What Is the Marine Mammal Protection Act?

Two Stellar sea lions on kelp-covered rocks.

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The Marine Mammal Protection Act, or MMPA, is the U.S. federal law restricting human actions that affect marine mammals. The MMPA was signed into law in 1972 by President Richard Nixon, making it one of many environmental policies established by the Nixon administration.

One of the most significant actions taken under the MMPA was the establishment of an "optimum sustainable population" (OSP). Instead of the traditional single-species approach to marine mammal management, OSP focuses on the role of marine mammals in the health of an ecosystem. The ecosystem-based approach remains widely implemented across the fishery industry today.

The MMPA also included immediate restrictions to the capture, import, and sale of marine mammals, controversially designating marine mammals as wildlife instead of natural resources. Before the MMPA, marine mammals were managed based on their benefits to humans. Instead, the MMPA invoked the "precautionary principle", preferring to manage marine mammals with a hands-off approach unless the state of a population required otherwise.

Background and Timeline

Public pressure in the 1960s and '70s is credited with the establishment of the MMPA. Until the 1960s, the only wildlife protected by U.S. federal law was the animals covered under the Migratory Bird Treaty Act of 1918. The Endangered Species Preservation Act (1966) and the Endangered Species Conservation Act (1969), both pre-cursors to the Endangered Species Act (1973), began the expansion of protections to wildlife in the United States.

Americans were particularly outraged over two specific forms of marine mammal exploitation: the killing of dolphins in pursuit of tuna and the hunting of fur seals for their fur. According to Lee Talbot, who was the chief scientist on the Council of Environmental Quality at the time, "[Congress] had never received such a large volume of letters on any subject, other than the Vietnam war." By 1971, over 40 different marine mammal bills had been introduced in Congress.


Many fur seals sitting on rocks.
Under the North Pacific Fur Seal Convention, fur seals can only be hunted on land.

Stuart Westmorland / Getty Images

The bill that became the Marine Mammal Protection Act had one chief competitor among the many other pieces of legislation introduced: the Ocean Mammal Protection Act. Unlike the MMPA, the Ocean Mammal Protection Act sought to put an immediate end to all treaties involving the "take" of marine mammals. The proposed bill took particular aim at the North Pacific Fur Seal Convention, an international agreement under which the hunting of fur seals was only permitted on land. Before this agreement, pelagic sealing destroyed fur seal populations.

Proponents of the MMPA criticized the Ocean Mammal Protection Act's "protectionist" approach, citing concerns that the bill's proposed departure from agreements like the North Pacific Fur Seal Convention could put the marine mammals at greater risk if it failed to replace the Convention with a new international agreement. Critics of the Ocean Mammal Protection Act also found the bill to lack a science-based approach to marine mammal conservation.

The House of Representatives Subcommittee on Fisheries and Wildlife Conservation rejected all bills that proposed a flat ban on the "taking" of marine mammals, including the Ocean Mammal Protection Act. By contrast, the subcommittee reported favorably on the Marine Mammal Protection Act. However, marine mammal "protectionists" blocked the bill from passing.

In 1972, an amended version of the MMPA was brought to the House floor. The amended bill added a five-year moratorium during which time no marine mammals could be taken or imported. The amended version of the MMPA passed the House by an overwhelming majority in March 1972. The legislation passed the Senate five months later and was signed into law by President Richard Nixon in October.


The MMPA was first significantly amended in 1981 to allow the National Marine Fisheries Service (NMFS) to issue permits to allow for the take of marine mammals "incidentally", or unintentionally. Incidental take permits are most commonly issued to commercial fishers due to the unintentional effects fishing can have on marine mammals. Military exercises, oil and gas exploration activities, scientific research, and construction projects also commonly obtain incidental take permits from NMFS. However, incidental take permits are only issued if an entity incorporates methods of reducing the chance of incidental take. To obtain an incidental take permit from NMFS, fishers are typically required to use specific equipment, avoid certain areas, or restrict fishing to certain time periods.


