Marine Mammals

views updated May 11 2018

Chapter 5
Marine Mammals

Marine mammals live in and around the ocean. They are warm-blooded, breathe air, have hair at some point in their lives, give birth to live young (as opposed to laying eggs), and nourish their young by secreting milk. Dolphins, whales, seals, sea lions, walruses, polar bears, manatees, and dugongs (manatee relatives) fall into this category.

Historically marine mammals have garnered a high level of public support and legal protection. During the 1960s the television show Flipper entertained American audiences with stories about a highly intelligent and love-able dolphin that befriended and helped a family. Such tourist attractions as Marineland in Florida and SeaWorld in California began featuring acrobatic dolphins and whales in very popular shows. The growing environmental movement seized on the public interest in marine mammals and lobbied for measures to protect animals that many people believed to be extremely smart and sociable.

At the time purse-seine fishing was widely practiced by commercial tuna fishers in the eastern tropical Pacific Ocean. This fishing method involved the use of enormous nets, often hundreds of miles long that were circled around schools of tuna. Many dolphins were inadvertently captured because they tend to mingle with fleets of tuna in this part of the ocean. Nontargeted animals captured during commercial fishing activities are called "bycatch." Dolphin bycatch became a major public issue. Hauling in the enormous tuna-filled nets was a lengthy process. As a result, the air-breathing dolphins were trapped for long periods under water, and often drowned. It is estimated that more than 400,000 dolphins and porpoises died per year in this manner during the late 1960s. Public outcry over these killings and general concern for the welfare of marine mammals led the U.S. Congress to pass the Marine Mammal Protection Act of 1972.


The Marine Mammal Protection Act (MMPA) was passed in 1972 and substantially amended in 1994. The original act noted that "certain species and population stocks of marine mammals are, or may be, in danger of extinction or depletion as a result of man's activities." However, it was acknowledged that "inadequate" information was available concerning the population dynamics of the animals being protected.

The Marine Mammal Protection Act prohibits the taking (hunting, killing, capturing, and harassing) of marine mammals. The act also bars importation of most marine mammals or their products. Exceptions are occasionally granted for scientific research, public display in aquariums, traditional subsistence hunting by Alaska Natives, and some incidental capture during commercial fishing operations. The goal of the MMPA is to maintain marine populations at or above "optimum sustainable" levels.

Whales, dolphins, seals, and sea lions were put under the jurisdiction of the National Marine Fisheries Service (NMFS), an agency of the National Oceanic and Atmospheric Administration (NOAA) in the U.S. Department of Commerce. Polar bears, walruses, sea otters, manatees, and dugongs were put under the jurisdiction of the U.S. Fish and Wildlife Service (FWS), an agency of the U.S. Department of Interior.

The Marine Mammal Protection Act requires the NMFS and FWS to conduct periodic surveys to estimate populations and predict population trends for marine mammals in three regions of U.S. waters: Pacific Ocean coast (excluding Alaska), Atlantic Ocean coast (including the Gulf of Mexico), and the Alaskan coast. The survey results are published in annual Stock Assessment Reports. Reports dating back to 1995 are available online at

The Marine Mammal Protection Act was passed a year before the Endangered Species Act. The MMPA was driven largely by public affection for marine mammals, rather than specific knowledge about impending species extinction. According to Eugene H. Buck in Fishery, Aquaculture, and Marine Mammal Legislation in the 109th Congress (Congressional Research Service, September 9, 2005), "some critics assert that the MMPA is scientifically irrational because it identifies one group of organisms for special protection unrelated to their abundance or ecological role." However, the MMPA is credited with promoting research about marine mammals and drawing attention to issues associated with bycatch mortality.


As shown in Table 2.1 in Chapter 2, there were only three marine mammal species on the first list of native endangered species issued in 1967. Over the following decades additional marine mammals were added as information became available on their population status. As of February 2006 there were fourteen species of marine mammals listed as endangered or threatened in the United States. (See Table 5.1.) Another fourteen foreign species were also listed.

Endangered and threatened aquatic mammals, February 2006
U.S. species
Status*TypeCommon nameScientific nameNote
*E=endangered; T=threatened; XN=nonessential experimental population
source: Adapted from "Listed U.S. Species by Taxonomic Group," in Threatened and Endangered Species System (TESS), U.S. Department of the Interior, U.S. Fish and Wildlife Service, February 10, 2006, (accessed February 10, 2006)
EWhaleBlue whaleBalaenoptera musculusBaleen plate
EWhaleBowhead whaleBalaena mysticetusBaleen plate
EWhaleFinback whaleBalaenoptera physalusBaleen plate
EWhaleHumpback whaleMegaptera novaeangliaeBaleen plate
EWhaleRight whale (northern & southern)Balaena glacialis incl. australisBaleen plate
EWhaleSei whaleBalaenoptera borealisBaleen plate
EWhaleSperm whalePhyseter catodon=macrocephalusToothed
ESea-lionSteller sea-lionEumetopias jubatusEared
ESealCaribbean monk sealMonachus tropicalisEarless, presumed extinct
TSealGuadalupe fur sealArctocephalus townsendiEared
ESealHawaiian monk sealMonachus schauinslandiEarless
TOtterNorthern sea otterEnhydra lutris kenyoniSouthwest Alaska stock
T (XN at San Nicolas Island)OtterSouthern sea otterEnhydra lutris nereisCalifornia stock
EManateeWest Indian manateeTrichechus manatusFlorida stock
Foreign species
EWhaleGray whaleEschrichtius robustusWestern north Pacific Ocean
EDolphinChinese River dolphinLipotes vexilliferChina
EDolphinIndus River dolphinPlatanista minorPakistan
EPorpoiseCochito (or vaquita)Phocoena sinusMexico (Gulf of California)
ESealMediterranean monk sealMonachus monachusMediterranean, northwest African coast and Black Sea
ESealSaimaa sealPhoca hispida saimensisFinland
EOtterCameroon clawless otterAonyx congicus=congica microdonNigeria
EOtterGiant otterPteronura brasiliensisSouth America
EOtterLong-tailed otterLontra= lutra longicaudisSouth America
EOtterMarine otterLontra lutra felinaPeru south to Straits of Magellan
EOtterSouthern river otterLontra=lutra provocaxArgentina, Chile
EManateeAmazonian manateeTrichechus inunguisSouth America
TManateeWest African manateeTrichechus senegalensisWest coast of Africa
EDugongDugong dugonPalau (western Pacific Ocean)

Table 5.2 shows that $71.2 million was spent by federal and state agencies during fiscal year 2004 on specific marine mammal species listed under the Endangered Species Act (ESA).

