Helen Scales’ beautifully illustrated new book, Around the Ocean in 80 Fish & Other Sea Life, reveals much about the stresses we are placing on the marine world. In this exclusive extract, we feature two of her most iconic, extraordinary, ocean inhabitants – from one of the largest, to one of the smallest
Illustrations by Marcel George
SPERM WHALE – Physeter macrocephalus
FROM EVEN just a glimpse of a head above the waves, sperm whales are easy to identify. Their noses are huge and square, and their breath is lopsided, with vapour shooting off to the left. They breathe through one nostril. The other is closed off, its interior tubes involved in the whale’s production of sound.
Sperm whales hunt in the dark, deep sea and, like giant swimming bats, search for prey using echolocation. They snort air along their nostrils, past vibrating flaps called monkey lips, and send volleys of clicks through the water. Then they listen carefully for the echoes to locate their next squid.
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Sperm whales are one of the marine species that people got to know well by hunting, butchering and processing millions of them. For centuries, European and American whalers chased sperm whales in order to harvest various valuable body parts.
The most important commodity was the golden liquid encased in their noses. It was named spermaceti because people wrongly thought it was sperm (now, it’s thought that spermaceti focuses the whales’ beams of sound as they hunt in the depths of the ocean). Whalers scooped hundreds of gallons of spermaceti from each sperm whale’s enormous nose. It was valued highly as a fine oil that burns clear and bright.
Spermaceti lit the streets of nineteenth-century Europe and America, and it was burned in the powerful lamps of lighthouses.
Whalers also searched inside sperm whales for another valuable product. Ambergris is the sperm whale’s equivalent of the oyster’s pearl. The whales secrete a waxy substance that protects their insides from hard squid beaks. Usually, they get rid of this slippery mass quickly in their faeces, but a small proportion of sperm whales naturally have a constriction in their intestines and the congealed beaks build up into a large, solid mass.
Ambergris is still an expensive perfume ingredient. In many countries, it’s illegal to own and trade it, but occasionally million-dollar lumps wash up on beaches.
When a sperm whale’s digestive system is working normally, it performs a silent service to the planet. While hunting in the deep, most of their body functions shut down to save oxygen for the muscles and brain. Back on the surface, the whale breathes and defecates, releasing iron-rich liquid faeces that act as the perfect fertiliser and trigger blooms of plankton, the tiny algae that harness carbon from the atmosphere.
Before commercial whaling, there were enough sperm whales swimming in the ocean around Antarctica to remove two million tonnes of carbon from
the atmosphere every year.
People have found uses for another sperm whale body part, To pass the downtime on whaling voyages that lasted for years, sailors practised the art of scrimshaw, using needles to scratch pictures into whalebone and sperm whale teeth. Still today, in Fiji, when men ask their sweetheart’s parents for permission to marry, some will make a traditional offering of sperm-whale teeth strung on braided cords. Some families have a stash of heirloom teeth – known as tabua – ready for such occasions.
Fijians have never hunted whales, but they collected teeth from beached animals and in the past traded them from the neighbouring island, Tonga. Now the international trade in any sperm-whale body parts is prohibited.
The limited supply of genuine teeth (there are fakes on the market) can sell for as much as a thousand dollars apiece, and young men often save up for years to buy enough tabua before they can get engaged.
When commercial hunting began in the North Pacific, sperm whales were not too difficult to catch. They often tried to defend themselves by crowding together at the surface. This was an effective strategy against their only other natural predators – orcas – but made them more vulnerable to humans. However, old logbooks of whaling ships have revealed that within two years the whalers’ success rate dropped by 58 per cent.
Scientists think that sperm whales learned how to escape upwind, and even to attack whaling boats. What’s more, the whales probably taught each other how to protect themselves.
Sperm whales live in highly social, matrilineal families. It’s possible that families with experience of whalers showed more naive whales what to do when they were attacked. Even though sperm whales got wise to American whalers, still a huge number were killed, and the hunt ramped up as diesel-powered ships and explosive harpoons were introduced.
