Funny, I was watching this video the other day and noticed very quickly, cavitation. Weather it's because the foil is close to the surface, lower pressure has caused it like Bille said! but it is very noticeable. I tried to see where it formed from, I took some screen shots and it looks like it came from a wing tip.....
You can see it at 3.29
IMO it is rather ventilation of the foil tip, that travels with the foil sometimes hundreds of meters from the catch of the air.
Cavitation would cease in less than one meter. First sign of cavitation is a high pitch sound you can hear somtimes at speed and that's the sign to improve your foil surface/setup.
But looking back at the wake, you will not see any bubbles, as they are tiny and disappear very quickly.
High pitch sound comes from collapse of milions of these bubbles.