In February 2006 the U.S. Fish and Wildlife Service announced its intention to conduct a status review to determine if polar bears should be proposed for listing under the ESA as a threatened species. The decision was driven by what the agency called "substantial scientific

The ten listed marine entities with the highest expenditures under the Endangered Species Act, fiscal year 2004
Common nameSpecies total
source: Adapted from "Table 1. Reported FY2004 Expenditures for Endangered and Threatened Species, Not Including Land Acquisition Costs," in Federal and State Endangered and Threatened Species Expenditures: Fiscal Year 2004, U.S. Department of the Interior, U.S. Fish and Wildlife Service, January 2005, (accessed February 11, 2006)
Steller sea-lion (western & eastern)$42,557,321
Right whale (northern & southern)$12,369,623
West Indian manatee$9,861,677
Hawaiian monk seal$2,321,146
Sperm whale$2,270,475
Southern sea otter$734,386
Humpback whale$666,282
Bowhead whale$190,117
Finback whale$72,160
Blue whale$66,594
Sei whale$66,129
Guadalupe fur seal$1,000

and commercial information" indicating that polar bear populations may be imperiled.

As of February 2006 ESA-listed endangered and threatened marine mammals fell into five main categories: whales, dolphins and porpoises, seals and sea lions, sea otters, and manatees and dugongs.


Whales are cetaceans, or marine mammals that live in the water all the time and have torpedo-shaped, nearly hairless bodies. (See Figure 5.1.) There are approximately seventy known whale species. The so-called "great" whales are the largest animals on Earth. In general, the great whale species range in size from thirty to 100 feet in length. There are thirteen whale species normally considered to be "great" whales. The blue whale is the largest of these species.

Whales are found throughout the world's oceans; however, many species are concentrated in cold northern waters. Although they are warm-blooded and do not have fur, whales can survive in very cold waters because they have a thick layer of dense fat and tissue known as blubber lying just beneath the skin. This blubber layer can be up to a foot thick in larger species.

Most whales have teeth. A handful of species filter their food through strong flexible plates called baleen. (See Figure 5.2.) Baleen is informally known as "whalebone." It is composed of a substance similar to human fingernails. Baleen whales strain large amounts of water to obtain their food, mostly zooplankton and tiny fish and crustaceans. Nearly all of the "great" whales are baleen whales.

Many marine mammals can vocalize (make sound). Whales, in particular, use sound to communicate with each other and for navigational purposes. Some whale vocalizations are audible to human ears. These sounds are known as "whalesong."

Whales are believed to be highly intelligent. Scientists use a measure called the Encephalization Quotient (EQ) to compare the relative intelligence of different species. EQ is a number based on the ratio of brain mass to body mass. For example, the average human brain is much larger than needed just to operate an organism the size of a human. This extra capacity indicates higher intelligence. Likewise, the brains of cetaceans, such as whales, are larger than expected, indicating that they probably are very intelligent animals.

Imperiled Whale Populations

As of February 2006 seven whale species had been listed for protection under the ESA in U.S. waters: humpback whales, sperm whales, bowhead whales, northern right whales, sei whales, fin whales, and blue whales. In addition, the ESA covers southern right whales in the southern hemisphere and gray whales, a species that inhabits the northwest Pacific Ocean. All of these whales are considered "great" whales. All but the sperm whale have baleen plates.

The National Marine Fisheries Service publishes annual Stock Assessment Reports ( that provide population estimates for endangered whale species in U.S. waters. Surveys of all species are not conducted every year. As of February 2006 final reports were available for the Pacific Coast (2004), Atlantic and Gulf Coasts (2003), and Alaskan Coast (2003). Summing survey results from each report provides a rough estimate of the minimum population of each species:

  • Blue whale—1,692
  • Bowhead whale—8,886
  • Fin whale—5,004
  • Humpback whale—5,655
  • Northern right whale—291
  • Sei whale—72 (based on incomplete data)
  • Sperm whale—10,956

The NMFS notes that sei whale populations are extremely difficult to estimate. The whales prefer the open sea and rarely enter U.S. waters. Also, they tend to travel alone or in small groups, making them difficult to count.

The northern right whale is also known as the North Atlantic right whale because it is primarily found along the eastern coast of the United States. Although a few sightings have been confirmed in the North Pacific Ocean, there is no official estimate of that population. The National Marine Fisheries Service considers both populations to be of the same species. However, this opinion is disputed by some scientists. As of 2006 the World Wildlife Fund estimated that there were only 350 northern right whales in existence worldwide (

The northern right whale is the most endangered of the great whales. It was once the "right" whale to hunt because it swims slowly, prefers shallow coastal waters, and floats upon death. The species was nearly driven to extinction by whaling, which was banned in 1937 when the population had been reduced to an estimated 100. Despite decades of protection, the northern right whale population has not recovered, and as of 2006 the WWF estimated no population increase at all since the 1980s. Some scientists believe the animal is in grave danger of becoming extinct within only a few decades.

Threats to Whales

Whale populations are imperiled due to a long history of hunting by humans. As early as the eighth century, humans hunted whales for meat and whalebone (baleen). Whales were relatively easy for fishermen to catch because the animals spend a great deal of time at the surface of the water and provide a large target for harpoons. Advances in shipbuilding and the invention of the steam engine allowed fishermen greater access to whale populations, even those in Arctic areas that had previously been out of reach. By the nineteenth century, large numbers of whales were being killed for blubber and baleen. Blubber was rendered to extract whale oil, which was used to light lamps. Baleen was valued for making fans, corsets, and other consumer goods.

