for administering regulations concerning polar bears, walrus, sirenians, and sea otters; the National Marine Fisheries Service of the U.S. Department of Commerce is responsible for whales, dolphins, seals, sea lions, and other marine mammals not regulated by FWS. In addition, another independent body established under the MMPA, the Marine Mammal Commission, maintains a scientific committee to advise on issues related to marine mammal conservation. Those species designated as endangered are further protected under the Endangered Species Act of 1973.

Threats to marine mammal populations worldwide are many. They result, for example, from fishing (the use of gillnets, driftnets, ghost nets, long lines, the yellowfin tuna purse seine, rolling hooks), pollution (agricultural runoff, industrial waste, petroleum spills, trash dumping), deforestation and development of the rain forests, damming, oil field development, mining, heavy-vessel traffic, and other human activities.

Twenty species of marine mammals are listed as endangered under U.S. provisions (see the tables in this appendix), although some of them appear to be gaining in population and may be removed from endangered status (Brownell et al., 1989). For example, the eastern or California stock of the gray whale Eschrichtius robustus has apparently recovered from severe exploitation and thus was proposed for removal from the endangered species list by the U.S. Department of Commerce as of 7 January 1993 (Marine Mammal Commission, 1992). Some other marine mammals, such as the Gulf of California porpoise (vaquita) and the Yangtze River dolphin (baiji), appear to be headed for extinction. However, the majority of species are not endangered or seriously threatened.

The larger cetaceans include Physeteridae (sperm whales), Ziphoidea (beaked whales and bottlenose whales), and suborder Mysticeti (baleen whales) (Table B-1). Eight of the largest species are listed as endangered.

The sperm whale has been on the U.S. List of Endangered and Threatened Wildlife, even though there may be more than a million sperm whales in the world's oceans. Some specific populations are apparently depleted even though the world population is relatively large.

Because of their past exploitation by whalers and recent publicity about this exploitation, most large baleen whales are assumed by the public to be endangered species. However, in the absence of the

FRONT MATTER (R1-R16)

EXECUTIVE SUMMARY (1-7)

1 A REVIEW OF CURRENT KNOWLEDGE (8-24)

2 REGULATORY BARRIERS AND POSSIBLE ALTERNATIVES (25-39)

3 TOPICS FOR FUTURE RESEARCH (40-62)

APPENDIX A COMPARISON OF SOUND-PRESSURE REFERENCE LEVELS IN AIR AND WATER (63-64)

APPENDIX B AN INTRODUCTION TO MARINE MAMMALS (65-73)

APPENDIX C COMPARISON OF YEARLY SOUND ENERGY FROM OCEANOGRAPHIC RESEARCH AND SUPERTANKERS (74-75)