While the author is discouraged about the fate of the bluefin tuna, and her final note is one of worry, her last three paragraphs are mostly about things that could work:
And yet this is never where the new fish stories, or stories about the fish stories, wind up. Just when things seem bleakest, hope—dolphinlike—swims into the picture. David Helvarg concludes his memoir-cum-ecological-disaster narrative “Saved by the Sea” by declaring that, owing to a new attitude in Washington, things seem “to be looking up for the ocean.” Similarly, Roberts closes his chronicle of more than a millennium of overfishing by asserting, “We can restore the life and habits of the sea because it is in everyone’s interest that we do so.”
The way to keep fishing, according to Roberts, lies in not fishing—or, at least, in not fishing everywhere. He proposes that huge swaths of the sea be set aside as so-called “marine protected areas,” or M.P.A.s, where most commercial activity would be prohibited. In “Four Fish,” Paul Greenberg argues that the salvation of wild fish lies in farmed ones, though not in the kind you’ll find on ice at Stop & Shop. (Today, most farmed fish are fed on wild-caught fish, a practice that only exacerbates the problem.) Greenberg is a believer in what’s sometimes called “smart aquaculture,” and thinks we should be eating species like Pangasius hypophthalmus, commonly known as tra. Tra happily feed on human waste and were originally kept in Southeast Asia to dispose of the contents of outhouses. Michael Weber, the author of “From Abundance to Scarcity,” is encouraged by the introduction of new regulatory mechanisms such as “individual transferable quotas,” or I.T.Q.s. The idea behind I.T.Q.s is that if fishermen are granted a marketable stake in the catch they will have a greater economic interest in preserving it.
M.P.A.s, smart aquaculture, and I.T.Q.s—these are all worthy proposals that, if instituted on a large enough scale, would probably make a difference. As Roberts notes, it is in “everyone’s interest” to take the steps needed to prevent an ocean-wide slide into slime. But it is also in everyone’s interest to save the Atlantic bluefin tuna. Still, it is being fished to the edge of extinction, which is why a hopeful ending is not always the most convincing one.
The relevant agencies that would have to sign off on the sea preserves are the same ones that green-lit all the overfishing to date and show absolutely no sign of even acknowledging why we've moved on to fishing things like the patagonian toothfish (itself now overfished).
If that's the best reason he's got, the ocean is doomed. It's in everyone's best long term interests to do so, but quite a lot of countries are convinced it's in their best short-term interest to overfish, and they will not think about the long term.
There are two reasons for that; profit and preventing starvation. There are areas of the world that would not have enough food to survive if they stopped fishing the way they do. The only solutions would be to send them food, or implement population control.