I see 3 sushi restaurants on the same street, start to extrapolate in my head, and wonder how we hadn't extinguished most edible fish species decades ago. From what I've read and heard on the subject, my understanding is: (1) some we have (touched upon at end of Jiro Dreams of Sushi, for example), (2) we are in the process of doing so to most the rest, (3) fish farms are increasingly making up the difference.
Fish stocks are being depleted. We are running the earth down.
Many species have disappeared before we even began to walk. Many will after we are all dead.
The earth, and life as we know it, have both faced and survived much worse.
We are merely ruining one of the many ecosystems our planet has supported and will support.
It just so happens to be the only one we definitely know we can thrive in ¯\_(ツ)_/¯