Book Review

Nomads of the Oceans: The mystery behind sea turtles: Their unique super senses, astonishing navigational skills and how they shape the Sea

German title: Nomaden der Ozeane: Das Geheimnis der Meeresschildkröten: Ihre einzigartigen Supersinne, ihr erstaunliches Orientierungsvermögen und wie sie die Meere formen.

If you are interested in learning more about sea turtles, Frauke Bagusche’s book Nomads of the Oceans is a worthwhile read. Unfortunately, it is currently only available in German. Therefore, I have embarked on the endeavour of writing a comprehensive book summary for non-German speakers.

Marine biologist Frauke Bagusche, born in Germany in 1978, earned her doctorate at the University of Southampton in the United Kingdom. Following her graduation, she was appointed the head of the Marine Biology Station in the Maldives and embarked on a transatlantic sailing expedition to raise awareness about marine plastic pollution. Together with a colleague, she established the non-profit organisation “Blue Mind” and currently works as a freelance lecturer, providing training on topics related to plastic pollution, climate change, and overfishing in the oceans. She is also the author of “The Blue Wonder: Why the Sea Glows, Fish Sing, and Other Astonishing Insights from the Ocean.”

With that settled, let us dive into the fascinating world of sea turtles and uncover the truth about these remarkable creatures.

Globally there are seven sea turtle species roaming the oceans, namely the flatback, green, hawksbill, loggerhead, olive ridley, Kemp’s ridley, and leatherback sea turtle. Turtles have been around for more than 150 million years and have survived many mass-extinctions along the way.


If we picture turtles, we often describe them to be slow, but also very resilient and kind-hearted, from which we do not expect any harm. But where did they get this from? Where did turtles evolve from?

The first chapter on the evolution of sea turtles positively surprised me, as I never paid much attention to where turtles came from and how their evolution came about. Many years scientists believed that turtles derived from extinct reptiles. But in 2015 palaeontologists discovered a fossil in Germany, which shook the world of science. This 240-million-year-old fossil showed a link between lizard and turtle. This ancient turtle species Pappochelys rosinae had a lizard-like appearance but featured expanded stomach ribs like the plastron (stomach shield) in turtles. This discovery was a breakthrough in our understanding of turtle evolution, clarifying that snakes and turtles are more closely related than previously thought.

Super senses

Deviating from their terrestrial counterparts, sea turtles possess a distinct morphology and physiology tailored to their marine existence. Their flattened carapace, streamlined body, and flipper-like extremities allow them to smoothly navigate the aquatic realm. Despite lacking the ability to withdraw their heads and limbs for protection, sea turtles have developed remarkable physiological adaptations to thrive in their saltwater domain. Specialized salt glands located at the corners of their eyes aid in regulating excess salt intake, a crucial adaptation for survival in seawater. The presence of horny papillae within the oesophagus allows sea turtles to efficiently consume jellyfish, an important component of their diet. Sea turtles possess eyes that function effectively in both land and water, enabling them to navigate both environments with ease.

They also have an exceptional sense of smell underwater, enabling them to locate food sources and allowing them to detect potential threats or mates. Even within their eggs, sea turtles exhibit sophisticated communication mechanisms. Embryos produce clicks, chirps, cackles, and grunts, coordinating their hatching process. Regarding thermoregulation, sea turtles are partially endothermic, meaning they can maintain their body temperature to some extent. However, swimming in waters below 10°C can pose challenges for most sea turtle species, except for the leatherback turtle.

Believe it or not, sea turtles can sense touch on their thick carapace, so next time you stroke a turtle make sure to be gentle!

Furthermore, sea turtles are remarkable divers, reaching depths that would be unimaginable for most land-dwelling reptiles. Most species can dive to depths of up to 54 meters, while the leatherback turtle can plunge to astonishing depths of up to 1,200 meters. Additionally, sea turtles can hold their breath for several hours, allowing them to explore the underwater world extensively.

A Guide to sea turtle identification

Subsequently, Bagusche tackles in-depth descriptions of each species and their identification methods. While her explanations are comprehensive, they could benefit from further simplification, particularly for novice readers. Integrating a visual aid, such as a graph from the esteemed Queensland Marine Turtle Field Guide, would significantly enhance the identification process and make it more accessible to a wider audience. This guide provides a clear and concise roadmap for identifying sea turtles. It begins by assessing the carapace type, distinguishing between scales (present in all species except leatherbacks) and ridges (unique to leatherbacks). For turtles with scales, the number of costal scales along the carapace sides serves as a key identifier. Four pairs indicate a hawksbill, flatback, or green sea turtle, five pairs signal a loggerhead, and six pairs identify an olive ridley.

