A compact and informative handbook, ranging from the great whales and porpoises to the otter, walrus, and various seals (and though ""not a marine mammal in the strictest sense,"" even the polar bear is included), with notes on characteristics, behavior, hunting history and protection status for each. In addition to incidental information on particular species--the pilot whales' suicidal habit of beaching themselves en masse, we learn, might be due to parasitic nematodes in their inner ears, which upset their sonar navigation systems--there are many examples of wasteful exploitation. Pelagic sealing, outlawed in 1911, lost four to six seals for each one taken; passengers bound for the Klondike once lined the rails of steamships, idly slaughtering walrus by the thousands; and Stellar's Sea Cow, which nourished the stranded crew of the Russian ship Saint Peter in 1741 (the meat tasted like fine veal, noted ship's doctor Stellar), was extinct by 1786--though the sea otter, also heavily exploited since Saint Peter survivor reports, has recently made a comeback thanks to conservationist efforts. McClung notes other areas of progress without overlooking the problems--abalone fishermen's resentment of the sea otters' competition, the dangers to porpoises of purse-seine tuna fishing, the refusal of Japan and the Soviet Union to comply with international whaling restrictions. McClung ends his unemotional survey with a persuasive summary of the damage we've done to the sea and of organized efforts to save it. Succinct and solid.