THE AMZAZON RIVER DOLPHIN

The Amazon river dolphin (Inia geoffrensis), also known as the boto, bufeo or pink river dolphin, is a species of toothed whale classified in the family Iniidae. Three subspecies are currently recognized: I. g. geoffrensis (Amazon river dolphin), I. g. boliviensis (Bolivian river dolphin) and I. g. humboldtiana (Orinoco river dolphin). The three subspecies are distributed in the Amazon basin, the upper Madeira River in Bolivia, and the Orinoco basin, respectively.
The Amazon river dolphin is the largest species of river dolphin, with adult males reaching 185 kilograms (408 lb) in weight, and 2.5 metres (8.2 ft) in length. Adults acquire a pink color, more prominent in males, giving it its nickname "pink river dolphin". Sexual dimorphism is very evident, with males measuring 16% longer and weighing 55% more than females. Like other toothed whales, they have a melon, an organ that is used for bio sonar. The dorsal fin, although short in height, is regarded as long, and the pectoral fins are also large. The fin size, unfused vertebrae, and its relative size allow for improved manoeuvrability when navigating flooded forests and capturing prey.
They have one of the widest ranging diets among toothed whales, and feed on up to 53 different species of fish, such as croakers, catfish, tetras and piranhas. They also consume other animals such as river turtles and freshwater crabs.^[2]
In 2008, this species was ranked by the International Union for Conservation of Nature (IUCN) as being data deficient, due to the uncertainty regarding its population trends and the impact of threats. While hunting is a major threat, in recent decades greater impacts on population have been due to the loss of habitat and inadvertent entanglement in fishing lines.
It is the only species of river dolphin kept in captivity, mainly in the United States, Venezuela and Europe; however, it is difficult to train and a high mortality is seen among captive individuals.

 

 

 

 

Taxonomy

An Amazon river dolphin as depicted in Brehms Tierleben, 1860's

The species Inia geoffrensis was described by Henri Marie Ducrotay de Blainville in 1817. Originally, the Amazon river dolphin belonged to the superfamily Platanistoidea, which constituted all river dolphins, making them a paraphyletic group.^[3] Today, however, the Amazon river dolphin has been reclassified into the superfamily Inioidea.^[4] There is no consensus on when and how they penetrated the Amazon basin; they may have done so during the Miocene from the Pacific Ocean, before the formation of the Andes, or from the Atlantic Ocean.^[5][6]
There is ongoing debate about the classification of species and subspecies with large international bodies being in disagreement. The IUCN recognizes three subspecies:^[7]I. g. geoffrensis (Amazon river dolphin), I. g. boliviensis (Bolivian river dolphin) and I. g. humboldtiana (Orinoco river dolphin).^[4] While the Committee on Taxonomy of the Society for Marine Mammalogy only recognizes the first two of these.^[8]
However, based on skull morphology in 1994, it was proposed that I. g. boliviensis was a different species.^[9] In 2002, following the analysis of mitochondrial DNA specimens from the Orinoco basin, the Putumayo River (tributary of the Amazon) and the Tijamuchy and Ipurupuru rivers, geneticists proposed that genus Inia be divided into at least two evolutionary lineages: one restricted to the river basins of Bolivia and the other widely distributed in the Orinoco and Amazon.^[10][11] A recent study, with more comprehensive sampling of the Madeira system, including above and below the Teotonio Rapids (which were thought to obstruct gene flow), found that the Inia above the rapids did not possess unique mtDNA.^[12] As such the species level distinction once held is not supported by current results. Therefore, the Bolivian river dolphin is currently recognized as a subspecies. In addition, a 2014 study identifies a third species in the Araguaia-Tocantins basin,^[13] but this designation is not recognized by any international organization and the Committee on Taxonomy of the Society for Marine Mammalogy suggests this analysis is not persuasive.^[8]

Subspecies

The Bolivian river dolphin is a subspecies of Inia geoffrensis

Inia geoffrensis geoffrensis^[4] inhabits most of the Amazon River, including rivers Tocantins, Araguaia , low Xingu and Tapajos, the Madeira to the rapids of Porto Velho, and rivers Purus, Yurua, Ica, Caqueta, Branco, and the Rio Negro through the channel of Casiquiare to San Fernando de Atabapo in the Orinoco river, including its tributary: the Guaviare.
Inia geoffrensis boliviensis^[4] has populations in the upper reaches of the Madeira River, upstream of the rapids of Teotonio, in Bolivia. It is confined to the Mamore River and its main tributary, the Iténez.^[14]
Inia geoffrensis humboldtiana^[4] are located in the Orinoco River basin, including the Apure and Meta rivers. This subspecies is restricted, at least during the dry season, to the waterfalls of Rio Negro rapids in the Orinoco between Samariapo and Puerto Ayacucho, and the Casiquiare canal. This subspecies is not recognized by the Committee on Taxonomy of the Society for Marine Mammalogy,^[8] but is recognized by the IUCN.^[7]

Biology and ecology

Description

Male Amazon river dolphins are either solid pink or mottled grey/pink.

The Amazon river dolphin is the largest river dolphin. Adult males reach a maximum length and weight of 2.55 metres (8.4 ft) (average 2.32 metres (7.6 ft)) and 185 kilograms (408 lb) (average 154 kilograms (340 lb)), while females reach a length and weight of 2.15 metres (7.1 ft) (mean 2 metres (6.6 ft)) and 150 kilograms (330 lb) (average 100 kilograms (220 lb)). It has very evident sexual dimorphism, with males measuring and weighing between 16% and 55% more than females, making it unique among cetaceans, where females are generally larger than males.^[15]
The texture of the body is robust and strong but flexible. Unlike oceanic dolphins; the cervical vertebrae are not fused, allowing the head to turn 90 degrees.^[16] The flukes are broad and triangular, and the dorsal fin, which is keel-shaped, is short in height but very long, extending from the middle of the body to the caudal region. The pectoral fins are large and paddle-shaped. The length of its fins allows the animal to perform a circular movement, allowing for exceptional maneuverability to swim through the flooded forest but decreasing its speed.^[17]
The body color varies with age. Newborns and the young have a dark grey tint, which in adolescence transforms into light grey, and in adults turns pink as a result of repeated abrasion of the skin surface. Males tend to be pinker than females due to more frequent trauma from intra-species aggression. The color of adults varies between solid and mottled pink and in some adults the dorsal surface is darker. It is believed that the difference in color depends on the temperature, water transparency, and geographical location. There is one albino on record, kept in an aquarium in Germany.

Amazon river dolphins have a heterodont dentition

The skull of the species is slightly asymmetrical compared to the other toothed whales. It has a long, thin snout, with 25 to 28 pairs of long and slender teeth to each side of both jaws. Dentition is heterodont, meaning that the teeth differ in shape and length, with differing functions for both grabbing and crushing prey. Anterior teeth are conical and later have ridges on the inside of the crown. Despite small eyes, the species seems to have good eyesight in and out of the water. It has a melon on the head, the shape of which can be modified by muscular control when used for biosonar. Breathing takes place every 30 to 110 seconds.^[17]

Longevity

Apure the dolphin lived for forty years at the Duisburg Zoo

Life expectancy of the Amazon river dolphin in the wild is unknown, but in captivity, the longevity of healthy individuals has been recorded at between ten and thirty years. However, the average longevity in captive animals is only 33 months.^{[18][better source needed]} An individual named Apure at Duisburg Zoo, Germany, is estimated to have lived more than forty years, being captured from the wild at age nine.^[19]

Behavior

The Amazon river dolphin are commonly seen singly or in twos, but may also occur in pods that rarely contain more than eight individuals.^[20] Pods as large as 37 individuals have been seen in the Amazon, but average is three. In the Orinoco, the largest observed groups number 30, but average is just above five.^[20] Typically, social bonds occur between mother and child, but may also been seen in heterogeneous groups or bachelor groups. The largest congregations are seen in areas with abundant food, and at the mouths of rivers. There is significant segregation during the rainy season, with males occupying the river channels, while females and their offspring are located in flooded areas. However, in the dry season, there is no such separation.^[16][21] Due to the high level of prey fish, larger group-sizes are seen in large sections that are directly influenced by whitewater (such as main rivers and lakes, especially during low water season) than in smaller sections influenced by blackwater (such as channels and smaller tributaries).^[20] In their freshwater habitat they are apex predators and gatherings depend more on food sources and habitat availability than in oceanic dolphins where protection from larger predators is necessary.^[20]
Captive studies have shown that the Amazon river dolphin is less shy than the bottlenose dolphin, but also less sociable. It is very curious and has a remarkable lack of fear of foreign objects. However, dolphins in captivity may not show the same behavior that they do in their natural environment, where they have been reported to hold the oars of the fishermen, rub against the boat, pluck underwater plants, and play with sticks, logs, clay, turtles, snakes, and fish.^[4]
They are slow swimmers; they commonly travel at speeds of 1.5 to 3.2 kilometres per hour (0.93 to 1.99 mph) but have been recorded to swim at speeds up to 14 to 22 kilometres per hour (8.7 to 13.7 mph). When they surface, the tips of the snout, melon and dorsal fins appear simultaneously, the tail rarely showing before diving. They can also shake their fins, and pull their tail fin and head above the water to observe the environment. They occasionally jump out of the water, sometimes as high as a meter (3.14 ft). They are harder to train than most other species of dolphin.^[4]

