This means that after fertilization, eggs remain dormant in the female's uterus until the following December, January or February, when they attach to the uterine wall and start to develop. Females usually have their first litter at age three. Pups weigh 4-5 ounces and are blind and toothless at birth. They do not open their eyes for five weeks, and their mother keeps them in the den until they are three or four months old. The female breeds shortly after giving birth, but she will not allow a male near her young for several months.
Males are polygamous.
When a young otter emerges from the den, its mother must teach it to swim. After several such lessons, young otters begin to enter the water on their own and eventually play, hunt and feed in it. By autumn, they are nearly adult size. They may remain with their mother until she is ready to bear another litter. Curious and playful, otters romp and wrestle with each other or play by themselves, even as adults.