Searcher carries a good variety of Baja books in our on-board library, but sometimes people like to bring their own field guides along as well. We asked Rob Nawojchik (naturalist on the January, 2011 tour) for his reccomendation:

When the Searcher is in Baja California, a modest library occupies two shelves in the main salon.
Often, following a hike or a whale watching session, the salon is abuzz with activity as volumes are pulled from the shelves and pages flipped open, as species are identified and life history information is shared.
Many of the books are devoted to marine mammals. Some focus on one species, or one geographic area, and
these are definitely worth a look. But time and time again, when searching for answers to a wide variety of
questions about the marine mammals we see on our trips, I pick up one book: the National Audubon Society Guide to Marine Mammals of the World. In fact, I use this book extensively at home before the trip when preparing my evening lectures. It’s much more than a field guide, although it functions well in species identification. Every species of marine mammal is allotted several pages that include photographs and sections on general description, range and habitat, behavior, reproduction, food and foraging, status and conservation, and other topics. The illustrations of Pieter Folkens make the guide especially valuable.
As Searcher passengers can attest, marine mammals are particularly difficult to photograph, and it’s rare to capture the entire animal out of the water, especially in a way that illuminates all diagnostic features.
Folkens’ illustrations depict key characteristics, and with the photographs, range maps, and other information in each section, allow for reliable identifications.

Four prominent marine mammalogists have provided readable and informative text. Despite being published in 2002 (almost a decade ago), I still find the Guide to be accurate and relatively current—a tribute to the authors for providing the best available knowledge. Books can be expensive, especially those richly illustrated with photos, illustrations, and maps. This Guide is modestly priced (I paid US $26.95 for my copy) and provides a lot of book (527 pages and tons of information). If you’re on a limited budget or have limited shelf space and are agonizing over which one marine mammal book to buy, you certainly can’t go wrong with this one. Like me, you’ll find yourself referring to it over and over again.

National Audubon Society Guide to Marine Mammals of the World, Randall R. Reeves, Brent S. Stewart, Phillip J. Clapham, and James A. Powell, Alfred A Knopf, Inc., New York, 2002
(ISBN 0-375-41141-0)