A bill to amend the Marine Mammal Protection Act of 1972 with respect to the taking of marine mammals incidental to the course of commercial fishing operations.

Amends the Marine Mammal Protection Act of 1972 to require the Secretary of Commerce or of the Interior, as appropriate to the respective jurisdiction of each under such Act to issue permits for the taking of marine mammals in specified numbers incidental to commercial fishing operations for yellowfin tuna during the 1977 and 1978 calendar years.

Requires the Secretary to establish and maintain a program under which observers are placed aboard fishing vessels to collect data relevant to the conservation of porpoise stocks, and to observe the fishing methods and gear used in fishing for yellowfin tuna. Requires the Secretary to place such an observer aboard each fishing vessel of four hundred tons or more for each fishing trip.

Prohibits the issuance of such permit for 1978 unless the permittee agrees to provide the Secretary with a suitable vessel with which to carry out further research regarding fishing gear and methods which will reduce the incidental taking of marine mammals and the conservation of porpoise stocks.