The Marine Mammal Protection Act (MMPA) was enacted in 1972 largely in response to concerns that human activities were contributing to the decline of the populations of certain marine mammal species. The underlying focus of the MMPA is the implementation of policies to prevent the decline of marine mammal species beyond the point where they would stop being functioning parts of their ecosystems.
The MMPA prohibits the taking of any marine mammal in U.S. waters, with the exception of certain cases such as through permitted activities, where "take" is defined as hunting, harassing, capturing, or killing a marine mammal or attempting to do so. The MMPA is unique in that its underlying intent is the management of marine mammal stocks to help them achieve their optimum sustainable populations within their ecosystems, rather than managing for the benefit of commercial exploitation. The MMPA was amended in 1994 to provide certain exceptions to the take prohibitions, establish provisions for the preparation of marine mammal stock assessment reports, implement a program addressing interactions between commercial fisheries and marine mammals, and institute studies of pinniped interactions with fisheries. NOAA's National Marine Fisheries Service (NMFS) is charged with carrying out the mandates of the MMPA for the protection of whales, dolphins, porpoises, seals, and sea lions, while the U.S. Fish and Wildlife Service is charged with protecting walruses, manatees, otters, and polar bears.