Michael McFadyen's Scuba Diving - Osborn Shoal East
Located directly off Cronulla Beach, Osborn Shoal (this is the name preferred by the NSW Geographical Names Board) is one part of a reef that can be found intermittently from Kurnell to Bundeena across Bate Bay. Like Merries Reef further to the north, the top of the shoals is generally flat and covered in kelp, although some parts are covered with sponges. Once you drop off the top, however, things change. On the eastern, northern and southern sides a sharp drop off takes place with the depth going from 12 to 20 or more metres in some spots. These are the best sections. The normal dive here is at the northern end of Osborn Shoal.
This article is about the eastern side of Osborn Shoal. From Port Hacking, head out to the north-east once you pass Oak Park towards the Cape Baily Lighthouse at Kurnell. The GPS Marks of S34ΒΊ 03' 34.1" E151ΒΊ 11' 17.7" (using WGS84 as the map datum). If you use another datum you may be about 220 metres off the wreck. See my GPS Page for more details and how to convert readings.
In a north-easterly breeze, run in over the shoals from a south-westerly direction. As soon as the depth sounder shows a drop in depth from about 16 metres to 22 metres, drop anchor. This should place you on the reef edge. In a north-westerly or westerly breeze, run in from the sand and drop anchor when the reef comes up from 22 metres to 16 metres. If you do this you should be aware that it is often very difficult to get a good anchor hold on the reef itself.
After descending to the anchor, if you are not already on the reef edge, swim to the east and you will find the reef edge. You will be near a sort of corner where the reef turns from the north to the west. Head to the north at first, keeping away from the actual bottom of the wall, closer to the sand edge. Examine all the small rocks off the reef and the small overhangs as you go. There are excellent sponge life, small gorgonias and sea squirts along the wall and the rocks. On the sand there are some sea dragons and some serpent eels.
There are cuttlefish, some eastern blue devilfish and lots of one-spot pullers, yellowtail and quite a few black reef and yellow-tail leatherjackets in this area as well. After about 10 minutes turn around and come back along the wall's bottom. Once back near the anchor, you will notice that the reef here is a little different to the section that you have already explored. The reef is slanted at 45° towards the east and there are two parallel reefs. There is a gap in between which you can swim easily. When you get to the southern end of this bit, turn to the right and go west. You will see that the wall here is a bit more prominent than the section already explored.
Come back to the east and past the angled reef there are lots of boulders out to the south-east. I am not sure how far they extend. head back to the anchor area and if you have any time left, explore the top of the reef before ascending.
Sealife that you will almost certainly see at Osborn Shoal includes many different kinds of nudibranchs, with colours varying from white to pink to blue and other beautiful colours. Fish to be found here include blue groper (very friendly), red morwong, cuttlefish, mado, stripey, common bullseye, crimson-banded wrasse, maori wrasse, silver sweep, sergeant baker, old wife, striped seapike, white ear, black reef leatherjacket, yellow-striped leatherjacket, Port Jackson sharks, one-spot puller, ladder-finned pomfret, blue-striped goatfish, yellowtail, pufferfish, eastern blue devil (very beautiful) as well as the previously mentioned serpent eels. Large dusky flatheads and common stingarees can be seen on the sand and you will almost certainly see common sea-dragons near the rocks on the eastern side and west of the cave. I have even seen tiny firefish near the cave.
This dive site is one that needs more exploring to fully appreciate. Over the coming year I hope to explore it more.
The visibility here is usually quite good, with 9 to 12 metres being average and often more than 15 metres.