Between Worlds: Understanding Marine Mammals
Story and photos by Marty Snyderman
At first, the encounter was pure adrenaline rush. I had been close to whales before, but not so many times that I wasn't overwhelmed by the situation. Size is a big factor. A whale can easily be 400 times the size of a Sumo wrestler. It is often impossible to see a whale's entire body because its length exceeds the visibility. In 30- to 40-foot/9- to 12-m vis, if you are close to the head, you cannot see the tail of a California gray whale, much less that of a humpback, fin or blue whale. The day of their birth, newborn calves are far bigger than humans. So it's easy to understand why size alone is enough to get your undivided attention. Grace, beauty, power and a feeling of being in wilderness with a magnificent creature, not knowing what is going to happen next, combine to make the moment unforgettable.
As the whale swam toward me, it was obvious that the animal knew I was there. It slowed and veered slightly to its left. The whale was a southern right whale, a mature female. Now less than 10 feet/3 m away, she stopped dead in the water.
I felt incredibly small, but not threatened. More awed, humbled and incredibly fortunate. There was no question that the whale was eyeballing me, giving me the once-over. This time I was being looked at in much the same way I look at a nudibranch or an angelfish. I found myself staring into a tennis ball-sized eye that was most definitely looking back at me. I'd give anything to know what was going on inside that whale's brain. I think anyone would.
Perhaps no one fully understands humankind's affinity for other mammals, but undoubtedly they occupy a special place in our view of the animal kingdom. And for divers, marine mammals hold a special place in our hearts, not just whales, but all marine mammals, a group that includes seals, sea lions, walruses, dolphins, porpoises, manatees, dugongs and sea otters.
What Makes a Mammal a Mammal?
Mammals are warm-blooded vertebrates. Evolutionary specialists maintain that marine mammals are the descendants of creatures that once lived on land. Considerable evidence links marine mammals with their terrestrial counterparts. Like their land-dwelling cousins, marine mammals utilize lungs, not gills, to breathe air, and mothers nurse their young via mammary glands, hence the term "mammals." Most mammals have some body hair, and many marine mammals possess at least skeletal remnants of the legs they gave up eons ago.
As mammals evolved, many species developed characteristics that equipped them for survival in the aquatic environment. Because water conducts body heat away so much faster than air, one of the biggest obstacles marine mammals faced was the challenge of keeping warm, especially considering the fact that it is vital for all mammals to maintain a constant body temperature. Comparatively large creatures have proportionately less surface area exposed to water than smaller animals do, and not surprisingly, many species of marine mammals are rather large. Their size enables them to retain body heat more efficiently.
Whales, dolphins, porpoises, seals, sea lions and walruses further combat cold with a thick layer of insulating fat, called blubber, which is located just underneath their skin. Fat layers also serve as an important energy reserve for times when food is scarce. Seals, sea lions and walruses also have insulating body hair, or fur. Sea otters and fur seals lack a significant fat layer, relying instead on a combination of their voracious feeding habits and a dense pelt of fur with oils that repel water.
Whales and Dolphins
Whales and dolphins are known as cetaceans, from both the Greek and Latin for "whales." The order Cetacea is divided into two suborders: Mysticeti, the baleen whales, and Odontoceti, the toothed whales. Being toothless, baleen whales feed primarily on plankton and small fishes they strain from the water. When feeding, these whales swim open-mouthed through dense concentrations of prey, then close their mouths to expel the water. The prey, whether krill, plankton or small fish, is trapped by tough, flexible, horny sheets of modified hair known as baleen. The synthetic-looking baleen gives the appearance of an oversized scrub brush.
With plankton and small fishes being so bountiful, many baleen whales grow to enormous proportions. In fact, the largest creature ever to roam the Earth, the blue whale, is a baleen whale. Blue whales commonly reach lengths of 100 feet/33 m, and sizes up to 120 feet/39 m are reported. An animal in this size range weighs close to 300,000 pounds/135,750 kg. Even the minke whale, the smallest of the baleen whales, is quite a large animal, reaching a length of 29 feet/9 m. Other species of baleen whales include the finback, humpback, northern right (also known as the bowhead), southern right, Bryde's and California gray whale.
