Humpback whale / Megaptera novaeangliae / Family - Balaenopteridae
Whales are mammals that live in the sea but they have more in common with humans, dogs and other land mammals than they do with other marine animals such as sharks and fish. Up to about fifty million years ago whales' ancestors lived on land.
As mammals, whales are warm blooded, have mammary glands to suckle their young and have to surface to breathe air. However, many features typical of land mammals have been lost.
The whales' nostrils have moved to the top of their heads and are called 'blowholes'. They have no hind limbs and their skin is extremely sensitive and smooth. Rather than having body hair to keep them warm, whales and dolphins have a thick insulating layer of fat or blubber under their skin. Their bodies are streamlined and their forelimbs are compact flippers used for balance and steering. The humpback whale has the longest flippers of any whale. They are about five metres long - a third of the whale's total body length.
Whales also possess horizontal tail fins called flukes and a fin on their back. Flukes have no skeletal support and are not related to any typically mammalian structure. They are skin outgrowths connected to the body muscles by a complex network of tendons and tough connective fibres. Powerful up- and-down strokes of the flukes propel the animal forward.
Whales are divided into two groups: those with teeth and those without. Those with teeth are known as toothed whales, and include species such as the sperm whale and short and long-finned pilot whales. The other group of larger whales (including blue, fin, sei and minke whales) are the so-called baleen whales that use baleen plates to sieve their prey from the sea.
Whales without teeth have baleen which consist of vertical plates fringed with stiff bristles hanging down from the upper jaw. Seawater is passed through the baleen and schools of tiny animals such as shrimp-like krill and microscopic plankton are filtered from the water. The 'great whales' such as the blue whale ( the largest creature ever to have lived), right whales and humpback whales are all examples of baleen whales.
Some baleen whales are called 'rorquals.' These have deeply grooved skin around their lower jaw and throat which forms a pouch that can expand allowing the whale to take in large mouthfuls of water. The tongue forces the water out again, filtering it through the baleen. Rorquals, found in the Great Barrier Reef Marine Park include the humpback, minke and Bryd's whales. Those baleen whales that don't have throat grooves swim through the water with their mouths open, allowing the water and food to continuously flow through the baleen.
Feeding and breeding habits cause baleen whales to undergo some of the longest migrations in nature. They spend the summers in the polar regions because food is plentiful with huge populations of krill, plankton and small fish. In winter, the whales move to warmer tropical waters. Here they mate, or give birth. Pregnancy lasts ten to twelve months and calves are suckled and looked after for up to one year. Females often stay together as a group, helping with each other's calves.
One population of humpback whales annually migrates along the east Australian coastline. The whales spend the summer months in the cold Antarctic waters, but from July to October can be sighted throughout much of the warm, shallow waters of the Great Barrier Reef. Here they breed giving birth to offspring that can weigh up to 1.5 tonnes and can be over four metres long. The young calves gain weight rapidly during the first few months but remain close to their mothers on the return journey of 5000 kilometres to the Antarctic. After twelve months, they have grown to eight metres (more than half as long as their parents) and are independent.
Whales with teeth are active hunters. Some, such as killer whales, eat sharks, seals, dolphins and birds as well as squid and fish. Beaked whales and pilot whales all have teeth. In fact, dolphins and porpoises are really small-toothed whales. The largest toothed whale is a sperm whale.
Breathing in the sea
Whales breathe air through their lungs and therefore must surface regularly. Often the first sighting of whales in an area is the 'blow'. This is warm, moisture-laden air that condenses into water vapour to form a mist-like cloud when exhaled through the blowhole. Baleen whales have blowholes divided into two, while toothed whales have a single blowhole.
All whales can stay submerged longer when feeding or when in danger. The sperm whale can hold its breath for nearly two hours! It also holds the record for being the deepest diving whale - it can descend to three kilometres.
Whales have a most efficient circulation system. As well as breathing less often and taking deeper breaths than land mammals, they have more oxygen-carrying red blood cells and can regulate where their blood is distributed. During a deep dive only essential organs such as the heart and brain get oxygen-rich blood flowing through them. When whales are being particularly active or swimming in warm water they can cool themselves by passing more blood through their flukes and fins. The heat is lost to the surrounding water.
Sense and intelligence
The question of intelligence is extremely difficult to measure. An animal's ability to perform 'clever tricks' in captivity and exhibit gentleness towards humans should not be confused with its ability to understand and reason. Brain size in whales varies with the different species.
Whales obtain much of the information about their surroundings from touch-sensitive organs in their skin and from sounds in the environment. Toothed whales use the added facility of echolocation to help them find food and navigate. This highly sophisticated sense involves producing a series of clicks that travels through the water, echoes off any object in its path and returns to the sender for interpretation. The sound is focused by fat deposits in the animal's forehead and lower jaw. This method of 'seeing' with sound is similar to the sonar equipment used in ultrasound scanning and echo sounders.
The toothed whales also seem to have the ability to sense the Earth's magnetic field. This assists them with navigation but can also lead them astray. It may be the reason for the mass strandings of whales that occur from time to time along our shoreline.
Whales also produce sounds (high-pitched whistles and groans) for communication purposes. Humpbacks seem to be the most vocal of all and produce elaborate 'songs' that last for hours. Consisting of repeated patterns made up of different moans, sighs and high squeaks, all humpbacks in the same area sing the same songs and only the males sing. Singing seems to be most frequent at or near breeding grounds (not necessarily in Australia).
The migratory patterns of eastern Australian humpbacks are so predictable and so close to the shoreline that the whales were easy targets when commercial harvesting began. The whales were mainly hunted for their blubber which was boiled into oil for lighting and lubrication. The oil was also made into margarine, soap and cosmetics.
The baleen or 'whalebone' was softened and trimmed to make stiffeners for clothes, whips and umbrellas.
Within ten years the combined effect of whaling at Tangalooma, Moreton Island in Queensland; Byron Bay in northern New South Wales and by the Antarctic fleets reduced the population of eastern Australian humpbacks by more than 95 per cent! Consequently, in 1962 the industry collapsed and, in time, humpback whales were proclaimed to be a protected species. Their numbers started to increase slowly and now there are believed to be around 2000 individuals, about twenty per cent of the pre-whaling population.
Nowadays, a new industry involving humpbacks has evolved - whale watching. This has the positive effect of allowing many people the opportunity to learn about these great animals in their natural habitat but has the potential to cause some stress to breeding animals. Strict guidelines have been implemented to ensure their safety. There are limits of approach to an individual or group of whales for swimmers (no closer than 100 metres and no more than three vessels at any one time) and aircraft (no closer than 300 metres). When within a 300-metre range of whales, vessels have specific guidelines for their speed, acceleration and direction of approach. If any whale shows signs of distress or alarm, all contact must be abandoned.
Threats to survival
Globally, despite restrictions on whaling, humans continue to have an impact on whale numbers. Whales belong to food chains where pesticides, heavy metals and other contaminants have accumulated. They must also cope with pollution such as oil spills, possible entanglement in discarded fishing lines, and with other hazards from increased boat traffic and from construction activity along the coastline.
These threats are difficult to control and we should all be aware of our individual responsibility to try to preserve these magnificent creatures.