There has been concerns for a number of years now about the decline, if not crash, of fish populations across the world, with one prediction being the end of ocean fish populations by 2050:
http://www.telegraph.co.uk/news/uknews/1533125/All-seafood-will-run-out-in-2050-say-scientists.html
https://www.washingtonpost.com/posteverything/wp/2014/06/03/the-end-of-fish/?utm_term=.8ee99bf45449
More recent studies indicate that the end of fish date has shifted much closer, with a University of Washington study finding that populations of older fish have dropped by 72 percent on average, and for some species, such as red snapper, by more than 95 percent. Older fish tend to be veteran reproducers, and have more offspring. Natural News was quite alarmed about this and proclaimed that the collapse of fish populations “may lead to the fall of human civilization”:
https://www.naturalnews.com/2017-09-28-fish-populations-are-absolutely-collapsing-across-the-oceans-of-the-world.html
The techno-fanatics are not worried and proclaim that aqua culture will be easier and more economical in the long run, anyway. Maybe so, that depleting fish reserves by the over-fishing conducted by the West, and massive assault by Asia, will leave many millions, if not billions of poorer people, who cannot afford the techno-splendour of aqua culture on vast scales, without a major source of protein. They are not going to like this, and will migrate. And, the chattering class here in the West, will fall over themselves to relieve their guilt/affluence complex, letting ‘em in, as the song by Paul McCartney and Wings, Let ‘Em In (1976), said:
https://www.youtube.com/watch?v=0p4drWtJ0Ug
How did a generation ever go for this sort of stuff anyway? Spengler must have been right.