Great Northern Diver

I finally managed to catch up with the juvenile G N Diver that had taken up residence on West Kirby Marine Lake! The bird is feeding well and catching plenty of small crabs. Although I've been over to Hilbre several times recently and passed the marine lake the weather wasn't conducive to sitting around trying to photograph a bird that spends a great deal of its time submerged.

Although it caught several crabs whilst I watched it ate them underwater. It appeared to catch them, surface and then shake them with its head underwater before swallowing them. Washing the mud off?

If you look carefully at the bill there's a notch on the lower mandible about halfway along. I've never noticed this before and wonder  if the bill has been damaged or if this is normal.