The Web of Life – Marine Mammals

Marine Mammals

Marine mammals came a long way down the evolutionary pike before turning back to the sea.

The Cretaceous extinction event 66 MYA removed many of the large predators from the oceans. Sharks alone remained.

Sea level was high. Many continental shelves were flooded. There were many shallow seas and lagoons.

Thus, conditions offered easy opportunities for adaptation to aquatic life. The potential of nutritious riches beckoned quite a few mammal clades, from rodents to ungulates.

50 MYA, even-toed ungulates from India took to the waters. Over a period of 15 million years, they became the marine mammals known as cetaceans, which includes whales, dolphins, and porpoises. All cetaceans breathe air. Cetacea’s closest living terrestrial relatives are even-toed ungulates, such as deer and the hippopotamus.

Opportunities for a liquid lifestyle are ongoing. 2 rat species in the Congo and Ecuador respectively are in the early stages of adapting to an aquatic existence. Changes in fur and feet are evident. Yet their heritage is still quite apparent.

Marine mammals are gregarious and impressively intelligent. The freedom of the seas has often heightened the joys of conspecific company, most apparently for cetaceans.

Aquatic life makes different demands than on land. The mammals that returned to the ocean brought with them native intelligence that was furthered by their aquatic conversion.


Visitors to commercial oceanariums can only be impressed by the easily learned tricks that humans have forced upon otters, seals, dolphins, and whales to perform. What visitors do not see is the toll that imprisonment takes on the inmates of an oceanarium.

Marine mammals consistently have a high death rate in captivity from sensory and social depravation, and from emotional depression. In the wild, an orca easily roams 200 kilometers a day with family and friends. In a tank, an orca is lucky to travel 90 meters, with another prisoner or 2 in the cell-tank. In the wild, male orca whales live 50–60 years; females 80–90.

At Sea World in San Diego, which has the best track record of keeing marine mammals alive, an orca might last 6 years or less. The record goes to a female captured at 3 years old, lasting 15 years in captivity before succumbing.

It is not unusual for imprisoned orcas to commit suicide by ramming themselves against their concrete enclosures. Infants born in captivity typically die within months.

Sea Otters

Sea otters are the smallest of the marine mammals. They are related to weasels.

Sea otters can walk on land but are quite capable of living exclusively at sea; even giving birth there.

Sea otters live in north Pacific coastal waters 15–23 meters deep, usually within a kilometer of shore. They avoid areas with severe ocean winds. Sea otters prefer areas with a soft seabed that harbors edible fare.

Sea otters have webbed front paws with retractable claws. Their powerful webbed feet function like flippers.

Sea otters are the only marine mammal capable of lifting and turning over rocks on the seabed; a common practice in searching for prey. Sea otters are also the only marine mammal to catch fish with forepaws rather than between the jaws.

Sea otter lung capacity is twice that of any comparable land mammal, letting them dive deep: up to 55 meters.

Not all sea otter’s terrestrial habits washed away by going to sea. They are still territorial during breeding season: from spring to a peak in autumn. Off the California coast, adult males defend patches of kelp forest. To prevent being carried by currents away from his territory while snoozing, a sea otter wraps himself around the end of a kelp strap to anchor himself, then puts his paws over his eyes and goes to sleep.

Whereas sea otters forage alone, they like to rest together in single-sex groups, termed rafts. A raft may comprise 10–100 sea otters. Male rafts tend to be larger than female ones.

During breeding season, adult males patrol the boundaries of their territories to exclude other males. A sense of civility prevails. Fighting is rare.

Adult females, which outnumber males by 5 to 1, move freely among male territories, choosing their mates. Males without their own patch of kelp congregate in large rafts and swim through areas with females seeking a mate.

Sea otters are polygynous, though temporary pair bonding occurs between a female in heat and her mate.

Females may practice embryonic diapause: delaying implantation of the embryo in the uterus. The embryo remains dormant until implanted. Pregnancy lasts 4 months.

Females almost always birth a single pup. Twins occur 2% of the time, in which case only 1 survives. Sea otters typically breed every year.

Sea otters are vocal. The cry of a pup is similar to a seagull. Females coo when content. Males grunt. Frightened or distressed sea otters hiss, whistle, or, in the extreme, scream.

Sea otters are playful and sociable, yet they spend much of their time alone. An adult can care for itself in foraging, grooming, and defense.

Sea otters spend a good part of their day hunting for food. Of the 100 or so different prey that sea otters eat, individuals have their own favorite foods.

Sea otters pluck snails and other snacks from kelp. They burrow into underwater mud for clams.

