(Also worked on this area for a bit) There are EU regulations requiring fishing vessels over 15m to use AIS (the UK also abides by these) so within Europe the

(Also worked on this area for a bit) There are EU regulations requiring fishing vessels over 15m to use AIS (the UK also abides by these) so within Europe the standards are reasonably consistent. Regulations are considerably more relaxed or less effectively enforced in other jurisdictions which is reflected in the data; it's possible the 98% of all fishing vessels operating off Thailand without AIS are all legal. But given the reputation of larger vessels operating in that region for slavery, perhaps not. Agree there are privacy-related reasons why you might ideally not want competing vessels seeing which waters you fish, but AIS alone doesn't tell anyone whether it's any better than other waters (and fishermen have no shortage of other data points to plan their activity or other boats to follow if they really don't have any better heuristics). Regulatory evasion is rife even in effectively-regulated areas not least because the industry is convinced some of the regulations are actually wrong, especially when it comes to localised quotas. You knows there's an issue when a former operator of a commercial fleet in Europe tells you candidly, that their skippers (who are all tracked by AIS/VMS) would definitely expect any catch logging system to allow them to lie about which points on their voyage yielded most of the fish....