AIS is not a "silver bullet". Although many ships are transitioning to
"ECDIS" wherein they will end up having a screen with a chart/radar/AIS
overlay, it is not all that common yet.
In most cases you are still dealing with a seperate AIS screen which only
list the targets and is only usefull if you have some reason to look at
it..... so .....if they haven't seen the target visually and/or on radar,
they may not check the AIS to see what's about/around.
Prudence would say visual..... check the radar for targets with and without
AIS, check the AIS for targets missed on radar.... and back to
visual....i.e., with each new system you improve your lookout
capabilities.....but only if you use them.

otn