A sea otter dives to the ocean floor and grabs a sea urchin or mollusk. She then finds a good rock, tucking it under her arm. Otter armpits are fleshy and pouchlike, a natural toolbox. Holding lunch in its mouth, the otter comes to surface. Floating on its back, the otter places the rock on her stomach, and smashes the meal-to-be against it.

Not being a bivalve that needs opening, abalones are ready-to-eat, other than tenaciously clinging to their home rock. A sea otter will get an abalone for takeout by hammering at the abalone’s attachment point with a suitable rock until it comes free. Sea otters retain their favorite tools for reuse later.

In keeping the populations of benthic herbivores in check, sea otters affect their ecosystem in an outsized way. They are keystone species for preventing loss of habitat by kelp eaters, such as sea urchins. North Pacific coast areas bereft of sea otters become urchin barrens: a surfeit of sea urchins graze local kelp forests out of existence.

Sea otter culling of mussels liberates space for species that otherwise would be out-competed. Thus, sea otters promote biodiversity.

Few animals prey upon sea otters, owing to their pungent scent glands, which many predators find distasteful. Orca and sea lions do eat sea otters. Great white sharks are known to take lethal chunks out of sea otters, though there is no evidence that these sharks consider sea otters palatable enough to eat.

Sea otters have the thickest fur of any mammal: 10 times the density of that on a human’s head. That has made their fur valuable to more than themselves. As with so many furry animals, particularly the smaller ones, predation by humans decimated sea otter populations. By the turn of the 20th century they were near extinction. Only belated legal prohibitions saved them. The slaughter of sea otters resulted in urchin barrens along the California coast.


Man had always assumed that he was more intelligent than dolphins because he had achieved so much – the wheel, New York, wars, and so on – while all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man – for precisely the same reasons. ~ English writer Douglas Adams

Dolphins descended 50 MYA from terrestrial hoofed mammals. In the 20th century there were nearly 40 species in the dolphin family across 17 genera. Most species live in particular ocean regions; 5 are river dolphins.

The size range in the dolphin family is considerable. An adult popoto may be 1.2 m, 40 kg. An orca whale grows to 9.5 m, 10 tonnes.

Everything about a dolphin’s graceful body is designed for fast swimming with minimal energy: perfect for pursuing prey. While the well-known bottlenose dolphin has a top speed of 30 km per hour, spotted dolphins go up to 40 km/h, with some of the swiftest are able to sprint at 50 km/h. How exactly dolphins can swim so fast remains a mystery, though it is, of course, a confluence of traits that provide sleek design and economical propulsion.

Dolphins can dive to 300 meters and stay down for 5 or 6 minutes, then surface quickly without getting the bends (dissolved gases in tissues at depth, which can create painful air bubbles when surfacing quickly).

Dolphins are an aquatic analogue of human life, albeit adroitly living in an aquatic world whereas mankind has only despoiled Nature. The ancient Greeks recognized the qualities of dolphin intelligence and sociality. Dolphins were held in high esteem, often featured in frescos, pottery, and coins. Killing a dolphin was punishable by death.

 Intelligence Physiology

Oceanic dolphins have senses of vision, hearing, taste, and touch, but seemingly no sense of smell, as they lack a physical olfactory system beyond the fetal stage. Smell isn’t useful to an air-breathing mammal spending most of its time underwater, with no need to sniff the air. That said, taste typically relies upon smell, so perhaps dolphins smell within the context of taste. Not much is known about the dolphin sense of taste except that individual dolphins have preferences for certain foods, indicating a fine sense of taste.

Dolphin senses are generally quite keen. Dolphins have rather excellent eyesight, both above and below water. Their lens and cornea instantly adjust between water and air. They see almost 360° around them, with a narrow range of high-quality binocular depth perception directly in front, and a small blind spot directly behind.

In their descent dolphins acquired 2 senses suited to their adopted habitat: echolocation and magnetic-field detection. Echolocation provides an accurate means for detecting objects when out of view. Magnetic-field detection facilitates orientation on a scale of thousands of miles. The dolphin mind thus incorporates a confluence of senses into a “vision” for which there is no human equivalent.

Dolphins in the northern hemisphere tend to idly swim in anticlockwise circles, whereas dolphins in the southern hemisphere saunter-swim clockwise. It is likely that dolphins sense the Coriolis force, caused by the Earth’s rotation and the inertia of the mass experiencing the effect. That would be impressive, as the Coriolis effect is quite small, as Earth completely rotates but once a day. The effect would only be noticeable as a subtle motion over a long distance and time. Dolphins idly swim against the Coriolis force.

