I think you are reading it wrong.
It isn’t claiming that all CO2 went up by 28% due to fishing vessels.
It claims that the amount of CO2 from fishing vessels increase by 28% over that time. A much more reasonable claim. Basically if fishing increase by 28% over those 20 years, this would be completely expected.
Because these people just make up this data to justify their agenda.
There is no way they could measure the CO2 from fishing vessels in the open ocean over a 20 year period. And then come up with an exact number like 28%? Not even close to being credible.
Unless someone has a better take on this, this is all bunch of crappola.
If that’s true, then they should be alarmed if there are more city buses running then 20 years ago that the this means there is more exhaust from the buses than 20 years ago. IOW, they are anti-growth.