What I remember from reading The New Yorker article about tuna.

Worldwide fish caught has declined since the 80s.

There are no big tuna left (they used to be huge). We’re now killing the children, before they have a chance to breed. The worldwide population is collapsing, and thousands of fishermen will be out of work, just like when cod populations collapsed a decade ago.

For more, read Elizabeth Kolbert’s article.