Black-headed gull fishing for small plaice.

I sat on the beac for several hours today waiting for the Bonaparte's Gull to show up which it had done most days this last week but I hadn't been lucky enough to get a photo (until today).  I amused myself by watch a Black - headed Gull that was bobbing away in the surf just in front of me.  Every now and then it would take to the air and dive beneath the surf.   This was a good photo opportunity of course but I hadn't realised what it was actually doing?  It was spying very small flatfish on the sea botton and then diving to catch them.  This is obviously a technique that it has developed and it was very successful catching several during the time that I watched it.