The Marine Mammal Protection Act (MMPA) is a federal law enacted on October 21, 1972, that makes it illegal to hunt, capture, kill, or harass any marine mammal in U.S. waters. It was the first law of its kind anywhere in the world, establishing a broad moratorium on the “taking” of marine mammals and setting a national policy to keep their populations healthy enough to remain functioning parts of ocean ecosystems.
Which Animals the MMPA Protects
The act covers all mammals that depend on the ocean to survive. That includes whales, dolphins, porpoises, seals, sea lions, walruses, manatees, dugongs, sea otters, and polar bears. Two federal agencies split the responsibility: NOAA Fisheries manages whales, dolphins, porpoises, seals, and sea lions, while the U.S. Fish and Wildlife Service handles polar bears, walruses, sea otters, manatees, and dugongs. A third body, the Marine Mammal Commission, provides independent scientific oversight and advises both agencies.
What “Take” Actually Means
The legal core of the MMPA is its moratorium on “take,” which is defined far more broadly than most people expect. Under the law, take means to harass, hunt, capture, collect, or kill any marine mammal, or to attempt any of those actions. It also covers collecting dead animals or their parts, temporarily restraining or detaining a marine mammal, tagging one, operating a boat or aircraft negligently near one, and feeding or attempting to feed one in the wild. In practical terms, if you approach a resting seal on a beach or toss fish to a wild dolphin, you could be violating federal law.
The law divides harassment into two tiers. Level A harassment is any act that has the potential to injure a marine mammal. Level B harassment is any act that could disrupt behavioral patterns like migration, breathing, nursing, breeding, feeding, or sheltering, even if no physical injury occurs. This distinction matters because permits and penalties hinge on which level of harassment is involved.
Exceptions and Permits
The moratorium on take is not absolute. The MMPA allows certain exceptions through a permitting process. Scientists can obtain permits for research. Marine parks can apply for permits related to public display. And U.S. citizens or companies whose activities might unintentionally affect marine mammals, such as construction projects, energy exploration, or military exercises, can apply for authorization to “incidentally take” small numbers of animals.
These incidental take authorizations come in two forms. An Incidental Harassment Authorization (IHA) covers activities expected to cause only harassment, not injury or death, and lasts up to one year. An Incidental Take Regulation (ITR) is more involved, covering activities for up to five years (or seven years for military readiness activities). To receive either authorization, applicants must demonstrate that the total impact on the affected species will be negligible and won’t interfere with subsistence hunting by Alaska Native communities, which is separately exempted under the law.
How Populations Are Monitored
The MMPA requires NOAA Fisheries and the Fish and Wildlife Service to prepare stock assessment reports for every marine mammal population in U.S. waters. These reports track each population’s size, geographic range, growth trends, and the estimated number of animals killed or seriously injured by human activity each year. They also document which commercial fisheries interact with each population and whether the stock is at a healthy level.
A key concept in this monitoring is “potential biological removal,” or PBR, which is the maximum number of animals that can be removed from a population by human causes without pushing it into decline. When human-caused deaths exceed PBR for a given stock, that population gets flagged as “strategic,” triggering additional protections and a formal recovery plan. The MMPA’s management goal is to keep every population at or above its “optimum sustainable population” level, defined as the range between a population’s maximum growth rate and its carrying capacity.
How Well the Act Has Worked
Some species have become iconic conservation success stories under the MMPA. Eastern North Pacific gray whales rebounded from near-extinction driven by commercial whaling, and several sea otter populations recovered substantially after decades of fur trade depletion. Many pinniped species, including California sea lions, also benefited from the moratorium because their predictable haul-out sites and breeding areas had made them easy targets before the law took effect.
Not all populations have recovered, though. Species like the North Atlantic right whale remain critically depleted despite more than 50 years of protection. Factors like ship strikes, entanglement in fishing gear, and habitat degradation continue to suppress some populations. The MMPA’s framework is designed to identify these struggling stocks through the assessment process and escalate protections accordingly, but recovery depends on whether the specific threats can be effectively managed.
Penalties for Violations
Violating the MMPA carries real consequences. Civil penalties can reach $25,000 per violation for knowing violations by importers or exporters of wildlife, or $12,000 for violations of other regulations under the act. Even unintentional violations can result in fines of up to $500 each. On the criminal side, knowingly violating key provisions can bring fines up to $50,000 and up to one year in prison. Lesser criminal violations carry fines up to $25,000 and six months of imprisonment.
Import Rules for Foreign Seafood
The MMPA doesn’t just regulate activity in U.S. waters. It also affects international trade. Foreign nations that export fish and fish products to the United States must demonstrate that their commercial fisheries meet marine mammal protection standards comparable to U.S. rules. NOAA Fisheries evaluates each nation’s fisheries individually through a process called “comparability finding determinations.” Nations whose fisheries fail this review are banned from exporting those specific products to the U.S. The most recent round of these determinations, finalized in 2025, resulted in import prohibitions taking effect January 1, 2026, for fisheries that could not meet the standard. This provision effectively extends the MMPA’s influence well beyond American borders, pressuring fishing industries worldwide to reduce marine mammal bycatch.