Courtship

Adult males have been observed carrying objects in their mouths such as branches or other floating vegetation, or balls of hardened clay. The males appear to carry these objects as a socio-sexual display which is part of their mating system. The behavior is "triggered by an unusually large number of adult males and/or adult females in a group, or perhaps it attracts such into the group. A plausible explanation of the results is that object-carrying is aimed at females and is stimulated by the number of females in the group, while aggression is aimed at other adult males and is stimulated by object-carrying in the group."^[22] Before determining that the species had an evident sexual dimorphism, it was postulated that the river dolphins were monogamous. Later, it was shown that males were larger than females and are documented wielding an aggressive sexual behavior in the wild and in captivity. Males often have a significant degree of damage in the dorsal, caudal, and pectoral fins, as well as the blowhole, due to bites and abrasions. They also commonly have numerous secondary teeth-raking scars. This suggests fierce competition for access to females, with a polygynous mating system, though polyandry and promiscuity cannot be excluded.^[23]
In captivity, courtship and mating foreplay have been documented. The male takes the initiative by nibbling the fins of the female, but reacts aggressively if the female is not receptive. A high frequency of copulations in a couple was observed; they used three different positions: contacting the womb at right angles, lying head to head, or head to tail.^[6]

Reproduction

Breeding is seasonal, and births occur between May and June. The period of birthing coincides with the flood season, and this may provide an advantage because the females and their offspring remain in flooded areas longer than males. As the water level begins to decrease, the density of food sources in flooded areas increases due to loss of space, providing enough energy for infants to meet the high demands required for growth. Gestation is estimated to be around eleven months and captive births take 4 to 5 hours. At birth, calves are 80 centimetres (31 in) long and in captivity have registered a growth of 0.21 metres (0.69 ft) per year. Lactation takes about a year. The interval between births is estimated between 15 and 36 months, and the young dolphins are thought to become independent within two to three years.^[6]
The relatively long duration of breastfeeding and parenting suggests a strong mother-child bond. Most couples observed in their natural environment consist of a female and her calf. This suggests that long periods of parental care contribute to learning and development of the young.^[6]

Diet

Amazon river dolphin feeding

The diet of the Amazon river dolphin is the most diverse of the toothed whales. It consists of at least 53 different species of fish, grouped in 19 families. The prey size is between 5 and 80 centimetres (2.0 and 31.5 in), with an average of 20 centimetres (7.9 in). The most frequently consumed fish belong to the families Sciaenidae (croakers), Cichlidae, and Characidae (tetras and piranhas). The dolphin’s dentition allows it to access shells of river turtles and freshwater crabs.^[2][4] The diet is more diverse during the wet season, when fish are spread in flooded areas outside riverbeds, thus becoming more difficult to catch. The diet becomes more selective during the dry season when prey density is greater.^[17]
Usually, these dolphins are active and feeding throughout the day and night. However, they are predominantly crepuscular. They consume about 5.5% of their body weight per day. They sometimes take advantage of the disturbances made by boats to catch disoriented prey. Sometimes, they associate with the distantly-related tucuxi (Sotalia fluviatilis), and giant otters (Pteronura brasiliensis) to hunt in a coordinated manner, by gathering and attacking fish stocks at the same time. Apparently, there is little competition for food between these species, as each prefers different prey. It has also been observed that captive dolphins share food.^[2][4]

Echolocation

Amazonian rivers are often very murky, and the Amazon river dolphin is therefore likely to depend much more on its sense of echolocation than vision when navigating and finding prey. However, echolocation in shallow waters and flooded forests may result in many echoes to keep track of. For each click produced a multitude of echoes are likely to return to the echolocating animal almost on top of each other which makes object discrimination difficult. This may be why the Amazon river dolphin produces less powerful clicks compared to other similar sized toothed whales.^[24] By sending out clicks of lower amplitude only nearby objects will cast back detectable echoes, and hence fewer echoes need to be sorted out, but the cost is a reduced biosonar range. Toothed whales generally do not produce a new echolocation click until all relevant echoes from the previous click have been received,^[25] so if detectable echoes are only reflected back from nearby objects, the echoes will quickly return, and the Amazon river dolphin is then able to click at a high rate.^[24] This in turn allow these animals to have a high acoustic update rate on their surroundings which may aid prey tracking when echolocating in shallow rivers and flooded forests with plenty of hiding places for the prey.

Communication

Like other dolphins, river dolphins use whistling tones to communicate. The issuance of these sounds is related to the time they return to the surface before diving, suggesting a link to food. Acoustic analysis revealed that the vocalisations are different in structure from the typical whistles of other species of dolphins.^[26]

Distribution and population

The main branch of the Amazon River near Fonte Boa, Brazil, with multiple floodplains, lakes and smaller channels. The Amazon river dolphin is observed here throughout the year

Amazon river dolphins are the most widespread river dolphins. They are present in six countries in South America: Bolivia, Brazil, Colombia, Ecuador, Peru, and Venezuela, in an area covering about 7,000,000 square kilometres (2,700,000 sq mi). The boundaries are set by waterfalls, such as the Xingu and Tapajós rivers in Brazil, as well as very shallow water. A series of rapids and waterfalls in the Madeira River have isolated one population, recognized as the subspecies I. g. boliviensis, in the southern part of the Amazon basin in Bolivia.^[4]
They are also distributed in the basin of the Orinoco River, except the Caroni River and the upper Caura River in Venezuela. The only connection between the Orinoco and the Amazon is through the Casiquiare canal. The distribution of dolphins in the rivers and surrounding areas depends on the time of year; in the dry season they are located in the river beds, but in the rainy season, when the rivers overflow, they disperse to the flooded areas, both the forests and the plains.^[4]
Studies to estimate the population are difficult to analyze due to the difference in the methodology used. In a study conducted in the stretch of the Amazon called Solimões River, with a length of 1,200 kilometres (750 mi) between the cities of Manaus and Tabatinga, a total of 332 individuals was sighted ± 55 per inspection. Density was estimated at 0.08- 0.33 animals per square kilometer in the main channels, and 0.49 to 0.93 animals per square kilometer in the branches. In another study, on a stretch of 120 kilometres (75 mi) at the confluence of Colombia, Brazil and Peru, 345 individuals with a density of 4.8 per square km in the tributaries around the islands. 2.7 and 2.0 were observed along the banks. Additionally, another study was conducted in the Amazon at the height of the mouth of the Caqueta River for six days. As a result of the studies conducted, it was found that the density is higher in the riverbanks, 3.7 per km, decreasing towards the center of the river. In studies conducted during the rainy season, the density observed in the flood plain was 18 animals per square km, while on the banks of rivers and lakes ranged from 1.8 to 5.8 individuals per square km. These observations suggest that the Amazon river dolphin is found in higher density than any other cetacean.^[4]

Habitat

The Amazon river dolphin is located in most of the area's aquatic habitats, including; river basins, major courses of rivers, canals, river tributaries, lakes, and at the ends of rapids and waterfalls. Cyclical changes in the water levels of rivers take place throughout the year. During the dry season, dolphins occupy the main river channels, and during the rainy season, they can move easily to smaller tributaries, to the forest, and to floodplains.^[6]
Males and females appear to have selective habitat preferences, with the males returning to the main river channels when water levels are still high, while the females and their offspring remain in the flooded areas as long as possible; probably because it decreases the risk of aggression by males toward the young and predation by other species.^[6]

Migration

In the Pacaya-Samiria National Reserve, Peru, photo-identification is used to recognize individuals based on pigmentation patterns, scars and abnormalities in the beak. 72 individuals were recognized, of which 25 were again observed between 1991 and 2000. The intervals between sightings ranged from one day to 7.5 years. The maximum range of motion was 220 kilometres (140 mi), with an average of 60.8 kilometres (37.8 mi). The longest distance in one day was 120 kilometres (75 mi), with an average of 14.5 kilometres (9.0 mi).^[27] In a previous study conducted at the center of the Amazon River, a dolphin was observed that moved only a few dozen kilometers from the dry season and wet season. However, three of the reviewed 160 animals were observed over 100 kilometres (62 mi) from where they were first registered.^[14] Research in 2011 concluded that photo-identification by skilled operatives using high-quality digital equipment could be a useful tool in monitoring population size, movements and social patterns.^[28]

Interactions with humans

In captivity

A trained Amazon river dolphin at the Acuario de Valencia

The Amazon river dolphin has historically been kept in dolphinariums. Today, only three exist in captivity: one in Acuario de Valencia in Venezuela, one in Zoologico de Guistochoca in Peru, and one in Duisburg Zoo in Germany. Several hundred were captured between the 1950s and 1970s, and were distributed in dolphinariums throughout the US, Europe, and Japan. Around 100 went to US dolphinariums, and of that, only 20 survived; the last died at the Pittsburgh Zoo in 2002.^[16]

