As we chug out of the little harbour, the view of russet hills and the blue peak of Beinn Alligin is distractingly gorgeous, but it's forgotten as soon as we look down through the glass hull at the teeming life below. Straight away we are soaring over settlements and busy highways. Striking out over the flat, sandy floor of the loch, a young brown crab scuttles purposefully towards who knows what, narrowly missing two more industrious souls coming the other way, like traffic passing at a crossroads. Occasionally there are flashes of silver as shoals of herring slide past.