During the height of the whaling days, many species of baleen whales were heavily sought after by humans. Unfortunately, some populations were hunted to extinction, and many others were pushed to the brink. Today many species have made significant comebacks, and while the future looks brighter than it did not too many years ago, bowheads, southern right and some other baleen whales still face perilous futures.
As their name suggests, toothed whales possess a mouthful of relatively large teeth. They are also equipped with strength, speed and sufficient size to make them formidable predators. Their prey includes salmon, tunas, giant squid, dolphins and other whales, including blue whales, and sharks. Toothed whales possess a single blowhole, or nostril, while all baleen whales have a pair of blowholes positioned on top of the head. On the surface, it is often possible to identify a whale in the distance by the spray from the blowhole.
The sperm whale is the largest species of toothed whale. Extraordinary creatures, sperm whales are capable of the deepest and longest-lasting dives of all whales, having been documented to reach depths in excess of 10,000 feet/3,050 m while remaining underwater for 90 minutes as they scour the depths for food. Giant squid are thought to be among their favorite prey items. For many years filmmakers and authors such as Herman Melville (Moby Dick) have exploited the potential conflict between these marine behemoths, but to date no one has managed to film a real-life confrontation.
The star performer at many aquatic parks, the killer whale, or orca, is a widely recognized toothed whale. Males are easily distinguished by their towering, triangular dorsal fin, which can be over 6 feet/2 m tall. Though males are larger than females, killer whale societies are matriarchal, with the pods being dominated by the most powerful female. Other well-known toothed whales include pilot whales, the all-white beluga whales and narwhals, an Arctic species characterized by the long tusks found in the males.
Dolphins and Porpoises
Surprising to many, dolphins and porpoises are toothed whales. While the terms "dolphin" and "porpoise" are often used interchangeably, dolphins and porpoises are actually different types of animals described in separate families within the suborder of toothed whales. Among the 10 families of toothed whales, six include dolphins and porpoises.
Dolphins are characterized by their comparatively longer beaks and conical-shaped teeth. Porpoises have more rounded heads with no distinct beak, and their teeth are somewhat flattened. Most species of porpoises reach a maximum length of less than 7 feet/2.3 m, while many dolphins are considerably larger.
Collectively speaking, dolphins and porpoises roam subpolar, temperate and tropical oceans, as well as some freshwater rivers. Porpoises tend to congregate in groups of 10 or fewer (though pods of 50 have been documented), while dolphins tend to gather in larger pods that are often very active at the surface. Common dolphins, for example, sometimes travel in herds that number as many as 1,000 animals. Supreme divers, common dolphins are capable of descending to 925 feet/280 m while remaining submerged for as long as eight minutes.
Like many marine mammals, dolphins and porpoises tend to be highly gregarious animals. Throughout their lives, most dolphins and porpoises depend in one way or another on other members of their species for their own survival. Their social nature probably has more to due with the requirements imposed by hunting and reproduction rather than an innate sense of "friendliness." Cooperative hunting is practiced by many species in order to help them corral, confuse and capture prey. In addition, many species are believed to communicate among members of their pod in order to find the most productive areas in which to pursue prey.
While humans often anthropomorphize dolphins and porpoises, painting a picture which presents these animals as "friendly," in the wild dolphin societies can be very violent and competitive. Physical dominance plays an important role in forming the social hierarchy within a pod.
Most dolphins and porpoises live in salt water, but five species of river dolphins are known to inhabit China's Yangtze River, India's Ganges and Indus Rivers, and South America's Amazon River.
