By Lloyd Edwards
Going 40 nautical miles (80km) south from Cape Recife is no easy task. Picking the best weather day and sea conditions is vital. We met at the Nelson Mandela Bay Yacht Club at Sparrows fart and headed off with a group of avid adventurers. Although we saw plenty of other action along the way, for this post I will focus on the magnificent Sperm whales.
We had the head guide of Naturaliste Charters in Bremmer Bay, Australia on board. Machi Yashika has specialises in spotting killer whales and other cetaceans in the often-adverse offshore conditions. She had her eye in on this occasion and found us three male sperm whales. They were all feeding at the continental drop off. We managed to catch them on the surface replenishing their Oxygen levels before heading down into the depths in search of their squid diet.
About Sperm Whales
Believe it or not, Sperm whales get their name from the fact that people originally thought that the oil contained in the organ that makes up its head was the animal’s sperm! This whale was made famous in Herman Melville’s Moby Dick, a book based on his hunt for the giant white whale. It was the demand for this spermaceti oil that led to them being the most heavily exploited of all the large whales. This is the only part of whale products that cannot be synthetically produced and still used by NASA. This is the largest toothed whale and also has the largest brain of any animal on the planet. It is also one of the strangest looking cetaceans, with its huge head and lumpy and wrinkled skin. Besides killer whales and humans, they are the most widely distributed animal on earth. They live for 70 years or longer.
In our waters they have been observed about 50km south off Cape Recife. This is where the continental shelf starts dropping down from 200 metres to 1, 5km. They will hunt along this drop off. They dive on average for around 45 minutes and will rest for five to 15 minutes between dives. They are found here in winter. In summer they move towards the poles, the largest males going to the edge of the polar ice. Like all rules there are exceptions. Ten Sperm whales were spotted by marine mammal observers doing seismic surveys 20km south east of Cape Recife during December 2013. We managed to get the survey stopped and postponed as they were planning to do it while the humpback migration was still underway. I arrived with my logbook full of humpback whale sightings during December and managed to convince the chief geologist and crew to change their plans!
As with all toothed whales the Sperm whale exhibits sexual dimorphism, males historically reaching 20 metres while on average 16 metres while females just 12 metres. In males the head is proportionately larger than females who in turn have a longer rear part of their bodies. They have a single s shaped blowhole on the front left side of the head. The dorsal fin is noticeably short and is followed by a series of knuckles which reach the flukes. There lower under slung jaw looks small compared to the rest of the animal but is not. They average 25 teeth in the lower jaw although some smaller teeth do break through the skin in the upper jaw. The teeth can grow up to 25 cm in length and were used in the art of scrimshaw.
These animals have an incredible social structure and become very attached to one another. If they are attacked by killer whales which are seldom fatal, they all go into a formation with their heads pointing towards each other, known as a “rosette”. Even if the killer whales manage to separate one from the group, two of the others will escort it back into the position even at risk of getting injured themselves. Unfortunately for them, whalers knew this and would consequently wipe out entire groups. Even after their parents had been killed, young whales would hang around the boats for extended periods.
Like some other cetaceans, sperm whales demonstrate a culture that is passed down through the generations. It could be used to teach the younger whales where to find alternative food sources when one runs out. The have different clans and even communicate with their own sounds or “codas”.
There are two main groupings of Sperm whales. The first is the breeding schools, which in our area are made up of 10 to 15 females and their offspring. In other parts of the world these groups could extend into their hundreds and historically thousands. Once the males reach puberty, they will move off and join the bachelor pods which can be up to 50 strong. Once they become socially mature, they will live in small groups or lead a solitary life, only mixing for a few hours during the breeding season. When he does so, he becomes the absolute focus of attention. They crowd around him and rub themselves on his huge body.
Calves are born at 3, 5 to 4, 5 metres and weigh a ton. In whale terms, a long pregnancy, which last 15 to 16 months. Nursing will carry on for two years as the calf will not be able to undertake dives as deep as the parents. It either waits alone on the surface or with a minder to protect it against predations by killer whales. It keeps its pectoral fin close to its body so that killer whales cannot get a hold. Milk remains have been found in immature females at seven years of age and males of 13 years which really makes them the ultimate mommy’s boys! Due to the constant attention given to the calves the breeding interval is five years.
Sperm whales are the absolute masters of deep diving. The longest dive ever recorded was for two hours and 18 minutes, while the deepest was to 2035 metres. There have been unconfirmed reports of them reaching 3, 2 km. At these depths the lungs will collapse and they rely on Oxygen stored in the blood and muscles. The heartbeat slows and oxygen is only sent to the vital organs like the heart and brain.
We are still not sure how they feed at these depths. Some argue that loud acoustic pulses are generated that stuns their prey. It seems however that they are produced too infrequently for the amount of prey consumed, which can be a ton and a half for large males. They may well use these pulses which can be detected 60km away to locate their prey. Although they may be effective against fish, this is not part of their diet. It would not work on their main prey item of small to medium sized squid of between one and three kg. The clue could be the white marking around the lips. Combined with bioluminescence from plankton being disrupted by the whale’s movement, it may attract prey towards the animal. When it gets close enough, it is simply sucked in. Either way it is a highly effective predator, the largest ever seen in the oceans or on land. Although they are often portrayed in titanic battles with giant squid, this is not their chief source of food. They can eat up to 27 species of cephalopods, deep sea fish and sharks.
These animals were hunted more than any other whales until they were protected in 1982 which was only implemented in 1988. The population was estimated to be 1, 1 million before whaling and current estimated are between 300 000 and 450 00. This makes them the most abundant of all the great whales.
