The first difference between Otter and seal is the family they belong to. Otter belongs to the family mustelidae, while the seal belongs to the family Phocidae. The different ways by which they keep themselves warm is another thing to note. Otters make use of their dense fur to keep themselves warm, while there is a blubber deposit under the skin of seals.
These two creatures also have a notable difference in their physical traits. While the seals are known to spend more if their time on the land, the otters use more of their time in the sea.
The seals also give birth and do their breeding on the land, while the otters mate and give birth in the sea. Seals feed on fish more than the otters; otters prefer to feed more on invertebrates. Otters posse paws, while seals posse flippers. The flippers make the seals have the ability to swim better in water, together with their streamlined body.