The research project they linked in the article [1] talks about 700 sardines needed for 1 farmed salmon which is not a great i/o but supposedly there's a shift away from fishmeal towards soy, algae, insect protein, etc to where fishmeal is more like 15% of farmed fish diet. Note these are wild fish as input so the notion of farming distinct & preserving wild stocks isn't accurate. Per the comments, there were plenty of NYT readers who were not aware of the downsides so I'm not as critical about it as you. Besides yield there's other considerations like disease spread and genetic degradation to wild stocks, sealice, pollution spillover, and so on.