We have huge industries devoted entirely to finding and killing that life. Why would we worry about whether, when we do that, it's living in a shipwreck we gave it or a reef that grew over time?
Reefs can't be fishing-protected areas because of the presence of fish. The presence of fish is how we pick fishing-intensive areas.
Not. Complex problems don't have simple answers.
We don't define fisheries by the presence of fish. We define fisheries by the presence of fish that --can be-- fished. This means normally age, not number. And age can't be measured easily in many species so we use size instead. Distance to the coast, population status and life cycle are also hugely influential.