Factsheet - Sperm Whales

FACT SHEET - "Sperm Whales of Greece - Life in the Trenches" (Part 2)

Sperm Whales - Physeter macrocephalus

  • Class - Mammalia
  • Order - Cetacea
  • Suborder - Odontoceti
  • Family - Physeteridae
  • Genus - Physeter
  • Species - Physeter macrocephalus

Introduction:

Of all the great whale species, sperm whales above all others have inspired poetry, myths and books. One of the greatest novels ever written was Moby Dick by Herman Melville, the story of the hunt for a great sperm whale.

Yet almost everything about the lives of sperm whales remains a mystery to scientists. We know virtually nothing of the intelligence of this ancient cetacean. What we do know is that sperm whale social organization is highly complex, and this whale's huge skull encloses the largest brain of any animal on earth, at a weight of up to 9 kilograms.

Evolution:

Mammals evolved more than 200 million years ago as air breathing, land dwelling animals. While these first mammals lived a nocturnal lifestyle in the shadow of the large dinosaurs of the Jurassic and the Cretaceous Eras, the die-out some 66 million years ago of the large reptiles led to a massive expansion of mammal species. The earliest known true whales appeared about 50 million years ago.

The evolutionary roots of whales can be traced back to a common ancestor of even-toed ungulates, meaning that the closest living relatives of cetaceans today, are hippos, pigs and camels.

Whales have undergone major evolutionary adaptations as a result of the change to an aquatic lifestyle. Several physical features have been modified. Most obviously their bodies became streamlined, their forelimbs developed into flippers which help the whale stabilize and steer itself while swimming. The hind limbs disappeared externally, while the tail is large and powerful, supporting strong muscular flukes that the whales move up and down to propel them forward through the water. During the course of evolution, the nostrils shifted from the snout to the top of the skull above the eye sockets. This allowed the whale to breath while most of its head remained submerged.

Modern cetaceans encompass two suborders, the mysticetes (baleen whales) and the odontocetes (toothed whales).

Sperm whales are the largest of the toothed whales. They are among the deepest diving cetaceans and are found in all of the world's oceans. Sperm whales evolved around 25 million years ago and have remained basically the same for the last 20 million years.

Sperm whale only has teeth on its lower jaw. Photo-Chris Johnson

Anatomy and physiology:

Physical description-

Sperm whales are unique in that there is nothing else in the world's ocean that looks remotely like a sperm whale. It has an enormous squared off, blunt nose, weighing upwards of 15 tons that can account for up to one third of it's total body length. This nose houses the spermaceti organ that is filled with waxy spermaceti oil. The small under slung jaw is lined with 18 - 25 pairs of ivory teeth that fit neatly into sockets in the upper jaw.

Sperm whales are usually a dark, brownish grey, while the skin around the mouth and often patches on the underside of the body are white. The wrinkly, corrugated skin of the sperm whale is unmistakable, and unique to this species. The wrinkles are horizontal, occurring only on the rear two thirds of the body - the skin on the nose and head is smooth. The purpose of their prune like skin remains a mystery.

Dimensions-

One would be hard pressed to encounter a more extreme or impressive animal than the adult male sperm whale. As the largest, toothed predator on earth, he may reach lengths of over 18 m (60 ft) and weigh 60 tons. He has nothing to fear and is the undisputed king of his ocean home.

Sperm whales exhibit the greatest sexual dimorphism of any cetacean, with females averaging 10 meters (35 ft) in length and a weight of around 12 tons - 1/3 to 1/5 of the weight of their male counterparts. Because whalers targeted larger sperm whales, there is variation in size between oceans, depending upon exploitation.

Life history:

Sound Production-

Sperm whales are highly acoustic animals that emit powerful, regular clicks almost continuously while they are underwater. In large males, one third of the body length is dedicated to the huge nose, the world's largest biological sound generator.

The incredibly successful evolution of sperm whales as acoustic specialists, is due to the fact that sound propagates through water more effectively than any other form of energy, indeed sound travels through water five times faster than it does in air. We know that the sperm whale spends its life immersed in sound.

The spermaceti organ inside the sperm whale nose, is used to conduct sound.

It is believed that the animal uses a directional sound beam as a kind of acoustic flashlight. Approximately every second, the whale emits a powerful directional click from its huge nose. The clicks propagate away from the whale and bounce back as echoes from the bottom and intended prey items. By listening for and analyzing these echoes, the whale creates an acoustic picture of its surroundings, allowing it to navigate, locate, home in on and perhaps catch prey - a process called echolocation.

 

As well as slow, regular echolocation clicks, sperm whales also make distinct patterns of clicks called 'codas'. Codas are an intriguing form of communication, like a type of conversation that sounds like Morse code. It is believed these clicks are used for maintaining social cohesion in groups of females and calves and are usually heard when a group is at the surface socializing, and when sperm whales meet others in a social group.

Diving Behavior-

A sperm whale fluking. Photo - Chris Johnson

In order to exploit the food sources of deeper waters, sperm whales have to stay submerged at great depth for extended periods of time. Sperm whales are masters of this discipline and may dive to depths of 2000 meters, where the hydrostatic pressure exceeds 200 atmospheres. They are capable of holding their breath for an extraordinary, two hours, although most dives last around 45 minutes.

So how do they hold their breath for so long?

This can be accomplished in two ways, either by lowering oxygen demands or increasing oxygen storage. Sperm whales have evolved to perform both tasks.

Large animals have a much lower specific metabolism than smaller animals. A mass unit of an animal can carry a certain amount of oxygen, irrespective of the size of the animal that it is a part of. Those two facts in combination mean that a large animal can hold its breath longer than a small animal. While diving, sperm whales lower their metabolic rate, slow down their heartbeat and shunt blood mainly to their vital organs, thereby conserving precious oxygen.

