Cowshark passing overhead

Sea life: Broadnose sevengill cowsharks

Trawling through Tony’s YouTube page the other night, I realised that he has a whole lot of videos of broadnose sevengill cowsharks – most of them less than half a minute long – that have never seen the light of day on this blog. It’s a shame not to share them, as these sharks are magnificent and curious, and come obligingly close for the camera.

So, for your delectation, here are some broadnose sevengill cowsharks, filmed at Shark Alley in False Bay last year. This site can be done as a boat dive, but it’s incredible in that you can do it as a shore dive, too. It’s physically strenuous and involves a short surface swim, but can be done by a reasonably in-shape and adventurous diver.

The reason for the presence of these sharks in False Bay is unknown. They are caught by anglers (even up the West Coast) and found up and down parts of the South African coastline, but seem to come to Shark Alley to rest. We’ve dived with them numerous times and never failed to see several of them on a dive. They are generally placid (we’ve only had one slightly scary experience with them), curious, and self-contained. They have big eyes and small, smiling mouths.

Some of the sharks display white spots on their backs, which is a fungal infection. We saw far more white-spotted sharks when we dived Shark Alley last year, compared to recent dives there. These spots, in combination with the distinctive freckled markings (I fit right in!) that these sharks display, can be used to identify unique individuals.

Many, many of the sharks we see are marked in some way. There are signs of bites from other sharks, and I think most of these are sustained during mating behaviour. The females – if other shark species are anything to go by – are gripped by the males near their dorsal fin during copulation. Hence the tooth marks.

Some of the sharks also show signs of conflict with humans, and this is very sad and disturbing. We often see sharks with large hooks in their lips or gills – these hooks are usually made of stainless steel and will not rust away. Some of these are snoek fishing hooks (I imagine the shark was accidentally snagged), and some are from anglers who deliberately try to catch these sharks. Unlike great whites, they are not a protected species.

The sevengill cowsharks compete with great whites for some of their prey, such as soupfin and smooth-hound sharks. They are often hooked at the northern end of False Bay, while hunting these other shark species. They also eat seals, shysharks, gully sharks, and fish species such as roman. They are ambush predators, and when visibility is poor they are a lot more confident and approach far more closely than they would otherwise.

Research is planned by Save Our Seas to determine whether the interaction between the great whites and sevengill cowsharks over prey causes some sort of habitat partioning in False Bay (since, of course, great white sharks eat cowsharks too). There is anecdotal evidence that they either are able to hunt in groups or (more likely) that their opportunistic feeding behaviour gives rise to several sharks feeding on the same prey item simultaneously.

Diving with sevengill cowsharks in Cape Town is a rare and special opportunity. Tony has pointed out before that it will change your view of sharks forever.

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Clare

Lapsed mathematician, creator of order, formulator of hypotheses. Lover of the ocean, being outdoors, the bush, reading, photography, travelling (especially in Africa) and road trips.