Fish or foul? The rise of deep-sea farming

The enclosures stretch the length of an Olympic-size swimming pool, but from above they appear as floating dots scattered across the ocean. Inside, fish mill about as the submerged pens sway to the sea currents

Known as off shore fish farms, these structures have appeared around the world in recent years. Their proliferation in open waters, often sitting several miles off coastlines, has sparked heated debate: some see them as the next frontier for the sustainable production of fish such as Atlantic salmon, sea bass and cobia ; others describe them as “factory farming of the sea”.

What almost everyone can agree on is that these deep-sea farms are poised to surge in the coming years. Between 1961 and 2017, global demand for fish grew