Ocean Giants

Throughout its history Earth has been home to animals of epic proportions. These monsters have included dragonflies the size of small planes, dinosaurs that were so big that the very ground trembled when they walked and huge land mammals such as the woolly mammoth, which were actually seen by early man! Most of these colossal animals are now extinct however, with only the occasional over-sized fossil being found as the the only indication that they ever even existed. Despite the loss of these species, Earth is still filled with giants and none are bigger and heavier than the whales. 

10: Gray whale - 45 feet/40 tonnes

The gray whale, Eschrichtius robustus, is the only surviving member of its family,  Eschrichtiidae, which first appeared  over 30 million years ago. Gray whales were nicknamed devil fish during the whaling era because of their violent behaviour when hunted.

Gray whales are famous for their 14, 000 mile (22, 000 kilometre) migration route that takes them from the Bering and Chukchi Seas in the summer to Mexico over the winter. This route was once believed to have been the longest migratory journey undertaken by any animal, but recent evidence now suggests that some humpback whales can travel even further!

9: Sei whale - 48 feet/45 tonnes

The sei whale, Balaenoptera borealis, is one of the fastest species of cetaceans (the family of whales, dolphins and porpoises) and has been recorded swimming at speeds of 30 mph (50 kph).

Sei whales need to consume nearly 1, 000 kilograms of copepods (small crustaceans), krill and zooplankton every day in order to meet their energy requirements. Sei whales are a type of baleen whale, which means that they eat by filtering the organisms out of the water as they swim. Sei whales can be found in most of the world's oceans, although they are not found in polar waters.

8: Humpback whale - 45 feet/48 tonnes

The humpback whale, Megaptera novaeangliae, is easily identifiable by its  knobbly head and unusually long pectoral fins. Male humpbacks produce one of the most complex songs out of any whale species, which can last for as long as 20 minutes and are often repeated for hours at a time. Although the function of their songs is not conclusively known, it is believed that they have a role in attracting a mate.

Humpback whales are one of the most wide-spread species of whale and can be found throughout the world's oceans. They have an intensive migration route and travel over 16, 000 miles (25, 000 kilometres) a year from the cold polar waters where they spend their summer to the tropical or subtropical waters where they breed and give birth in the winter.

7: Sperm whale - 50 feet/60 tonnes

The sperm whale, Physeter macrocephalus, is the largest living species of toothed animal and has the  largest brain of any animal in the world.

Sperm whales feed predominantly on giant squid, which they dive for to depths of up to 3 kilometres. This feat makes them the deepest diving animal and they navigate in the complete darkness using echolocation. The clicks that they produce  for their echolocation have a range of 60 kilometres and are the loudest sound produced by any animal.

6: Bowhead whale - 55 feet/75 tonnes

The bowhead whale, Balaena mysticetus, lives in the frigid waters within the Arctic Circle. In order to keep warm here the whale has a huge layer of blubber that accounts for up to 50% of its total body mass.

Bowhead whales are unique among mammals because their bones never fuse. This means that they keep growing throughout their entire lives and individuals as long as 70 feet have been found (although this post uses the average length of each species, else it would be higher up the list). Remarkably bowhead whales are believed to live for over 200 years due to their low body temperature and females have been found over the age of 100 that are still fertile!

5: North Atlantic right whale - 52 feet/100 tonnes

With only 400 individuals of the species left in existence, the North Atlantic right whale (Eubalaena glacialis) is one of the most endangered whales in the world. This is despite its protection under the Marine Mammal Protection Act of 1972 and the U.S. Endangered Species Act of 1973.

Like all right whales, North Atlantic right whales can be distinguished by their broad back that lacks a dorsal fin and the callosities (thickened skin) above its eyes.  They continuously feed on copepods and other small invertebrates such as krill, pteropods and larval barnacles by skimming them out of the water and migrate from the Gulf of Maine to their calving areas off Georgia and Florida in the winter.

4: Finback whale - 90 feet/74 tonnes

The finback whale, Balaenoptera physalus, is also called the fin whale, razorback whale or  the common rorqual.  It is  the second longest animal in the world, but its thin body means it is lighter than some species of much shorter whale.

Finback whales feed off schooling fish, squid, crustaceans and krill and are unbelievably fast. So fast in fact, that they are faster than the quickest ocean steamship! This attribute has earned them the esteemed title of being the 'greyhounds of the sea'.

3: Southern right whale - 58 feet/110 tonnes

The Southern right whale, Eubalaenna australis, is recovering well since it became protected in 1937 and is now classified as being of 'Least Concern' by the IUCN, with its population growing by an estimated 7% each year.

