Maybe I'm just falling victim to corporate propaganda, but I'm pretty sure wild (Alaskan) salmon is truly sustainably fished, as are sardines and anchovies
This is something I follow constantly and the numbers are actually terrifying. Some rivers have okay returns of some species of salmon, but some like sockeye are at incredibly low numbers. They are by some measures on the brink of extinction, and many spawning runs are extinct already.
In BC, sockeye returns are currently being tracked daily and the result so far is that less are returning than ever before, and the amount returning is far less than the department of fisheries and oceans' lowest estimates. It's an emergency in my opinion. People shouldn't be eating sockeye.
I'm not sure about sardines and anchovies. I know herring have been seriously overfished, so I have doubts that anything we fish is sustainable at the moment. I hope it is.
Another thing to consider is that what we call a glut of sockeye these days is still a paltry return compared to what was once possible. 100 years ago, before a certain landslide occurred in one of BC's major rivers, our largest returns were estimated to be almost 40,000,000 fish. This year, we're seeing around 600,000 fish. We were expecting 4,800,000.
Something fascinating about this is if you look up the conservation status of the pacific sockeye salmon, it's Least Concern. There certainly are some populations in some rivers that are doing better than others, but the overall trend is a steady downward pattern.
This year it's not clear why numbers are so low, but a sound guess would be that the generation spawning this year's returners were largely impacted by pre-spawn mortalities. Numbers look good going into the river, but they end up dying before they can spawn. Research into this phenomenon isn't well-funded, but it's a known problem.
US: https://www.seafoodwatch.org/
UK: https://www.mcsuk.org/goodfishguide/search
Both have mobile apps I believe.