put it this way, there is no known numbers for otters, or even population estimate. How can something which could actually be in excess be deemed as endangered still?? I tell the people I work with that love otters that the so called 'its only nature' route is not true, as they are rehabilitated and released instead of being left to die...that is not natural... there is no argument to it which makes me chuckle when they try. If you find a dying animal then nature intends for it to die!!
It happens with every animal, including humans. i.e. without prolonging life with complex surgery and drugs there wouldn't be a failing medical service (I still blame the Government for not funding it properly). Too many otters = no birds, fish, frogs, etc. too many lions = no gazelles. too many cows = no long grass in the field.