Life in the open ocean, and sharks

Into the Great Wide Ocean. Life in the Least Known Habitat on Earth. Johnsen, S. 2024. Princeton University Press, Princeton, NJ, USA. x+228pp. US$24.95 (hardcover). ISBN 978-0-691-18174-5. Shark. The Illustrated Biography. Abel, D. C., and S. A. Maycock, 2025. Princeton University Press, Princeton, NJ, USA. 224pp. US$29.95 (hardcover). ISBN 978-0-691-26167-6. These 2 books are eye-openers to marine life and habitats that most of us will never experience firsthand. The authors are research scientists and science communication writers, so readers get accurate research imparted as well-written and humorous stories and relevant land-based comparisons to maintain reader attention. The open ocean, which is an amazing 90% of the world's habitable space, is a complete mystery to most of us. Sharks, in contrast, are more familiar, but there is much more to them than the media stereotype of sleek, powerful killers. Into the Great Wide Ocean shows that the open ocean is extremely difficult to study, shipboard research notoriously hard, and the inhabitants of the open ocean impossible to observe without disturbing them. This sounds rather negative, but the author treats readers to positive personal experiences, humor, and engaging stories. The book is as much about how research at sea is conducted, and the scientists and crew, as it is about marine life. Johnsen admits to being obsessed by machines and describes his first sight of the Johnson-Sea-Link submersible as a “wondrous thing, looking for all the world like a helicopter without propellers mated to a bank vault.” The book covers the top 1000 feet of the water column, which has received far less attention than the deep sea, despite being where most of the life is. Initial chapters cover the physical forces of gravity, pressure, and light and how animals and phytoplankton have adapted to these. These topics occupy a large chunk of the book, and the author does not shy away from the necessary technical explanations of the physics and chemistry of the open ocean, but his text is enlivened with personal experiences to keep readers entertained while exploring the problems and solutions of life in this alien world. Life in the ocean, buoyed by water, exists in a much larger 3-dimensional volume than is possible on land or in air, but maintaining a particular optimum depth is vital. The need to avoid sinking to the deep sea and to move around to catch food and find mates has generated a wide range of adaptations. Readers will be familiar with swimming but not as much with adjusting buoyancy, unless they are scuba divers. Some fishes have gas-filled swim bladders—which apparently were tough enough to be used as condoms around a hundred years ago. Many oceanic creatures are essentially blobs of jelly with buoyancy near neutral, but antisinking ploys include producing lighter-than-water oils, parachutes of wide-spreading mucilage that double as fishing nets, and growing protuberances in every direction such that the animals look like tiny Sputniks—both bizarre and beautiful. Johnsen begins the chapter on food by highlighting the enhanced importance of food to the scientists and crew on research vessels. Ninety percent of the time life at sea is crushingly dull. Only meals and sleep mark the passage of time, and food can become an obsession on the well-stocked ships. By contrast, in the open ocean food is relatively scarce, and how to find it and avoid being eaten yourself is a constant challenge. Some large animals actively hunt prey, as on land. But most of the small creatures catch tiny food particles with ingenious mucus nets and filters. To avoid being eaten, many are almost completely transparent or camouflage themselves. By contrast, a few venomous or foul-tasting animals look striking as a warning; the author likens this to never eating another lobster sandwich after eating a spoiled one in Nova Scotia. Finding a reproductive partner in the open ocean is particularly difficult. The author compares this with a human party where it is pitch dark and dead silent with only dim flashing lights to indicate anyone is there at all and at this party you must somehow find a life partner. Many marine creatures just rely on discharging vast amounts of sperm and eggs into the water, relying on sheer numbers for a few to survive. Others look after their offspring. The example of Phronima shrimp, which eats a living salp and then uses its case as a baby buggy, is well-known to marine biologists. Johnsen compares these shrimp to the gruesome parasitic wasps whose young hatch inside caterpillars and eat them alive and quotes Darwin's observation that a beneficent God could never have designed such a creature. Darwin, he says, would have been even more disturbed if the wasp had returned to push the caterpillar along like a mobile nursery. The final chapter begins with an insight into shipboard life and the coping strategies that develop among a ship's community. However, little is known about communities in the open ocean, and a major reason for this is that, with current research tools, it is not possible to study creatures in this habitat without disturbing them. This remains an apparently insurmountable challenge to open ocean research. The book is not directly about conservation. The author says that we save what we love, and we love what we see—and only a tiny fraction of people have seen below the surface of the open sea. Before scientists can ask people to preserve this important and fragile environment, they need to show them that it is there and the beauty of what lives in it, which is the aim of this book. I was delighted to come across a reference to Alister Hardy, a British marine biologist who wrote a classic book on plankton in the 1950s, which is still the best book on plankton I have read. Johnsen says “he is a hero of mine because he combined science with both good writing and excellent art.” This book does the first 2 admirably, and the simple line drawings scattered throughout are pretty good too. At the end of the