T hey cover more than two-thirds of Earth’s surface, support much of its biodiversity, produce more than 50% of planetary oxygen and absorb 20–35% of human-created carbon dioxide emissions. Oceans were once considered boundless resources, yet, by 1983, pioneering whale conservationists Stephen Leatherwood and Randall Reeves were writing in The Sierra Club Handbook of Whales and Dolphins that “the seas are by no means dead, but they are unques- tionably less alive than they were when humanity discovered them”. Ecological connections between species form a tangled web. Intentional perturba- tions can lead to unintended consequences, or even shift an ecosystem from one state into another. With the human population soaring towards 8 billion — consuming, polluting and emitting as it grows — oceans face unprecedented challenges, as do their denizens. Nearly 3 million whales were killed in the twentieth century; the animals must now negotiate hazards such as ship strikes and noise. And global harvests of ocean fish by humans have hit 1 trillion a year. Now, three books — by palaeobiologist Nick Pyenson, eminent krill scientist Stephen Nicol and historian Jason Colby — explore oceans from the perspectives of whales and krill across palaeontologi- cal, decadal and even annual timescales. They examine the evolutionary history and ecology that led to today’s ecosystems, and provide insights into ocean-resource management and how changing public sentiment influences the politics behind this. Pyenson’s Spying on Whales is a palae- ontological howdunnit embedded in a travelogue devoted to chasing living and extinct whales. The author — curator of fossil marine mammals at the Smithsonian Institution in Washington DC — takes us to field sites from Antarctica to Alaska. His narrative captures the excitement of suction-cup tagging of humpback whales, MARINE CONSERVATION Sea changes and whale tales Sascha Hooker on three books tackling challenges faced by oceans and marine life. Sperm whales (Physeter macrocephalus) socialize in the Indian Ocean. Spying on Whales: The Past, Present, and Future of Earth’s Most Awesome Creatures NICK PYENSON Viking (2018) The Curious Life of Krill: A Conservation Story from the Bottom of the World STEPHEN NICOL Island (2018) Orca: How We Came to Know and Love the Ocean’s Greatest Predator JASON M. COLBY Oxford University Press (2018) 184 | NATURE | VOL 558 | 14 JUNE 2018 TONY WU/NATUREPL.COM ©2018MacmillanPublishersLimited,partofSpringerNature.Allrightsreserved.