"VOYAGE OF THE TURTLE: IN PURSUIT OF THE EARTH'S LAST DINOSAUR" BY CARL SAFINA; HENRY HOLT, HARDBACK, $27.50

When there has long been an abundance of something, it's difficult to believe we'll ever be without it. Some argue the world may be without fresh water soon, and in his latest book, leading conservationist Carl Safina raises awareness of the plight of giant leatherback sea turtles. Though their numbers are increasing in the Atlantic, they have declined 95 percent in the Pacific in just the last 20 years. After following this disappearing dinosaur of the sea, he presents his discoveries in hopes that humans will realize leatherbacks need us to "chart a path to its future."

More than a call to action, "Voyage of the Turtle," which reaches bookstores Wednesday, is an engaging, literary documentary of Safina's study of the leatherback's fate, meeting "with those who still worship it, those tracking it with satellites, and those whose valuation of sea turtles merely reflects their own lust and cravings." Largely taken up with optimistic searching and waiting for a leatherback sighting, as well as cat-and-mouse games of catching and tagging, the book tracks his ambitious journey from the Atlantic to the Pacific. What he uncovers are the myriad problems turtles face, including erosion in Trinidad, condos and beach chairs in Florida, shrimping in South Carolina, government in Costa Rica, poverty in Mexico, and more — all the way to Papua New Guinea.

Although there are no leatherbacks in Hawai'i, Safina recognizes the state's success in tripling the number of green sea turtles since the passing of the Endangered Species Act. And before moving on to a discussion of leatherbacks in the Pacific, he devotes an entire chapter to the Hawai'i Longliners Association controversy in the '90s, when instead of looking for solutions to endangered species getting killed during longline fishing, the fisheries service spent 10 years doing anything "to allow the fishing to continue without inconvenience — and hope(d) no one noticed." Eventually, the resulting laws requiring the use of new turtle-saving hooks made Hawai'i a potential leader in exporting new, more effective methods to other countries.

Foremost, though, are the challenges to survival that leatherbacks face across the globe. Those he determines most detrimental are egg taking and long-line fishing, but also human alteration of the environment through urban sprawl, illuminating the atmosphere, beach walls, and byproducts such as plastic and rubbish.

Safina does well connecting and moving the reader forward. There are just a few diversions that appear without sufficient context, such as a trip with swordfish harpooners that has little to do with turtles.

On the whole, though, Safina's adventures are smoothly conveyed in experiential, journal-like sections, interspersed with history and facts, which allow the reader to feel right there with him. His love of the turtles and the sea is perpetually evident, and his writing often poetic, if overly so. The turtle is at times lost in too many metaphors, often mixed. In one string, the leatherback is described "as long as a man," then as "lying like a just-crashed saucer," and again "as wondrous as a fallen angel." The descriptions can be overwrought, even trite, but Safina's voice and personality springs from the page with a genuineness that allows any flaws to be overlooked.

As a hunter "who has killed many fish," Safina sees working for smart fishing as central to turtle survival, and is quick to mention that the U.S. fishing industry is well-managed. The strength of his message, however, lies in the recognition that the perpetuation of the natural world must be balanced with economics. In Hawai'i, tourism is a powerful motivator, but Safina argues that "well-regulated tourism" — the North Shore's turtle magnet Laniakea Beach comes to mind — "seems to benefit both people and turtles."

Ultimately, "humans can move elsewhere; turtles cannot," and what happens in, say, Hawai'i, which is along expansive turtle migration routes, can affect turtles in Monterey. Therefore, Safina convincingly argues, it's up to us to work locally to achieve global success — for turtles and humans.

Christine Thomas' reviews appear regularly in the San Francisco Chronicle.