The dolphin brain has 2 hemispheres, like the human brain, but the dolphin brain has 4 lobes to 3 for a person. The 4th brain lobe processes sensory input, whereas human sensory processing is split hemispherically.

Dolphin brain architecture may facilitate faster mental uptake, and complex assessment beyond human ability, especially considering the nature of sensory input.

Dolphins’ early brain mass to body weight ratio exceeds humans. Humans catch up at 3 to 4 years of age, but dolphins retain a larger brain mass than humans throughout life. The neocortex of the dolphin brain has more convolution than humans.

Dolphins employ differentiated processing in their brain hemispheres, as each hemisphere has a separate blood supply, something exclusive to dolphins. Dolphins can independently move their eyes. Half of their brain sleeps at a time, so they can swim while they snooze.


To say that dolphins are highly intelligent is understatement. Dolphins show a capacity for symbolic logic, including applied mathematics. Dolphins comprehend contextual syntax: that specific sequences may have different meanings for the same linguistic elements.

Dolphins learn the names of many objects, people, and understand symbolic reference to objects not present, and communicate this information. Trained dolphins understand gestural commands to repeat actions in terms of objects or locations, as well as abstract commands, such as to “do something new and different.”

Dolphins readily pick up tool tricks, and rather easily learn complicated gymnastics. A captive dolphin used a broken tile to scrape seaweed from the tank bottom, imitating a diver who had cleaned the tank using a vacuum hose. A 2nd dolphin then copied the 1st dolphin in the same maneuver.

Dolphins will toss seashells and other objects during play. Adult males sometimes throw things to attract the attention of a female.

Dolphins have a beak-like projection from their heads called a rostrum. The rostrum is sensitive, and, like human skin, can be scarred. Dolphins nuzzle each other using their rostrum.

Dolphins are savvy fishers, using a variety of stratagems. They can also be vigorous diggers, burrowing as deep as their pectoral fins on their backs, in search of tasty crustaceans or bottom-dwelling fish.

While digging on the seabed, a dolphin might encounter a stinging fish or cut its rostrum on buried sharp coral. So, before digging, a dolphin finds a suitably sized sponge, and puts it on its rostrum to act as a protective cushion against abrasion. Dolphin mothers teach their daughters to sponge before digging.

Dolphins and whales create bubble nets to catch prey: herding a school of fish into a tighter ball by the diversionary tactic of laying sheets of bubbles, as a feint to cause confusion and fear. Humpback whales are also known to use various bubble pattern techniques, including curtains, clouds, and cylinders as well as nets. Different tactics are culturally transmitted among groups.

Dolphins have a great capacity for imitation. Captive dolphins imitate the sounds found in their environment and the motions of the people which they observe.

A dolphin recognizes itself when looking in a mirror. Like people, dolphins use a mirror to examine themselves, noting marks on their bodies. As with elephants, it took researchers considerable trial and error to devise an experiment that convinced them that dolphins had mirror-test self-awareness.


The social structure and associated behavior of dolphins is unique in the animal kingdom. ~ zoologist Michael Krützen

Dolphins are exceedingly gregarious, forming circles of friends. While dolphins typically swim in pods of 2 to over a dozen, they sometimes merge pods into large groups, and then split off again after minutes or hours, sometimes with different members in different pods. Group sizes are fluid, corresponding with food availability and relative safety from predators.

Though both sexes are highly social, male and female dolphins have different social mores. Females and their calves form bonds of affection that last a lifetime. Young females may return to their natal group, to their mother and other relatives, to rear their calves.

Males form alliance and coalitions: cooperating in group defense and employing numerous feeding strategies that require orchestrated behavior for successful fishing.

Adult males have long-lasting best friends. Adult males and females consort briefly for breeding only.

Dolphins carry on conversations with one another: talking using a variety of vocalizations, combined with a wide range of subtle body language. Dolphins have a “signature whistle” that is its name. Young dolphins learn their family’s signature whistles and adopt portions of it to individually identify themselves. The signature whistle thus comprises both an individual name and a family name (surname).

While females coin their own name, a male commonly adopts his mother’s signature. As males leave their natal group, this naming convention allows brothers of different ages to readily recognize each other as close kin.

Dolphins’ musical skills become more sophisticated as they age; which is to say that dolphins become better conversationalists as they get older.

When dolphin groups meet up that know each other. One dolphin of each group takes the lead and exchanges signature whistles. After some conversation, the groups are likely to merge for a while and renew acquaintances.

