial whaling, pending fuller understanding of the population dynamics and degree of endangerment of each commercial species.

Even with this moratorium, several aboriginal groups were allowed to maintain their traditional whale hunts. These include hunting of bowheads and greys by Northwest Coast and Eastern Russian Native groups; minke and fin whales by Greenlanders; and humpbacks by Caribbean Natives. Two countriesJapan and Norwayhave attracted attention for continued whaling in the face of the moratorium, although each offers reasons why its whale catch falls within the few types of exceptions allowed by the IWC.* One such exception is for scientific research, and in part the controversy surrounds whether the research permits given out by these countries are simply used to skirt the regulations banning commercial harvesting. Despite these controversies, the ban on whaling has been an enormous success, and the populations of all types of whales have grown since the moratorium was instituted.

Other marine mammals have also been the subject of concern, most notably dolphins. While not a target of significant commercial harvesting themselves, they do get caught in large trawling nets designed to catch tuna. Like all mammals, dolphins must breathe air, and once caught in the nets, they drown. "Dolphin-friendly" tuna, which is not harvested via this fishing practice, is now marketed; international environmental monitoring groups work to ensure that companies that advertise dolphin-friendly tuna actually are using safe practices.

At the same time marine mammals were being increasingly protected from hunting, scientists increasingly came to appreciate the intelligence of marine mammals. It is no coincidence that the performing animals at Sea World and elsewhere are marine mammals: learning the tricks they display requires significant intelligence, which is not found in fish. While captivity continues to be the major environment in which humans interact with marine mammals, whale watching has become a significant tourist industry for some coastal towns, and it is even possible to "swim with the dolphins" in some warm-water bays. (In the United States, however, swimming with marine mammals is not legal.)

It is difficult to accurately compare the intelligence of different species, because the way humans measure intelligence often relies on skills possessed especially by themselves, such as language-based thinking and manipulation of objects with the hands. Despite these inherent limitations, it is clear that whales and dolphins are especially intelligent creatures, capable of solving puzzles and jumping through hoops for food rewards, and also having complex social systems and a type of "language." Researchers are attempting to understand these languages in hopes of learning more about these creatures and the societies they form.

see also Arts, Water in the; Ecology, Marine; Food from the Sea; Life in Water; Pollution of the Ocean by Sewage, Nutrients, and Chemicals.

Amy G. Beier (taxonomic orders)

Richard Robinson (human connection)


Berta, Annalisa, and James L. Sumich. Marine Mammals: Evolutionary Biology. San Diego, CA: Academic Press, 1999.

Cahill, Tim. Dolphins. Washington D.C.: National Geographic Society, 2000.

Reynolds III, John E., and Daniel K. Odell. Manatees and Dugongs. New York: Facts on File, Inc., 1991.

Reynolds III, John E., Randall S. Wells, and Samantha D. Eide. The Bottlenose Dolphin: Biology and Conservation. Gainesville, FL: The University Press of Florida, 2000.

Riedman, M. The Pinnipeds: Seals, Sea Lions, and Walruses. Los Angeles: University of California Press, 1990.

Sterling, Ian. Polar Bears. Ann Arbor, MI: University of Michigan Press, 1988.

Internet Resources

International Whaling Commission. <>.


Keiko, the killer whale featured in the 1993 Hollywood movie Free Willy, was captured in the Atlantic Ocean near Iceland in 1979. In 1996, largely in response to increased public awareness about his captive living conditions, Keiko was moved to a custom-built facility at the Oregon Coast Aquarium, then to an open-ocean pen in an Icelandic bay in 1998.

With the help of his caretakers, Keiko underwent reintegration into Iceland's wild orca population through monitored interactions and ocean "walks." Keiko was allowed to wander free in January 2003, once other orcas had migrated to the same waters. Caretakers continue to support his reintegration, monitoring his health and progress.

* See "Sustainable Development" for a photograph related to Japan's whale harvesting.

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Marine Mammal Program

Marine Mammal Program


The U.S. Navy has used marine mammals, or cetaceans, for military purposes since the late 1950s. Atlantic bottle-nose dolphins, Pacific white-sided dolphins, and California sea lions are currently used in military operations, and training has also been conducted with belugas, killer whales, and pilot whales. Because dolphins have superior sonar that is currently unmatched by technology and sea lions have an excellent sense of directional hearing along with sensitive low light vision, these marine mammals are extremely well suited for search and rescue and swimmer defense operations.

History of marine mammals in the military. In the 1959, the United States Navy established a marine mammal program at Marineland near Los Angeles, California. Naval researchers were initially interested in studying the hydrodynamics of dolphin swimming in order to better understand boat and submarine design. Dolphins can attain high swimming speeds and can maintain those speeds for long periods of time. Marine scientists found that the dolphin's keen sense of echolocation was ideal for finding lost equipment on the sea floor and for locating enemy mines and torpedoes. In addition, dolphins are extremely intelligent and trainable. One of the first dolphins involved with the program was a Pacific white-sided dolphin named Notty.

