To me, that's an interesting question. There is no doubt that otters have a sex. There are male otters and female otters, otherwise, there wouldn't be any baby otters.
Otters have sex roles, too, at least around mating and pup-reading.
There are mommy otters and daddy otters, each with roles. There may even be other roles that ae defined by sex in an otter clan, as there are in other mammals, but not being much of an expert in aquatic mammals, I would be hard pressed to know what they might be. So otters have sex, and sex roles. I don't think so. I believe that gender is a communication of role and status that assumes symbols of gender.