SPERM WHALE FACT SHEET

SPERM WHALES - (Physeter macrocephalus)

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

Introduction:

Whales are the largest animals on the planet. They retain the ability to inspire awe and wonder in us. Cloaked in the mystery of the sea, leading lives far removed from our own, they have fascinated us for centuries with their immense size, grace and power. Of all the great whale species, there is one above all others that continues to fascinate us- the sperm whale. Men have chased them and killed them, all the while gazing into the ocean with amazement at a presence they could barely explain. They have inspired poetry, myths and books, while it remains undisputed that 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 fascinating and most ancient of cetaceans. 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 kg.

Odontocetes, like this Sperm Whale, have a single blowhole

Photo: Chris Johnson

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 Era, 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 shortly after this massive reptilian die-out, 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.

Mystecetes, like this Blue Whale, have two blowholes.

Photo: Chris Johnson

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 of modern whales have externally disappeared, while the tail is large and powerful, supporting strong muscular flukes that the whales move up and down to propel them 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 mystecetes (baleen whales) and the odontocetes (toothed whales). The largest of the toothed whales is the sperm whale They are among the deepest diving cetaceans and are found in all of the world's oceans. Sperm whales evolved 25 million years ago and have remained basically the same for the last 20 million years.

Anatomy and physiology:

Physical description

Sperm whales are unique in that there seems to be nothing in the world's oceans that looks like a sperm whale... It has an enormous squared off, blunt nose, weighing upwards of 15 tonnes, 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 underslung jaw is lined with 18 - 25 pairs of teeth that fit neatly into sockets in the upper jaw.

Sperm whales are usually 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 unmistakeable 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.

A Sperm Whale.

Iain Kerr

Dimensions

One would be hard pressed to encounter a more extreme or impressive animal than the adult male sperm whale, by any measure it is a most magnificent animal. Being the largest, toothed predator in the sea, he may reach lengths of over 18 m (60 ft) and a weight of more than 60 tonnes. 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 m (35 ft) in length and a weight around 12 tonnes-1/3 to1/5 of the weight of their male counterparts (although size differences vary between oceans depending upon exploitation, when larger males in particular were targeted by whalers).

Life history

Sound Production

Sperm whales are highly acoustic animals that emit powerful; regular clicks almost continuously while they are underwater. In large males, up to one third of the entire body length is made up of 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.

It is believed that the animal uses a 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 from the bottom and intended prey items. By listening for and analysing these echoes, the whale creates an acoustic picture of its surroundings, allowing it to navigate, locate, home in on and perhaps catch prey - the sperm whale is echolocating.

As well as slow, regular echolocation clicks, sperm whales also make a series of rapid fire or 'coda' clicks. It is believed these clicks are used for maintaining social cohesion in groups of females and calves

A Sperm Whale fluke

Photo: Chris Johnson

Diving Behavior

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, 1.5 hours, although most dives last for around 45 minutes. So how do they accomplish this?

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 thereby oxygen.

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, but we also know they sometimes prey on giant squid. The sperm whale must locate and catch its 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.

(Image - giant squid? And small squid)

Distribution and Social behavior:

Sperm whales are cosmopolitan animals. They inhabit the blue waters of all of the world's oceans and are often found in deeper areas around canyons and trenches, and along steep drop-offs, diving to depths up to 2 kilometers. They are known as the most social of all the great whales. Sperm whales were easy prey for whalers as it was well known that members of a group would come to the aid of a companion in distress, so by injuring a single member of the pod, the whalers were often able to pick off the entire herd one by one.

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 tonnes), at an age of some 30 years, the males migrate at unknown intervals to tropical waters in pursuit of receptive females

Illustration: Chris Johnson

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 40 minutes the animals return to the surface in a coordinated manner.

A group of socializing sperm whales

Photo: Chris Johnson

Small calves cannot follow the adults on deep and long dives, and therefore, are either left alone on the surface, looked after by their mother or a babysitter - another member of the group. . Calves can be vulnerable to predation from large sharks or orcas. It has been suggested that calves actually follow the clicks of the group from the surface so as not to get lost or be left behind. The calves themselves are capable of producing clicks at less than a week old, and these clicks may assist the 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.

Threats:

Orcas are known to attack and kill even adult female sperm whales, though it is the young who are the most vulnerable.However, humanity is by far the greatest threat to sperm whales. Humans have hunted these animals commercially since the 1700's. Whaling has substantially reduced most population stocks. Where once the great sperm whale herds may have numbered in the millions, today's estimates put the global population at around 350,000. Factory ship whaling for sperm whales was prohibited by the International Whaling Commission (IWC) in 1979.

Sperm Whales were hunted for centuries. Today, they are still taken under the guise of ‘scientific whaling’

Photo: Courtesy of WHALEWORLD Museum, Albany, Australia

Despite the moratorium on whaling, Japan recently added sperm whales to the list of cetaceans hunted under the guise of 'scientific' whaling. They have begun to hunt sperm whales in the North Pacific and intend to increase their quota. The meat, oil and other products from these 'scientific' whaling operations are sold in Japan on the open market.

Other threats to sperm whales include 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, and noise pollution from seismic operations, sonar and shipping traffic.