This is a question that Docents at Point Lobos deal with all the time. We have to evaluate the situation and make suggestions as best we can. As near as I can tell the Marine Mammals Act says that you can’t intentionally disturb a marine mammal, but does not give specifics on distances or activities.
We have guidelines that say you can’t be within 50 ft of one or 150 ft of a mother and pup. I haven’t found the origins of these guidelines, but they seem reasonable.
And yet, you can be 30 ft away and not disturbing the otter at all or be 200 ft away and talking in a loud voice that obviously disturbs them. For me if I am taking a shot and the otter looks at me, I am too close. It is time to back away quietly.
If the otter responds to your shutter, you are too close, back away.