Marine mammals

What makes a marine mammal a marine mammal? They must meet the characteristics of all mammals — they breathe air through lungs, are warm-blooded, have hair (at some point during life), and produce milk to nurse their young — while also living most or all of their lives in or very near the ocean. 

Humpback whale and calf.
Humpback whales are navigating an ocean of change
In late December 2015, Ed Lyman started getting calls from whale watching companies on the island of Hawai‘i. “Ed, how are the whales off Maui?” tour operators were asking. “We’ve never seen them arrive this late.”

Marine mammals represent a variety of ecological roles, including herbivores (manatees), filter feeders (baleen whales), and top predators (killer whales). Mammals evolved on land around 160 million years ago. Each taxonomic marine mammal group evolved from a different group of land mammals, whose ancestors separately ventured back into the ocean environment. Despite these different origins, many marine mammals evolved similar features — streamlined bodies,  paddle-like limbs and tails — through convergent evolution.

Male elephant seal.
Voyage of the seal
NOAA research helps identify differences in elephant seal feeding patterns

There are over 70 different species of cetaceans. Cetaceans are categorized into two main groups: baleen whales (mysticetes) and toothed whales (odontocetes). They spend their lives in water, and have many adaptations offsite linkto their entirely aquatic lifestyle. 

Pinnipeds are in the suborder pinnipedia, which means “fin-footed.” These carnivores use flippers to move both on land and in the water. Pinnipeds spend the majority of their lives swimming and eating in water and come onto land or ice floes to bear their young, rest, and molt. 

Like cetaceans, sirenians also spend their whole lives in water. They are the only entirely herbivorous group of marine mammals. Sirenians are named for sirens, the legendary Greek sea beauties who lured sailors into the sea. Some think historic mermaid sightings were actually sirenians, not the mythical half women, half fish. 

The marine fissipedsoffsite link are considered marine mammals, but spend most of their time on land and only part of the time in the water, mainly to hunt for their food.

A response team led by the Hawaiian Islands Humpback Whale National Marine Sanctuary, working closely with NOAA Fisheries, successfully rescued an entangled humpback whale in 2013. Rescuers managed to cut away only 40 feet of trailing line on the first day of the response. But they also attached a satellite tag into the trailing gear, allowing them to relocate the animal a few days later. During the second attempt, they removed an additional 200 feet of line and two buoys, completing the rescue.
How NOAA disentangles a tangled-up whale
Every year, dozens of whales become entangled in fishing gear off the U.S. Atlantic coast. The Atlantic Large Whale Disentanglement Network works to save them...

Threats and protection

Threats to marine mammals are largely from human impacts, including accidental capture in fishing gear, habitat destruction, poaching, pollution, harassment, and ship strikes. All marine mammals in waters of the United States are protected under the Marine Mammal Protection Act (MMPA). NOAA Fisheries collaborates with several partners to protect these species. Anyone can help protect marine mammals by showing proper ocean etiquette. Admire them from a distance; never touch, feed, harm, or swim with a marine mammal.

Pygmy killer whale in foreground with Research Vessel Ocean Starr in background.
Marine mammal survey spots unusual species
An on-going NOAA Fisheries marine mammal and ecosystem survey off the West Coast has sighted several surprising species of tropical cetaceans and birds, never before documented so far north...


The education resources in this collection provide educators and students opportunities to explore the adaptations, population dynamics, ecology, threats, behaviors, and anatomy of marine mammals. This collection includes resources to help students better understand the biology of marine mammals as well as their role in protecting these species.


Updated February 2019