Advice needed on how to increase views on YouTube

[sitech1]

My son has been uploading mainly Doctor Who-inspired music videos to You Tube for about 2 years now. This time last year, he uploaded an Amy Pond video that got over 20,000 views before it was blocked for copyright reasons (although he tries his best to avoid copyright issues and this is the only video he's ever had blocked). Not including this his average view rate up until recently was around 1,000, but this has fallen off dramatically over the last few months and he's struggling to get as many as 500 views. He's naturally quite upset about this. He wants to be a film/tv editor when he leaves education, so it's very important to him. I'm no expert on these things, but I can't see any drop in quality and I'm at a loss as to why people aren't watching his videos anymore. Can anyone advise me? Is there anything he can do to increase his view-rate?

I've done a bit of a search on LJ for Doctor Who communities similar to the Torchwood ones I'm part of, but I don't know enough about them to know whether or not they would be a useful forum to post to.

This is a link to his YouTube account if anyone wants to see what sort of videos he's doing.

http://www.youtube.com/user/TheDoctorsAssisstant