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
Interesting, I just had a look at the wording of the agreement on the SPRFMO site and it's stricter than I would have thought (as such things go).
In particular all bottom trawlers will have to have an observer and if any evidence of a vulnerable ecosystem is found (e.g. they pull up some cold water coral or sponges) they have to stop fishing anywhere within 5 nautical miles of the location and report it to the secretariat. From then on the 5nm around that spot are added to the list of areas closed to bottom trawling.
Of course the entire section starts with the phrase "These interim measures are voluntary and are not legally binding under international law" but that's pretty standard.