Threats

The region of the Amazon in Brazil has an extension of 5,000,000 km² (1,900,000 sq mi) containing diverse fundamental ecosystems.^[29][30] One of these ecosystems is a floodplain, or a várzea forest, and is home to a large number of fish species which are an essential resource for human consumption.^[31] The várzea is also a major source of income through excessive local commercialized fishing.^[29][32][33] Várzea consists of muddy river waters containing a vast number and diversity of nutrient rich species.^[22] The abundance of distinct fish species lures the Amazon River dolphin into the várzea areas of high water occurrences during the seasonal flooding.^[34]
In addition to attracting predators such as the Amazon river dolphin, these high-water occurrences are an ideal location to draw in the local fisheries. Human fishing activities directly compete with the dolphins for the same fish species, the tambaqui (Colossoma macropomum) and the pirapitinga (Piaractus brachypomus), resulting in deliberate or unintentional catches of the Amazon river dolphin.^{[35][36][37][29][38][39][40][41]} The local fishermen overfish and when the Amazon River dolphins remove the commercial catch from the nets and lines, it causes damages to the equipment and the capture, as well as generating ill will from the local fishermen.^{[37] [39][40]} The negative reactions of the local fishermen are also attributed to the Brazilian Institute of Environment and Renewable Natural Resources prohibition on killing the Amazon river dolphin, yet not compensating the fishermen for the damage done to their equipment and catch.^[41]
During the process of catching the commercialized fish, the Amazon river dolphins get caught in the nets and exhaust themselves until they die, or the local fishermen deliberately kill the entangled dolphins.^[31] The carcasses are discarded, consumed, or used as bait to attract a scavenger catfish, the piracatinga (Calophysus macropterus).^[31][42] The use of the Amazon river dolphin carcass as bait for the piracatinga dates back to 2000.^[42] Increasing demand for the piracatinga has created a market for distribution of the Amazon river dolphin carcasses to be used as bait throughout these regions.^[41]
Of the 15 dolphin carcasses found in the Japurá River in 2010–2011 surveys, 73% of the dolphins were killed for bait, disposed of, or abandoned in entangled gillnets.^[31] The data do not fully represent the actual overall number of deaths of the Amazon river dolphins, whether accidental or intentional, because a variety of factors make it extremely complicated to record and medically examine all the carcasses.^[31][36][39] Scavenger species feed upon the carcasses, and the complexity of the river currents make it nearly impossible to locate all of the dead animals.^[31] More importantly, the local fishermen do not report these deaths out of fear that a legal course of action will be taken against them,^[31] as the Amazon river dolphin and other cetaceans are protected under a Brazilian federal law prohibiting any takes, harassments, and kills of the species.^[43]

Conservation

In 2008, the International Whaling Commission (IWC) expressed concern for captured botos for use as bait in the Central Amazon, which is an emerging problem that has spread on a large scale. The species is listed in Appendix II of the Convention on International Trade in Endangered Species Fauna and Flora (CITES), and Appendix II of the Convention on the Conservation of Migratory Species of Wild Animals,^[44] because it has an unfavorable conservation status or would benefit significantly from international co-operation organized by tailored agreements.
According to a previous assessment by the Scientific Committee of the International Whaling Commission in 2000, the population of botos appears great and there is little or no evidence of population decline in numbers and range. However, increased human intervention on their habitat is expected to, in the future, be the most likely cause of the decline of its range and population. A series of recommendations were issued to ensure proper follow-up to the species, among which is the implementation and publication of studies on the structure of populations, making a record of the distribution of the species, information about potential threats as the magnitude of fishing operations and location of pipelines.^[45]
In September 2012, Bolivian President Evo Morales enacted a law to protect the dolphin and declared it a national treasure.^[16][46]
In 2008, the species was listed on the Red list of endangered species, but in 2011, the IUCN stated it as Data Deficient (DD).^[1] The species was previously listed as "vulnerable" but the conservation status changed due to the limited amount of currently available information on threats, ecology, and population trends. In areas where these dolphins have been studied, they appear well extended and relatively abundant. However, these areas represent only a small proportion of the total distribution of the species and are often sites where the animals are protected. Consequently, the information from these areas may not be representative, and may not be valid in the long term.^[1]
Increasing pollution and gradual destruction of the Amazon rainforest add to the vulnerability of the species. The biggest threats are deforestation and other human activities that contribute to disrupt and alter their environment.^[4] Another source of concern is the difficulty in keeping these animals alive in captivity, due to intra-species aggression and low longevity. Captive breeding is not considered a conservation option for this species.^[47]

In mythology

Main article: Encantado (mythology)

In traditional Amazon River folklore, at night, an Amazon river dolphin becomes a handsome young man who seduces girls, impregnates them, and then returns to the river in the morning to become a dolphin again. Similarly, the female becomes a beautiful, well - dressed,wealthy - looking and young woman. She goes to the house of a married man, places him under a spell to keep him quiet, and takes him to a thatched hut and visits him every year on the same night she seduced him. On the 7th night of visiting, she changes the man into a female - baby or male, and soon transfers it into his own wife's womb. The mythology is said to be the cycle of a baby. This dolphin shapeshifter is called an encantado. The myth has been suggested to have arisen partly because dolphin genitalia bear a resemblance to those of humans. Others believe the myth served (and still serves) as a way of hiding the incestuous relations which are quite common in some small, isolated communities along the river.^[48] In the area, tales relate it is bad luck to kill a dolphin. Legend also states that if a person makes eye contact with an Amazon river dolphin, he or she will have lifelong nightmares. Local legends also state that the dolphin is the guardian of the Amazonian manatee, and that if one should wish to find a manatee, one must first make peace with the dolphin.
Associated with these legends is the use of various fetishes, such as dried eyeballs and genitalia.^[48] These may or may not be accompanied by the intervention of a shaman. A recent study has shown, despite the claim of the seller and the belief of the buyers, none of these fetishes is derived from the boto. They are derived from Sotalia guianensis, are most likely harvested along the coast and the Amazon River delta, and then are traded up the Amazon River. In inland cities far from the coast, many, if not most, of the fetishes are derived from domestic animals such as sheep and pigs.^[49]

Gallery

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  Amazon river dolphin skull (Inia geoffrensis)
  
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  Heart of the Amazon river dolphin
  
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  Amazon river dolphin (Inia geoffrensis)
  
  
  
  Amazon river dolphin range 
  
  
  
  

THE COMMON BOTTLENOSE DOLPHINS

The common bottlenose dolphin (Tursiops truncatus), or Atlantic bottlenose dolphin, is the most well-known species from the family Delphinidae.
Common bottlenose dolphins are the most familiar dolphins due to the wide exposure they receive in captivity in marine parks and dolphinaria, and in movies and television programs.^[4] The common bottlenose dolphin is the largest species of the beaked dolphins.^[5] They inhabit temperate and tropical oceans throughout the world, and are absent only from polar waters.^{[4][5][6][2][7]} Until recently, all bottlenose dolphins were considered as a single species, but now the Indo-Pacific bottlenose dolphin^[2][7] and Burrunan dolphin have been split from the common bottlenose dolphin.^[3][8] While formerly named simply as the bottlenose dolphin, this term is now applied to the genus as a whole.^[1][9][10] The dolphins inhabit warm and temperate seas worldwide. As considerable genetic variation has been described among members of this species, even between neighboring populations, many experts consider that additional species may be recognized.^[3][9]

 

Description

The common bottlenose dolphin is grey in color and may be between 2 and 4 m (6.6 and 13.1 ft) long, and weighs between 150 and 650 kg (330 and 1,430 lb).^[8] Males are generally larger and heavier than females. In most parts of the world, the adult's length is between 2.5 and 3.5 m (8.2 and 11.5 ft) with weight ranging between 200 and 500 kg (440 and 1,100 lb).^[5][9] Newborn calves are between 0.8 and 1.4 m (2 ft 7 in and 4 ft 7 in) long and weigh between 15 and 30 kg (33 and 66 lb).^[9] They can live as long as 40–50 years.^[11] Sexual maturity varies by population, and ranges from 5–14 years of age.^[11] Dolphins have a short and well-defined snout that looks like an old-fashioned gin bottle, which is the source for their common name.^[12] Like all whales and dolphins, though, the snout is not a functional nose; the nose has instead evolved into the blowhole on the top of their heads. Their necks are more flexible than other dolphins' due to five of their seven vertebrae not being fused together as is seen in other dolphin species.^[13]

Behavior

K-Dog, trained by the US Navy to find mines and boobytraps underwater, leaping out of the water

Common bottlenose dolphins live in groups called pods that typically number about 15 individuals, but group size varies from pairs of dolphins to over 100 or even occasionally over 1000 animals for short periods of time.^[9] Their diets consist mainly of eels, squid, shrimp and wide variety of fishes.^[1][6] They do not chew their food, instead swallowing it whole. Dolphin groups often work as a team to harvest schools of fish, though they also hunt individually. Dolphins search for prey primarily using echolocation, which is a form of sonar. They emit clicking sounds and listen for the return echoes to determine the location and shape of nearby items, including potential prey.^[14] Dolphins also use sound for communication, including squeaks emitted from the blowhole, whistles emitted from nasal sacs below the blowhole, and sounds emitted through body language, such as leaping from the water and slapping their tails on the water. Their heads contain an oily substance that both acts as an acoustic lens and protects the brain case.

Life expectancy

Common bottlenose dolphins typically live to be around 25 years old, in captivity they have been known to live to around 50.