Three dolphins underwater.
Dolphins are particularly susceptible to being hurt by certain commercial tuna fishing methods.

Scott Portelli / Getty Images

In 1984, the MMPA was amended to address the effect of tuna fishing on marine mammals, particularly dolphins. While the MMPA already regulated tuna fishing within U.S. waters, much of the tuna imported to the United States comes from international waters outside of the protections of the MMPA. Under the 1984 amendment to the MMPA, the United States could only import fish and fish products from nations using certain fishing technology or with regulations in place designed to reduce the risk of hurting or killing marine mammals. Under the amended MMPA, countries must have a marine mammal incidental take rate that is comparable to that of the United States.


The MMPA was amended again in 1988 to set stricter standards for the incidental take of marine mammals for all commercial fishing operations, with the exception of commercial tuna fishing. Commercial fishermen who received an exemption to the stricter incidental take standards could be required to take a fishing observer on board. The amendment also mandated fisheries observers on a portion of vessels in fisheries with frequent impacts to marine mammals.

This substantial amendment also established specific procedures for determining whether a marine mammal population is "depleted". The amendment required recovery plans for all depleted species. A reward system was also established by the 1988 amendment to encourage the reporting of MMPA violations.


A 1992 amendment to the MMPA established the Marine Mammal Health and Stranding Response Program, which mandates marine mammals in distress receive emergency help. A grant program was added in 2010 to help fund eligible stranding network programs.


The 1994 amendment to the MMPA authorized the "take" of marine mammals for certain purposes, including scientific research and public display. This amendment also required marine mammal stock assessments for the first time. Under the amendment, all marine mammal stocks are required to be re-assessed every three years. Certain stocks must be re-assessed annually.


Republican congresswoman Jaime Herrera Beutler of Washington State proposed an amendment to the MMPA in 2017 to allow NMFS to issue one-year permits for the killing of sea lions in the Columbia River. According to the amendment, the booming population of sea lions was hurting local salmon populations. The amendment would have allowed up to 100 sea lions be killed to protect salmon. The amendment passed the House in 2018 but was never brought to the Senate floor.


In 2019, republican congressman Mike Johnson of Louisiana proposed to amend the MMPA to eliminate permit requirements for a variety of actions known to hurt marine mammals. Johnson's amendments also sought to make the process of obtaining an incidental take permit easier. Under Johnson's amendment, if NMFS failed to respond to a request for an incidental take permit within 45 days, the permit would be automatically authorized. The proposed amendment failed to pass the house in a 160-259 vote.

Marine Mammal Protection Act Successes

A harbor seal in a kelp forest.
Harbor seals are one of the marine mammals that has benefited greatly from the Marine Mammal Protection Act.

Douglas Klug / Getty Images

The MMPA is credited with a number of environmental successes. Since the bill was signed into law in 1972, none of the marine mammals protected under the MMPA have gone extinct in the United States. In addition, a number of marine mammals have recovered substantially since the passing of the MMPA, including harbor and gray seals in New England and California sea lions, harbor seals, and elephant seals along the Pacific Coast. In some cases, recovery has returned species to their carrying capacity, or the maximum size the environment can likely support.

As of 2014, 18% of the marine mammal stocks recognized under the MMPA were listed as endangered or threatened under the Endangered Species Act. Most of these stocks were listed after their first assessment. However, three stocks were only recently listed under the Endangered Species Act and an additional three are pending consideration. No stocks protected under the MMPA have been removed from the endangered species list once added, although the Eastern stock of Steller sea lions came close to being de-listed in 2012.

Despite the lack of improvement for some marine mammal populations, the MMPA continues to promote the conservation of marine mammals in the United States. The stock assessments required under the 1994 amendment to the MMPA have generated a substantial body of research on U.S. marine mammals that would likely not have occurred in the absence of the MMPA. This research has increased the number of marine mammal stocks recognized under the MMPA. By understanding how marine mammals interact with one another to form separate, identifiable stocks, agencies and scientists can better manage marine mammal populations.

View Article Sources
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