Species deep dive: Sperm whale
- Mathilde
- 2 days ago
- 10 min read
‘’Blow! There is a blow on the horizon! Finally! We had been drifting through the deeper waters of Breiðafjörður for some time now, and we had seen some very distant blows. So we knew that there were whales in the area. But they all disappeared by the time we got close. The blow we saw was at an angle, so it’s probably a sperm whale, exactly the species we were hoping to find. However, sperm whales need to come to the surface close enough to us so we can actually reach the individual before it dives again. This newest blow definitely falls into this category. First, we needed to speed up to get closer quickly. But once we are 400/500 meters away, we slow down and then slowly move towards the sperm whale. The best way to approach the whale is to come parallel to it for the best view, never from behind. And let the animal come closer to you.
This is what happened with the sperm whale: he became curious and approached us. To which we cut the engines and started drifting. This resulted in the best possible sperm whale sighting (see video!): this individual came right next to us, dove down mere meters from the boat and its ecstatic crew and guests! We could truly enjoy the immense size of this male! I was in the wheelhouse, absolutely glued to the window, with my jaw on the floor. Iceland, 2025.
The encounter above was probably one of my favourite and best with a sperm whale (Physeter macrocephalus). For a long time, I really wanted to see these animals in the wild. Everyone knows about the story of Moby Dick, who is probably the most famous sperm whale. The story of Moby Dick, did have an interesting effect on sperm whales as a species, initially, they were perceived as monsters of the deep, but in recent times, the more we research these, actual gentle giants, the more we see how intelligent they are and that they are worthy of conservation. I am not really sure where my fascination comes from, but there is something about these animals, their size, their shape and their culture which are incredible. Sperm whales can be found throughout the planet’s oceans, including the colder regions such as the Arctic and Antarctic, and in the warmer tropical areas like the Caribbean Sea and the Azores. So there are plenty of places on the planet where one can try and see sperm whales in the wild.
My first attempt to spot this toothed giant was in 2010, on holiday with my parents in Norway. We were in Andenes, just north of the Lofoten, and wanted to go on a whale-watching tour. We were in Andenes an entire weekend; unfortunately, the weekend was dominated by a storm, so all trips were cancelled. It would then take me another 13 years before I finally got to see them. I saw my first sperm whale in 2023 in the Azores, off the coast of the island of Pico, whilst on a whale-watching holiday with one of my best friends. I enjoyed seeing them then, but I never really got the enthusiasm I hoped for. Sometimes your imagination runs away with you beforehand, leaving the experience both amazing and underwhelming. When I got the job in Iceland, I knew we could see sperm whales, so I hoped seeing them there would give me the enthusiasm I hoped for in the Azores. Luckily, this hope proved true! The big males were incredible!
The largest animal with teeth!
You might be wondering what’s so special about the males? Sperm whales are the largest animals on the planet with teeth. With some males reaching an impressive maximum length of 20 meters! Of course, not every male reaches 20 meters; on average, their maximum length is between 14 and 20 meters. Females are much shorter, averaging between 10 and 12 meters. Sperm whales have one of the biggest sexual dimorphisms of all cetaceans. Male sperm whales can be almost 40% larger than females. When a sperm whale is born, it is between 3 and 4,5 meters in length. What is astounding about these whales is how long it takes for them to reach their full size: females reach their physical maximum length around 30 years old, while male sperm whales take way longer —around 50 years! Can you imagine that you are still growing until you're 50!
Naturally, it's not just the length but also their weight that differs between the sexes. Males can weigh up to 55 tons, while females can weigh up to 15 tons. Seeing these males in the wild, next to our 24m whale-watching boat, really puts in perspective how massive these boys are. With their rectangular head, with a blow hole on the top left, wrinkly skin and massive fluke (tail). Absolutely incredible! We now know they are big and heavy, but what does their life look like? Let’s take a deep dive into the life of the sperm whale!
