The VMS systems reduce the need for active patrolling which makes this sort of thing much more manageable.
The trick, as with all agreements reached by Regional Fisheries Management Organisations, will be the willingness of the individual flag states to enforce the rules on vessels flagged to thier nations.
And, of course, remember to look at the list of nations that agreed. Only they have any obligation to abide by these measures, flags of convenience are a problem that refuses to go away.
It will be interesting to see the actual wording of the agreement