In this scenario, Antarctic Krill will be sustainable, as long as consumers are willing to pay the price of the end product.
Ditto to the other sources of quality marine proteins and fatty acids, such as fish meal. As long as there is money to be made, and the market will bear the cost, the show will go on. Perhaps in a more limited capacity, due to regulations etc, but it will go on.
As soon as the average consumer is no longer willing to pay for the more quality ie expensive raw ingredients, one will start seeing more feed ingredients such as soy, corn, and other terrestrial based sources. It doesn’t seem that many years ago when peas were the latest novel form of protein for fish, now we have black fly larvae, and even forms of algae supplying protein. The reality is, nothing will ever beat a quality marine protein, such as fish meal. Certainly there are numerous lower cost ways to get the job done, but nutritionally better? Not even close.
So at the end of the day, the real driving force behind the harvesting of the oceans protein, will be up to us, the consumers. I suspect that for many folks, at some point it will make more $ense, to eat more peanut butter, hot dogs and beans, vs a fillet of fish, or a beef steak. Hell, for many folks this is already a reality. Keeping fish in a glass box, will be an expense that is out of reach for the average person. Owning a pet dog or cat will follow. At that point, which is beginning to seem like it will be in the near future, the over harvesting of krill in the South Antarctic will be the least of everyone’s worry.