I believe much of the Otter problem may be exaggerated by environmental, and climate problems. I've be well aware of Otters on two rivers that I frequented, both out of state and I never saw any evidence of harm, nor sport killing. Strangely I've seen them eat fish on several occasions, and it was always SMB, but the river was famous for its population of SMB.
Its seems that for every area that they are suspected of decimating or causing harm, there are areas where they exist, and cause no harm.
The bottom line is that man is the biggest single reason for the majority of declines in wildlife, and not as a political entity, but as individuals.