Distribution

The common bottlenose dolphin can be found in the temperate, subtropical and tropical oceans worldwide.^[15] Some bottlenose populations live closer to the shore (inshore populations) and others live further out to sea (offshore populations). Generally, offshore populations are larger, darker, and have proportionally shorter fins and beaks. Offshore populations can migrate up to 4,200 km (2,600 mi) in a season, but inshore populations tend to move less. However, some inshore populations make long migrations in response to El Niño events.^[9] The species has occurred as far as 50° north in eastern Pacific waters, possibly as a result of warm water events.^[16] The coastal dolphins appear to adapt to warm, shallow waters. It has a smaller body and larger flippers, for maneuverability and heat dispersal. They can be found in harbors, bays, lagoons and estuaries. Offshore dolphins, however, are adapted to cooler, deeper waters. Certain qualities in its blood, suggest it is more suited to deep diving. Its considerably larger body protects it against predators and helps it retain heat.^[17]

Intelligence

Main article: Cetacean intelligence

The common bottlenose dolphin has a bigger brain than humans.^[18] Numerous investigations of bottlenose dolphin intelligence include tests of mimicry, use of artificial language, object categorization, and self-recognition.^{[19][20][21][22][23][24]} This intelligence has driven considerable interaction with humans. Common bottlenose dolphins are popular in aquarium shows and television programs such as Flipper.^[25] They have also been trained for military uses such as locating sea mines or detecting and marking enemy divers, as for example in the U.S. Navy Marine Mammal Program.^[26][27] In some areas, they cooperate with local fishermen by driving fish toward the fishermen and eating the fish that escape the fishermen's nets.^[28]

Other human interactions

This is "Biskit", a three months fetus, removed from its deceased mother during post mortem in 1993 and now on display at the Dolphin Discovery Centre in Bunbury, South West (Western Australia)

Five dolphins jumping in show.

Some interactions with humans are harmful to the dolphins. Dolphin hunting industry exists in multiple countries including Japan, where common bottlenose dolphins are hunted for food annually in the town of Taiji,^[29] and the Faroe Islands. Also, dolphins are sometimes killed inadvertently as a bycatch of tuna fishing.^[30][31]
Tião was a well-known solitary male bottlenose dolphin that was first spotted in the town of São Sebastião in Brazil around 1994 and frequently allowed humans to interact with it. The dolphin later became infamous for killing a swimmer and injuring many others, which earned it the nickname of killer dolphin.

Conservation

The North Sea, Baltic, Mediterranean and Black Sea populations of the common bottlenose dolphin are listed on Appendix II^[32] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS) of the Bonn Convention), since they have an unfavorable conservation status or would benefit significantly from international cooperation organized by tailored agreements.^[33]
The species is covered by the Agreement on Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas (ASCOBANS), the Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and Contiguous Atlantic Area (ACCOBAMS), the Memorandum of Understanding for the Conservation of Cetaceans and Their Habitats in the Pacific Islands Region,^[34] and the Memorandum of Understanding Concerning the Conservation of the Manatee and Small Cetaceans of Western Africa and Macaronesia.^[35]

Marine pollution

 


Bottle nosed dolphins are the most common apex predators found in coastal and estuarine ecosystems along the southern coast of the USA^[36] , thus serve as an important indicator species of bioaccumulation and health of the ecosystem.
Dense human development along the eastern coast of Florida and intense agricultural activity have resulted in increased freshwater inputs, changes in drainage patterns, and altered water quality (i.e. chemical contamination, high nutrient input, decreased salinity, decreased sea grass habitat, and eutrophication^[37] Demand for an increasing population among the Gulf Coast increases the need for oil and gas exploration and can also cause detrimental effects on the ecosystem and future population of top predators.
It is believed that some diseases commonly found in dolphins are related to human behaviors, such as water pollution. Water pollution is linked to point and non-point source pollution. Point source pollution comes from a single source such as an oil spill^[38],and/or chemical discharge from a specific facility. The Environment impact of the Deepwater Horizon oil spill^[39], caused a direct impact and still serves as a long term impact of future populations. Bottle nose dolphins use these important habitats for calving, foraging, and feeding. Environmental impacts or changes from chemicals or marine pollution can alter and disrupt endocrine systems, effecting future populations. For example, oil spills have been related to lung and reproductive diseases in female dolphins. A recent study,^[40] suggested signs of lung disease and impaired stress in 32 dolphins that were captured and assessed in Barataria Bay, Louisiana, USA. Out of these 32 dolphins, 10 were found pregnant and upon a 47 month check up, only 20% produced feasible calves, compared to a previous success rate of 83%, in the same area. It is believed that a recent oil spill in this area, is partially to blame for these severely low numbers.

Dense human development along the eastern coast of Florida and intense agricultural activity have resulted in increased freshwater inputs, changes in drainage patterns, and altered water quality (i.e. chemical contamination, high nutrient input, decreased salinity, decreased sea grass habitat, and eutrophication^[41] High nutrient input from agriculture chemicals and fertilizers causes Eutrophication^[42], and hypoxia, causing a severe reductions in water quality. Excess of phosphorus and nitrogen from these non-point sources deplete the natural cycle of oxygen by overconsumption of algae. Harmful algal blooms are responsible for dead zones and unusual mortality events of bottlenose dolphins consuming these toxic fish from the brevetoxin produced by dinoflagellate, Karenia brevis. ^[43] Brevetoxins are neurotoxins that can cause acute respiratory and neurological symptoms including death in marine mammals, sea turtles, birds, and fishes.^[44] 





Common bottlenose dolphin range (in blue)

THE MARINE MAMMALS

Marine mammals are aquatic mammals that rely on the ocean and other marine ecosystems for their existence. They include animals such as seals, whales, manatees, sea otters and polar bears. They do not represent a distinct taxon or systematic grouping, but rather have a polyphyletic relation due to convergent evolution, as in they do not have an immediate common ancestor. They are also unified by their reliance on the marine environment for feeding.
Marine mammal adaptation to an aquatic lifestyle varies considerably between species. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Seals and sea-lions are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating, breeding and molting. In contrast, both otters and the polar bear are much less adapted to aquatic living. Their diet varies considerably as well; some may eat zooplankton, others may eat fish, squid, shellfish, sea-grass and a few may eat other mammals. While the number of marine mammals is small compared to those found on land, their roles in various ecosystems are large, especially concerning the maintenance of marine ecosystems, through processes including the regulation of prey populations. This role in maintaining ecosystems makes them of particular concern as 23% of marine mammal species are currently threatened.
Marine mammals were first hunted by aboriginal peoples for food and other resources. Many were also the target for commercial industry, leading to a sharp decline in all populations of exploited species, such as whales and seals. Commercial hunting lead to the extinction of †Steller's sea cow and the †Caribbean monk seal. After commercial hunting ended, some species, such as the gray whale and northern elephant seal, have rebounded in numbers; conversely, other species, such as the North Atlantic right whale, are critically endangered. Other than hunting, marine mammals can be killed as bycatch from fisheries, where they become entangled in fixed netting and drown or starve. Increased ocean traffic causes collisions between fast ocean vessels and large marine mammals. Habitat degradation also threatens marine mammals and their ability to find and catch food. Noise pollution, for example, may adversely affect echolocating mammals, and the ongoing effects of global warming degrade arctic environments.

 A humpback whale (Megaptera novaeangliae), a member of infraorder Cetacea of the order Cetartiodactyla

Taxonomy

Marine mammals of varying sizes and shapes

A polar bear (Ursus maritimus), a member of family Ursidae.

A sea otter (Enhydra lutris), a member of family Mustelidae.

California sea lions (Zalophus californianus), members of the family Otariidae.

A West Indian manatee (Trichechus manatus), a member of order Sirenia.

A common minke whale (Balaenoptera acutorostrata), a member of the order Cetartiodactyla.

Classification of extant species

Phylogeny of marine mammals

Mammalia Afrotheria Hyracoidea Procaviidae Tethytheria Proboscidea Elephantidae Sirenia Dugongidae (dugongs) Trichechidae Trichechus manatus (West Indian manatee) Trichechus senegalensis (African manatee) Trichechus inunguis (Amazonian manatee; freshwater species) Laurasiatheria Euungulata Cetartiodactyla Whippomorpha Hippopotamidae Cetacea Mysticeti (baleen whales) Odontoceti (toothed whales, except river dolphins) Ruminantia Perissodactyla Ferae Pholidota Carnivora Feliformia Caniformia Canidae Arctoidea Ursidae Ursus maritimus (polar bear) all other ursids Mustelidae Enhydra lutris (sea otter) Lontra felina (marine otter) †Neovison macrodon (sea mink) all other mustelids Pinnipedia Otariidae (eared seals) Odobenidae (walruses) Phocidae (earless seals)

The taxa in bold are marine.[1]

Main article: List of marine mammal species

• Order Cetartiodactyla^[2]
  • Suborder Whippomorpha
    • Family Balaenidae (right and bowhead whales), two genera and four species
    • Family Cetotheriidae (pygmy right whale), one species
    • Family Balaenopteridae (rorquals), two genera and eight species
    • Family Eschrichtiidae (gray whale), one species
    • Family Physeteridae (sperm whale), one species
    • Family Kogiidae (pygmy and dwarf sperm whales), one genus and two species
    • Family Monodontidae (narwhal and beluga), two genera and two species
    • Family Ziphiidae (beaked whales), six genera and 21 species
    • Family Delphinidae (oceanic dolphins), 17 genera and 38 species
    • Family Phocoenidae (porpoises), two genera and seven species
• Order Sirenia (sea cows)^[2]
  • • Family Trichechidae (manatees), two species
    • Family Dugongidae (dugongs), one species
• Order Carnivora (carnivores)^[2]
  • Suborder Caniformia
    • Family Mustelidae, three species
    • Family Ursidae (bears), one species
  • Suborder Pinnipedia (sealions, walruses, seals)
    • Family Otariidae (eared seals), seven genera and 15 species
    • Family Odobenidae (walrus), one species
    • Family Phocidae (earless seals), 14 genera and 18 species
• Order Chiroptera
  • Family Vespertilionidae
    • Myotis vivesi (fish-eating bat)^[3]

