We think of otters as the cute little aquatic creatures who float on their backs and rub their cheeks in viral videos, but how do we tell the difference between river otters and sea otters? What makes each species unique, and what are the signs that make each one recognizable?
Taxonomically speaking, there is actually only one species of sea otter! The sea otter (Enhydra lutris) can be split into two regional subspecies, the Northern sea otter and the Southern sea otter, but in actuality, this is the one and only species of otter that is a lifelong ocean-dweller.
On the other hand, there are 12 different species of river otter found around the world, from the North American river otter to the Japanese river otter to the Asian small-clawed otter. These remaining otters can be found in rivers, lakes, and freshwater wetlands.
The one exception to these rules is the Marine otter (Lontra felina) — these otters are the only species of otter outside the Sea otter that reside in and around saltwater environments. The distinction between these two is important: the sea otter will spend its entire life floating in the ocean, swimming, feeding, and reproducing. The marine otter simply lives near the ocean, diving in only to feed.
It’s actually quite easy to understand the physical differences between sea otters and river otters once we understand that there is actually only one species of true sea otter. The sea otter we know is quite a bit larger in stature than the average river otter, the largest adults weighing up to 100lbs, heavier even than the largest river otter, the Giant otter (Pteroneura brasiliensis).
Most immediately noticeable is the difference in fur types — river otters have short, sleek fur, while sea otters are distinctly ‘fluffy’, with long, fuzzy fur that’s extremely dense and warm. Sea otters also notably have two very large back feet, webbed and streamlined for paddling and swift swimming in unpredictable ocean waters. The sea otter’s legs aren’t made for walking, like river otters’ are, but for constant swimming.
It may seem obvious, but the best way to tell if you’re looking at a river otter or a sea otter is just paying attention to the body of water you’re observing! Sea otters will be in the sea, river otters will be in the river. It’s as easy as that! Some river otters can be found in wetlands and lakes, but the general idea is the same: if the otter isn’t floating in the ocean, it’s most likely a river otter, and vice versa!
River otters and sea otters might be similar in name, but these two different classifications and populations are actually quite different in many ways, in the same way dogs have different breeds.
In addition to this, once you know the fundamentals of what to look for, it’s quite easy to differentiate whether or not an otter is a sea otter or a river otter — one is large and fluffy and the other is small and streamlined. And always keep in mind where you’re looking — if you’re at the ocean, chances are you’re looking at a sea otter as opposed to a river otter. This goes both ways!