I’m sure you could guess the most prevalent difference between river otters and sea otters. Yes, one species lives in freshwater, while the other lives in marine environments. But did you know that their habitat isn’t the biggest difference between them? Here’s everything you need to identify the hypothetical otter you’re dealing with.
Overview
Let’s get started with the complicated taxonomy of river and sea otters. They both belong to the Mustelidae family along with ferrets, weasels, polecats, badgers, grisons, martens, and wolverines. The 66 existing mustelid family members are all divided into 8 subfamilies, which are further divided into 22 different genera. Thus, sea and river otters belong to the same family, but not the same genus.
Physical Appearance
Despite their close family ties and similar names, sea and river otters have little in common when it comes to physical appearance. Sea otters have a stocky build with a short, flat tail and large feet. In contrast to this, you have river otters with their sleek body shape, long and pointy tail, and small feet. River otters have two layers of coarse fur, but sea otters have thick, dense fur that consists of up to one million hairs per square inch.
Size
The main difference between river and sea otters would be their size, or at least their weight. Sea otters with their stocky bodies are without a doubt the larger and heavier species. They can reach up to 100 lbs., while river otters rarely surpass the 33 lb. mark. Sea otters can actually stand up to 4 feet tall, but river otters can be as long as 5.5 feet from head to tail.
Diet
It should come as no surprise to you that sea and river otters have slightly different diets, especially since they stay in very different habitats. Our slender friends enjoy a range of creatures, including freshwater crustaceans. Their diets mainly consist of fish, frogs, and crayfish. Sea otters also enjoy fish every now and then, but they’re much better at sourcing clams, mussels, crabs, sea urchins, snails, and abalones. They also eat larger creatures, like octopuses.
Both species are slightly opportunistic, so they’ll settle for seaweed, birds, rodents, small mammals, and rabbits if they can’t find their meal of choice. Fortunately, this doesn’t happen quite often because sea otters are known for their ability to use tools. For instance, they know how to use rocks to open shells.
Behavior
As we’ve established, these animals are in the same family, but they’re quite different from each other. They also display these differences in their behavior. For one, the sea otter is a social creature, while the river otter would much rather stay alone and defend their territory. Furthermore, sea otters are primarily aquatic, so they spend as little time on land as possible, while river otters are often spotted burrowing in riverbanks.
Habitat
This one’s all in their names, but yes, sea and river otters do live in seas and rivers. Sea otters are exclusively marine animals, and they primarily live in the North Pacific Ocean. This is where they eat, sleep, breed, birth, and hunt. River otters have more options, and they can live in anything from a lake or river to a wetland, as long as there’s enough food and little danger.
Other Differences
Reproduction: Sea otters only birth a single pup at a time in most cases, while river otters actually have litters that consist of three to four pups at a time.
Mating: The mating behaviors of sea otters and river otters differ in various ways. Sea otters are polygynous, so males mate with multiple females in their territories, but they can also be monogamous, so they’ll mate for life. River otters have a much looser approach as both males and females mate with multiple otters throughout their lives. Sea otters are also more aggressive than river otters when mating and the male may actually bite the female’s nose.
Speed: Sea otters can reach up to 5.6 mph underwater, which makes river otters the faster species. They can reach speeds of up to 8.7 mph.
Lifespan: Sea otters for 12 to 15 years, which is longer than river otters, who only live for 9 to 12 years.
Conservation status: According to the IUCN Red List, sea otters are classified as Endangered, which is horrible since they play a vital role in sea urchin regulation and kelp forest protection. River otters face some threats, but they’re considered to be safe from extinction at the moment.
Similarities
Prey: Sadly, both river and sea otters are considered predators and prey. River otters need to stay on the lookout for bobcats, domestic dogs, cougars, bears, alligators, and coyotes. On the other hand, sea otters are preyed on by killer whales, sharks, wolves, bald eagles, and bears. So, basically the majority of the animals you can find in Alaska.
Grooming: Both species have waterproof fur and they spend a lot of time maintaining it. They use their paws to remove dirt and roll on land to dry themselves. Furthermore, they actually create more buoyancy and insulation by blowing into their fur.