Evolution

Illustration of †Prorastomus, an early sirenian (40 mya)

Marine mammals form a diverse group of 129 species that rely on the ocean for their existence.^[4][5] They do not represent a distinct taxon or systematic grouping, but instead have a polyphyletic relationship. They are also unified by their reliance on the marine environment for feeding.^[6] Despite the diversity in morphology seen between groups, improved foraging efficiency has been the main driver in their evolution.^[7][8] The level of dependence on the marine environment for existence varies considerably with species. For example, dolphins and whales are completely dependent on the marine environment for all stages of their life; seals feed in the ocean but breed on land; and polar bears must feed on land.^[6] Twenty three percent of marine mammal species are threatened.^[9][10]
The cetaceans became aquatic around 50 million years ago (mya).^[11] Based on molecular and morphological research, the cetaceans genetically and morphologically fall firmly within the Artiodactyla (even-toed ungulates).^[12][13] The term "Cetartiodactyla" reflects the idea that whales evolved within the ungulates. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. Under this definition, the closest living land relative of the whales and dolphins is thought to be the hippopotamuses.^{[14][15][16][17]}
Sirenians, the sea cows, became aquatic around 40 million years ago. The first appearance of sirenians in the fossil record was during the early Eocene, and by the late Eocene, sirenians had significantly diversified. Inhabitants of rivers, estuaries, and nearshore marine waters, they were able to spread rapidly. The most primitive sirenian, †Prorastomus, was found in Jamaica,^[8] unlike other marine mammals which originated from the Old World (such as cetaceans^[18]). The first known quadrupedal sirenian was †Pezosiren from the early Eocene.^[19] The earliest known sea cows, of the families †Prorastomidae and †Protosirenidae, were both confined to the Eocene, and were pig-sized, four-legged, amphibious creatures.^[20] The first members of Dugongidae appeared by the end of the Eocene.^[21] At this point, sea cows were fully aquatic.^[20]
Pinnipeds split from other caniforms 50 mya during the Eocene. Their evolutionary link to terrestrial mammals was unknown until the 2007 discovery of †Puijila darwini in early Miocene deposits in Nunavut, Canada. Like a modern otter, †Puijila had a long tail, short limbs and webbed feet instead of flippers.^[22] The lineages of Otariidae (eared seals) and Odobenidae (walrus) split almost 28 mya.^[23] Phocids (earless seals) are known to have existed for at least 15 mya,^[24] and molecular evidence supports a divergence of the Monachinae (monk seals) and Phocinae lineages 22 mya.^[23]
Fossil evidence indicates the sea otter (Enhydra) lineage became isolated in the North Pacific approximately two mya, giving rise to the now-extinct †Enhydra macrodonta and the modern sea otter, Enhydra lutris. The sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands, mainland Alaska, and down the North American coast. In comparison to cetaceans, sirenians, and pinnipeds, which entered the water approximately 50, 40, and 20 mya, respectively, the sea otter is a relative newcomer to marine life. In some respects though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth.^[25]
Polar bears are thought to have diverged from a population of brown bears, Ursus arctos, that became isolated during a period of glaciation in the Pleistocene^[26] or from the eastern part of Siberia, (from Kamchatka and the Kolym Peninsula).^[27] The oldest known polar bear fossil is a 130,000 to 110,000-year-old jaw bone, found on Prince Charles Foreland in 2004.^[28] The mitochondrial DNA (mtDNA) of the polar bear diverged from the brown bear roughly 150,000 years ago.^[28] Further, some clades of brown bear, as assessed by their mtDNA, are more closely related to polar bears than to other brown bears,^[29] meaning that the polar bear might not be considered a species under some species concepts.^[30]
In general, terrestrial amniote invasions of the sea have become more frequent in the Cenozoic than they were in the Mesozoic. Factors contributing to this trend include the increasing productivity of near-shore marine environments, and the role of endothermy in facilitating this transition.^[31]

Distribution and habitat

Marine mammal species richness: A) All species (n = 115), B) Odontocetes (n = 69), C) Mysticetes (n = 14), D) Pinnipeds (n = 32), based on data from 1990–1999^[32]

Marine mammals are widely distributed throughout the globe, but their distribution is patchy and coincides with the productivity of the oceans.^[33] Species richness peaks at around 40° latitude, both north and south. This corresponds to the highest levels of primary production around North and South America, Africa, Asia and Australia. Total species range is highly variable for marine mammal species. On average most marine mammals have ranges which are equivalent or smaller than one-fifth of the Indian Ocean.^[9] The variation observed in range size is a result of the different ecological requirements of each species and their ability to cope with a broad range of environmental conditions. The high degree of overlap between marine mammal species richness and areas of human impact on the environment is of concern.^[4]
Most marine mammals, such as seals and sea otters, inhabit the coast. Seals, however, also use a number of terrestrial habitats, both continental and island. In temperate and tropical areas, they haul-out on to sandy and pebble beaches, rocky shores, shoals, mud flats, tide pools and in sea caves. Some species also rest on man-made structures, like piers, jetties, buoys and oil platforms. Seals may move further inland and rest in sand dunes or vegetation, and may even climb cliffs.^[34]:96 Most cetaceans live in the open ocean, and species like the sperm whale may dive to depths of −1,000 to −2,500 feet (−300 to −760 m) in search of food.^[35] Sirenians live in shallow coastal waters, usually living 30 feet (9.1 m) below sea level. However, they have been known to dive to −120 feet (−37 m) to forage deep-water seagrasses.^[36] Sea otters live in protected areas, such as rocky shores, kelp forests, and barrier reefs,^[37] although they may reside among drift ice or in sandy, muddy, or silty areas.^[38]
Many marine mammals seasonally migrate. Annual ice contains areas of water that appear and disappear throughout the year as the weather changes, and seals migrate in response to these changes. In turn, polar bears must follow their prey. In Hudson Bay, James Bay, and some other areas, the ice melts completely each summer (an event often referred to as "ice-floe breakup"), forcing polar bears to go onto land and wait through the months until the next freeze-up. In the Chukchi and Beaufort seas, polar bears retreat each summer to the ice further north that remains frozen year-round.^[39] Seals may also migrate to other environmental changes, such as El Niño, and traveling seals may use various features of their environment to reach their destination including geomagnetic fields, water and wind currents, the position of the sun and moon and the taste and temperature of the water.^{[34]:256–257} Baleen whales famously migrate very long distances into tropical waters to give birth and raise young,^[40] possibly to prevent predation by killer whales.^[41] The gray whale has the longest recorded migration of any mammal, with one traveling 14,000 miles (23,000 km) from the Sea of Okhotsk to the Baja Peninsula.^[42] During the winter, manatees living at the northern end of their range migrate to warmer waters.^[43]

Adaptations

Further information: Aquatic locomotion

The anatomy of a dolphin showing its skeleton, major organs, and body shape

Marine mammals have a number of physiological and anatomical features to overcome the unique challenges associated with aquatic living. Some of these features are very species specific. Marine mammals have developed a number of features for efficient locomotion such as torpedo shaped bodies to reduce drag; modified limbs for propulsion and steering; tail flukes and dorsal fins for propulsion and balance.^[33] Marine mammals are adept at thermoregulation using dense fur or blubber, circulatory adjustments (counter-current heat exchangers); torpedo shaped bodies, reduced appendages, and large size to prevent heat loss.^[33]
Marine mammals are able to dive for long periods of time. Both pinnipeds and cetaceans have large and complex blood vessel systems which serve to store oxygen to support deep diving. Other important reservoirs include muscles, blood, and the spleen which all have the capacity to hold a high concentration of oxygen. They are also capable of bradycardia (reduced heart rate), and vasoconstriction (shunting most of the oxygen to vital organs such as the brain and heart) to allow extended diving times and cope with oxygen deprivation.^[33] If oxygen is depleted, marine mammals can access substantial reservoirs of glycogen that support anaerobic glycolysis of the cells involved during conditions of systemic hypoxia associated with prolonged submersion.^[44][45][46]
Sound travels differently through water, and therefore marine mammals have developed adaptations to ensure effective communication, prey capture, and predator detection.^[47] The most notable adaptation is the development of echolocation in whales and dolphins.^[33] Toothed whales emit a focused beam of high-frequency clicks in the direction that their head is pointing. Sounds are generated by passing air from the bony nares through the phonic lips.^{[48]:p. 112} These sounds are reflected by the dense concave bone of the cranium and an air sac at its base. The focused beam is modulated by a large fatty organ known as the 'melon'. This acts like an acoustic lens because it is composed of lipids of differing densities.^[48]:121[49]
Marine mammals have evolved a wide variety of features for feeding, which are mainly seen in their dentition. For example, the cheek teeth of pinnipeds and odontocetes are specifically adapted to capture fish and squid. In contrast, baleen whales have evolved baleen plates to filter feed plankton and small fish from the water.^[33]
Polar bears, otters, and fur seals have fur, one of the defining mammalian features, that is long, oily, and waterproof in order to trap air to provide insulation. In contrast, other marine mammals – such as whales, dolphins, porpoises, manatees, dugongs, and walruses – have lost long fur in favor of a thick, dense epidermis and a thickened fat layer (blubber) in response to hydrodynamic requirements. Wading and bottom-feeding animals (such as manatees) need to be heavier than water in order to keep contact with the floor or to stay submerged. Surface-living animals (such as sea otters) need the opposite, and free-swimming animals living in open waters (such as dolphins) need to be neutrally buoyant in order to be able to swim up and down the water column. Typically, thick and dense bone is found in bottom feeders and low bone density is associated with mammals living in deep water. Some marine mammals, such as polar bears and otters, have retained four weight-bearing limbs and can walk on land like fully terrestrial animals.^[50]

