Unless there is some kind of global control on catching, for example, blue-fin tuna (which travels outside of nationally controlled waters), "gone" seems more likely. The feedback loop of, the rarer the fish - the higher the price, will push some species to extinction in the wild.

I've never eaten sushi, so I'm not familiar with what fish are normally eaten, but can these fish be farm-raised?

Yes they can, they are farming a fish called Cobia in Queensland Australia that is a sashimi grade fish. The farming process is surprisingly good too, they worked with a local company and sorted out a crop based land grown food pellet for the fish to remove a large amount of reliance on pulling their food source from the ocean.

http://www.abc.net.au/news/2016-04-01/cobia-to-kick-start-mu...

Farm raising tuna is difficult. Not sure if it is done commercially yet and, even if successful, I would guess wild caught tuna will still be highly prized in Japan. It is really the Japanese market that is and will keep driving the high end of the fish market.

It's a little more complicated than just 'farmed vs wild-caught', as a lot of tuna is wild-caught, then transferred to floating pens to fatten up for up to a year. Penned tuna are neither truly wild, nor considered farmed as there is no breeding stock.

Sure. You'd have to be pretty lucky to find a wild salmon in a sushi place - and if you did it'd probably be twice the price.

A somewhat recent development in packing fish is automated cutting and vacuum packing - alive to wrapped in less than 30 (or so) seconds.

This is afaik also being done on factory ships, with fish like cod. Still rather new (a few years?) and expensive - but a great way to treat fish. Many of the advantages of flash freezing without the down sides.

We've eaten things to extinction before, so no, don't assume anything.

https://www.britannica.com/list/6-animals-we-ate-into-extinc...

I'm still hesitant to agree that we caused the mammoth extinction. There just weren't enough people at the time to do it with the technology we had, especially in places that lack enough cliffs.

We've had spears for quite a while now.

https://www.youtube.com/watch?v=mAvEmzjL_lA

That's a remarkable list, thank you for sharing it.

The problem is that then it becomes more lucrative to harvest.

For example, the high price of tusk and horn isn't saving the elephants and rhinos.

Perhaps, but not necessarily. There are real concerns that with a combination of temperature rises, ocean acidification, and trophic cascades caused by overfishing, the oceans will entirely die in the medium term. They are certainly in the process of dying (like nearly all ecosystems under the assault of 'economic growth').

Your assuming population response is linear, it isn't. Passenger pigeon showed us that populations can collapse rapidly below certain thresholds.

Increasing the incentive to catch every last one, presumably?

as long as it isn't subsidized like the livestock industry.