Global Fishing Watch checking 2 million gigabytes of satellite data from 2017 to 2021 found 72% to 76% of the fishing boats
are untracked, unregulated, and catch unreported.
They could separate out commercial shipping, oil platform service, and other boats, from fishing boats.
They don’t say if they could separate 3 or 4 guys chasing  trophy Swordfish/Sailfish from guys dragging nets on the bottom for everything. 
I suspect there's damn few of the former and lots of the latter. 

 There are a lot of unknowns, a huge bunch of unknowns they didn’t even know existed. 
But they discovered an average of 20 boats a week enter the Great Barrier Reef Marine Park.
In addition to 5 boats a week in Galapagos Marine Reserve. 
It's a pretty safe bet they don't have a handle on fish stock depletion.

https://www.smithsonianmag.com/smart-news/satellite-maps-reveal-rampant-fishing-untracked-dark-vessels-oceans-180983539/