On December 2, 1946, the representatives of fourteen nations signed the International Convention for the Regulation of Whaling to form the International Whaling Commission (IWC). The signatory nations were Argentina, Australia, Brazil, Canada, Chile, Denmark, France, the Netherlands, New Zealand, Peru, South Africa, United Kingdom, United States, and the Union of Soviet Socialist Republics. The IWC was formed as a means to regulate the industry and limit the number and type of whales that could be killed. The Marine Mammal Protection Act of 1972 banned commercial whaling in U.S. waters. As of February 2006 there were sixty-six member nations in the IWC.

Centuries of whaling severely depleted whale populations. Low birth rates and high mortality rates due to a variety of factors have prevented many species from recovering. Like other marine animals, whales are endangered by water pollution and loss or degradation of habitat. However, the biggest threats to the northern right whale are believed to be entanglement in fishing gear and ship strikes.


Entanglement of whales in fishing gear is a major problem, as noted by the National Marine Fisheries Service in "What Kinds of Fishing Gear Most Often Entangle Right Whales?" (Right Whale News, November 2005). The article describes recently published research related to whale entanglement. According to studies conducted in 2003 by the New England Aquarium, 71.9% of all known northern right whales have been entangled at least once in fishing gear. In 2005 researchers from Duke University investigated thirty-one cases of right whale entanglements and tried to identify the type of fishing gear involved in each case. They found that nearly a third of the whales had become entangled in lobster pot gear, mostly buoy lines. It was concluded that any type of fishing line that rises vertically in the water column poses a "significant entanglement risk" to northern right whales.


As shown in Figure 5.3 the National Marine Fisheries Service documented nearly 300 ship strikes on large whales off the U.S. East Coast between 1975 and 2002. Strikes on northern right whales are particularly troublesome because so few of the animals remain in existence. According to the NMFS fourteen northern right whales were confirmed killed by ship strikes between 1991 and 2002.

Figure 5.4 shows the locations of ship strikes on northern right whales that occurred between 1990 and 2000 along the North American coastline. Most strikes in U.S. waters occurred along the Massachusetts coast near Cape Cod and along the Georgia and northern Florida coastline. These areas are near or within critical habitats designated by the National Marine Fisheries Service for the whales. The southern critical habitat is the only known calving area of the northern right whale and is used from mid-November to mid-April. During calving season the NMFS performs aerial surveys and alerts ships about whales in their vicinity. In addition, federal law requires that ships remain 500 yards from right whales. Any sightings of dead, injured, or entangled whales must be reported to authorities.

In January 2006 the NMFS announced that a dead right whale calf had been reported by a fishing crew near the Florida shore. The animal was towed to shore and found to have large propeller marks and other wounds on its body, indicating it had been struck by a ship. The whale was male and only one month old.

In 2004 the National Marine Fisheries Service announced plans to propose rules requiring routing changes and speed limits for large vessels traveling in U.S. coastal waters frequented by northern right whales. The agency was still developing the rules in May 2005 when several environmental and animal groups petitioned the NMFS requesting that a temporary emergency regulation be imposed until the permanent rules could be issued. The petitioners asked for a speed limit of 12 knots (13.8 miles per hour) for all ships entering and leaving major East Coast ports during time periods of high use by right whales. In September 2005 the NMFS formally denied the petition. Two months later, three of the petitioners—the Defenders of Wildlife, the Humane Society of the United States, and the Ocean Conservancy—filed a lawsuit against the NMFS accusing the agency of "failing to protect" northern right whales as required by law. The lawsuit had not been resolved as of early 2006, when the petitioners filed papers that added the U.S. Coast Guard as defendants in the suit for their failure to adequately protect the whales in U.S. waters.

Whale Recovery Plans

Table 5.3 is a table published by the National Marine Fisheries Service in 2004 showing the status of recovery plans for endangered whale species. As of February 2006 no recovery plans had been developed for bowhead or sperm whales. A draft recovery plan was published in 1998 for fin and sei whales and is undergoing revision. A recovery plan for the Pacific population of the northern right whale is under development. Final plans have been published for the blue whale (1998), humpback whale (1991), and the Atlantic population of the northern right whale (2005).

Table 5.3 also shows the recovery priority numbers assigned by the NMFS to each endangered whale species. Priority numbers can range from a value of 1 (highest priority) to 12 (lowest priority). The northern right whale has a priority level of 1, indicating strong concern about its abundance and chances for survival as a species.

The recovery plan for the North Atlantic right whale lists five goals for recovering the species. In order of importance, the goals are:

  • Significantly reduce sources of human-caused death, injury and disturbance
  • Develop recovery criteria based on demographic criteria
  • Identify, characterize, protect, and monitor important habitats
Endangered and threatened whale species in the United States, 2004
Species/ESU/DPSaDate listed reclassifiedEndangered Species Act statusPopulation/ESUa trendRecovery priority numberbStatus of recovery plan
aESU=evolutionarily significant unit; DPS=distinct population segment.
bRecovery priority numbers are designated according to guidelines published by the National Marine Fisheries Service (NMFS) on June 15, 1990 (55 FR 24296). Priorities are designated from 1 (high) to 12 (low) based on the following factors: degree of threat, recovery potential, and conflict with development projects or other economic activity.
cDuring the timeframe for this report (2002–2004), two separate endangered species of right whale in the Northern Hemisphere were listed: the North Atlantic right whale (Eubalaena glacialis) and the North Pacific right whale (Eubalaena japonica). In January 2005, NMFS published a final rule to remove this distinction, thereby reverting to the previously used taxonomy of one endangered species—the northern right whale (Eubalaena glacialis)—for both North Pacific and North Atlantic populations. This report, therefore, uses the taxonomy at time of publication (northern right whale), noting that the taxonomic split may be reinstated in the future pending an upcoming status review and following ESA listing procedures.
source: Adapted from "Table 1. ESA-Listed Species under NMFS' Jurisdiction Including Listing Status, Trends, Priority Numbers, and Recovery Plan Status," in Biennial Report to Congress on the Recovery Program for Threatened and Endangered Species (October 1, 2002–September 30, 2004), U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Office of Protected Resources, 2004, (accessed February 14, 2006)
Blue whale6/2/1970EndangeredIncreasing7Completed 07/1998
Bowhead whale6/2/1970EndangeredIncreasing9None
Fin whale6/2/1970EndangeredUnknown7Draft completed 07/1998—under revision
Humpback whale6/2/1970EndangeredIncreasing3Completed 11/1991
Northern right whalec6/2/1970EndangeredUnknown1Completed 12/1991 (Atlantic), draft revision completed 2004; under development (Pacific)
Sei whale6/2/1970EndangeredUnknown3Draft completed 07/1998—under revision
Sperm whale6/2/1970EndangeredUnknown7None
  • Monitor the status and trends of abundance and distribution of the whale population
  • Coordinate federal, state, local, international and private efforts to implement the recovery plan


