Kelsey, a scientist and author (Saving Sea Otters), meditates in 20 linked essays on the resident and visiting cetaceans-including whales, dolphins and orcas-of the Gulf of California. To convey what's known and suspected about the underwater mammalian lifestyle, Kelsey interviews dozens of contemporary ocean scientists-Exequiel Ezcurra, Bruce Mate, Fred Sharpe, husband-and-wife team Hal Whitehead and Linda Weilgart-and places their research in context alongside data on African elephant herds, antelope and wildebeest feeding strategies, the behaviors of predators and (especially) the dynamics of her own family (mom to two young daughters, Kelsey's first chapter is titled ""Extreme Motherhood""). Focusing on social relationships and culture, Kelsey finds research (including submarine observations of sea-floor whale carcasses) that reveals some critical and previously unsuspected roles. Brilliant at pursuing seemingly unrelated trails back down the blowhole, Kelsey illuminates the ""humanity"" of whales, and the human threat to them; for instance, she explains why canned tuna is never really ""dolphin safe"" (motorized boats used to herd dolphins away from tuna cause sonic chaos, separating mothers from pups with often fatal results). Kelsey's cogent, compassionate work makes clear the sophistication and importance of whale communities, and how current efforts to save them may not be enough. 30 color illus.