Otters are semi-aquatic mammals known for their agile movements and playful demeanor. These carnivores are highly adaptable to diverse aquatic environments across nearly every continent. They rely on water for hunting, travel, and shelter.
Sea Otters: Masters of the Marine Environment
Sea otters (Enhydra lutris) are exclusively marine mammals, primarily inhabiting shallow coastal waters of the North Pacific Ocean. These animals are often found amidst kelp forests and rocky coastlines, where they forage for food. Unlike many other marine mammals, sea otters do not possess a blubber layer for insulation. Instead, they rely on their exceptionally dense fur, which can have up to one million hairs per square inch, to trap a layer of air against their skin and provide warmth in cold ocean waters.
Sea otters spend most of their lives in the ocean, even sleeping while floating on their backs, often anchored by kelp to prevent drifting. Their diet primarily consists of marine invertebrates such as sea urchins, clams, mussels, and crabs, which they retrieve from the seafloor. They are one of the few animals known to use tools, using rocks to crack open hard-shelled prey.
River Otters: Life in Freshwater Ways
River otters, such as the North American river otter (Lontra canadensis), are primarily found in freshwater habitats across North America. These predators thrive in rivers, lakes, wetlands, and ponds, where they navigate both water and land. Their streamlined bodies and powerful tails enable efficient swimming, and they can close their nostrils for underwater dives.
River otters construct dens, often called holts, in burrows along riverbanks, under roots, or in hollow logs. Their diet is diverse, consisting mainly of fish, but also including crustaceans like crayfish, frogs, and other small aquatic animals. They are known for their playful behavior, frequently sliding down muddy or snowy banks into the water.
Bridging the Divide: Otters in Mixed Waters
While many otters are specific to either freshwater or saltwater, some species and individuals demonstrate adaptability to brackish water environments. These transitional zones, such as estuaries, deltas, and coastal marshes, represent areas where fresh and saltwater mix. Otters may utilize these habitats for foraging opportunities or as pathways between different bodies of water.
Certain otter species, like the Eurasian otter (Lutra lutra), are known to inhabit both freshwater rivers and coastal marine areas. The North American river otter can also be found in coastal marshes and even rocky seacoasts, where they forage and travel in saltwater. This flexibility allows them to exploit a wider range of resources and expand their territorial reach.