Dolphins and porpoises are toothed cetaceans. They are similar in shape; however, dolphins are generally larger than porpoises and prefer shallower, warmer waters. Dolphins tend to have long bottlenoses and cone-shaped teeth, as opposed to the flatter noses and teeth found in porpoises. Porpoises are members of the Phocoenidae family, which includes only six existing species. Dolphins are members of the Delphinidae family, a large family containing at least thirty known species. Most dolphin and porpoise populations around the world are hardy and not in danger of extinction. However, there are several species that are in trouble due to limited geographical distribution.

There are no U.S. species of dolphin or porpoises listed under the ESA. There are three foreign species listed as endangered as shown in Table 5.1: the Chinese River dolphin, the Indus River dolphin, and the cochito. The Chinese River and Indus River dolphins live in freshwater rivers in China and Pakistan, respectively. Their numbers are considered to be extremely small. In both cases extensive river damming, water drawdown due to human consumption, fishing, and pollution are blamed for the declines.

The cochito (or vaquita) is a kind of porpoise found only in the Gulf of California, a narrow body of water that separates the western Mexican mainland from the Baja California peninsula. This stretch of water is known in the United States as the Sea of Cortez and contains a great diversity of sea life. Cochitos are among the rarest of all marine mammals. According to the NMFS the cochito species has been nearly eliminated because so many of the animals have become entangled in fishing lines and drowned.

Protection of Prevalent Dolphins

Although they are not considered endangered or threatened, dolphins receive special consideration under U.S. law because of public concern about them. Dolphins are believed to be highly intelligent. They have a high encephalization quotient, perhaps the highest of any animal, besides humans. In addition, many people have been exposed to dolphins through marine entertainment parks, movies, television shows, and even personal encounters and sightings at tourist beaches. As a result, there is widespread public fondness for the animals.

Dolphins are protected by the Marine Mammal Protection Act and laws designed to limit their capture during tuna fishing. In 1990 large U.S. tuna canning companies announced they would no longer purchase tuna caught in a manner that endangered dolphins. The companies began labeling their products "Dolphin Safe" if their practices met specific standards established by the U.S. government. The International Dolphin Conservation Program Act, passed in 1992, reduced the number of legally permitted dolphin deaths. This act also made the United States a dolphin-safe zone in 1994, when it became illegal to sell, buy, or ship tuna products obtained using methods that kill dolphins.


Seals, sea lions, and walruses are considered pinnipeds. This designation comes from the Latin word pinnipedia, which means "feather or fin foot." Pinnipeds have fin-like flippers. Although they spend most of their time in the ocean, pinnipeds come on shore to rest, breed, give birth, and nurse their young. Areas preferred for breeding, birthing, and nursing are called rookeries. Pinnipeds not yet of reproductive age congregate at shore areas known as "haul-outs."

Seals and sea lions were hunted extensively during the 1800s and early 1900s for their blubber, fur, and meat. They continue to be imperiled by human encroachment of haul-out beaches, entanglement in marine debris and fishing nets, incidental catches, disease, and lack of food due to competition from humans for prey species.

Imperiled Seal and Sea Lion Populations

As of February 2006 there were four U.S. species and two foreign species of seals and sea lions listed under the ESA as shown in Table 5.1. The species are Caribbean monk seal, Guadalupe fur seal, Hawaiian monk seal, Mediterranean monk seal, Saimaa seal, and Steller sea lion. However, the Caribbean monk seal has not been sighted since 1952 and is presumed by the NMFS to be extinct.


The Guadalupe fur seal breeds along the eastern coast of Isla de Guadalupe, Mexico. The island is approximately 400 miles west of Baja California. Although populations once included as many as 20,000 to 100,000 individuals, decline and endangerment resulted from extensive fur hunting in the 1700s and 1800s. The species was believed extinct in the early twentieth century, but a small population was discovered in 1954. NMFS scientists believe that the population is now on the increase.


Hawaiian monk seals are the only pinnipeds found on Hawaii and are endemic to those islands—that is, they occur nowhere else on Earth. Hunting was the primary cause of population decline. Hawaiian monk seals are also extremely sensitive to human activity and disturbance and now breed exclusively on the remote northwestern Hawaiian Islands, which are not inhabited by humans. Most females give birth to a single pup every two years, a reproductive rate lower than other pinniped species. The seals also fall prey to shark attacks and mobbing, violent mating acts perpetuated by adult male seals on females and pups of both sexes. Mobbing can result in fatal wounds or drowning. Scientists monitoring seal populations have relocated males guilty of repeated mobbing. The National Marine Fisheries Service Web site ( estimates the species population at around 1,400 animals.


Mediterranean monk seals inhabit remote areas around the Mediterranean Sea and northwest African coast. Most are found off the coasts of Mauritania/Western Sahara, Greece, and Turkey. According to the Seal Conservation Society there are only about 300 of the seals believed to be in existence. Mediterranean monk seals are very sensitive to disturbance. As humans have encroached on beaches and coastal areas, the seals have retreated to isolated caves.

In 1997 there was a massive die-off in a colony of the seals near Mauritania. The exact cause is not known; however, a virus or "red tide" event is generally blamed. This was a severe blow to the seal population. The animals are also purposely killed by fishermen, who consider them a nuisance and competition for limited fish stocks. Scientists fear that Mediterranean monk seals could become extinct with a few decades.


Saimaa seals are found only in the cold waters of the Saimaa Lake system in eastern Finland. Their numbers were decimated by hunting over the centuries to the point of extinction. However, protection measures and fishing restrictions allowed some measure of recovery. In 2005 the World Wildlife Fund estimated that there were approximately 250 Saimaa seals remaining, making them one of the most endangered species in the world. Although the number of seals has been slowly increasing, they are still imperiled by entanglement in fishing nets when they leave protected areas of the lake.


