No idea about first ascent, but that is a very prominent boulder there. We called it the Rubic's Cube on our visit. You did well to get your dog over, guess its a swimmer, but don't they always stand around in the most unhelpful places.

Hi Mark, seems to be a fair bit of potential on Bryher. Good to know you and others are also enjoying these islands. We often stay at the campsite on St. Agnes - there's lots of good bouldering scattered around there. The dogs always up for an adventure but not really focused on their spotting duties