The life of sperm whales
After a gestation period of 14 to 16 months, a sperm whale calf is born. All sperm whales start their life in the warm waters of the (sub) tropics, where they are born in social groups of females and other calves/youngsters. Female sperm whales are highly social and prefer the warmer deep waters of our oceans. These social groups consist mainly of related individuals: (grand) mothers, sisters, aunts, and their offspring. They (females) tend to stay in these matrilineage groups for their entire lives. The females work together to raise and protect the calves, sometimes even nursing calves from others. When they are born, sperm whales don’t have any teeth, and for at least 2 years, they depend on milk. On average, the calves feed on their mother’s milk until they are 5 years old. However, the length of lactation in sperm whales is highly variable: young females might continue to lactate with their mum until they are 7,5 years old, and young males even until they are 13! The milk of a sperm whale is incredibly thick, consisting of almost 50% fat, and you can compare its thickness to butter or toothpaste! Whilst they are still toothless, they feed using suction feeding, or the adults give the young their food. The teeth of sperm whales begin to grow once they reach sexual maturity, which, on average, is around the age of 10. They have only 36–52 teeth in the lower jaw and none in the upper jaw. Once they are old enough to hunt for themselves, they start going on deep dives, into the depths of the ocean in search of deep-sea squid and deep-sea fish. Generally, sperm whales dive to a depth of 600 meters and remain underwater for up to 45 minutes. However, the deepest recorded dive of a sperm whale is 2035 meters, and the longest dive recorded was 138 minutes.
These long dive times do make it tricky for us whale watchers to see the sperm whales; it takes plenty of patience. In both the Azores and Iceland, this patience definitely gets tested. The plus for the Azores, and other tropical location, is that people generally come specifically to see the sperm whales; in Iceland, however, this is often not the case. And then the patience of guests can be taxing, but getting close to a sperm whale, seeing it breathe on the surface and then lifting its enormous fluke in the air before a dive is always very rewarding.
Echolocation and sperm whale dialects.
Whilst diving into the darkness, sperm whales hunt using echolocation. Their entire body evolved specifically for these deep dives. In their large rectangular head, they have a 5-meter-long organ, which is the world’s most powerful echolocation system; the spermaceti organ. The name comes from the whalers, who, upon opening the sperm whale, saw a white, waxy-filled organ and assumed that the white wax was sperm. They couldn’t have been more wrong. The initial echolocation, click, is produced in the monkey’s lips, and travels through the spermaceti to the frontal air sac, where the click is bounced back towards the junk, where the click is amplified through 20 acoustic lenses, before it’s broadcast into the open ocean. The echolocation will bounce back on their prey, and they receive the clicks back through their lower jaw. These clicks can be incredibly loud, up to 230 decibels! This makes the sperm whale also the loudest animal on the planet! Let’s compare these 230dB with something we can all imagine, like a fire alarm. The sound of a fire alarm can range from 65 to 120 dB.
The sperm whale's clicks can be heard up to 60km away! These echolocations aren’t only used for hunting; sperm whales actually have at least five different types of clicks, used for hunting, orientation, and communication. One of the most important clicks for females is codas. Codas are used for social interactions; each region where sperm whale families occur has its own distinctive codas or dialect. Sperm whale groups from different regions wouldn’t be able to understand the dialect if they were to come across another group. There is even evidence that these sperm whales have specific codas for individual whales, as if they have names. There is still so much we can find out about sperm whales' communication skills. Project Ceti is doing exactly that, and they have already found that these codas have specific structure blocks that could be seen as a sort of alphabet. And with this ‘alphabet’, they form many different types of codas. (https://www.projectceti.org/)
Migration of the males
What is interesting is that it’s mostly females who use these codas; males hardly ever use these codas. And that might be due to the more solitary nature of males. Once males reach their sexual maturity, they leave their mother and their family. Male sperm whales don’t immediately mate once they are sexually mature. Initially, when they leave, they will still form a social group with other young males, grow together, and travel around the oceans. These social groups are called Bachelor Schools. Quite often in the animal kingdom, males either engage in competitive relationships or, if they form all-male groups, they do so to protect females; in this case, all the males are related to each other. Research has shown that the individual male sperm whale in these Bachelor Schools are not related to one another; they meet along the way and form a group. They stay together until they are sociosexually mature at around 20-25 years old. Once the males are sociosexually mature and ready to mate, they leave these bachelor schools and lead more solitary lives. These Bachelor Schools and lone individuals migrate great distances, they leave the warm tropical waters and head towards colder regions, such as Iceland, Norway, New Zealand, and Antarctica. So when we see sperm whales in Iceland, we are 100% certain that we are seeing male sperm whales. On occasion, they migrate back to warmer waters to find a mate, then return to colder waters.