Dolphins learn to copy each other’s signature whistle so they can talk about another dolphin who may not be there. To get another’s attention, a dolphin will call by name.

A dolphin can read another dolphin’s emotional state. Their range of senses facilitates this. Echolocation allows a dolphin to sense another’s heart rate.

The way that a dolphin approaches another conveys a message. Coming on from the front or side, especially accompanied by a loud call, is an act of aggression. An approach from an oblique angle is much less threatening.

Tail slaps from a female tells an amorous male that she is not interested. A tail slap at the surface when upside down indicates extreme annoyance. Youngling minders herd their juvenile charges together using tail slaps.

Dolphins sometimes swim in tight formations, watching their neighbors to the side and behind. A head turn from one in the back steers companions in the specified direction.

Dolphin socializing is not done at a distance. Tactile sensation is important.

A mother and her infant will swim along with frequently fleeting touches of pectoral flippers. A mother may summon her child for a rub simply by rapidly rotating her flippers.

2 adults touch flippers when they meet. Friends may swim together with one resting a flipper on the other. Between adults, most touches and rubs are between dolphins of the same sex.

Bottlenose dolphins are the bonobos of the sea: sex is a prolific expression of affection. Bottlenose copulate for sheer enjoyment. Females like sex even when they are not fertile.

“Rostrum rides” are always pleasurable. One dolphin places its beak into the genital slit of its partner, then pushes forward while emitting stimulating sonar clicks.

The genitals of both male and female dolphins are recessed behind genital slits. Females can be recognized by mammary slits on either side of their genital slit.

A bottlenose mother may have melon-to-genital contact with her offspring. A dolphin’s melon is the hump just behind its rostrum.

Dolphins demonstrate empathy, especially toward those of their kind, but also to other species. Stories abound of dolphins helping hapless humans in the water.

Dolphin society is not all chat and compassion. Dolphins establish dominance hierarchies. Males are dominant to females.

Female social standing is a matter of seniority. Older females and their calves occupy the center of a group, with younger, less dominant females relegated toward the periphery.

As with many mammal species, males are more overtly aggressive. Though unusual, a challenging male dolphin may fight so violently as to kill his rival.

Battle scars on the skin are badges of victories. The more scarred a male is, the less likely he is to be challenged to a fight. A scarred male is more attractive to a female as someone who has shown his mettle.

Some dolphin groups mix socially with other species. Bottlenose dolphins have been seen consorting with humpback dolphins, gray whales, right whales, and sperm whales. These associations typically tend to be brief: lasting but a few days. But some are enduring, lasting for years.

Sharks and dolphins are commonly competitors: living off the same prey. Relations between the two are typically respectful, though size matters. A large shark might make a meal of a smaller dolphin. Orcas also have a taste for dolphin meat.

Conversely, a group of humpback dolphins were observed chasing away a 5-meter great white shark off the coast of South Africa. Dolphins readily see off small sharks that come too close.

Sometimes common cause can be found. Pods of pilot whales have been seen off Hawaii, traveling with oceanic whitetip sharks. Whitetip sharks are aggressive but typically slow-moving, albeit well known for their “feeding frenzy” behavior.

The two species are similarly sized: close enough to ensure mutual respect. Whitetips typically run to 3 meters, while adult pilot whales are 5.5–6.5 meters. (Males are a meter longer than females.)


Orca, often mistakenly called killer whales, are actually oceanic dolphins. Populations typically comprise stable matrilineal family groups, termed pods. Orcas are gregarious.

Female orcas hit menopause around 40. Besides humans and elephants, orcas are one of the few mammals that live long past their reproductive years.

Like elephants, orca groups are led by postmenopausal females. Their well-steeped wisdom is appreciated.

Adult male orcas, one of nature’s most effective killers, are mama’s boys at heart: they fare much better when mom is with them. Those whose mother dies are 14 times more likely to perish within a year of mom’s demise. The probable reason is that they love their mothers so much that, for some, the grief of loss is too much to bear.

Both sons and daughters stay with their mothers into adulthood; a closeness unusual for mammals.

Orcas have striking patterns of black and white. Their back side is black, while their belly is striped white with black on the sides and gray saddle patches. They also have white eye blazes. The patterned coloration has various advantages. For one, it may make an orca less recognizable as it moves in for a kill.

Countershading is a common camouflage in many marine species. An object of uniform hue under sunlit skies looks lighter dorsally and darker ventrally. Reversing that pattern lets an animal shed shadows and fade into its surroundings.