Steller sea lions are large animals, with males reaching a length of about eleven feet and weight of 2,500 pounds. Females are significantly smaller. Steller sea lions are found in Pacific waters from Japan to central California, but most populations breed near Alaska and the Aleutian Islands. The breeding season is from May through July. The species was named after George Wilhelm Steller, a German scientist who studied the animals when he accompanied Russian explorer Vitus Bering on an expedition to Alaska in 1741.

The Steller sea lion population is divided into two stocks as shown in Figure 5.5. The eastern stock inhabits the area east of Cape Suckling, Alaska, and extends down the west coast of Canada and the U.S. mainland. The western stock is found west of Cape Suckling and extends across the Aleutian Islands to Russia and Japan.

According to the National Marine Fisheries Service, the western stock declined by 75% between 1976 and 1990. In April 1990 the Steller sea lion was listed under the ESA as threatened. Over the following decade the western stock continued to decline. This stock was declared endangered in 1997. The eastern stock increased at a rate of approximately 3% per year from the 1980s to the 1990s as shown in Figure 5.6. This stock remains classified as threatened.

Steller sea lion populations have declined for a variety of reasons including bycatch, illegal and legal hunting, predation, and disease. In addition, scientists believe that the animal has experienced reduced productivity due to the indirect effects of climate change and competition from humans for prey species (food fish).

In February 2004 the North Pacific Universities Marine Mammal Consortium reported that population declines may be explained by the fact that Steller sea lions had switched from eating fatty fish to fish with low fat content. In particular, their diet now consists primarily of pollock and flatfish, rather than herring. The low fat content of the new diet prevents Steller sea lions from building up enough blubber to survive and reproduce in their cold aquatic habitat.

The NMFS has conducted surveys of Steller sea lion populations since 1985. These surveys are primarily aerial. The most popular rookeries and haul-outs are photographed from the air, and the animals are counted from examination of detailed photographs. During the summer of 2005 the first Alaska-wide aerial pup count was conducted. The results are shown in Figure 5.7 for target rookeries in the Gulf of Alaska and the Aleutian Islands. Pup populations have declined dramatically since the 1980s. However, the numbers appeared to level off during the early 2000s.

As shown in Table 5.2 species-specific expenditures under the ESA for Steller sea lions totaled $42.6 million in fiscal year 2004, accounting for 60% of expenditures on all marine mammals. The Steller sea lion ranked third in spending among all species covered by the ESA. (See Table 2.8 in Chapter 2.)

Recovery Plans for Seals and Sea Lions

Table 5.4 shows the status of recovery plans for endangered seal and sea lion species as of February 2006. No plans have been developed for Caribbean monk seals (which are believed to be extinct) or Guadalupe fur seals. A recovery plan published in 1983 for the Hawaiian monk seal is currently being revised. Likewise, a plan published in 1992 for the eastern and western stocks of the Steller sea lion is also being revised.

Table 5.4 also shows the recovery priority numbers assigned by the NMFS to each endangered seal and sea lion species. Priority numbers can range from a value of 1 (highest priority) to 12 (lowest priority). The Hawaiian monk seal has a priority level of 1, indicating strong concern about its abundance and chances for survival as a species.


Sea otters are the smallest marine mammals in North America. They are furry creatures that grow to be about four feet in length and weigh up to sixty-five pounds. Otters are related to weasels and mink and are members of the Mustelidae family. Sea otters are almost entirely aquatic and inhabit relativly shallow waters along rocky coasts of the North Pacific Ocean. They eat a wide variety of marine invertebrate. Sea otters are the only animals, besides primates, known to use tools. They use rocks and other objects to smash open the hard shells of clams and crabs to get the meat inside.

Although they inhabit cold waters, sea otters do not have a blubber layer to keep them warm. Instead, they have extremely dense fur coats and high metabolism rates. Their fur coats are waterproof, but only if kept clean. This makes sea otters very susceptible to water contaminants, such as oil.

Imperiled Otter Populations

At one time sea otters were very populous along the entire U.S. West Coast from Southern California to Alaska. Their thick and lustrous fur made them a target of intesive hunting for many centuries. By the dawn of the twentieth century sea otters were on the brink of

Endangered and threatened seal and sea lion species in the United States, February 2006
Species/ESU/DPSaDate listed reclassifiedEndangered Species Act statusPopulation/ESUa trendRecovery priority numberbStatus of recovery plan
aESU=evolutionarily significant unit; DPS=distinct population segment.
bRecovery priority numbers are designated according to guidelines published by the National Marine Fisheries Service (NMFS) on June 15, 1990 (55 FR 24296). Priorities are designated from 1 (high) to 12 (low) based on the following factors: degree of threat, recovery potential, and conflict with development projects or other economic activity.
cThis species was first listed as threatened via a 240-day emergency rule on 4/10/1990, then officially listed as threatened in a final rule on 11/26/1990. NMFS separated the species into western and eastern DPSs via a final rule on 5/5/1997, which maintained the eastern DPS as threatened and reclassified the western DPS as endangered.
source: Adapted from "Table 1. ESA-Listed Species under NMFS' Jurisdiction Including Listing Status, Trends, Priority Numbers, and Recovery Plan Status," in Biennial Report to Congress on the Recovery Program for Threatened and Endangered Species (October 1, 2002–September 30, 2004), U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Office of Protected Resources, 2004, (accessed February 14, 2006)
Seals and sea lions
Caribbean monk seal3/11/1967EndangeredPresumed extinct12None
Guadalupe fur seal12/16/1985ThreatenedIncreasing10None
Hawaiian monk seal11/23/1976EndangeredDeclining1Completed 03/1983; under revision
Stellar sea lion—eastern distinct population segment (DPS)4/10/1990; 11/26/1990; 5/5/97cThreatenedIncreasing10Completed 12/1992; under revision
Stellar sea lion—western distinct population segment (DPS)4/10/1990; 11/26/1990; 5/5/97cEndangeredDeclining7Completed 12/1992; under revision

extinction. In 1911 they became protected under the International Fur Seal Treaty and their numbers began to increase. By the mid-1980s there were approximately 110,000 to 148,000 sea otters around the world. Nearly half lived in the Aleutian Islands off the coast of Alaska. A much smaller population survived off the California coast.

