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WHALES might as well be aliens. They live on the same planet as us but we seldom cross paths: hidden in the ocean depths, they remain mysterious.

Take their size. Blue whales are the biggest species that has ever lived, exceeding any dinosaurs. The heaviest reliably measured specimen weighed 136.4 tonnes, more than the weight of a Boeing 757 at take-off. Intriguingly, their ancestors were much smaller. Why did they evolve to be giants – and how do they capture enough food to sustain themselves?

These are just a few of the big questions that Nick Pyenson, curator of fossil marine mammals at the Smithsonian Institution’s National Museum of Natural History, tries to answer. In his fascinating book, Spying On Whales, we follow his adventures travelling from Antarctica to Alaska to tag whales, hunt their fossils or gain access to their dead bodies, which are hard to come by.

Tales of Pyenson’s fieldwork often read like detective stories. Take the events at Cerro Balena, Spanish for “whale hill”. A construction company busy widening the Pan-American Highway in Chile’s Atacama Desert uncovered the site, with dozens of complete skeletons of whales, seals and sloths. Pyenson and his team had to race against the clock to study them: roadworks were due to begin in less than a month.

Removing the huge fossils and preserving them would be no easy task, not to mention the fact that by displacing them the team would lose valuable clues about how the whale skeletons ended up there. Was this a mass stranding? Some other catastrophe? Or did they just pile up over time?

Spying on Whales delves into the evolutionary history of these mysterious marine mammals, from their beginnings on land to their transition to the sea over a mere 10 million years. At times, however, explanations can get in the way of the drama. But what Pyenson highlights so well is the struggle to address our shocking ignorance. Some parts of whale anatomy, for example, and many body functions are still unknown. Pyenson describes his own accidental discovery of a peculiar sensory organ in rorqual whales when working at a whaling station in Hvalfjordur, Iceland.

While advancing our knowledge will mostly depend on disciplines working together, Pyenson’s stint in Iceland also involved a more uncomfortable partnership. Industrial-scale whale hunting has been banned since 1986 in most countries, after nearly 3 million cetaceans were wiped out in the last century for their meat, oil and blubber.

But Iceland continued to hunt, albeit with an annual quota. This gave Pyenson a rare chance to access carcasses. He rationalised his situation by telling himself that the whales would be killed anyway and at least he was putting their deaths to good use.

Even so, the repercussions of whaling haunt us as we look to the future. Some populations, such as minke whales, have recovered, but others, among them the blue whale, are now endangered. Our inability to clean up our act in terms of climate change and pollution only adds to the challenges facing their survival. Adapting will be key, as “they live at the mercy and curse of human civilization”, writes Pyenson.

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This article appeared in print under the headline “Ways of the whale”