ABSTRACT
In addition to the 30,000 different kinds of fishes and the hundreds of thousands of invertebrate species down to the protozoa, a few kinds of higher vertebrates, little more than a hundred in all, provide or provided an economic resource much greater in value than their small number might imply. The thirty-one species of seals, eighty-eight of whales and dolphins and porpoises, and four of sea-cows are warm-blooded, air-breathing mammals, descended from ancestors that lived on land but took to an aquatic way of life to which they have become highly adapted. They have given a harvest of meat, oil, leather, and many other useful things and, because most of them are gregarious at some time of their annual life cycle, are often available for exploitation in large numbers. The seals come ashore or climb on to floating ice to breed, and consequently can be attacked on foot, but the whales are completely aquatic and must be pursued in ships and boats.