Sea lions, seals and walruses are described in the order Pinnipedia, from the Latin "fin-footed." In pinnipeds the limbs have evolved into flippers, an obvious advantage for an aquatic lifestyle. Despite the often awkward appearance of their rotund bodies on land, pinnipeds are superb swimmers and divers. Pinnipeds spend much of their time at sea, but they also have strong ties to land. Highly social animals, they often come ashore, or haul out, to rest and bask in the sun, and they also gather on land or ice to breed and bear young. Pups of both sexes and young females without pups tend to be far more gregarious than sexually mature males or females. Adult males can be quite aggressive toward humans as well as other members of their own species, and females who have recently pupped can be quick to defend perceived threats to their young.
Worldwide, there are five species of sea lions. Steller sea lions attain the largest size, with full-grown males weighing as much as a ton. Easily trained, California sea lions commonly star at marine parks around the world. In the wild, California sea lions range from British Columbia in the north to Ecuador's Galapagos Islands on the equator. The remaining three species, the Australian, or blonde, sea lion, the South American sea lion and Hooker's sea lion, are found in parts of the Southern Hemisphere.
Twenty-five species of seals can be found worldwide, with most inhabiting temperate, polar and subpolar seas. Occurring in the southern Atlantic and Indian Oceans, southern elephant seals are the largest of all pinnipeds. Full-grown males, known as bulls (females are known as cows), attain proportions of 15 feet/5 m and 5,000 pounds/6,800 kg.
It is quite common to observe different species of seals and sea lions mixed with one another, both on land and in the water. In fact, during the spring, Point Bennett on California's San Miguel Island is inhabited by six different species of pinnipeds, the largest known number of pinnipeds at any one time anywhere in the world.
Most pinnipeds prey largely on a variety of fishes, mollusks and crustaceans. However, the leopard seal is a notable exception. These aggressive hunters also prey upon penguins and other seals in Antarctica. Photographs of leopard seals are rather rare, due to both the inhospitable conditions of their range and their aggressive temperament. Great white sharks, tiger sharks, killer whales, polar bears and Arctic foxes are known to prey upon a variety of pinnipeds.
Perhaps the most surprising thing about seals and sea lions is that they are not as closely related as many people assume. Scientists continue to pursue their evolutionary paths, but there is considerable evidence to suggest that seals and sea lions evolved from different ancestors. Surprisingly, seals are thought by many specialists to be more closely related to bears and cats than to sea lions.
However, sea lions and seals do share many common characteristics. All of these animals possess a thick hide with a heavy layer of fat underneath to protect them from their cold surroundings. Members of both groups have modified fore and hind limbs called flippers. However, the size and use of the flippers differ. Being used as the chief means of propulsion in the water, the fore flippers of sea lions are comparatively large. Sea lions use their smaller hind flippers as a rudder to help them steer, while seals propel themselves with their rear flippers. Seals are unable to point their hind flippers forward, and as a result they tend to be less mobile on land.
Found only in the Arctic near coasts on pack ice and ice edges, walruses are pinnipeds that are probably best known for their impressive canine teeth, commonly called tusks. In mature males the 3-foot-/1-m-long tusks are long and straight, while in females the tusks are shorter and slightly bowed. The tusks, which grow throughout a walrus's life, are used both to dig through the seabed in search of mollusks, worms and fishes, and to help the animals pull and brace themselves as they travel along the icy landscape. Sexually mature males also use the tusks in combat against other males when vying for mates.
Manatees and Dugongs
Manatees are marine mammals described in an order of vertebrates known as Sirenea. This name is derived from the Greek word for sirens, mythical temptresses who lured sailors to their deaths. The name alludes to the fact that ancient mariners are reported to have mistaken these 1,500-pound/680-kg mammals for mermaids. A close-up look at their algae-covered, sausage-shaped bodies makes most people hope they are never at sea long enough to make a similar mistake.
Attaining a size of 13 feet/4 m and 800 pounds/360 kg, the species commonly called the West Indian manatee inhabits a number of Florida's springs and spring-fed rivers, as well as some mud flats and estuaries in several Central American countries, most notably Belize. During most of the year, Florida's manatees disperse into small groups, and it is not unusual to encounter solitary animals. However, during winter they tend to congregate in areas with warmer water, such as Florida's famed Crystal River. Like other species of manatees, West Indian manatees spend the vast majority of their lives in shallow water, never venturing onto land and only rarely traveling into the deeper waters of the open sea.
