Spotted gully shark (Triakis megalopterus)
Image from video clip by Gareth Randle.
Another spotted gully shark
A pyjama shark (Poroderma africanum)
A broadnose spotted seven-gill cowshark (Notorynchus cepedianus)
Photos Guido Zsilavecz
The spotted gully shark is a common sight at Pyramid rocks. Their presence is unpredictable, but they prefer warmer waters, and are hence less likely to be seen in the middle of winter. They like either the dense kelp beds close inshore, where Gareth filmed his, or the caves close to Pyramid rock itself. They attain a length of 1.65 m (only - shows how one can overestimate size underwater!). They feed on small prey - crabs and small fish, and have only small teeth. They are thus completely harmless to divers. Probably because of their lower rank within the food chain they are also very skittish - as long as you remain a few meters behind or above one they will stay around, but once one becomes aware of a diver it will dissapear with a few small flicks of the tail. At Pyramid one can often see several at one time, but if one flees all others go with it, so if you see one, stop swimming, remain calm, and do not move suddenly - in that way you'll see more of it!
For its size the spotted gully has very large pectoral and dorsal fins - in fact, its scientific name, megalopterus comes from mega - large, and pterus - wing or fin, hence large-finned. The colour is generally a dark grey with black irregularly spaced spots all over.
The other sharks Gareth mentioned, the nurse/raggedtooth and pyjama are quite different to a spotted gully. Raggedtooth sharks do not really occur in Cape Town waters (they may, I have not seen one yet). They tend to be much bulkier, with a smallish head and a deep, fat body, usually in a light brown. The pyjama shark, as shown, has very distinct black/dark grey and white stripes along the body. It also does not grow as large as a spotted gully.
The one larger shark which also may be encountered at Pyramid is the seven-gill cowshark. It can be readily distinguished from a spotted gully by its much blunter head, and the lack of a first dorsal fin - or rather, the single dorsal fin is set well back, leaving the back "bare". They prefer the less-dense kelp zone between the inshore thick kelp and Pyramid rock itself. Their behaviour is also completely different, in that they may inspect divers, but otherwise swim around completely unconcerned. Their diet consists of much larger prey, with large ones (they grow up to 3 m!) tackling even seals, and while I have never seen any aggressive behaviour, it is best not to corner one of them, tease it, pull its tail, or something similarly silly.
For further details, see Coastal Fishes of the Cape Peninsula and False Bay, available directly from SURG.
Coastal fishes of the Cape Peninsula and False Bay, a divers' identification guide, G Zsilavecz, 2005.
Smiths' Sea Fishes, MM Smith and PC Heemstra, 1986.