Ecology

Diet

Killer whale hunting a Weddel seal

All cetaceans are carnivorous and predatory. Toothed whales mostly feed on fish and cephalopods, followed by crustaceans and bivalves. Some may forage with other kinds of animals, such as other species of whales or certain species of pinnipeds.^[34]:169[51] One common feeding method is herding, where a pod squeezes a school of fish into a small volume, known as a bait ball. Individual members then take turns plowing through the ball, feeding on the stunned fish.^[52] Coralling is a method where dolphins chase fish into shallow water to catch them more easily.^[52] Killer whales and bottlenose dolphins have also been known to drive their prey onto a beach to feed on it.^[53][54] Other whales with a blunt snout and reduced dentition rely on suction feeding.^[55] Though carnivorous, they house gut flora similar to that of terrestrial herbivores, probably a remnant of their herbivorous ancestry.^[56]
Baleen whales use their baleen plates to sieve plankton, among others, out of the water; there are two types of methods: lunge-feeding and gulp-feeding. Lunge-feeders expand the volume of their jaw to a volume bigger than the original volume of the whale itself by inflating their mouth. This causes grooves on their throat to expand, increasing the amount of water the mouth can store.^[57][58] They ram a baitball at high speeds in order to feed, but this is only energy-effective when used against a large baitball.^[59] Gulp-feeders swim with an open mouth, filling it with water and prey. Prey must occur in sufficient numbers to trigger the whale's interest, be within a certain size range so that the baleen plates can filter it, and be slow enough so that it cannot escape.^[60]

Sea otters have dexterous hands which they use to smash sea urchins off rocks.

Otters are the only marine animals that are capable of lifting and turning over rocks, which they often do with their front paws when searching for prey.^[61] The sea otter may pluck snails and other organisms from kelp and dig deep into underwater mud for clams.^[61] It is the only marine mammal that catches fish with its forepaws rather than with its teeth.^[62] Under each foreleg, sea otters have a loose pouch of skin that extends across the chest which they use to store collected food to bring to the surface. This pouch also holds a rock that is used to break open shellfish and clams, an example of tool use.^[63] The sea otters eat while floating on their backs, using their forepaws to tear food apart and bring to their mouths.^[64][65] Marine otters mainly feed on crustaceans and fish.^[66]
Pinnipeds mostly feed on fish and cephalopods, followed by crustaceans and bivalves, and then zooplankton and warm-blooded prey (like sea birds).^[34]:145 Most species are generalist feeders, but a few are specialists.^[67] They typically hunt non-schooling fish, slow-moving or immobile invertebrates or endothermic prey when in groups. Solitary foraging species usually exploit coastal waters, bays and rivers. When large schools of fish or squid are available, pinnipeds hunt cooperatively in large groups, locating and herding their prey. Some species, such as California and South American sea lions, may forage with cetaceans and sea birds.^[34]:168
The polar bear is the most carnivorous species of bear, and its diet primarily consists of ringed (Pusa hispida) and bearded (Erignathus barbatus) seals.^[68] Polar bears hunt primarily at the interface between ice, water, and air; they only rarely catch seals on land or in open water.^[69] The polar bear's most common hunting method is still-hunting:^[70] The bear locates a seal breathing hole using its sense of smell, and crouches nearby for a seal to appear. When the seal exhales, the bear smells its breath, reaches into the hole with a forepaw, and drags it out onto the ice. The polar bear also hunts by stalking seals resting on the ice. Upon spotting a seal, it walks to within 100 yards (90 m), and then crouches. If the seal does not notice, the bear creeps to within 30 to 40 feet (9 to 10 m) of the seal and then suddenly rushes to attack.^[71] A third hunting method is to raid the birth lairs that female seals create in the snow.^[70] They may also feed on fish.^[72]

A dugong feeding on the sea-floor

Sirenians are referred to as "sea cows" because their diet consists mainly of sea-grass. When eating, they ingest the whole plant, including the roots, although when this is impossible they feed on just the leaves.^[73] A wide variety of seagrass has been found in dugong stomach contents, and evidence exists they will eat algae when seagrass is scarce.^[74] West Indian manatees eat up to 60 different species of plants, as well as fish and small invertebrates to a lesser extent.^[75]

Keystone species

Further information: Keystone species

Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins, in check. Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens, with abundant sea urchins and no kelp forest.^[76] Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems,^[77] and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California^[65] However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors.^[65] The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries.^[65]

Antarctic fur seal pups (left) vs. Arctic harp seal pup (right)

An apex predator affects prey population dynamics and defense tactics (such as camouflage).^[78] The polar bear is the apex predator within its range.^[79] Several animal species, particularly Arctic foxes (Vulpes lagopus) and glaucous gulls (Larus hyperboreus), routinely scavenge polar bear kills.^[80] The relationship between ringed seals and polar bears is so close that the abundance of ringed seals in some areas appears to regulate the density of polar bears, while polar bear predation in turn regulates density and reproductive success of ringed seals.^[81] The evolutionary pressure of polar bear predation on seals probably accounts for some significant differences between Arctic and Antarctic seals. Compared to the Antarctic, where there is no major surface predator, Arctic seals use more breathing holes per individual, appear more restless when hauled out on the ice, and rarely defecate on the ice.^[80] The fur of Arctic pups is white, presumably to provide camouflage from predators, whereas Antarctic pups all have dark fur.^[80]
Killer whales are apex predators throughout their global distribution, and can have a profound effect on the behavior and population of prey species. Their diet is very broad and they can feed on many vertebrates in the ocean including salmon,^[82] rays, sharks (even white sharks),^[83][84] large baleen whales,^[85] and nearly 20 species of pinniped.^[86] The predation of whale calves may be responsible for annual whale migrations to calving grounds in more tropical waters, where the population of killer whales is much lower than in polar waters. Prior to whaling, it is thought that great whales were a major food source; however, after their sharp decline, killer whales have since expanded their diet, leading to the decline of smaller marine mammals.^[41] A decline in Aleutian Islands sea otter populations in the 1990s was controversially attributed by some scientists to killer whale predation, although with no direct evidence. The decline of sea otters followed a decline in harbor seal and Steller sea lion populations, the killer whale's preferred prey, which in turn may be substitutes for their original prey, now reduced by industrial whaling.^[87][88][89]

Whale pump

Main articles: Whale pump and Whale fall

"Whale pump" – the role played by whales in recycling ocean nutrients^[90]

A 2010 study considered whales to be a positive influence to the productivity of ocean fisheries, in what has been termed a "whale pump". Whales carry nutrients such as nitrogen from the depths back to the surface. This functions as an upward biological pump, reversing an earlier presumption that whales accelerate the loss of nutrients to the bottom. This nitrogen input in the Gulf of Maine is more than the input of all rivers combined emptying into the gulf, some 25,000 short tons (23,000 t) each year.^[90] Whales defecate at the ocean's surface; their excrement is important for fisheries because it is rich in iron and nitrogen. The whale feces are liquid and instead of sinking, they stay at the surface where phytoplankton feed off it.^[90][91]
Upon death, whale carcasses fall to the deep ocean and provide a substantial habitat for marine life. Evidence of whale falls in present-day and fossil records shows that deep sea whale falls support a rich assemblage of creatures, with a global diversity of 407 species, comparable to other neritic biodiversity hotspots, such as cold seeps and hydrothermal vents.^[92] Deterioration of whale carcasses happens though a series of three stages. Initially, moving organisms, such as sharks and hagfish, scavenge soft tissue at a rapid rate over a period of months to as long as two years. This is followed by the colonization of bones and surrounding sediments (which contain organic matter) by enrichment opportunists, such as crustaceans and polychaetes, throughout a period of years. Finally, sulfophilic bacteria reduce the bones releasing hydrogen sulphide enabling the growth of chemoautotrophic organisms, which in turn, support other organisms such as mussels, clams, limpets, and sea snails. This stage may last for decades and supports a rich assemblage of species, averaging 185 species per site.^[93]

Interactions with humans

Threats

Exploitation

Marine mammals were hunted by coastal aboriginal humans historically for food and other resources. These subsistence hunts still occur in Canada, Greenland, Indonesia, Russia, the United States, and several nations in the Caribbean. The effects of these are only localized, as hunting efforts were on a relatively small scale.^[33] Commercial hunting took this to a much greater scale and marine mammals were heavily exploited. This led to the extinction of the †Steller's sea cow (along with subsistence hunting) and the †Caribbean monk seal.^[33] Today, populations of species that were historically hunted, such as blue whales (Balaenoptera musculus) and the North Pacific right whale (Eubalaena japonica), are much lower than their pre-whaling levels.^[94] Because whales generally have slow growth rates, are slow to reach sexual maturity, and have a low reproductive output, population recovery has been very slow.^[47]
A number of whales are still subject to direct hunting, despite the 1986 moratorium ban on whaling set under the terms of the International Whaling Commission (IWC). There are only two nations remaining which sanction commercial whaling: Norway, where several hundred common minke whales are harvested each year; and Iceland, where quotas of 150 fin whales and 100 minke whales per year are set.^[95][96] Japan also harvests several hundred Antarctic and North Pacific minke whales each year, ostensibly for scientific research in accordance with the moratorium.^[94] However, the illegal trade of whale and dolphin meat is a significant market in Japan and some countries.^[97]

