It's been a while since I read "The Perfect Protein" by Andy Sharpless, but IIRC their argument is that it's not just fish, but particular populations of fish.

It's been a while since I read "The Perfect Protein" by Andy Sharpless, but IIRC their argument is that it's not just fish, but particular populations of fish. Some wild fish are fine to eat - others are either at risk or are keystone species that shouldn't be wiped out. Also the method of fishing makes a difference as well. Hence the contrasting advice.