Manatees possess flippers that assist in maneuverability, while thrust is supplied by their rounded, paddlelike tails. While usually appearing sluggish and lazy, West Indian manatees have been clocked at a speed of 12 miles/19 km per hour.
Manatees are herbivores, their favorite foods being a variety of sea grasses. Adult manatees consume as much as 100 pounds/45 kg of sea grass in a single day. Manatees breathe through nostril flaps located near the top of their head, a position that enables them to inhale life-sustaining air with minimal effort.
The West Indian manatee is an endangered species. By far, the worst threat comes from man, with habitat encroachment and collisions with boats primarily responsible for their demise. Floridians have taken many steps to reduce pressures from divers, boaters, fishermen and commercial interests, but the future of manatees continues to hang in the balance.
Three species of manatee occur in the Northern Hemisphere, and one, the dugong, occurs in the Southern Hemisphere. All four species are commonly referred to as sea cows. A little over 200 years ago, a fifth species known as the Steller's sea cow occurred in the Bering Sea. Discovered by Western man in 1741, in 1768, only 21 years later, the species was extinct due to overhunting.
Sea otters are members of the weasel family. Their ancestors are thought to have returned to the sea much more recently than those of other marine mammals (an estimated 5 to 7 million years ago), making sea otters more closely related to their terrestrial cousins than are other marine mammals.
Sea otters are the only marine mammals that lack a layer of blubber to keep them warm. Yet they live in cold water, and like all mammals they must maintain their core temperature. Two things help sea otters combat this problem. One, they have extremely dense fur, and two, they eat, and eat, and eat some more. Juveniles consume up to 35 percent of their body weight each day by devouring sea urchins, crabs, lobsters, abalone, scallops, snails, worms and more. A full-grown male sea otter can reach a length of almost 5 feet/1.5 m and weigh close to 85 pounds/38 kg. Consuming as much as 15 percent of their body weight in a single day, male sea otters eat in excess of 5,000 pounds/2,250 kg of food annually. Females attain a maximum size of 4 feet/1.2 m and 60 pounds/27 kg.
Sea otters are one of only a comparative handful of animals that are known to use tools. They can frequently be observed resting on their backs at the surface while using rocks to crack open crabs, mussels, urchins and other prey items. While diving, otters have been observed to use rocks to knock scallops and mussels off of other rocks.
Excellent swimmers and divers, sea otters prefer to hunt in water that is 70 feet/21 m or shallower, but when food is scarce they are known to venture into considerably deeper areas. Hunting dives can last up to four minutes, but they are usually not that long.
For thousands of years, sea otters ranged from Alaska to the lower part of Mexico's Baja peninsula. However, in the late 1700s hunters and trappers from Europe, Russia and America hunted sea otters to near extinction before the otters were granted some much-needed protection. Sea otters have made a considerable comeback, and today they thrive in many places along the western coast of North America. While most people consider their comeback a good thing, some commercial fishermen oppose the effort on the grounds that sea otters compete with the fishermen for limited resources.
Whether or not you ever dive with a whale, dolphin, porpoise, pinniped, manatee or sea otter, the mere fact that these animals are free to roam the seas greatly enriches our world and our sport.
Echolocation in Marine Mammals
Although their ability to see in air is suspect, the majority of marine mammals are thought to have a keen sense of vision in water. However, roughly 20 percent, including some whales, dolphins and pinnipeds, augment their vision with a sophisticated faculty known as echolocation. In essence, animals such as bottle-nosed dolphins and killer whales perceive reflected sounds in order to gain insight into their surroundings.
