Why not? Ban fish from unsustainable and environmentally unfriendly sources. 10 million New Yorkers represent enough buying power to marginally change the economic incentives for fishing companies worldwide.
Considering for cities like NY and SF the majority of seafood served is not what is advertised, despite existing legislation to the contrary, I think enforcement is the problem.
I imagine the only substantial course of action would be to ban ocean fishing vessels from the entire coast.