Historical and modern range of northern sea otters

The most profitable furs in the fur trade were those of sea otters, especially the northern sea otter which inhabited the coastal waters between the Columbia River to the south and Cook Inlet to the north. The fur of the Californian southern sea otter was less highly prized and thus less profitable. After the northern sea otter was hunted to local extinction, maritime fur traders shifted to California until the southern sea otter was likewise nearly extinct.^[98] The British and American maritime fur traders took their furs to the Chinese port of Guangzhou (Canton), where they worked within the established Canton System. Furs from Russian America were mostly sold to China via the Mongolian trading town of Kyakhta, which had been opened to Russian trade by the 1727 Treaty of Kyakhta.^[99]
Commercial sealing was historically just as important as the whaling industry. Exploited species included harp seals, hooded seals, Caspian seals, elephant seals, walruses and all species of fur seal.^[100] The scale of seal harvesting decreased substantially after the 1960s,^[101] after the Canadian government reduced the length of the hunting season and implemented measures to protect adult females.^[102] Several species that were commercially exploited have rebounded in numbers; for example, Antarctic fur seals may be as numerous as they were prior to harvesting. The northern elephant seal was hunted to near extinction in the late 19th century, with only a small population remaining on Guadalupe Island. It has since recolonized much of its historic range, but has a population bottleneck.^[100] Conversely, the Mediterranean monk seal was extirpated from much of its former range, which stretched from the Mediterranean to the Black Sea and northwest Africa, and only remains in the northeastern Mediterranean and some parts of northwest Africa.^[103]
Polar bears can be hunted for sport in Canada with a special permit and accompaniment by a local guide. This can be an important source of income for small communities, as guided hunts bring in more income than selling the polar bear hide on markets. The United States, Russia, Norway, Greenland, and Canada allow subsistence hunting, and Canada distributes hunting permits to indigenous communities. The selling of these permits is a main source of income for many of these communities. Their hides can be used for subsistence purposes, kept as hunting trophies, or can be bought in markets.^[104][105]

Ocean traffic and fisheries

By-catch is the incidental capture of non-target species in fisheries. Fixed and drift gill nets cause the highest mortality levels for both cetaceans and pinnipeds, however, entanglements in long lines, mid-water trawls, and both trap and pot lines are also common.^[106] Tuna seines are particularly problematic for entanglement by dolphins.^[107] By-catch affects all cetaceans, both small and big, in all habitat types. However, smaller cetaceans and pinnipeds are most vulnerable as their size means that escape once they are entangled is highly unlikely and they frequently drown.^[94] While larger cetaceans are capable of dragging nets with them, the nets sometimes remain tightly attached to the individual and can impede the animal from feeding sometimes leading to starvation.^[94] Abandoned or lost nets and lines cause mortality through ingestion or entanglement.^[108] Marine mammals also get entangled in aquaculture nets, however, these are rare events and not prevalent enough to impact populations.^[109]
Vessel strikes cause death for a number of marine mammals, especially whales.^[94] In particular, fast commercial vessels such as container ships can cause major injuries or death when they collide with marine mammals. Collisions occur both with large commercial vessels and recreational boats and cause injury to whales or smaller cetaceans. The critically endangered North Atlantic right whale is particularly affected by vessel strikes.^[110] Tourism boats designed for whale and dolphin watching can also negatively impact on marine mammals by interfering with their natural behavior.^[111]
The fishery industry not only threatens marine mammals through by-catch, but also through competition for food. Large scale fisheries have led to the depletion of fish stocks that are important prey species for marine mammals. Pinnipeds have been especially affected by the direct loss of food supplies and in some cases the harvesting of fish has led to food shortages or dietary deficiencies,^[112] starvation of young, and reduced recruitment into the population.^[113] As the fish stocks have been depleted, the competition between marine mammals and fisheries has sometimes led to conflict. Large-scale culling of populations of marine mammals by commercial fishers has been initiated in a number of areas in order to protect fish stocks for human consumption.^[114]
Shellfish aquaculture takes up space so in effect creates competition for space. However, there is little direct competition for aquaculture shellfish harvest.^[109] On the other hand, marine mammals regularly take finfish from farms, which creates significant problems for marine farmers. While there are usually legal mechanisms designed to deter marine mammals, such as anti-predator nets or harassment devices, individuals are often illegally shot.^[109]

Habitat loss and degradation

Further information: Marine mammals and sonar and Effects of climate change on marine mammals

Map from the U.S. Geological Survey shows projected changes in polar bear habitat from 2005 to 2095. Red areas indicate loss of optimal polar bear habitat; blue areas indicate gain.

Habitat degradation is caused by a number of human activities. Marine mammals that live in coastal environments are most likely to be affected by habitat degradation and loss. Developments such as sewage marine outfalls, moorings, dredging, blasting, dumping, port construction, hydroelectric projects, and aquaculture both degrade the environment and take up valuable habitat.^[47] For example, extensive shellfish aquaculture takes up valuable space used by coastal marine mammals for important activities such as breeding, foraging and resting.^[109]
Contaminants that are discharged into the marine environment accumulate in the bodies of marine mammals when they are stored unintentionally in their blubber along with energy.^[47] Contaminants that are found in the tissues of marine mammals include heavy metals, such as mercury and lead, but also organochlorides and polycyclic aromatic hydrocarbons.^[47] For example, these can cause disruptive effects on endocrine systems;^[108] impair the reproductive system, and lower the immune system of individuals, leading to a higher number of deaths.^[47] Other pollutants such as oil, plastic debris and sewage threaten the livelihood of marine mammals.^[115]
Noise pollution from anthropogenic activities is another major concern for marine mammals. This is a problem because underwater noise pollution interferes with the abilities of some marine mammals to communicate, and locate both predators and prey.^[116] Underwater explosions are used for a variety of purposes including military activities, construction and oceanographic or geophysical research. They can cause injuries such as hemorrhaging of the lungs, and contusion and ulceration of the gastrointestinal tract.^[94] Underwater noise is generated from shipping, the oil and gas industry, research, and military use of sonar and oceanographic acoustic experimentation. Acoustic harassment devices and acoustic deterrent devices used by aquaculture facilities to scare away marine mammals emit loud and noxious underwater sounds.^[109]
Two changes to the global atmosphere due to anthropogenic activity threaten marine mammals. The first is increases in ultraviolet radiation due to ozone depletion, and this mainly affects the Antarctic and other areas of the southern hemisphere.^[47] An increase in ultraviolet radiation has the capacity to decrease phytoplankton abundance, which forms the basis of the food chain in the ocean.^[117] The second effect of global climate change is global warming due to increased carbon dioxide levels in the atmosphere. Raised sea levels, sea temperature and changed currents are expected to affect marine mammals by altering the distribution of important prey species, and changing the suitability of breeding sites and migratory routes.^[118] The Arctic food chain would be disrupted by the near extinction or migration of polar bears. Arctic sea ice is the polar bear's habitat. It has been declining at a rate of 13% per decade because the temperature is rising at twice the rate of the rest of the world.^[79][119] By the year 2050, up to two-thirds of the world's polar bears may vanish if the sea ice continues to melt at its current rate.^[120]

Protection

Signatory countries of the International Whaling Commission (IWC)

The Marine Mammal Protection Act of 1972 (MMPA) was passed on October 21, 1972 under president Richard Nixon^[121] to prevent the further depletion and possible extinction of marine mammal stocks.^[122]:5 It prohibits the taking ("the act of hunting, killing, capture, and/or harassment of any marine mammal; or, the attempt at such") of any marine mammal without a permit issued by the Secretary.^[122]:10 Authority to manage the MMPA was divided between the Secretary of the Interior through the U.S. Fish and Wildlife Service (Service), and the Secretary of Commerce, which is delegated to the National Oceanic and Atmospheric Administration (NOAA). The Marine Mammal Commission (MMC) was established to review existing policies and make recommendations to the Service and NOAA to better implement the MMPA. The Service is responsible for ensuring the protection of sea otters and marine otters, walruses, polar bears, the three species of manatees, and dugongs; and NOAA was given responsibility to conserve and manage pinnipeds (excluding walruses) and cetaceans.^[122]:7
The 1979 Convention on the Conservation of Migratory Species of Wild Animals (CMS) is the only global organization that conserves a broad range of animals, of which includes marine mammals.^[123][124] Of the agreements made, three of them deal with the conservation of marine mammals: ACCOBAMS, ASCOBANS, and the Wadden Sea Agreement.^[125] In 1982, the United Nations Convention on the Law of the Sea (LOSC) adopted a pollution prevention approach to conservation, which many other conventions at the time also adopted.^[126]
The Agreement on the Conservation of Cetaceans in the Black Sea, Mediterranean Sea and contiguous Atlantic area (ACCOBAMS), founded in 1996, specifically protects cetaceans in the Mediterranean area, and "maintains a favorable status", a direct action against whaling.^[126] There are 23 member states.^[127] The Agreement on the Conservation of Small Cetaceans of the Baltic and North Seas (ASCOBANS) was adopted alongside ACCOBAMS to establish a special protection area for Europe's increasingly threatened cetaceans.^[126] Other anti-whaling efforts include a ten-year moratorium in 1986 by the IWC on all whaling,^[128] and an environmental agreement (a type of international law) the International Convention for the Regulation of Whaling which controlled commercial, scientific, and subsistence whaling.^[129]
The Agreement on the Conservation of Seals in the Wadden Sea, enforced in 1991, prohibits the killing or harassment of seals in the Wadden Sea, specifically targeting the harbor seal population.^[130]
The 1973 Agreement on the Conservation of Polar Bears between Canada, Denmark (Greenland), Norway (Svalbard), the United States, and the Soviet Union outlawed the unregulated hunting of polar bears from aircraft and icebreakers, as well as protecting migration, feeding, and hibernation sites.^[131]
Various non-governmental organizations participate in marine conservation activism, wherein they draw attention to and aid in various problems in marine conservation, such as pollution, whaling, bycatch, and so forth. Notable organizations include the Greenpeace who focus on overfishing and whaling among other things, and Sea Shepherd Conservation Society who are known for taking direct-action tactics to expose illegal activity.^[132]

