When the term “marine mammals” is used, images of friendly bottlenose dolphins, breaching humpback whales, roly-poly seals or even docile manatees often come to mind. Still, there are about 125 different species that share the world’s oceans. This week, we will take a dive with some of those lesser-known species that may not immediately come to mind.
In July of this year, scientists believe they may have encountered one of the rarest marine animals in the world, a spade-toothed whale, so elusive they’ve never been seen alive. The 16-foot-long whale washed ashore in New Zealand on July 4th and, if correct, the beaked whale species is so rare, that little is known about them.
Before we examine others, let’s first clarify the different types of marine mammals:
➊ Cetaceans
This includes whales, dolphins, and porpoises. They are further broken into toothed (odontocetes) and baleen (mysticetes).
➋ Pinnipeds
This group includes seals and sea lions, with the word meaning “fin-footed,” a reference to their four flippers used to navigate in and out of the water.
➌ Marine fissipeds
This group includes species such as sea otters and polar bears that more resemble land mammals but use the ocean for their source of food.
➍ Sirenians
Named after the mythical sirens that called out to sailors in ancient times, this group covers manatees and dugongs.
Leopard seal (Hydrurga leptonyx)
Leopard seals are ferocious undersea predators, deriving their name from their spotted coat and a large mouth filled with razor-sharp, teeth. While most seals dine on fish, leopard seals feed on warm-blooded animals such as seabirds, penguins and other seals. This expansive diet helps them find sustenance regardless of whether they are on land or water.
Bearded seal (Erignathus barbatus)
The patch of luxurious whiskers on its face aren’t just fashionable, but functional, as it uses them to feel along the sea floor to look for food. Found primarily in the frigid Arctic waters, bearded seals are the largest of the four species of Arctic seals and can grow to eight feet long and weigh in at about 800 pounds.
Amazon River dolphin (Inia geoffrensis)
Also known as the “boto,” or “pink dolphin” they are one of only five species of freshwater dolphins, four of which are severely endangered, and the last of which has gone extinct. Despite its colorful nickname, the Amazon River dolphin is naturally white but will take on a pink, blue, or brownish hue depending on diet and environment. They are considered to be essentially blind, with tiny eyes and limited vision, They locate their prey predominantly through echolocation.
Hector’s dolphin (Cephalorhynchus hectori)
Found almost exclusively off the coast of New Zealand, it is known as the world’s smallest dolphin. The Hector’s dolphin only grows to about 110 pounds (or about the size of a mountain lion). Considered to be one of the rarest dolphin species in the world, Hector’s are often called the “Mickey Mouse dolphin,” named for their rounded dorsal fins that resemble mouse ears.
Vaquita (Phocoena sinus)
These little stubby-nosed porpoises are also known as the “Gulf of California porpoise,” and their name means “little cow” in Spanish. There are thought to be only about 10 of these little creatures left (measuring about 4-5 feet) in the shallow waters of the Gulf of California, near Mexico’s Baja peninsula. Commercial fishing and habitat changes have critically reduced their numbers.
Blainville’s beaked whales (Mesoplodon densirostris)
Also known as the dense-beaked whale, Blainville’s beaked whales spend most of their time in deep offshore waters and are therefore still mysterious to scientists. They can plunge to 3,000 feet in search of squid and fish while traveling in small groups of less than ten individuals, typically with more females than males.
Rough-toothed dolphins (Steno bredanensis)
Deriving their name from their distinctive ridged teeth, rough-toothed dolphins are found in tropical and temperate waters around the world. They primarily travel in groups which can reach up to 150 individuals. While they are smaller than common dolphins, they will often co-mingle with other dolphin species and resemble a more primitive form of dolphin species than their sleeker cousins, the bottlenose.
These are just a few of many marine mammals that are more obscure when discussing marine mammals. Regardless of the species, however, marine mammals face threats around the world, from entanglement, marine debris, and ghost gear. And regardless of the species, if you spot a marine mammal or sea turtle in distress, be sure to contact the Marine Education Research and Rehabilitation hotline at 302.228.5029.
Rob Rector has served as naturalist and board member for 20 years, is a certified Protected Species Observer, and leads weekly dolphin observation tours that use citizen science to gather information on our local Bottlenose Dolphin populations.