In the twentieth century alone, whalers killed more than 760,000 sperm whales. It’s thought around 360,000 are alive today.
NUDIBRANCH – Nudibranchia
NUDIBRANCHS, otherwise known as sea slugs, are phenomenally more beautiful than their terrestrial counterparts. Thousands of species are decorated in rainbow colours and patterns, and not just tropical seas but also cooler waters are home to all sorts of stunning sea slugs.
For some, their bright colours are camouflage. Banana-yellow sea slugs, for example, live and feed on yellow sponges. For others, the colours are a warning to would-be predators that these soft-bodied, shell-less molluscs are not good to eat.
Many sea slugs are laced with bad-tasting chemicals. That is why swimming sea slugs, known as sea angels, are kidnapped by little crustaceans called amphipods, which carry them around as if they were a backpack. Fish and other predators know to leave the amphipod alone or risk a revolting mouthful of noxious sea angel.
One particular species of sea slug, Jorunna parva, became an internet sensation. Nicknamed sea bunnies, they’re fuzzy and white with a pair of fluffy ‘ears’ that are, in fact, sensory organs called rhinophores which detect chemicals in the water. Their ‘tails’ are actually their gills, which poke out – as they do in all nudibranchs (‘nudibranch’ means naked gill).
As well as nudibranchs, an assortment of other gastropods go by the name of sea slug, including plakobranchs and pteropods. Their collective feature is a lack of external shell. Among them, sea slugs perform a variety of unique tricks. Several are kleptomaniacs. Leaf sheep (Costasiella kuroshimae) are bright-green sea slugs that graze on algae and in doing so become solar-powered.
They keep the algae’s chloroplasts, the tiny structures that stack up the sun’s energy to make food, and put them on their skin, where they continue to photosynthesise. This means that when there’s not a lot of algae around to eat, leaf sheep can simply bask in the sun, drawing on their inbuilt food factories. In a similar way, but this time for defence, sea swallows (Glaucus atlanticus) steal the stinging cells from the Portuguese man o’ wars they feed on. These striking blue sea slugs push intact stingers into their finger-like projections called cerata.
Sea slugs have remarkable abilities to regrow parts of their bodies. One species (Chromodoris reticulata) has a disposable penis that drops off after it mates, then regrows within 24 hours. Another (Elysia marginata) has the rather more alarming trick of ripping off its own head. The decapitated head wanders around on its own for a while and eventually grows a whole new body (the abandoned body lives on for only a few days, and doesn’t grow a new head). It’s possible the sea slug does this to rid itself of a body that’s become infested with parasites.
Besides revealing many of the intricate wonders of nature, sea slugs have also taught us a lot about human brains. Since the 1960s, the neuroscientist Eric Kandel has been studying a type of sea slug called the California sea hare (Aplysia californica) to try to find out how memories are made. He picked sea hares because they have large nerve cells that can be seen even without a microscope. There are also not too many of them: about 20,000, compared to 100 billion neurons in humans.
Even with this simple nervous system, sea hares learn and remember things. Gently prod one and it retracts its external gill and siphon. Over time, sea hares learn to respond differently to different stimuli. Kandel watched how individual sea-hare nerves changed as memories formed. He saw that short-term memories lead to temporary changes in the connections between nerves. Long-term memories, on the other hand, cause lasting anatomical changes in the brain. What’s true in these molluscs is also true in humans. In the year 2000 Kandel shared a Nobel Prize for his work understanding memory function, as inspired by sea hares.
In 2021 another team of scientists figured that artificial intelligence could get smarter by becoming more like sea slugs. Two key signs of intelligence in the simple minds of sea hares are habituation (becoming used to a stimulus over time) and sensitisation (reacting more strongly to new stimulus). At the moment, AI is not very good at remembering new, important things while forgetting things that don’t matter much.
The scientists managed to get a quantum material to behave in a similar way to sea slugs, via habituation and sensitisation, a first step towards making better self-driving cars and those all-important social-media algorithms.