Resting & Photoidentification
When you see sperm whales, you see them resting at the surface. It almost looks as if there is a tree floating in the sea. They do this with good reason. After their long, deep dives, they need to replenish the oxygen in their bodies, which they do by resting and breathing deeply. They, like all whales, have a very efficient respiratory system. With a single breath, they can replenish 80%-90% of their oxygen. We humans, in comparison, only replenish 10%-15% per breath. This is also because we humans are involuntary breathers, whereas whales are conscious breathers. Sperm whales have adapted really well to these great dives; for example, they don't store oxygen in their lungs; rather, they store most of it in their blood and muscles. They use the protein myoglobin in their bloodstream to store oxygen. So when they go for a dive, hardly any oxygen remains in their lungs, and they can even pre-collapse their lungs. The pre-collapse prevents nitrogen from entering the bloodstream and, therefore, prevents decompression sickness. It’s still possible for sperm whales to get decompression sickness; this mostly happens if they suddenly rise up to the surface in haste.
On average, they remain at the surface for 5 to 15 minutes. Where they breathe around 4 times per minute. This gives whale watchers plenty of time to get closer to the whales and enjoy a good, respectful view. However, it’s always really important not to approach them from the back, as this might spook them and cause them to dive early. After they have rested enough, they will start preparing for another deep dive. It’s possible to predict this, as on their second-to-last breath, they already start arching their body. But when they really go for a deep dive, you will know by the big arch in the back, before they lift their giant fluke in the air.
The shape of their fluke is unique to each individual, like human fingerprints; it’s possible to identify individual sperm whales by looking at their tails. Researchers use photo-identification to research and identify the different sperm whales. We, too, collect photoidentification photos of sperm whales. And one of my colleagues is currently working on our very own sperm whale photo catalogue!
Sperm whales; what an incredible species of whale! Not everyone might have this species on their bucketlist, but I hope that, after reading this blog, have become more interested in the sperm whale. And who knows, maybe come join me in Iceland with Láki tours, April through June are the best months to potentially see the sperm whale in Breiðafjörður, Iceland.
Source:
Eguiguren, A., Clarke, C. M. K., & Cantor, M. (2023). Sperm whale Reproductive Strategies: Current knowledge and future directions. In Sex in cetaceans. Morphology, Behavior, and the Evolution of sexual strategies (pp. 443–467). https://doi.org/10.1007/978-3-031-35651-3_19
Kobayashi, H., Whitehead, H., & Amano, M. (2020). Long-term associations among male sperm whales (Physeter macrocephalus). PLoS ONE, 15(12), e0244204. https://doi.org/10.1371/journal.pone.0244204
Gašper Beguš, Maksymilian Dabkowski, Ronald L. Sprouse, David F. Gruber, Shane. (2025) The phonology of sperm whale coda vowels. GerobioRxiv 2025.06.09.658556; doi: https://doi.org/10.1101/2025.06.09.658556
Carwardine, M. (2019). Handbook of Whales, Dolphins and Porpoises. Bloomsbury Publishing.
Project CETI •-- Home. (n.d.). https://www.projectceti.org/
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