The news this morning that Pret a Manger have removed tuna sandwiches from their shelves in light of the unsustainably intense fishing pressure wild tuna stocks are now under, is the one story I found heartening today. And it comes hot on the heels of the campaign to get stricken bluefin tuna off the menu at celebrity canteen Nobu.

As a former marine and fisheries biologist, one of the principal reasons that I moved into more mainstream environmental communications and campaigning was the frustration of being utterly ignored. It has been painfully obvious for decades that we're destroying our oceanic wealth, yet politicians don't seem to listen to the simple, brutal truth that if we don't stop catching all the fish … there won't be any fish left.

Charles Clover's new film, The End of the Line, based on his excellent but downright alarming book of the same name, is also seeking to engage a broader public audience on what is happening beneath the surface of our seas with their tacit support. We are taking a wonderful, bountiful and phenomenally productive natural resource and systematically hunting it to extinction, leaving the oceans poorer and depriving humanity of a vital source of protein, potentially forever.

Aliens spinning past our blue planet would note that seven-tenths of it is ocean, and 90% of that is more than a kilometre deep. Yet even in these dark, abyssal depths we are relentlessly pursuing slow-growing, deep water species to meet the burgeoning global appetite for fish. Imagine if we practiced the same sort of hunting on land, using satellite tracking, sonic scanning devices to find and hunt down the very last cows roaming our countryside and then used a massive machine gun to kill them, along with everything else in the vicinity as a sort of terrestrial "bycatch". Before moving on to hunt down the last sheep, and then pigs once the cows had run out or they were too hard to find. Crazy as it sounds this is more or less what happens in our seas.

Part of the problem is the heroic romance coupled with the invisibility of the fishing industry. We still hold notions of brave men in small boats, battling the elements to return with a natural harvest. While this is true for small, inshore fishermen, it's the huge industrial-scale, ocean factory trawlers that are really raping the seas with trawl nets big enough for 13 jumbo jets to fly into. But all this goes on out of sight and out of mind offshore, with most consumers experience of fish being limited to a skinned fillet in a plastic supermarket tray.

The value of the UK fishing industry also seems relatively and almost pitifully small, with a total annual catch value of only £600m. Are we really prepared to destroy our wild fish stocks for such meagre returns?

The growth in Marine Stewardship Council accredited fisheries in the UK and globally is a source for some optimism, and public support for marine protected areas (83% think this is a good idea) that allow fish and shellfish populations to recover will also help.

These may not necessarily be enough for the tuna however, and the bluefin in particular is a spectacular and wonderful species. A hot-blooded fish that can reach half-a-ton and 4m in length (though few get to this size these days), these incredible beasts were once abundant. But the allowable catch quotas have usually been around double what the science recommends. As a result the populations are so low collapse is almost inevitable. A moratorium is needed to bring these amazing fish back from the brink - and not just so they can end up as sushi.