As food

Pilot whale meat (bottom), blubber (middle) and dried fish (left) with potatoes, Faroe Islands

Main articles: Marine mammals as food, Whale meat, and Seal meat

For thousands of years, indigenous peoples of the Arctic have depended on whale meat. The meat is harvested from legal, non-commercial hunts that occur twice a year in the spring and autumn. The meat is stored and eaten throughout the winter.^[133] The skin and blubber (muktuk) taken from the bowhead, beluga, or narwhal is also valued, and is eaten raw or cooked. Whaling has also been practiced in the Faroe Islands in the North Atlantic since about the time of the first Norse settlements on the islands. Around 1000 long-finned pilot whales are still killed annually, mainly during the summer.^[134][135] Today, dolphin meat is consumed in a small number of countries worldwide, which include Japan^[136][137] and Peru (where it is referred to as chancho marino, or "sea pork").^[138] In some parts of the world, such as Taiji, Japan and the Faroe Islands, dolphins are traditionally considered food, and are killed in harpoon or drive hunts.^[136]
There have been human health concerns associated with the consumption of dolphin meat in Japan after tests showed that dolphin meat contained high levels of methylmercury.^[137][139] There are no known cases of mercury poisoning as a result of consuming dolphin meat, though the government continues to monitor people in areas where dolphin meat consumption is high. The Japanese government recommends that children and pregnant women avoid eating dolphin meat on a regular basis.^[140] Similar concerns exist with the consumption of dolphin meat in the Faroe Islands, where prenatal exposure to methylmercury and PCBs primarily from the consumption of pilot whale meat has resulted in neuropsychological deficits amongst children.^[139]

The Faroe Islands population was exposed to methylmercury largely from contaminated pilot whale meat, which contained very high levels of about 2 mg methylmercury/kg. However, the Faroe Islands populations also eat significant amounts of fish. The study of about 900 Faroese children showed that prenatal exposure to methylmercury resulted in neuropsychological deficits at 7 years of age

— World Health Organization ^[139]

Ringed seals were once the main food staple for the Inuit. They are still an important food source for the people of Nunavut^[141] and are also hunted and eaten in Alaska. Seal meat is an important source of food for residents of small coastal communities.^[142] The seal blubber is used to make seal oil, which is marketed as a fish oil supplement. In 2001, two percent of Canada's raw seal oil was processed and sold in Canadian health stores.^[143]

In captivity

Main article: Marine mammal park

Aquariums

Cetaceans

Performing killer whale at SeaWorld San Diego, 2009

Various species of dolphins are kept in captivity. These small cetaceans are more often than not kept in theme parks and dolphinariums, such as SeaWorld. Bottlenose dolphins are the most common species of dolphin kept in dolphinariums as they are relatively easy to train and have a long lifespan in captivity. Hundreds of bottlenose dolphins live in captivity across the world, though exact numbers are hard to determine.^[144] The dolphin "smile" makes them popular attractions, as this is a welcoming facial expression in humans; however the smile is due to a lack of facial muscles and subsequent lack of facial expressions.^[145]
Organizations such as World Animal Protection and the Whale and Dolphin Conservation Society campaign against the practice of keeping cetaceans, particularly killer whales, in captivity. In captivity, they often develop pathologies, such as the dorsal fin collapse seen in 60–90% of male killer whales. Captives have vastly reduced life expectancies, on average only living into their 20s. In the wild, females who survive infancy live 46 years on average, and up to 70–80 years in rare cases. Wild males who survive infancy live 31 years on average, and up to 50–60 years.^[146] Captivity usually bears little resemblance to wild habitat, and captive whales' social groups are foreign to those found in the wild. Captive life is also stressful due the requirement to perform circus tricks that are not part of wild killer whale behavior, as well as restricting pool size. Wild killer whales may travel up to 100 miles (160 km) in a day, and critics say the animals are too big and intelligent to be suitable for captivity.^[147] Captives occasionally act aggressively towards themselves, their tankmates, or humans, which critics say is a result of stress.^[148] Dolphins are often trained to do several anthropomorphic behaviors, including waving and kissing—behaviors wild dolphins would rarely do.^[149]

Pinnipeds

A sea lion trained to balance a ball on its nose

The large size and playfulness of pinnipeds make them popular attractions. Some exhibits have rocky backgrounds with artificial haul-out sites and a pool, while others have pens with small rocky, elevated shelters where the animals can dive into their pools. More elaborate exhibits contain deep pools that can be viewed underwater with rock-mimicking cement as haul-out areas. The most common pinniped species kept in captivity is the California sea lion as it is abundant and easy to train.^[150] These animals are used to perform tricks and entertain visitors.^[151] Other species popularly kept in captivity include the grey seal and harbor seal. Larger animals like walruses and Steller sea lions are much less common.^[150] Pinnipeds are popular attractions because they are "disneyfied", and, consequently, people often anthropomorphize them with a curious, funny, or playful nature.^[152]
Some organizations, such as the Humane Society of the United States and World Animal Protection, object to keeping pinnipeds and other marine mammals in captivity. They state that the exhibits could not be large enough to house animals that have evolved to be migratory, and a pool could never replace the size and biodiversity of the ocean. They also oppose using sea lions for entertainment, claiming the tricks performed are "exaggerated variations of their natural behaviors" and distract the audience from the animal's unnatural environment.^[153]

Otter

Sea otters can do well in captivity, and are featured in over 40 public aquariums and zoos.^[65] The Seattle Aquarium became the first institution to raise sea otters from conception to adulthood with the birth of Tichuk in 1979, followed by three more pups in the early 1980s.^[154] In 2007, a YouTube video of two cute sea otters holding paws drew 1.5 million viewers in two weeks, and had over 20 million views as of January 2015.^[155][156] Filmed five years previously at the Vancouver Aquarium, it was YouTube's most popular animal video at the time, although it has since been surpassed.^[157] Otters are often viewed as having a "happy family life", but this is an anthropomorphism.^[158]

Sirenians

The oldest manatee in captivity was Snooty,^[159] at the South Florida Museum's Parker Manatee Aquarium in Bradenton, Florida. Born at the Miami Aquarium and Tackle Company on July 21, 1948, Snooty was one of the first recorded captive manatee births. He was raised entirely in captivity,^[160][161] and died at the age of 69.^[162] Manatees can also be viewed in a number of European zoos, such as the Tierpark in Berlin,^[163] the Nuremberg Zoo,^[164] in ZooParc de Beauval in France,^[165] and in the Aquarium of Genoa in Italy.^[166] The River Safari at Singapore features seven of them.^[167]

 

 

 A leopard seal (Hydrurga leptonyx), a member of the clade Pinnipedia of the order Carnivora

Military

A dolphin wearing a locating pinger, performing mine clearance work in the Iraq War

Main articles: United States Navy Marine Mammal Program and Military dolphin

Bottlenose dolphins and California sea lions were used in the United States Navy Marine Mammal Program (NMMP) to detect mines, protect ships from enemy soldiers, and recover objects. The Navy has never trained attack dolphins, as they would not be able to discern allied soldiers from enemy soldiers. There were five marine mammal teams, each purposed for one of the three tasks: MK4 (dolphins), MK5 (sea lions), MK6 (dolphins and sea lions), MK7 (dolphins), and MK8 (dolphins); MK is short for mark. The dolphin teams were trained to detect and mark mines either attached to the seafloor or floating in the water column, because dolphins can use their echolocative abilities to detect mines. The sea lion team retrieved test equipment such as fake mines or bombs dropped from planes usually out of reach of divers who would have to make multiple dives. MK6 protects harbors and ships from enemy divers, and was operational in the Gulf War and Vietnam War. The dolphins would swim up behind enemy divers and attach a buoy to their air tank, so that they would float to the surface and alert nearby Navy personnel. Sea lions would hand-cuff the enemy, and try to outmaneuver their counter-attacks.^[168][169]
The use of marine mammals by the Navy, even in accordance with the Navy's policy, continues to meet opposition. The Navy's policy says that only positive reinforcement is to be used while training the military dolphins, and that they be cared for in accordance with accepted standards in animal care. The inevitable stresses involved in training are topics of controversy, as their treatment is unlike the animals' natural lifestyle, especially towards their confined spaces when not training. There is also controversy over the use of muzzles and other inhibitors, which prevent the dolphins from foraging for food while working. The Navy states that this is to prevent them from ingesting harmful objects, but conservation activists say this is done to reinforce the trainers' control over the dolphins, who hand out food rewards. The means of transportation is also an issue for conservation activists, since they are hauled in dry carriers, and switching tanks and introducing the dolphin to new dolphins is potentially dangerous as they are territorial.^[168][169]