Southern right whales spend much the summer close to Antarctica where their calves are safer from being predated by killer whales and great white sharks. During the winter, when the conditions of Antarctica become too harsh for them to remain there, they migrate north to the warmer waters of Argentina and seem to spend many hours in a unique behaviour called 'sailing'. This behaviour is believed to be recreational and consists of the whales catching the wind in their flukes and letting it propel them through the water like  boats!

2: North Pacific right whale - 60 feet/120 tonnes 

The North pacific right whale, Eubalaena japonica, feeds mainly on copepods that it constantly filters out of the water while swimming. Its prey is so small that it needs to consume millions of them each day in order to provide the energy that it needs to survive.

Unlike many other species of whale, the North Pacific right whale does not seem to have a clear migratory pattern and the only notable annual difference in their distribution is when they are breeding, where they tend to move closer inland.

1: Blue whale - 100 feet/190 tonnes

The blue whale, Balaenoptera musculus, is a peaceful whale that eats krill - one of the smallest organisms on the planet. Although there were once believed to have been 200, 000 blue whales in the oceans, it is estimated that there are now only 10, 000 left due to their historical over hunting. Sadly, and despite now being protected, their numbers are not expected to recover due to their slow life cycles.

As far as we know the blue whale is the largest animal that has ever lived on this planet and is twice the weight of the biggest known dinosaur. In fact, blue whales are so big that their tongues alone can weigh as much as an elephant and their hearts as much as a small car!

"I spy with my HUGE eye, something beginning with w..."

One of last months posts, 'Hunting in the depths', featured sperm whales and talked about how they dove down into the depths of the oceans to hunt their main source of food, giant squid.

Obviously, giant squid want to avoid being eaten by sperm whales and are extremely vulnerable to attack due to the whales' fearsome arsenal. One of the main defences that they have evolved against the whales is developing incredibly large eyes that can measure more than 11 inches across! The large size of these eyes has long confused scientists because they are very expensive to make and are virtually completely useless in the deep oceans, where there is no light. This means that their eyes should have disappeared over the course of their evolution, like in many other species of deep cave-dwelling organism.

A sperm whale hunting a giant squid. Note the giant squids enormous eye, which works via a lens refracting light in the same way as a human eye does.

The fact that they possess such highly developed eyes, which can have lenses that are bigger than the entire human eye, means that this can't be the case. New research into giant squid by Professor Nilsson from Lund University, Sweden  has helped to 'shed light' onto the function of these eyes and explain why evolution has favoured their development rather than their loss.

The depths of the ocean are filled with bioluminescent organisms, which when disturbed, flash and glow. Thus, diving sperm whales agitate these organisms as they swim past and giant squid are able to see the light from this disturbance. The squid are able to gage the size of the organism and the direction that it is travelling in from this light and consequently, can determine whether or not the shape is a sperm whale to either ready itself against an attack or flee.

Therefore, the large eyes of giant squid have direct implications to the animal's survival so that in the past, individuals with biggest and best eyes survived for the longest and could breed the most. This meant that large eyes were under a strong selection pressure in giant squid, despite being useless for seeing anything else, so that today the species has abnormally large eyes.

Hunting in the depths

The sperm whale, Physeter macrocephalus (previously Physeter catodon), is a fearsome hunter and frequently dives to depths as deep as 3km in search of its main source of food - giant squid. Even though 3km doesn't sound like much, it is so deep that we struggle to build submarines that can withstand the extreme pressures even now; making the whales an amazing feat of evolutionary engineering, being one of the few animals that can survive the radical pressure change between the oceans' surface and its depths. Sperms whales can live for more than 70 years and males, which are more than 40% more massive than females, can grow to over 20 metres in length, weighing up to 57, 000kg. They have the largest brain of any animal and are also the largest living toothed species, although only males actually possess teeth, which can weigh up to a kilogram each.

A male sperm whale breaking up out of the ocean. Note its slender lower jaw, which increases the pressure of its bite (making it more powerful) and the thin, conical teeth that fit into alcoves in the whale's upper jaw - helping to trap anything that it bites in its mouth.

Sperm whales are named due to the large and well developed spermaceti organ that forms most of their head, which at times, can make up a third of an individual's total body length. This gives the whales a distinct body shape, making it difficult to confuse them with another species. Unfortunately, this made them easy targets for whalers in the Industrial Revolution, where they were killed for the whale oil that was harvested from the organ itself and from their blubber. Sadly, their population fell dramatically and, as a result, sperm whales are now protected and the species is classified as 'vulnerable' by the ICUN. Even though the organ has largely brought about the downfall the species, it is critical for their survival. This is fairly obvious really, when you think about the organ's large size compared to the whale's body and the energy that it must take in order to produce and maintain it.

