Voices in the Ocean:A Journey into the Wild and Haunting Worldof Dolphinsby Susan CaseyDoubleday, 2015Susan Casey, author of 2010's The Wave and The Devil's Teeth, her excellent 2005 book on great white sharks, returns with Voices in the Ocean, a passionate and richly readable account of dolphins – their world, their behaviors, and the humans whose lives revolve around studying them. She's inspired to undertake the subject by her interaction with a group of Spinner dolphins off the Kona coast of Hawaii's Big Island, and from there she seeks out the various scientists and marine biologists who study dolphins, beluga whales, “false” or pygmy killer whales, and other kinds of cetaceans – scientists like Robin Baird and Daniel Webster, who study the false killer whales who live and hunt in the very deep waters off the Kona coast and who heighten her own awareness of the dangers all wild cetaceans face:

Though dolphins have been hunting in the planet's waters for eons longer than we have, they are no match for our onslaught. But they want tuna and salmon and squid too. Where dolphins and commercial fisheries meet, the results can be devastating for dolphins, not just in Japan, where the surreal notion that cetaceans are gluttonously taking all the fish – as opposed to industrial fleets the size of cities scouring the seas with radar, sonar, fish aggregating devices, and spotter aircraft – has cost countless dolphin and whale lives, but even in Hawaii, where most of the false killer whales Baird studies, in three roving pods, have visible injuries from fisheries.

Casey's book ranges over a great deal of territory, from a brief look at the history of mankind's fascination with dolphins to some of the more bizarre and dangerous manifestations of that fascination in modern times, such as ritual tribal dolphin-killings and the iniquities of aquatic theme parks. And as in The Devil's Teeth, she balances these sections of her book with a generous helping of cetacean natural history, all of which is fascinating, although some of it can also be maddening in some very expected ways, the most pernicious of which is the old familiar sliding scale not of consciousness but of conscience – that an organism's complexity is measured by its similarity to humans, and that its degree of similarity to humans is the measure of its merit:

Though it might seem like no big deal, to conceive your own identity is a rare cognitive feat. The idea of a self is a pretty far-out abstraction, and to get that I am me and you are you and that we both have autonomy but there's also a relationship between us – this capacity was long considered unique to our own two-legged, opposable-thumbed species. It's not an ability that can be taken for granted: children don't begin to develop self-awareness until they're nearly two years old, along with feelings like sympathy and empathy. To know that dolphins operate in the same realms of consciousness we do raises a raft of fascinating questions about their interior lives and, in turn, the ethics of how we treat them.

Such considerations naturally grow from a discussion of that most favorite subset of dolphin studies, their cognition. The dolphin brain is very complex and has been that way for millions of years. Researchers (beginning with John Lilly, a much-maligned researcher and popularizer from a generation ago, whose works are here given touchingly serious consideration only slightly vitiated by the equally tolerant consideration given to gentle souls who've seen mermaids and oceangoing UFOs) are only beginning to parse the mysteries of the way cetaceans think about themselves and the world around them, so it's perhaps understandable that so many of the old primate biases would still be so firmly in place, as when Casey enthuses about the complex interaction of dolphin memory and social structure:

One of the key reasons anyone's brain ballooned in the first place, scientists believe, was to deal with the intricacies of a thriving social life. Keeping track of family and friends and acquaintances in an extended community, figuring out who owes whom a favor and who once betrayed the group and who treated your grandma with special kindness but is also related to the guy who stole your brother's girlfriend – the fine web of interactions between hundreds of individuals – is as challenging for dolphins as it is for us. We need every bit of our brainpower to navigate these relationships, using everything from memory to judgment to communication skills (even with Facebook).

Mentions of Facebook notwithstanding, anyone who's ever watched a close-knit group of animals – whether it be a herd of African elephants or a pack of hunting wolves or even a host of suburban house sparrows – will instantly recognize most of these social intricacies from their own observations and might then make the inference that since the passerine brain weighs less than a dolphin's eye, such intricacies might be less about size than about utilization. But Casey's examples are illuminating in any case, and her book draws on some of the best recent popular work on dolphins and whales, from Maddalena Bearzi and Craig B. Stanford's 2008 book Beautiful Minds: The Parallel Lives of Great Apes and Dolphins to D. Graham Burnett's 2012 book The Soundings of the Whale to Hal Whitehead and Luke Rendell's The Cultural Lives of Whales and Dolphins from earlier this year.The result is a fascinating and cautiously joyous celebration, a book any lover of nature should read. When it comes to first-rate works of popular natural history, this author is now three for three.