What is Marine Mammal?

The term “marine mammal” can be defined three different ways, and each of these ways carries with it implications about how we think of these animals.

Ecological definition: A “marine mammal” is any mammal species whose life depends upon the sea. That is, it is any mammal that lives in salt water and/or derives its food from a saltwater environment.

Taxonomic definition: The term “marine mammal” is defined as all the species in the following taxonomic orders: cetacea, pinnipedia, sirenia. In plain English, these are the whales, the seals, and the manatees.

Legal definition: In the US legal system, the term “marine mammal” is defined by the US Marine Mammal Protection Act (MMPA). This act of Congress establishes special protection for marine mammals and defines that term as including all members of cetacea, pinnipedia, and sirenia, AND the polar bear and the sea otter (since these two members of the order Carnivora arguably depend entirely upon the sea as well).

For the most part, the species included in the term “marine mammal” are the same regardless of which of these definitions you use. Consider the Atlantic Bottlenose Dolphin as just one example. It is ecologically a marine mammal because it lives in the saltwater of the Atlantic Ocean. It is taxonomically a marine mammal because it is a member of cetacea. And it is legally a marine mammal since it is covered by the US Marine Mammal Protection Act.

But there are exceptions. An interesting way to explore this is to answer the following riddle. When is a marine mammal not a marine mammal?

Example 1: The Lake Baikal Seal would be an example of a correct answer. It is a marine mammal taxonomically because it is a member of pinnipedia. But because the species is entirely isolated to the fresh waters of Lake Baikal in Siberia, it is not a marine mammal ecologically. It never encounters saltwater and it is a species that lives its entire life a thousand miles from the nearest ocean.

Example 2: The Sea Otter is a marine mammal both ecologically and legally since it lives in the sea and is covered by the MMPA. However it is not a marine mammal taxonomically since it is not a whale, a seal, or a manatee.

There are other examples. See if you can think of any!

Marine mammals have long held a special fascination for people. Perhaps it is their large size and graceful beauty, or perhaps it is because of our own love of the sea. Whatever the reason, it is certainly a sentiment that we share. Follow the links at the left to learn more about these wonderful creatures.


Content provided by Canisius College students under the direction of Michael Noonan, PhD.