In 1962, the marine mammal program was moved to Point Magu, California. Three years later, the Point Magu program established an underwater laboratory called Sea Lab II, which was 200 feet below the surface of the ocean. There a dolphin named Tuffy was trained to work with divers in experiments designed to see if the use of dolphins might help circumvent the dangers to humans inherent in deepwater diving. Tuffy's work also showed that dolphins could easily be trained to work without tethers in the open ocean. The successes of Sea Lab II led to the establishment of the Advanced Marine Biological Systems (AMBS) program, which currently funds military marine mammal programs.

In 1967, the marine mammal program was moved from Point Magu to Point Loma in San Diego, and a separate marine mammal training facility was opened in the Marine Corps Air Station in Kaneohe Bay, Hawaii. Both of these programs investigated the physiology and behavior of cetaceans, developed techniques for medical diagnosis and treatment, and worked to understand the communicative noises made by dolphins. In Hawaii, research was also conducted on the reproductive physiology of dolphins. In addition, investigators studied the cost and safety benefits of using marine mammals. In 1993, the facility at Kaneohe Bay was closed and most of the marine mammals were relocated to Point Loma.

During the Cold War, the Soviet Union also developed a marine mammal program. Dolphins were trained to search for underwater explosives and were used to guard coastal waters from attack. After the dissolution of the Soviet Union, the dolphins became part of the Ukrainian navy. In 1997, the Ukrainian navy donated the dolphins to a program that uses the animals in therapy for disabled children.

Training and maintenance. The U.S. Navy maintains the marine mammals in their training and operational programs in open-mesh enclosures in bays and harbors in the ocean. This allows the dolphins to experience their natural echolocation and social environments. During training, the animals are untethered in the open ocean. All operational training is based on positive reinforcement, using food for rewards. Animals are not punished for failure to perform tasks by withholding food. Survival rates for the marine mammals maintained by the navy are between 95 and 100 percent. During thousands of training exercises in the open ocean over a 30-year period, only seven animals have not returned to their enclosures.

Several groups have criticized the navy's marine mammal program, citing undue stress to and mistreatment of animals used for military purposes. In the 1980s, the Progressive Animal Welfare Society (PAWS) successfully sued the navy to halt its marine mammal program in Washington State. However, a committee appointed by the president reviewed the program in 1988 and 1990 and gave satisfactory or outstanding ratings to all aspects of the program. The National Marine Fisheries (NMFs) reported that survival rates of dolphins in the program were the highest of all organizations maintaining large numbers of cetaceans.

Marine Mammal Systems. The navy currently operates four Marine Mammal Systems (MMS) as part of its fleet. An operational MMS consists of four to eight marine mammals, an officer-in-charge, and several enlisted personnel. Before a MMS is approved for operations, it undergoes the same type of rigorous testing as other operational naval systems. It must prove effective and reliable as well as cost effective. Marine Mammal Systems are highly transportable and can be airlifted to any operational site. SPAWAR (Space and Naval Systems Center, San Diego) supports a deployed MMS, replenishing animals and providing training, documentation, and personnel.

The four operational MMS include both dolphin and sea lion systems. Mk4 and Mk7 are dolphin mine detection and location systems. They can be deployed from a ship in order to search for and mark mines that are tethered to the ocean floor. Mk5 is a sea lion mine detection system, which can detect mines to a depth of 1000 feet. The sea lions are trained to attach a grabber device to a mine so that naval personnel can recover it. Mk6 is a dolphin swimmer defense system. Dolphins are trained to locate an intruder trying to come ashore via the ocean.

Although dolphins and sea lions are the only marine mammals currently used in military operations, pilot whales, killer whales and beluga whales have also been involved with object search and recovery. These cetaceans have the ability to dive to extreme depths, much beyond those attainable by human divers. A project called Deep Ops studied the abilities of pilot whales and killer whales to recover objects from deep depths. The pilot whale was able to successfully recover a dummy torpedo from a depth of 1,654 feet using a gas-inflated recovery device. The killer whales recovered objects from 500 and 850 feet. Belugas were able to dive to 2,100 feet and were able to recover dummy torpedoes from 1,300 feet.

Marine mammal deployments. The military first used the dolphin swimmer detection system in the Vietnam War in 1970. This successful operation, which involved dolphins patrolling the waters near warships, brought an end to underwater sabotage in Cam Ranh Bay.

In 1987 and 1988, the navy used dolphins for mine surveillance in waters off Bahrain in the Persian Gulf. The animals patrolled the waters for mines and escorted Kuwaiti tankers through areas where the Iranian military was attempting to disrupt oil shipments.

Marine mammal systems were in operation during the Republican Party Convention in 1996. Both dolphin mine detection and location systems and sea lion swimmer defense systems were used to protect the waters off of San Diego from terrorist attack.

After British forces took control of the southern Iraq port city of Umm Qasr in 2003, the U.S. Navy brought in Atlantic bottlenose dolphins to search the bay for mines and mark them for destruction by human divers. Sea lions were also deployed around ships in Bahrain to detect and defend against armed swimmers. These sea lions were trained to attach floater devices to intruders so that security officers could apprehend them.



