I have heard the law says you have to be a mile off shore. I have shot Surf Scoters off of Point Loma. I did get checked by Harbor police and they drug me in for questioning. They also called DFG and they came on down to join in on the questioning, I never got cited for anything and they never found any black and white rules. This was before 9-11, I could only imagine what they would do now if they saw you with a loaded shotgun hunting in the ocean. Back in the day the south bay was off the hook. They outlawed it and made it a $100 fine if yiou got caught hunting back there. Alot of people still did it since driving to the Sea to hunt or wherever else would cost more than $100. They eventually caught on and raised the fine.
Found this out of regulations......other than this no requirements.
§507.5. Scull Boats.
Migratory game birds may not be taken by a scull boat or similar watercraft while under motorized power. The motor shall be removed from its mountings before any take or approach is attempted.
This section shall not prohibit shooting migratory game birds from scull boats or similar watercraft with motor attached if beached or anchored; nor shall it prohibit the use of a motor for the sole purpose of picking up dead or injured birds.