To further differentiate between hawksbill, flatback, and green sea turtles, the prefrontal scales located at the front of the head provide additional clues. Two pairs of prefrontal scales are exclusive to hawksbill turtles, while green and flatback turtles have only one pair. Flatback turtles possess an additional preocular scale, distinguishing them from green sea turtles, which lack this feature.

Ever heard of the “Lost years”?

In the next chapter, we learn about the hatching process of sea turtles and their remarkable journey back to their birthplace. Sea turtles lay a varying number of eggs depending on their species, with each clutch containing anywhere from 65 to 188 eggs. Sea turtle eggs can vary in size being as small as a golf ball and others as large as a billiard ball. The sex of sea turtles is also determined by temperature, with eggs incubated at temperatures below 28°C (82°F) developing into males and eggs incubated at temperatures above 31°C (88°F) developing into females. Interestingly sea turtles are born with a temporary “egg tooth” or “caruncle” to break out of their shells. Once hatched, they face numerous predators, from raccoons and dogs to seabirds and ocean creatures. Statistics show that only 1 in 1000 sea turtles survive to adulthood.

Loggerhead sea turtles, in particular, migrate to the Sargasso Sea in the Atlantic, a haven for marine life due to its abundance of sargassum seaweed. They spend about 10 years in this region before entering the “lost years” of their juvenile stage, where their activities remain largely a mystery to scientists. Upon reaching sexual maturity, they mate with multiple partners before returning to their natal beach to nest. This incredible navigation ability is attributed to their imprinting on the magnetic field of their birthplace.

Sea turtles: Survivors in Peril

In her final chapters, Bagusche highlighted the grave threats facing sea turtles in our big oceans. These magnificent creatures contend with a multitude of perils, including plastic pollution, habitat destruction, entanglement in fishing nets, and the relentless pursuit for their eggs, meat, and shells, often for dubious medicinal purposes or the production of jewellery.

Global warming further endangers their existence. As mentioned earlier, eggs incubated above 31°C produce female hatchlings. Should global temperatures continue to rise, this could skew the sex ratio, leading to an overabundance of females. Nevertheless, scientists remain optimistic about sea turtle populations, citing their demonstrated ability to adapt to changing environmental conditions. During warmer periods, males have an increased reproductive advantage, successfully fertilizing more females. Females have also exhibited behavioural flexibility, shifting their nesting times to cooler periods, or even migrating to cooler beaches to ensure favourable conditions for their offspring.

Management programs are essential to secure the survival of sea turtles. Unfortunately, illegal hunting persists in many corners of the world, necessitating the firm efforts of environmental organisations that tirelessly patrol beaches, preventing poachers’ attempts to steal eggs or capture turtles. Moreover, the data collected by turtle biologists is invaluable for monitoring the reproductive success of these endangered species. The IUCN Red List classifies nearly all sea turtle species as endangered, with three of the seven species critically endangered: the leatherback, hawksbill, and Kemp’s ridley sea turtles. The green and loggerhead sea turtles are also classified as endangered.

Our society needs to recognise that this is our only chance to positively impact our planet. The damage we have inflicted upon the Earth is undeniable—burning rainforests, emitting CO2 emissions into the atmosphere leading to global warming, melting polar ice caps, rising sea levels, and species extinction. Between 1970 and 2016, we have witnessed an average decline of 68% in reptile, fish, amphibian, and mammal populations.

A silver Lining?

Despite the grim outlook, Bagusche offers a beam of comfort. The 1979 Washington Convention, which prohibits the fishing and trade of all sea turtle species, has undoubtedly helped mitigate the misery of these creatures. Numerous turtle foundations worldwide, such as the Turtle Foundation, dedicate their unwavering efforts to protecting sea turtles, for which we are eternally grateful. Additionally in 2022, UN member states have unanimously resolved to tackle plastic pollution in the oceans.

My personal stance

While I applaud Frauke Bagusche for her dedication to sea turtle conservation and her efforts to raise awareness through this book, her writing style could benefit from greater structure and cohesion. Her tendency to stray from the main topic and present her thoughts in a stream-of-consciousness manner can make it challenging for readers to follow the narrative and fully grasp the key points. Nonetheless, Bagusche’s passion for sea turtles shines through, and her book undoubtedly contributes to the important cause of sea turtle conservation.

Cover image: Green turtle is going for air by Brocken Inaglory

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