The probability that there is many times more mercury in your sushi than there would have been 100 years ago, is 1.0 unless that sushi came from a fish farm. Whether it's enough to call it "poisoning" is open to debate. The EPA and FDA recommend you do not eat swordfish, shark, or king mackerel, ever, because of mercury.

We've already seen minimal to no regulation, in the 1970s. WRT mercury contamination of freshwater fish it was very bad. Perhaps some of you are too young to remember when American scientists used to debate whether the recommendation to eat fish no more than once a week was conservative enough or not. Fishermen in many areas are still advised not to each the fish they catch.

It's a bit of a moot point, since without regulation, the major freshwater and saltwater fish stocks would have crashed by now anyway. This doesn't always have to be government regulation. Maine lobstermen have regulated themselves for many years - not just outside the government, but illegally (because the punishments they imposed on violators were illegal).

Harvesting of freshwater fish in the US is, so I hear, switching over to fish farming. Not so much because of poison, but because there just aren't enough wild fish.