A sperm whale, with its box-like spermaceti organ clearly visible. The whale also has a very powerful, muscular body and thick, triangular flukes that allows it to dive to such extreme depths.

The oldest known function of the spermaceti organ is as a buoyancy aid. At the surface, whales reduce the blood flow to the organ by contracting the diameter all of the blood vessels it contains, in a process known as vasoconstriction. This causes the temperature of the organ to fall and the spermaceti wax solidifies, increasing in density. As the organ is in the whales head, it sinks and pulls the whale downwards head-first; thereby, helping it dive and stay submerged. When the whale wants to rise to the surface, usually to breathe (sperm whales can stay submerged for about 90 minutes at a time), the converse it true and the blood vessels dilate (expand), causing the wax to melt and decrease in density. Thus, the whale is pulled upwards head-first, which allows it to ascend more quickly. This could be potentially life-saving for a whale - imagine running out of breath 3km underwater...

Sperm whales live in small social groups, rather unimaginatively called units, which consist of multiple related females, one unrelated male and calves (both male and female - males leave the group once they sexually mature). In this photo, the unit is sleeping, which is identifiable since the whales always sleep in this vertical position; kept afloat by their spermaceti organs.

However, buoyancy aid is only a secondary function of the spermaceti organ, with it being primarily involved in echolocation. Water is an excellent absorber of light, so that 3km down it is completely dark - no sunlight penetrates to such depths. Interestingly, even if light did reach such depths, sperm whales would be unable to see as they shut their eyes very tightly to protect them against the pressure and cannot open them. Therefore sperm whales are completely blind at these depths, which isn't ideal for a predator. Echolocation, also seen in bats, is an ingenuous adaptation that allows the whales to form an image of their surroundings by generating a series of clicks using the phonic lips at the front of their nose. These clicks then pass into Junk Bodies in the spermaceti organ and are forced out into the water through the Junk's lens-like structure. The whales can then process these clicks as they are reflected back, bouncing off the objects in the water. This allows them to form a 'mental image' of their surroundings, which may be part of the reason why they have such large brains - forming the images requires a large amount of neural processing.

The spermaceti organ also has a third and much more sinister function. The broad-beam clicks that it uses to generate an image of its surroundings can be focused into a much narrower, more intense beam. This beam is used for hunting and is 'fired' at potential prey targets once they have been located. It is so intense that it stuns and completely disorientates its prey, allowing the whale to get close enough to bite it, which normally means game over for the unlucky animal. Further to this, the depths of the ocean are filled with bioluminescent phytoplankton and cyanobacteria, which light up when stressed. Thus, when they are hit by the narrow beam they light up and the sudden surge of flashing light can disorientate the giant squid, which can see at such depths, even more.

A photograph taken by a deep-water submersible that shows a male sperm whale attacking its prey, a giant squid. Giant squid are a formidable killer in their own right, possessing thousands of suckers that each contain razor sharp chitin rings and a great quantity of scars can be seen on the whale, as a result from past encounters.

As said previously, one of the most amazing abilities of sperm whales is their ability to dive down from the relatively low pressure of the surface, to the abyssal depths that are under enormous pressure. So, as you would expect, they have many physiological adaptations that allow them to do this. The main ones are that their entire body, including all of their viscera (internal organs) are designed to be crushed, yet continue to function. Their rib cage is highly flexible and can fold almost flat; their lungs secrete a unique pulmonary surfactant that contains detergents to stop their delicate alveoli sticking together; and their heart virtually stops beating during the dive, which is accomplished by a massive drop in their metabolism. The fact that their metabolism and heart rate slows down so dramatically allows them to hold their breath for much longer than they could have otherwise. However, this still wouldn't allow them to hold their breath for a dive of 90 minutes so, to increase this time, they have an enormous quantity of blood, which therefore, can hold an enormous quantity of oxygen. Sperm whales also have extensive reserves of a pigment in their muscles called myoglobin, which acts as an emergency store of oxygen. Thus, sperm whales are able to dive at great depths for an extended period of time.

Despite still being rare, the population of sperm whales is beginning to rise and it is faring much better than other endangered species of whale. Mainly because its hunting is now banned in almost every country, meaning that commercial whaling of sperm whales has ceased, it has no natural predators and giant squid are not fished by humans, so its food source is not declining. Therefore, it is likely that this truly amazing animal has survived industrial whaling and will grace our oceans for many years to come.