Figure 5.8 shows the distribution of sea otters in 1995. Biologists recognize two distinct populations. The northern sea otter extends from Russia across the Aleutian Islands and the coast of Alaska south to the state of Washington. The southern sea otter is found only off the California coast.

Beginning in the 1960s the U.S. Fish and Wildlife Service began translocating (moving) limited numbers of sea otters from established locations to new locations within their traditional range of distribution. Attempted translocations to Oregon failed; however, translocated colonies were established at four locations: southeast Alaska, Washington, and San Nicolas Island, California, in the United States, and Vancouver, British Columbia, in Canada. (See Figure 5.8.)


Southern (or California) sea otters were designated a threatened species in 1977. At that time the animals inhabited a small stretch of coastline in central California. Scientists feared that this isolated population was in grave danger of being wiped out by a single catastrophe, such as an oil spill. In 1987 the U.S. Fish and Wildlife Service decided to establish an "experimental population" of sea otters at another location. Over the next few years 140 sea otters were moved, a few at a time, to San Nicolas Island. It was hoped that these translocated animals would thrive and develop an independent growing colony. Unfortunately, the venture achieved only limited success. Many of the otters swam back to their original habitat; others died, apparently from the stress of moving. During the early 1990s the transport effort was abandoned. The FWS spent $3.8 million on the program between 1987 and 1995.

In October 2005 the U.S. Fish and Wildlife Service proposed officially ending the translocation program and removing the designation of "experimental population" for the thirty or so sea otters remaining at San Nicolas Island. These animals would be considered threatened under the ESA, just like their fellow southern sea otters. The FWS collected comments on this proposal and expected to make a final decision in 2006.

Figure 5.9 shows annual survey results for southern sea otter populations from 1983 through 2005. These surveys were conducted during the springtime and count both independent otters and pups. As indicated in Figure 5.9 the populations have been gradually increasing. In spring 2005 just over 2,700 otters were counted (2,417 independent otters and 318 pups).

In 2005 the U.S. Geological Survey (USGS) reported that the California otter population declined during the late 1990s for a surprising reason. The USGS National Wildlife Health Center found that more than 40% of otter deaths occurring between 1992 and 2002 were the result of parasitic, fungal, or bacterial infections. (See Figure 5.10.) Toxicological analyses indicated that the immune systems of the animals had been damaged by water pollutants, particularly butyltins and organochlorine compounds, such as polychlorinated biphenyls (PCBs). Butyltins are tin compounds widely used as wood preservatives and as a component of ship paints.

A revised recovery plan was issued for threatened southern sea otters in 2003. The primary recovery objective is management of human acitivities that could damage or destroy habitat (for example, oil spills). The plan notes that southern sea otters can be considered for delisting under the ESA when the average population level over a three-year period exceeds 3,090 animals. As shown in Figure 5.9 population trends through 2005 are encouraging. Absent of any catastrophic events, the

southern sea otter could achieve delisting within the next decade.


Translocations of northern sea otters to southeast Alaska, British Columbia, and Washington established thriving colonies in those areas. Likewise, populations in south central Alaska are believed to be stable or increasing. However, the stock of sea otters in southwest Alaska has experienced severe decline. In August 2005 the U.S. Fish and Wildlife Service listed the southwest Alaska distinct population segment (DPS) of the northern sea otter as "threatened" under the ESA.

The southwest Alaska DPS extends from the tip of the Aleutian Islands to a point roughly beneath the letter "A" in the word "Alaska" in Figure 5.8. Populations in this area have decreased dramatically since the mid-1980s, when more than 70,000 sea otters inhabitated southwest Alaska. Table 5.5 shows the decline in sea otter populations across the region since the 1980s and early 1990s. According to Douglas Burn in "Alaska Sea Otters: The Southwest Decline Continues" (February 2004,, surveys conducted in 2003 in the Aleutian Islands found that sea otter counts were down by 63% from the year 2000. Scientists are not sure of the reasons for the decline; however, there is suspicion that orca whales are preying on the otters.

Survey results for sea otter populations in southwest Alaska, 1986–2001
LocationYearCount or estimateDecline
source: "Table 1. Southwest Alaska Sea Otter Survey Results, 1986–2001," in Sea Otter Declines in Southwest Alaska: A Growing Concern, U.S. Department of the Interior, U.S. Fish and Wildlife Service, October 2001, (accessed February 13, 2006)
Aleutian Islands19928,044
North Alaska peninsula19869,061-13,091
South Alaska peninsula198615,346-17,835
Kodiak Archipelago198913,526

Foreign Species of Sea Otters

As shown in Table 5.1 there were five foreign otter species listed as endangered under the ESA as of February 2006. They populate areas of Africa and South America. All species are imperiled by illegal hunting for meat and fur. Loss of habitat and water pollution are also threats to their survival. The southern river otter of South America is in dire danger of extinction. According to the International Union for Conservation of Nature and Natural Resources' IUCN Red List of Threatened Species, the species is found in only a handful of isolated areas, all of which are threatened by massive deforestation and expanding fishing operations.


Manatees are large stout mammals that inhabit fresh waters and coastal waterways. They are from the Sirenian order, along with dugongs. There are only five Sirenian species, and all are endangered or extinct. Scientists believe that Steller's sea cow, the only species of cold-water manatee, was hunted to extinction during the 1700s.

The West Indian manatee, also known as the Florida manatee, primarily swims in the rivers, bays, and estuaries of Florida and surrounding states. (See Figure 5.11.) As shown in Table 5.1 this species is listed as endangered under the ESA.

Manatees are often called "sea cows" and can reach weights of up to 2,000 pounds. They swim just below the surface of the water and feed on vegetation. West Indian manatees migrate north in the summer, though generally no farther than the North Carolina coast. In 1995 a manatee nicknamed "Chessie" made headlines by swimming all the way to Chesapeake Bay. Eventually biologists, concerned about his health in cooler waters, had him airlifted back to Florida. During the winter many manatees huddle around warm water discharges from power plants and other industrial facilities. Although this can keep them warm, scientists worry that overcrowding in small areas makes the animals more susceptible to sickness.