The lighter surface with striping also tends to blend when viewed from below. The dark top side merges with the ocean depths when viewed from above.

The flashy patches break up an otherwise predictable contour of an approaching predator. All told, if not camouflaged, the patterning provokes uncertainty as to what is approaching.

The bodily patterns, particularly the striking eye patches, facilitate social behaviors, such as being able to readily see each other, for traveling and attacking in formation.

More generally, the overall patterning provides a means for visual signaling by body gestures. Males and females have different patterning in the genital area which renders the sexes visually distinct. The differences may be significant in courtship and mating.

Orca courtship behaviors are elaborate. They include chasing and splashing, gentle nudging and stroking, visible male erections, and loud percussive fluke and flipper slapping. For all that, mating takes place quickly between orcas in different pods.

The heads and faces of orcas are so contoured for a streamlined life underwater that they are expressionless. But orcas possess an impressive repertoire of ways to convey their feelings.

Communication is facilitated by orcas having keen eyesight and hearing, adapted for their undersea living conditions. Orca employment of echolocation, along with sight and hearing, provide rich mental images. Orca sense of touch is also exquisite.

Postures and gestures tell much: the direction an orca faces, its mouth movements, the shape of its body. Arching its back and assuming an S-shaped posture, which exaggerates its body size, is a threat display.

A dominant orca typically glances at a subordinate before quickly looking away. Subordinate orcas are more likely to stare.

The whites of orca eyes redden with aggression. Other expressions can be read in their eyes.

Orcas lack vocal cords yet they can produce an astonishing variety of sounds: from clicks to whistles to squawks to siren squeals. Pitch, volume, and timbre vary to convey nuances and import. Orca voices are individually identifiable.

All orca sounds are produced via a labyrinth of nasal passages under the blowhole. Orcas uses recycled air to vocalize; hence no bubbles when an orca speaks.

Provincial orcas speak in the pod dialect learned from mother. Transient orcas live in groups with varying membership from time to time. Their language is more in a state of flux, though the entire population shares a fairly uniform vocabulary.

Orcas are an apex predator, as they lack any natural predators. They commonly hunt in groups. Orca hunting techniques and vocalizations are typically group-specific and passed down from one generation to the next.

Transient orcas hunt wary prey, such sea otters, seals, and sea lions. Their hunting requires stealth, and so their conversations on the job are sparse. Transients talk less when foraging than fish-eating locals, who can chat between bites.

Orca mothers have been spotted teaching their children how to beach themselves and then escape on the next wave. This skill can let an orca snag something near the shoreline, such as a baby sea otter.

As with other cetaceans, orca culture is rich. Besides behaviors learned through imitation, such as various hunting techniques, an obvious display of culture comes in their local vocal dialects.

 Sea Lion Slam

In the polar regions, orca happily hunt a solitary sea lion they find on a small ice flow. It makes an excellent meal, but the catch is tricky. The sea lion’s sharp bite is to be assiduously avoided.

Several in the orca group simultaneously slap their tails in the water on one side of the floating ice where the sea lion lies, creating a force wave which rocks the ice flow. It can be enough to make the sea lion slip off the ice and into the water.

The sea lion panics and struggles to regain the relative safety of the ice shelf. While in the water, orcas take turns in quick succession ramming the sea lion from the back side, or bite at its tail end. They may blow bubbles about the seal to confuse it.

If a secure purchase can be made on the sea lion’s tail, an orca might fling it in the air and slam the sea lion against the water. Orcas enjoy playing with their prey.

If the sea lion makes its way back on the ice, it will be wave-pounded repeatedly, further discombobulating it. In what may take an hour or more, the sea lion is eventually exhausted.

Once subdued, the sea lion is securely bit by the tail and dragged down into the deep to drown. Dinner is served.

Pilot Whales

Pilot whales are another cetacean misnomer. They are instead oceanic dolphins; the 2nd-largest, behind orcas. There are 2 pilot whale species: short-finned and long-finned.

These gregarious creatures travel in pods of up to a hundred, with a dominant female acting as leader. They readily socialize with other dolphin species.

Unlike some other dolphins, long-finned pilot whales spend their lives in the same group. While mating may occur outside a pod, group members do not change their social affiliation.

The long-finned pilot whales that live in the Strait of Gibraltar stay there year-round. When an external threat is perceived, the whales swim synchronously; a typical technique for fish in fearful flight. This tight formation swimming keeps the whole group alert and responsive.

Pilot whales are perhaps best known for stranding themselves on beaches in disturbingly large numbers. Their close relations lead others to follow a friend in distress.