On the subject of fish and fishing.
I used to be avid angler in my early 20's every 2 weeks we would go to south china or around malaysian waters to fish over weekends.
Local fishermen in malaysia who do this for their living have a hard life they fish year round without fail sometimes they get a good catch but sometimes return empty handed their life is like a "straw in the wind" I ever seen a fisherman caught 200m of telco copper cable from his fishing handline worth about $40 scrap value he didn't get anything else that night but he was quite happy, then they also make extras ferrying tourists like us for weekend fishing excursions but sometimes tourist season is bad. Except for monsoon season where it is too dangerous to go out or ghost festival which they "pantang" only malay fishermen will go out to sea during ghost festival and when we follow them we usually get a bonanza catch because nobody else is fishing in the waters for a month which often surprises me how quickly fish stock will replenished.
In my opnion there's actually a lot of fish still in the seas, not all fish end up as fish meal, does it make any sense that mackerels caught in these waters are sorted and exported to a factory to ground into feed and sold to maybe countries that farm salmon, sorting and exporting labor transportation all cost money. Maybe in those countries that farm salmon they buy locally caught mackerel then it makes more sense.
My view is a lot of the fish that are caught around these waters are sorted. The good quality fish that can fetch high value like ikan kurau, red snappers, mackerels are sold to various small distributors in malaysia who then bring the fish to nearby cities like KL or singapore which are again sorted sold either to domestic market or packed and exported to other countries in the region like japan. So not all fish in japan are caught off japanese waters are radiated many fish in Japan are imported from around the world.
The not so common fish caught by malaysian fishermen are sold in local markets in fishing villages, if you go to the local fishing village markets during early mornings can see a lot of weird and interesting fish and many of them are fresh off the boat quality which are not more than 3 days old compares to the fish brought in by trawlers here which are still fresh because of deep freeze but are more than 2 weeks old already.
In singapore there are some areas that are protected and off limits to all civilian boats like around the live firing islands. I hear from the rumour mill that these waters are loaded with huge fish left to grow wild and undisturbed for many decades.