Imperiled Manatee Populations

Each year during cold weather biologists conduct surveys to determine the number of Florida manatees remaining in the wild. The numbers are estimates based on surveys conducted at known wintering habitats. The latest survey was performed in January 2005 and found 3,143 manatees living along the Florida coast. This number is up from 1,267 reported in 1991. Many manatees have scars on their backs from motorboat propellers—these allow individual manatees to be recognized. In a press release entitled "FWC Biologists Release Preliminary 2005 Manatee Mortality Data" (January 6, 2006, asp?id=26330), the Florida Fish and Wildlife Conservation Commission noted that "the manatee population appears to be doing fairly well" throughout much of the state. Populations in the northern and central parts of Florida are increasing or remaining stable. However, manatees in southwest Florida face extra threats due to their exposure to red tide incidents (proliferation of harmful algae in the water). Scientists warn that these populations "could decline significantly."

Threats to Manatees

Manatees are imperiled for a variety of reasons. Although they can live for fifty or sixty years, their birth rate is low. Mature females bear a single offspring only every three to five years. Many baby manatees die in the womb or soon after birth for unknown reasons. These are called perinatal fatalities. Disease, natural pathogens, and cold water temperatures are also deadly. However, motorboat strikes are the major documented cause of manatee mortalities. Manatees are large and swim slowly at the surface of the water. They often cannot move away from boats quickly enough to avoid being hit. Environmentalists have tried to protect manatees from boat collisions, and have successfully had several Florida waterways declared boat-free zones. There are also areas where boaters are required to lower their speeds.

During 1995 and 1996 a pneumonia-like virus killed more than 100 manatees in southern Florida. The disease, according to marine microbiologist John H. Paul and his colleagues, was caused by a red tide that occurred when toxin-producing aquatic organisms called dinoflagellates bloomed in large quantities ("A Filterable Lytic Agent Obtained from a Red Tide Bloom That Caused Lysis of Karenia Brevis [Gymnodinum breve] Cultures," Aquatic Microbial Ecology, 2002). The Florida Marine Research Institute reported in 2006 that human-related activity accounted for 30% of all manatee deaths between April 1974 and June 2005, most from watercraft collisions. (See Figure 5.12.) The cause of death could not be determined in 28% of the cases. Nonhuman causes were blamed for 42% of the deaths.

A lawsuit by the Save the Manatee Club and other environmental and conservation organizations in 2000 successfully required the state to implement new low-speed zones for boats and establish safe-haven areas for manatees. The rules were immediately challenged by individual boaters and boating organizations; however, the restrictions were upheld by Florida courts in 2002.

Foreign Manatee and Dugong Species

There are two surviving foreign species of manatees found in western Africa and in and around the Amazon River in South America. Both species are designated under the ESA as endangered and are in grave danger of extinction due to illegal hunting, deforestation, habitat destruction, and water pollution. The only remaining dugongs live in the coastal waters of the Indian Ocean and Pacific Ocean. Their populations are also considered imperiled. Dugongs around the tiny island of Palau in the western Pacific Ocean are considered endangered under the ESA.

Marine Mammals

views updated May 08 2018

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.

Marine Mammals

views updated May 29 2018

Marine Mammals

Mammals are vertebrates (animals with a backbone) that share characteristics of nursing their young with milk, breathing air, having hair at some point in their lives, and being warm-blooded. Marine mammals are the species of mammals that depend on the oceans for all or most of their lives. There are about 115 different species of marine mammals. Marine mammals vary from the small sea otter to the giant blue whale. Some of them live in groups, like dolphins, while others are solitary, like polar bears. All marine mammals share four characteristics:

  • They have a streamlined body shape that makes them excellent swimmers.
  • They maintain heat in their bodies with layers of fat called blubber.
  • They have respiratory (breathing) systems that allow them to stay underwater for long periods of time.
  • They have excretory (waste) systems that allow them to survive without drinking freshwater. Instead they obtain the water they need from the food they eat.

Marine mammals belong to three groups called orders. An order is a classification of a group of organisms, which eventually splits into species. Marine mammals are in the orders Cetecea, Carnivora, and Sirenia.

Order Cetacea

There are about seventy-seven species of cetaceans, which include whales, dolphins, and porpoises. All of these animals live their entire lives in the water. Cetaceans probably evolved from the hoofed mammals that were similar to horses and sheep. Their front legs became fins that are used primarily for steering, and their hind legs became extremely small flippers or flukes (tail fins) so as to streamline the animals for swimming. Cetaceans swim by moving their strong fluke up and down. They are grouped into two categories or suborders: Odontoceti, the toothed whales, and Mysteceti, the baleen whales.

Marine Mammals in the Military

Marine mammals have been used by the U.S. Navy for military purposes since the late 1950s. Modern day programs use Atlantic bottlenose dolphins, Pacific white-sided dolphins, and California sea lions, and training has also been conducted with beluga whales, orcas, and pilot whales. The Advanced Marine Biological Systems (AMBS) program, which supports military marine mammal programs, is located in Point Loma, California.

Dolphins can swim very fast and can maintain those speeds for extremely long periods of time. Also, dolphins use echolocation (sound waves) to detect prey and predators. In fact, dolphin echolocation is more sensitive than any equipment that has been developed by humans. Dolphins are particularly good at finding lost equipment on the seafloor and for locating enemy mines and torpedoes.

Sea lions have an excellent sense of hearing that allows them to detect the source of a noise, and they have vision that is very sensitive in low light. These skills make these marine mammals extremely well suited for military operations involving search and rescue.

Suborder Odontoceti The toothed whales account for about 90% of all cetaceans, including dolphins and porpoises as well as the orca (killer whale) and the sperm whale. Toothed whales hunt for prey, which they capture with their teeth. They also have one external hole called a blowhole for breathing. The toothed whales have a large brain for their size and are considered to be some of the most intelligent animals. They hunt using sophisticated echolocation, which is the method of detecting objects by listening to the reflected sounds that it calls out.

