One of my favourite books is Sperm Whales by Hal Whitehead. Reading this rounded off a lifetime of fascination with the species. Sperm Whales are one of the biggest animals on Earth. Indeed, they are also the largest toothed predator that ever lived. Yet we know hardly anything about them. We do know that Sperm Whales mostly eat squid. But how do Sperm Whales catch squid?
One of the clues might be in Jackie Higgins’ recent book Sentient. Biologists can sometimes ignore unproven ideas that might be obvious based on evidence from a different field. The fact is, Sperm Whales are supremely capable of using a combination of senses, including sound, touch and sight, to be able to picture their surroundings in what we would regard as complete darkness. A world in which we would might be blind, is one in which Sperm Whales see brilliantly.
But are we blind in such darkness? Higgins describes the power of our vision-cells to detect light at little more than a few photons. Our night-vision is far more acute than we know. Most of us have lost this sense, as we never practice it, so our brains don’t have use for it anymore. We’ve lost awareness of it, so perhaps, we’re too ready to disregard its importance for other animals.
Sperm Whales can see in the dark
We know that whales use a range of different senses, like we do, to home in on prey. Some senses are important to find the general area of food, some for detecting prey patches and others for the final attack.
Sperm Whales have bright white jawlines and it has been suggested the mere act of consuming squid, lines these with bioluminescent jelly. The jelly’s origin is from bacteria that live in the slime covering squid bodies. In the absolute darkness, nerve endings and adaptations we don’t even know about yet, are surely capable of amplifying this brightness. The whale’s mouth represents a corridor of light that would attract squid towards its jaw. Once in striking range, the squid distends throat grooves and sucks the squid inside its mouth.
There are plenty of deep sea animals that lure others with a faint glow. Sperm Whales’ eyes are also adapted to see blue light better. That’s not surprising, as red light is absorbed at such depths. The whales are sensing the light that isn’t absorbed, the small portion that gets reflected.
Sperm Whales use multiple senses to catch squid
Too often we seek single, simple explanations for how things work in the animal kingdom. Whether it’s behaviour, senses or ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More, a diversity of different confounding strategies combine to create what works.
Sperm Whales don’t just look for light. We know this, because they echolocate like bats. They are the loudest natural sound in the ocean and are able to ‘read’ the reflections of this sonar just as well as we can see. Or at least, with such sophistication, they can catch squid. We can’t comprehend what they ‘see’, we can only imagine it’s as ‘clear as day’ for a Sperm Whale.
The average size of a squid meal is quite small. Sperm Whales have to eat almost a tonne each day, which means catching up to 350-750 squid a day. It’s hard to imagine a whale dedicating energyEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More to capturing individual squid, especially as they aren’t particularly nutritious. There must be another way to find large concentrations and consume them on mass. Squid are fast though, so Sperm Whales have to be sneaky enough to find and gorge mouthfuls, on each dive.
Sperm Whales keep squid populations under control
A single Sperm Whale consumes about half a tonne of food a day. Scientists have estimated the total annual consumption of all Sperm Whales as equivalent to the catch of all human fisheries. Let’s put it another way. It’s equivalent to all the seafood consumed by all species of seabirds globally too. One species, Sperm Whale, has that effect on the planet.
As we have discussed before, the ‘impact’ of animals is positive. Sperm Whales are the likeliest survivors because for millions of years they’ve given just as much as they’ve taken from the ecosystems. Which means they’ve kept balance.
Today, squid populations are increasing and threatening whole fisheries in some areas. Squid have become a ‘pest’ because we have removed species like Sperm Whales that were keeping the planet’s deep-water food chainA single thread in a food web illustrating the chain of animals that eat each other. At the base of the food chain are small high-energy (fast metabolism) animals and at the other end large low metabolism animals. An example would be whales eating krill that eat plankton that eat algae. Or lions that eat gazelles that eat grass. More in check. This is what we learn about predators.
Even small numbers of large predatory megafaunaThe largest animals that represent the top of the trophic pyramid. These are the final building blocks in ecosystem structures for maximum entropy production. Megafauna can be measured at any spatial scale. The largest animal that ever lived on Earth is the Blue Whale. In a grassland, spiders could be considered megafauna The term is generally reserved for animals larger More are integral to ecosystem function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More. Remove them and the energy that was once distributed higher up, flows down into the base of the food pyramid. Everything then suffers. Squid outcompete other fish. Tuna and other pelagic fish populations decline (leading to nutritional decline for local people in lower income countries). The consequence for Sperm Whales is equally catastrophic. They don’t just eat squid. Remove other prey and the resilienceReferring to an ecosystem’s ability to maintain a steady stable-state. The need to build resilience is entirely anthropocentric and symptomatic of ecosystems that are damaged or declining, leading to loss of ecosystem services on which humans depend. More they have, to eat alternative food, disappears. The system starts to collapse like a house of cards.
Sperm Whales engineer their own fisheries
The biggest answer to ‘how do Sperm Whales catch squid?’ is that they know where to find squid. That is one of the most important factors of all. Sperm Whales, like all animals, engineer their own ecosystems. When we started fishing and whaling, we interfered with those processes and started to collapse the animal-driven mechanisms that built the system in the first place. Animals are part and parcel with ecosystems, as are we alongside.
Humans do not create fisheries. Animals created the fisheries that humans decided to harvest. We get this wrong all of the time. We are currently trying to maintain global fisheries and few have yet thought to ask, what about the collapse of Sperm Whale populations?
Sperm Whales are only able to know where to find squid because they have developed their own society and culture over millions of years. The spin off from their work is that we have food to eat and even a stable climate.
Their connection to the deep sea is through their remarkable sensory adaptations and they built the ecosystems that are disappearing in their absence today. Humans cannot continue to exist on a planet without Sperm Whales.
Sperm Whales are truly intra-planetary
Sperm Whales are the only species on Earth where an individual can have a home range that is the whole world. Males are genetically similar across ocean basins, meaning the whole world is their breeding ground. No other species, that we know, ‘owns’ the world as much as a Sperm Whale. This is a species that we should be worshipping for its millions-of-years-old wisdom. Sperm Whales know more about the function of our planet and are more connected to it at a planet-wide scale, in ways than humans can never imagine.
For these and many other reasons I don’t have time to explain, the answer about ‘how do Sperm Whales catch squid?’, is that Sperm Whales are the most extraordinary animal on Earth.
