Plus, that ignores fish produced on a fish farm. Not all fish come from the sea. Freshwater fish, shrimp, and molluscs can be produced in a man made lake or pond in a sustainable way that does not impact the oceans or naturally occurring fresh water sources.
Further, if we all go vegan without also changing our agriculture, that will mean more fertilizer run off making it's way into the oceans and degrading marine ecosystems.
Good article.