Bulletin of Atomic Scientists. "U.S., Ukraine at cross porpoises." <> (April 22, 2003).

Dolphins of War. <> (April 22, 2003).

MSNBC News. "Dolphins go to front lines in Iraq war." <> (March 25, 2003).

Public Broadcasting System. "The Story of Navy Dolphins." <> (April 22, 2003).

U.S. Navy Marine Mammal Program. <> (April 22, 2003).


Unexploded Ordnance and Mines

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Marine Mammal Protection Act (1972)

Marine Mammal Protection Act (1972)

Wendy Wagner

The Marine Mammal Protection Act of 1972 (P.L. 92522, 86 Stat. 1027) is one of the first federal laws to protect animals for their own sake, rather than simply preventing extinction or keeping populations sustainable for harvesting. At the time the law was passed, there was a consensus in Congress that the act was needed to rectify the consequences of "man's impact upon marine mammals, which has ranged from what might be termed malign neglect to senseless slaughter." Because of competing visions of how vigorously marine mammals should be protected, however, Congress did not impose an absolute moratorium on the "taking" of marine mammals. Although the law prohibited the "harassing, catching and killing" of all "mammals which are physiologically adapted to the oceans," including whales, dolphins, seals, walruses, and manatees, it allowed for some exceptions. The most notable was allowing unintentional (or "incidental") takes of mammals from "nondepleted stocks" by commercial fishing operations, usually on the condition of obtaining a permit from the National Marine Fisheries Service (NMFS).


The MMPA is solidly grounded in Congress's power to regulate interstate commerce, as stated in the Constitution. In 1984 in Balelo v. Baldrige, the commercial fishery industry challenged the constitutionality of the act under the Fourth Amendment, alleging it was an unconstitutional search and seizure because it required federal observers to be stationed aboard large fishing fleets to ensure compliance. The United States Court of Appeals for the Ninth Circuit rejected this constitutional challenge, holding that commercial fishing fleets were closely regulated and did not enjoy a protected privacy right.

Beyond their role in resolving constitutional challenges to the MMPA, the courts have played a major role in the evolution of the statute, which has been amended regularly (at least once every seven years). In 1988, for example, the U.S. Court of Appeals for the District of Columbia invalidated the NFMS program for permitting the "incidental takes" of marine mammals by commercial fisheries in Kokechik Fishermen's Association v. Secretary of Commerce. The court held that NMFS's program did not provide adequate assurance that marine mammal populations would be maintained at optimal levels. In response, Congress amended the MMPA to provide a more comprehensive system for identifying marine mammal populations that could tolerate "incidental takes" and those populations below optimal levels which could not tolerate losses. The courts have also played an important role in enforcing the act, which authorizes both the Commerce and Interior Departments to seek civil and criminal sanctions against persons taking a marine mammal in violation of the act.

In 1991 a dispute resolution panel of the General Agreement on Tariffs and Trade (GATT) determined that the MMPA violated an international trade agreement. The panel found that the U.S. ban on the importation of tuna from Mexico, imposed because Mexican fleets caught tuna in a way that harmed dolphins, was not a justified basis for restricting trade. Although the United States lost the dispute, it resolved its differences with Mexico diplomatically. Congress passed a second statute, modified later, which banned imports from countries that did not catch tuna in a dolphin-safe manner.


The MMPA appears to have made a significant difference in protecting marine mammals. For example, after the United States banned the import of tuna caught in ways that harm dolphins, the incidental deaths of dolphins dropped nearly 80 percent worldwide. The MMPA is complemented by the Marine Protection, Research, and Sanctuaries Act, which preserves marine mammal habitat more directly. The Endangered Species Act also provides more aggressive protections for marine mammals that are endangered or threatened with extinction.

See also: Endangered Species Act; Fish and Wildlife Conservation Act of 1980.


Bean, Michael J., and Melanie J. Rowland. The Evolution of National Wildlife Law, 3d ed. Westport, CN: Praeger, 1997.


The Marine Mammal Center. <>.

National Oceanic And Atmospheric Administration. <>.

What Is Dolphin-Safe Tuna?

In the Eastern Tropical Pacific, tuna swim beneath schools of dolphin. During the 1950s, fishers began to encircle dolphin with nets to trap the tuna swimming below, killing thousands of dolphins in the process. Since 1991 the United States has allowed tuna to be sold with a label designating it "dolphin-safe" if nets were not intentionally set for dolphins as a means of catching the tuna. According to the National Marine Fisheries Service, this arrangement reduced dolphin deaths from hundreds of thousands to approximately 2,000 per year. In 2002, however, the regulations were relaxed so that tuna could be labeled dolphin-safe even if dolphins were encircled by the tuna nets, as long as an on-board observer certified that no dolphins were harmed or killed by the procedure. Environmental groups protested the change, arguing that the successes of the previous policy would be reversed. According to the Earth Island Institute, "The Bush administration's claim that chasing and netting of dolphins is 'safe' for dolphins is fraudulent and must be overturned by the courts."

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