if you just became aware of tonic dumping off of ratalina or santa monica bay or san diego by private industry and the military
and have fished off the coast for any length of time
the only way you wouldn't be aware is to have lived in a cave under a turnip patch
dumping went on till 1972
with news articles discussing it locally since the 1950's
https://www.theguardian.com/environm...-toxic-history
the dumping went on for at least 75 years
mostly in deeper canyons
and as far as a complete biomass instant overnight change
again check out how many tons of sardines were harvested off the coast yearly for the last century
how overnight the catch crashed and then how overnight it reappeared just as big as it historically had been
same for bluefin
local contamination has little to do with migratory species such as tuna