Echolocating animals produce sharp sounds of varying frequencies and analyze the returning echoes to provide them with information about the size, shape and location of nearby objects. The emitted sounds are usually pulses of short clicks, some of which are well within the range of human hearing. In tests with captive dolphins, it has been demonstrated that the ability to echolocate is so well-developed that they can easily discriminate between objects of the same shape, size and color that were made from materials of slightly different densities. Wild dolphins have been observed to locate prey that was completely buried in the sand by using their ability to echolocate.
Although different species have developed their own methods of producing the clicks and processing the feedback, the general principles are essentially the same. For example, all toothed whales possess a relatively large, melon-shaped deposit of fat at the front of the head that apparently focuses the emitted clicks into a narrow, directional beam of sound. The reflected echoes are received by another fat deposit in their lower jaw. This information is sent to the brain, where it is analyzed.
Life at a California Sea Lion Rookery
Life at a California sea lion rookery reminds me of a typical day at an elementary school. Sometimes the scene is highly chaotic, filled with energy to the point of being completely out of control, and the adults present often appear to be more involved with performing a task rather than enjoying life. While bulls are busy defending their turf and females tend to the demands of motherhood, the pups are either going all out in play or sleeping, not going at all.
As a diver, if you observe pups when their energy level is high, you are in for a real treat. They constantly chase one another at break-neck speed. Sometimes the pups eagerly include humans in their games, swimming right up to divers and snorkelers, and playfully nipping at fins, snorkels and other pieces of gear.
While the entertainment is definitely rated a big "thumbs up," be careful not to make the mistake of taking any species of sea lion for granted. Bulls take the boundaries of their territory quite seriously. It is wise to give ground quickly if a bull barks at you or blows bubbles in your direction. Bulls can weigh as much as 700 pounds/320 kg, so given their size and demeanor, nothing more need be said to the wise.
How Marine Mammals Avoid the Bends
Given the fact that humans share many common characteristics with marine mammals, it is interesting to consider the special problems living in the sea as an air-breathing, warm-blooded creature poses for marine mammals. How, for example, do marine mammals avoid the bends?
Mother Nature has provided marine mammals with several vital adaptations that enable them to make extremely deep dives for extended periods of time, breathing air and still avoiding the bends. Though the issue is rather complex, key factors are: 1) the heart rate of marine mammals slows dramatically when they dive, a factor which dramatically reduces the amount of nitrogen introduced into their system; 2) as a whale descends, the air in its lungs compresses to a very small volume and is forced into nonabsorptive portions of the lungs (bronchioles, bronchi and trachea), as well as safe areas in the nasal passages where little gas exchange into the blood can take place. During ascent to the surface, the compressed air expands, refilling the lungs, and blood flow and gas exchange resume; and 3) circulation to less vital, peripheral body parts, which out-gas slowly, is greatly reduced when the animals dive. In addition, unlike scuba divers, whales are using only one breath, so they absorb comparitively less nitrogen than a continuously breathing scuba diver.
The Phenomenon of Delayed Implantation
Reproduction in marine mammals differs in several significant ways from that of land mammals. The gestation period of mammals is longer than that of the lower animals. The longer gestation period allows the embryo to be well-developed at birth, a factor that greatly increases the chance for survival.
Many marine mammals go without food during their mating season so that the adults can devote more energy and time to guarding, nursing and training their offspring. Fasting also enables some species to migrate great distances between their feeding and calving grounds in a shorter time because they do not have to spend time in the pursuit of food.
The phenomenon known as delayed implantation is also part of the reproductive picture of marine mammals. In many species sexually mature males and females are only together during the calving and breeding season. Nature has cleverly provided a way that enables these species to calve and mate within a very short time frame.
Females are capable of successful copulation within a few weeks after they deliver their young. However, the fertilized eggs are not implanted in the uterine wall for several months, hence the term "delayed implantation." This phenomenon enables the males and females to gather at a specific time of year, often in specific locations that they migrate to, for as short a time period as possible. The short time required is important, especially considering the fact that many species fast during that part of their annual cycle, and females need to replenish their own bodies from the demands imposed by caring for and nursing their offspring.