“whose mashgiach is standing on the boat or over seeing the processing that they ONLY take out the TUNA fish and dump the rest back?”
They don’t need to stand on the boat. They need to be at the processing plant and make sure that there are no octopi on the assembly line. Having said that, I believe that while the mashgiach has to be thorough, there is substantial leeway for chad bitrai batul which means that technically, you may have eaten dolphin (a great source of protein) or even Osama.