Skomer Island and the surrounding marine nature reserve is one of the most popular areas for diving in South Wales. On a good weekend dive boats converge from just about every slip and beach in Pembrokeshire to the wreck of the Lucy on the north side of Skomer Island, and to get there they have to cross a treacherous stretch of water called Jack Sound.
When the tide is running, currents in Jack Sound can reach 7 knots. The sea boils where rocks and ledges running across the sound cause sharp changes in depth. With an opposing wind, vicious standing waves form at either end of Jack Sound. It's dangerous enough to take a boat through it, so who could be mad enough to dive there?
That's what everyone seemed to tell me, and that is exactly what I thought until some friends and I tried it. Then wow; the current swept rocks of Jack Sound are just covered in rich and colourful marine life.
North of Tusker Rock (1). Breaking the surface at the north end of Jack Sound is Tusker Rock. A submerged plateau stretches north of the rock and running round the edge of the plateau is a wall.
The time to start a dive here is just before high water slack. The trick is to go out in the boat for 2 hours after high water and wait for the tumbling water and currents to subside. As soon as the surface water flattens, but is still just flowing northwards, it is time to dive.
Descend to the plateau and swim out northwards. The rocky seabed is covered in jewel anemones, dead men's fingers and hydroids. As you drift across the plateau there is a good chance of bumping into dogfish and crawfish resting on the rocks. Enough to make any dive, but don't stop to look for too long because you have to get to the wall before the current turns.
The wall appears suddenly. At first glance it looks plain and brown in the natural light, but shine a torch and what initially appeared to be a brown surface turns out to be a carpet of densely packed anemones. On corners and towards the top of the wall are clumps of white, orange and green plumose anemones. Conger eels and lobsters hide out in crevasses and holes at the base of the wall. Look but don't touch - this is still part of the marine reserve.
South of Tusker Rock (2). Following high water slack the current builds southwards and a wake forms behind Tusker Rock. Tight in behind the rock it is slack enough to dive all the way through to low tide.
This is a great location for macro life. If you have dived the north of Tusker Rock and seen some nudibranchs, you won't believe the number of nudibranchs that you can see here.
I have also seen the occasional octopus on this site, but the best places to find octopuses are at Wooltack Point (4) and at the south end of Jack Sound near the wreck of the Porthgain (8).