book is a further reading list, organized by chapter. I highly recommend this book for marine biology students and indeed anyone interested in the ocean. The deep sea, defined in Shark as deeper than 200 m, is home to over half of all known shark species. This is astonishing in light of the harshness of the deep-sea environment. This book aims to be a shark biography, telling the story of sharks’ whole lives, from birth and growing up, to family history and relationships, talents and skills, and significant events and life challenges. It does this with the minimum of scientific jargon and numerous entertaining and fascinating stories about sharks. In a rather unusual structure, the authors concentrate on 4 shark species, the great white shark (Carcharodon carcharias), sandbar shark (Carcharhinus plumbeus), small-spotted catshark (Scyliorhinus canicula), and spiny dogfish (Squalus acanthias). Between them, these 4 species largely represent the diversity of lifestyles, habitats, reproductive modes, and swimming styles of sharks as a whole (apart from the sharks of the very deep sea, for which there is still very little information). Other shark species are discussed that do things differently from the featured 4. The book is illustrated throughout with charming pencil and colored drawings. The first of 10 chapters is a basic introduction to sharks and outlines the variety of cartilaginous fishes of which sharks are the major group. Sharks are distinguished from their nearest cartilaginous relatives, the skates and rays, by the ability to detect very weak electromagnetic fields. Of course, teeth are a well-publicized feature of sharks, but did you know that they are continually replaced and that a shark's entire skin is made of modified teeth? The evolution of sharks through geological time and how they are currently classified is fascinating background to the currently existing 550 species. As a group, sharks have survived at least 4 major extinctions, but many species have been lost. Modern sharks may only represent a tiny fraction of what they once were. Fossils indicate that early sharks developed some bizarre adaptations and included the largest predatory fish that ever lived, the megalodon, around 18m long (60 feet), with teeth measuring 18 cm (7 inches). Today, sharks range from tiny deep-water lantern sharks to huge plankton-eating basking and whale sharks. They live in most areas of the marine realm, from tropical to polar regions, and from shallow sandbanks and mangrove swamps to the deep sea. A few sharks even live in freshwater lakes and rivers. The prenatal, early, and adult life of sharks is an absorbing read. The obviously besotted authors claim “there is nothing as cute as a newborn shark” and that newborn whale sharks are “as darling as can be.” Compared with bony fishes, sharks produce few young, and various strategies are employed to give their young the best start in life. Forty percent of sharks lay eggs, with the embryos protected in tough cases. Even as embryos, bamboo sharks can detect the electric signals of a predator nearby and instinctively stop moving inside their egg case until it goes away. The sawshark, as its name suggests, has a bizarre, long, projecting snout with teeth along each side. It gives birth to live young, which might make for a painful birth for the mother. However, the teeth of her unborn pup are folded back against the side of the saw while in the womb and pop out into their final positions only after birth. The sand tiger shark's embryos famously eat each other in the womb until only the 2 strongest are left, one in each of the mother's 2 uteruses. “Sharks that break the rules” are oddballs, including the pigfaced shark, sawsharks, goblin sharks, angel sharks, wobbegongs, and thresher sharks, all of which have strange features that have evolved to help them succeed in their particular niche. Human–shark relationships are referred to throughout the book and covered in more detail in a separate chapter. Over the ages, and in different cultures, sharks have been worshipped as gods, feared as demons, venerated as protectors, and blamed for catastrophes. The media hysteria over the much-exaggerated dangers of sharks to humans is debunked. The authors are keen to emphasize that as adults only a handful of the 540 or so shark species currently known are apex predators (i.e., at the very top of the food chain). I have personal experience with one of these, the broadnose sevengill shark, which frequently showed up on survey dives I participated in on the remote island of Tristan da Cunha. These primitive-looking sharks often investigated us closely, but could usually be fended off with an underwater camera. Maybe it is just as well that we divers had not read this book. Although the larger apex predators target a variety of prey, including marine mammals, the authors say that no shark includes humans as a regular part of its diet, although they admit that an exploratory bite could do some damage. One fun statistic is that for every person bitten by a shark, 5 people are bitten by New Yorkers! The final chapter is, inevitably, devoted to threats to sharks and their conservation. As with other fish stocks, overfishing is by far the biggest threat to sharks; they are especially vulnerable because they reproduce slowly. Habitat degradation, pollution, noise, and climate change also affect shark populations. However, the authors end on a positive note, in that hearts, minds, and action appear to be moving in the right direction for shark conservation. One mistake I spotted in the book is the distribution map of the small-spotted catshark, which does not occur in the Southern Hemisphere. A couple of illustrations that are supposed to show the diversity of sharks and their distribution in the water column do not work well. However, these are minor criticisms in an otherwise excellent read. I could open the book at almost any page and find a clever fact or interesting quote for this review. The authors obviously love sharks, and after reading this book readers might too.