Deep dive...into Sperm whales

There’s still a lot of mystery around sperm whales due to the fact that they spend so much of their life out at sea, far away from land. 

Though not the largest species of whale, the sperm whale (Physter macrocephalus) has the largest brain of any animal on the planet. It’s also the biggest species of all the toothed cetaceans.  

On average, a male sperm whale grows to 16 metres long with a female growing to 11 metres long. In appearance, the sperm whale is dark grey and has a torpedo shaped body with wrinkled, prune-like skin. Its tail, triangular in appearance, is clearly visible when the mammal swims headfirst into a deep dive. 

A sperm whale’s head makes up around a third of its body length and is square-shaped. It has short rounded dorsal fins, and the pectoral fins on either side of their bodies are also relatively small and paddle-shaped. 

Along with its block-shaped head, the sperm whale is easily recognisable because of its jaw, containing up to 52 cone-shaped teeth in the lower half of the mouth. 

Sperm whales get their name from ‘spermaceti’, the waxy substance found above and in front of the skull (that was much sought after by commercial whalers for use in products such as oil lamps and candles). We don’t fully know the function of this substance but experts believe it may help the whale regulate its buoyancy and/or to focus sound. 

The sperm whale is probably best known for the depiction in Herman Melville’s 19th century novel Moby Dick. The writer partially based the whale on a real life albino whale of that period called Mocha Dick who lived off Chile. He was hunted by whalers and managed to survive for years and years, fighting back with considerable ferocity.

On average, a sperm whale can live to 70 years of age, though there is evidence of the species living longer than that. 

Sperm whales live in stable and complex matrilineal groups and are often seen in pods of 15 to 20 whales. Male sperm whales usually hang out with the group until they’re in their 20s or 30s, when they tend to go their separate ways. Females usually stick with the group longer and form ‘nursery schools’ to collectively take care of calves and protect them from danger. 

Sperm whales when they are born are pretty big! They measure, on average, four metres long. As they can’t undertake the deep dives that their mothers can, they’re taken care of in the ‘nursery schools’ whilst mum is out hunting for food. 

Sperm whales inhabit the deep ocean and are rarely seen along coastlines except in areas where there are deep trenches or underwater canyons as you get closer to the shore. Kaikoura Canyon in New Zealand is one such place and is an important breeding ground for sperm whales.

The mammals are also spotted in island chains such as the Azores, Galapagos and the Canary Islands, and are seen in the Strait of Gibraltar, between Spain and Africa.

A small population of less than 1,500 sperm whales lives in the Gulf of Mexico. Scientists have discovered they are a distinct population – they’re smaller in size than other sperm whale populations (probably a response to limitations in their food sources) and they use combinations of calls different to other sperm whale populations.

Sperm whale migrations aren’t as well understood as the migrations of baleen whales such as humpback whales. Generally speaking, females and their young are more likely to stay in tropical waters year-round and adult males make long journeys into waters closer to the two polar regions. 

These toothed whales eat around one ton of food a day – feeding on large squid (particularly giant squid), fish, skates and sharks.

The species spends most of its life hunting for its prey, diving deep in order to catch it.  

Light becomes limited the further down into the ocean the sperm whales travel so they use their finely tuned echolocation skills to help them find prey. 

A sperm whale typically dives to a depth of 1,000 metres though they have been documented diving to 2,000 metres and more (which involves holding their breath for an estimated 1.5 to 2 hours). 

It’s no wonder then that they spend time recovering at the surface and taking lots of breaths after they re-emerge from a feeding dive. 

Sperm whales were once thought to have numbered 1.1 million worldwide, according to the American Cetacean Society. Their population was decimated by the whaling that occurred in the 18^th century right through to the 20^th century.

They were a popular target for commercial whalers for a few reasons: 1) spermaceti (waxy fluid contained in their heads that could be used for products such as oil lamps, lubricants, cosmetics and candles), 2) the blubber in their bodies, and 3) ambergris.

The latter is often described as one of the world’s strangest natural occurrences and only occurs in sperm whales. It’s a substance that forms around digested squid beaks in a whale’s stomach. It’s thought to occur so that the internal organs are protected from the sharp beaks.

Ambergris was highly prized by perfumeries as an ingredient, so it was something that whalers were eager to acquire and sell on.

Whaling is no longer a threat to the species and there is evidence that its population is recovering, though it is still a fraction of its previous number. It’s estimated there are now 360,000 sperm whales globally. However, it’s a difficult species to obtain accurate numbers on because it lives so far out to sea.

It’s considered by experts to have vulnerable to endangered status, depending on locality around the world.

All whales are vulnerable to ship strikes, which can injure or kill them. There isn’t a huge amount of documentation available on vessel strikes caused to sperm whales but as vessel traffic worldwide is increasing, the risk of collision increases with it.  
 
Vessel strikes are believed to be one of the main drivers of sperm whale population decline in the Mediterranean and could also be a threat to the survival of sperm whales in the Canary Islands. 

Underwater noise pollution, caused by humans, can interrupt and disturb the normal behaviour of whales. They use sound to communicate so any interruption interferes with that communication and to their ability to pick up signals in the environment.  

Like other whales, sperm whales can become entangled in different types of fishing gear. This can cause injury, fatigue, compromised feeding and even death. A technique that sperm whales have developed to remove fish from longline gear may unfortunately contribute to their entanglement.  
 
Depredation is when the whale uses its long jaw to create tension on the fishing line and this shakes fish off the hooks. The whale can become entangled or injured whilst trying to free up food this way. Find out more about depredation in this article in Hakai magazine.  

This can lead to both loss of habitat (as waters become warmer) and lack of food for sperm whales. Changing water temperatures can impact the timing of important cues for whales such as when it’s time to depart to feed or to migrate to breed.  

The feeding range of sperm whales is one of the greatest of all species on earth so it’s thought the species is less susceptible to food scarcity than other types of marine species.  

Plastics and micro plastics in the ocean pose a threat to whales, along with all other marine mammals and fish. Chemical pollutants entering into the water ecosystem also pose a serious threat to all creatures in our ocean, including sperm whales.  

Sperm whales are not regularly the target of natural predators, though there have been observations of orca whales attacking sperm whale pods. Large sharks are also thought to be occasional predators of sperm whale calves
 
Pods have been seen forming protective circles against potential attacks, positioning any vulnerable young or injured whales in the centre of their defensive formation.