Suborder Mysteceti The baleen whales have no teeth. Instead, they have bristly plates called baleen, which hangs like a curtain from their upper jaws. Baleen is made from a protein similar to that which makes up human fingernails. When it is eating, the baleen whale sucks in huge amounts of water and then forces the water out through its baleen, which acts like a sieve. These whales diet primarily on tiny animal plankton, animals that drift through oceans. Microscopic plankton are concentrated behind the baleen and then swallowed. Even though baleen whales feed on some of the smallest animals in the world, baleen whales are some of the largest animals in the world. The blue whale, the fin whale, and the gray whale all weigh more than 2 tons (9 metric tons). Baleen whales are also distinguished from toothed whales because they have two external blowholes instead of one.

Order Carnivora

The Carnivora include animals that prey on each other (meat-eaters) like dogs, cats, bears, and weasels. There are two suborders of carnivores that have marine representatives: the pinnipeds and the fissipeds.

Suborder Pinnipedia Pinnipeds include seals, sea lions, fur seals and walruses. They all have flippers that can be used to move around on land as well as on water. Although they swim much more efficiently than they walk on land, they do give birth to their young on land.

Seals account for nearly 90% of all pinnipeds. There are nineteen species that live in all of the oceans and even in a few lakes. Most seal species live near Antarctica and in the Arctic Circle. Seals do not have an external ear, although they can hear very well. They propel themselves with their rear flippers and use their front flippers for steering.

Sea lions and fur seals do have small external ears. Their hind legs are more flexible than those of seals, so they can move around better on land. They propel themselves with their front flippers when swimming.

Walruses are the largest of the pinnipeds. They do not have an external ear, but they can use their rear flippers for moving on land. The canine teeth (pointed, in the front) of walruses are enlarged into tusks. Walruses swim along the bottom of the ocean using their tusks like runners as they look for clams to eat.

Keiko the Whale

Keiko was an orca, or killer whale, that was featured in the 1993 Disney movie, Free Willy. Keiko inspired many people, both adults and children, to become aware of marine mammals and their incredible behaviors and skills. Keiko also instigated a large educational movement on the importance of marine mammals to the environment.

Keiko was born in the Atlantic Ocean near Iceland and captured when he was about two years old. After several transfers, Keiko was sold to an amusement park in Mexico City, Mexico, where he lived in a small tank. Keiko's health suffered; he was underweight and had many sores on his skin. The success of the movie prompted the movie studio and several charitable donors to buy Keiko from the aquarium in Mexico and to train Keiko for reintroduction into the wild.

In 1994, Keiko was moved to the Oregon Coast Aquarium in Newport, Oregon, where he was treated medically and taught learning skills that he would need to behave like a wild orca. Within a year, he gained nearly 1,000 pounds (2,200 kilograms); his skin sores healed and he learned to eat fresh fish.

After four years in Oregon, Keiko was transferred back to Iceland where he was kept in a pen in Klettvik Bay. Keiko was then trained to compete with birds and other fish for prey. He was fitted with a tracking device so that he could swim away from the pen and into the bay, while still remaining in contact with his caregivers. Eventually Keiko interacted with wild whales and spent days at a time in the open ocean.

In 2002, Keiko swam across the North Atlantic Ocean, covering a distance of 1,000 miles (1,600 kilometers) to the coast of Norway. The trip took nearly two months and Keiko arrived in excellent health. Keiko is considered the first whale to ever be successfully reintroduced into the wild. Keiko died on December 12, 2003, at the age of 27. He was the second oldest male orca to have been in captivity. (Wild orcas live for an average of 35 years.)

Suborder Fissipedia The suborder Fissipedia includes cats, dogs, raccoons, and bears, as well as two marine mammals: sea otters and polar bears. Sea otters are about 4 feet (1.2 meters) long, the smallest of the marine mammals. Their favorite food is sea urchins, which they eat by lying on their back and smashing them on a stone that is balanced on their chests. Polar bears wander long distances across sheets of floating ice in the Arctic hunting for seals and whales. They can swim between patches of ice using their powerful forepaws like oars.

Order Sirenia

The sirenians, also called sea cows, evolved from the hoofed land mammals, like the cetaceans. The Sirenia include the manatees, which are large plant-eating marine mammals, and the dugongs (commonly known as sea cows). They are the only plant-eating marine mammals, eating sea grasses and algae (tiny rootless plants that grow in sunlit waters) in warm waters. They grow to be quite large, up to 15 feet (4.5 meters) and weigh 1,500 pounds (680 kilograms).

Endangered Marine Mammals

According to the Endangered Species Act, an animal that could become extinct in all or part of its range is endangered. An animal's range is the entire area where it lives. Of the 115 species of marine mammals, 22 were considered endangered as of 2004, including the blue whale, the gray whale, the finback whale, the Hawaiian monk seal, the stellar sea lion, the marine sea otter, and all four species of dugongs and manatees. Much of the threat is due to human activity. People hunt these animals for their pelts, blubber, and meat, and destroy their habitat from overfishing and mining.

Juli Berwald, Ph.D.

For More Information


Garrison, Tom. Oceanography. 3rd ed. Belmont, CA: Wadsworth, 1999.

Morgan, Sally, and Pauline Lalor. Oceanlife. New York: PRC Publishing Ltd., 2001.

Thomas, Peggy. Marine Mammal Preservation. Brookfield, CT: Twenty-First Century Books, 2000.


Drumm, Laura. "About Marine Mammals." The National Marine Mammal Laboratory: National Oceanic and Atmospheric Administration. (accessed on August 12, 2004).

"Keiko, the Most Famous Whale in the World, Dies in Norway." The Humane Society of the United States. (accessed on August 12, 2004).

"Keiko's Story: The Timeline." The Humane Society of the United States. (accessed on August 12, 2004).

Myers, Phil. "Cetacea." Animal Diversity Web: The University of Michigan Museum of Zoology. (accessed on August 12, 2004).

"Pinniped Factsheets." International Marine Mammal Association, Inc. (accessed on August 12, 2004).

"U.S. Navy Marine Mammal Program." United States Department of the Navy (accessed on June 15, 2004).

Marine Mammal Program

views updated May 08 2018

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

Marine Mammal Protection Act (1972)

views updated May 14 2018

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."

About this article

Marine Mammals

All Sources -
Updated Aug 13 2018 About content Print Topic