That works if they're the only "tribe of sea people." If the situation is more like the Pre-Columbian Americas, or "local Orca pods," then going elsewhere is a problem. (Imagine "Admiral Starched Pants" finding out there are a lot of "sea people" in the aquatic world!;)

@drjekel_mrhyde said:

They have 75% of the Earth to hide in.

I believe that the government's secret project instigated the massive overfishing campaign in order to draw out the Mer people for capture and medical research. The bay normally probably provides a steady food source and probably greater security for the Mer people from the open ocean and its predators. Human beings are upsetting the equation of course and proving to be the ultimate predators.