At the beginning of its almost vertical descent into a dark and cold world, the whale arches is back and flukes. The swimming speed is a moderate 3 miles per hour (5-6 kph), corresponding to a steady, brisk walking pace of a person. If it swims too fast it will diminish its oxygen supplies and consequently shorten the dive duration. If it swims too slowly, it will not perform an effective search for prey items, nor will it be able to catch them. In between a series of fluke beats it glides to save energy and oxygen.

An illustration of a typical sperm whale dive. The largest males can dive to 2000 meters and hold their breath for up to 2 hours.

After some 10 minutes of descent, sperm whales on average stay at depth for approximately 25 minutes while searching for and ingesting prey before a 10-minute ascent back to the surface. The prey consists mainly of small to medium sized deepwater or bathypelagic squid, with an average mantle length of three feet and weighing 2-6 pounds. We also know they sometimes prey on giant squid. The sperm whale must locate and catch its mostly small and agile prey in complete darkness at temperatures of 4 degrees Celsius, and under enormous pressure. It is highly likely that echolocation plays a crucial role in locating the prey, but scientists do not actually know how sperm whales catch their prey. In order to maintain its body function, a medium sized sperm whale must catch some 100 to 250 prey items per day, roughly 3% of its body weight.

Distribution and Social Structure:

Sperm whales are cosmopolitan animals. They inhabit the blue waters of all of the world's oceans and are often found in deeper offshore areas around canyons and trenches. They can also be found close to shore around volcanic islands such as the Azores, the Galapagos and the Canary Islands, where steep drop-offs run along the coast.

Mature females together with juveniles and calves of both sexes, form social groups. These social groups are restricted to tropical and sub-tropical waters. Males disperse from their natal family at around six years of age, moving to the higher latitudes, sometimes even to the polar ice edge, where they will age and grow, usually in loose association with other immature males. When they mature sexually at around twenty-five years of age, the bulls leave their bachelor schools and become solitary. Once reaching physical maturity (14 meters, 35 tons), at an age of some 30 years, the males migrate at unknown intervals to tropical waters in pursuit of receptive females

Members of a social group usually dedicate most of their time to deep and long dives in the quest for food. The feeding dives are apparently synchronized, staying submerged for approximately 45 minutes the animals return to the surface in a coordinated manner.

Sperm whale distribution map.

Small calves cannot follow the rest of the group on foraging dives, and are either left alone at the surface, or looked after by their mother or a babysitter - another member of the group. It has been suggested that calves actually follow the clicks of the group from the surface so as not to get lost or left behind. Calves are capable of producing clicks at less than a week old, and these clicks may assist the babysitting adults in honing in on the calf after a long feeding dive.

It seems that perhaps once a day, or every few days, a dispersed group will come together and rest, travel slowly or socialize at the surface.

Status:

Where once the great sperm whale herds may have numbered in the low millions, today's estimates put the global population at around 350,000. They are listed as vulnerable under the World Conservation Union's (IUCN) Red List of endangered species.

The Mediterranean Sea is home to an isolated, and genetically distinct sub-population. Living in a semi-enclosed sea means there is little if any breeding with outside populations. Numbering in the low hundreds, Mediterranean sperm whales appear to be declining in number. This had led to the population being declared endangered by the IUCN in 2005.

This sperm whale is a survivor of a ship strike. Photo - Chris Johnson

Threats:

Few natural predators threaten sperm whale populations. Orcas are known to attack and kill adult female sperm whales, though it is the young who are the most vulnerable. Occasionally large sharks may prey on young or sick animals.

However, human pressures pose a far greater threat to sperm whales. Collisions with large vessels, entanglements in fishing nets, ingestion of marine debris such as discarded plastics, oil spills, the dumping of industrial wastes and other man made toxicants, noise pollution from seismic operations, sonar and shipping traffic and the unknown effects of climate change, all pose serious threats to sperm whales in varying degrees around the world.

Despite the moratorium on commercial whaling, Japan added sperm whales to the list of cetaceans hunted under the guise of 'scientific' whaling in 2000. They are now hunting sperm whales in the North Pacific. The meat, oil and other products from these so called 'scientific' whaling operations are sold in Japan on the open market.

What can you do?

Support conservation based, research organizations.

Many organizations offer opportunities for you to support their research, conservation and education programs, this includes participating in regulated whale watching. These funds assist with research, conservation and education programs. For more information go to:

Act responsibly

Act responsibly when disposing of chemical and plastic waste. Man made toxicants will always make their way into our waterways and eventually the oceans. Look for biodegradable alternatives.

Plastic pollution is ingested by marine creatures and is responsible for hundreds of thousands of entanglements every year. Dispose of plastics responsibly and recycle where possible, better still, use biodegradable alternatives where possible. Taking your own reusable bag to the supermarket to avoid plastic bags is a great and simple place to start.

Volunteer

Non-profit, Non-Governmental Organizations (NGO's) are often looking for volunteers and interns. By volunteering your time and skills to work with an NGO, you receive experience that assists in admission to higher education programs and an increase in employment options. In addition you receive the opportunity to work with the animals, while directly contributing to valuable research, education and conservation efforts.

Reading Materials:

  • "Sperm Whales - Social Evolution in the Ocean." - Hal Whitehead.
  • "Sperm Whales" - Jonathon Gordon.
  • "Moby Dick" - Herman Melville.
  • "In the Heart of the Sea." Nathanial Philbrick.

Genevieve Johnson has taught middle and high school students in the area of Environmental Education for over 12 years. She has also spent five years as a cetacean field researcher on an around the world science and education expedition. As well as teaching in a classroom, Genevieve designed the 'Class from the Sea' and 'Ocean Encounters' programs, designing curriculum and linking with students around the globe from the research vessel.