Its all very well getting in the water sharks, but its important to understand what they are and who they are. Here is some information gleaned from the web and scientific papers about our Sevengill Cowsharks as well this family of sharks.
What is a Cowshark?
Cow sharks, or the Hexanchidae, are a family of sharks characterized by extra pairs of gill slits. There are probably only two seven-gilled genera, Heptranchias and Notoryhncus
Cow sharks are considered the most primitive of all the sharks, because their skeletons resemble those of ancient extinct forms, with few modern adaptations. Their excretory and digestive systems are also unspecialised, suggesting that they may resemble those of primitive shark ancestors. Their most distinctive feature, however, is the presence of a sixth and, in two genera, a seventh, gill slit, in addition to the five found in all other sharks.Cow sharks are ovoviviparous, with the mother retaining the egg-cases in her body until they hatch.
There are just four species of cow shark, in three genera
- Genera Heptranchias
- Sharpnose Sevengill shark Heptranchias perlo
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- Genera Hexanchus
- Bluntnose sixgill shark, Hexanchus griseus
- Bigeye sixgill shark, Hexanchus nakamurai
- Genera Notorynchus
- Broadnose sevengill shark, “Notorynchus cepedianus
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Jean Tresfon
The Broadnose Sevengill Cowshark, Notorynchus cepedianus
This is the Cowshark we find along our coastline and the specie dived with at Millers point. It is called a number of names Cowshark, Sevengill shark or the full length Broadnose Sevengill cowshark, which has one too many descriptive nouns for my liking. We mostly just refer to them as Cows ! Not a very frightening name to attract shark divers. This shark is the only existing member of the genus Notorynchus, in the family Hexanchidae.
What does it look like?
The Sevengill Cowshark is gray or brownish with spots. It is very common in the kelp forests around the Cape. It is easily distinguished from the other common kelp dwelling species, the spotted gully shark, by its lack of dorsal fin and rounded head.
Steve Benjamin swimming with a Sevengill Cowshark by Jean Tresfon
What do Sevengill Cowsarks eat?
The sevengill shark, Notorynchus cepedianus, is a versatile and common predator that has often been overlooked as an important marine predator capable of feeding on a wide variety of prey species. Stomach content analyses were performed on specimens from California, USA, and southern Africa to investigate whether dietary differences occur in relation to sex and size. Of the 531 specimens examined, 365 (68.7%) contained prey items. The dietary trend with growth and maturity shifted from fish to sharks (chondrichthyans), with marine mammals becoming increasingly important in the larger size classes of N. cepedianus . Small N. cepedianus (<120 cm total length, TL) fed primarily on teleosts, whereas larger sharks primarily consumed chondrichthyans. Marine mammals made up about one-third of the diet of N. cepedianus >220 cm TL, while teleosts declined to 6% and 13% for male and female sharks, respectively. A decrease was observed in the dietary overlap of each successively larger size class. Ontogenetic changes in the diet of N. cepedianus may provide insight into understanding how adults enhance the survivorship of their young, who are often less experienced at foraging for prey and are more vulnerable to predation.
Sevengill Cowshark tooth
When are Sevengill Cowsharks sexually mature ?
Maturation in male sevengills begins at about 140 cm total length (TL). Most males mature at approximately 160 cm TL. Male sevengills have viable sperm throughout the year and seem capable of reproducing year-round. Females have a complex and prolonged maturation period and mature at a size in excess of 218 cm TL.
What are the threats to Sevengill Cowsharks?
In south africa these sharks are caught as part of the demersal shark fishery as well as a species targeted by recreational fishermen. Cowsharks are not protected and anyone can capture and kill a shark as long as its not in a marine reserve. These sharks are sometimes used as bait in the White shark industry.
In South Africa Cowsharks are the apex predator in their habitat, and once the reach maturity only a great white shark or Ocra would prey on them. The following is an abstract details such an attatck by Orca’s in Argintina.
On 21 December 1998, four killer whales (an adult male, two females or immature males, and one juvenile) attacked a group of sevengill sharks (Notorhynchus cepedianus) off the coast of Caleta Malaspina, Chubut, Argentina. Persecution, catches, and tossing behavior were performed by the two females or immature males in the inlet. Next day, carcasses of several sharks were found on the beach adjacent to the attack area. Seven of them were intact and sized approximately 2.5 m in length. The presence of complete sevengill shark carcasses on the beach suggests that they were attempting to avoid capture by the killer whales by stranding on the beach. Attacks on sevengills by killer whales in Caleta Malaspina are frequent in some years, especially from mid-December to mid-January when the sevengill seems to use the inlet as a nursery ground. The observation of the same male feeding both on pinnipeds in Peninsula Valdes and on sharks in Caleta Malaspina may indicate that at least some groups in the Southwestern Atlantic could regularly feed on both fish and marine mammals. This is the first report of an attack of killer whales on sharks off the coast of Patagonia, and the first report of toss- ing behavior in sharks.
Where can I dive with these sharks?
The best place to dive with these sharks is in Castle Rock Marine reserve at Miller’s point, Cape Town. This part of the peninsula coastline is below the Swartkopberge mountains. The small rocky peninsula of Miller’s Point juts out rather abruptly into the bay and provides a sheltered site for the slipway from which most of the boat launches in this area are made. There is sufficient reasonably level ground for extensive parking areas off the main road, including boat trailer parking.
Map to the Cowsharks of Cape peninsular, Cape Town
This area is characterized by granite reefs with sandy patches between them, and almost flat sand bottom further out. Many of the reefs are fairly large areas of massive ridges, gullies and occasional loose boulders on top, and some of these boulders are huge. The cowsharks stick to the kelp channel just 50m from the shore. One can shore dive or boat dive this site (Source)
Jean Tresfon
When can I dive with these sharks ?
There sharks are present year round with the best periods being Spring and Autumn. The best vis is during winter but storms can make conditions undivable for long periods. During summer there are many sharks but the strong trade winds make the visibility quite poor. Due to the relatively protection of the site it is divable most days of the year. We have had great shark dives in vis as low as 2m !
Water temperature during winter is usually between 13°C and 17°C, though it has been known to drop as low as 11°C, so a good suit is also needed here. In summer the temperature may rise above 20°C, but is more likely to be around 17°C to 19°C. (Source)
What should I do while diving with Sevengill Cowsharks ?
Sevengill Cowsharks, although generally docile, are large predatory animals capable of inflicting bodily harm to humans if provoked. Therefore a strict code of conduct must be adhered to when diving with the sharks.
- – No touching.
- – Divers should not interrupt swimming patterns of the sharks
- – Avoid boxing in of a shark, between two divers, or between a diver and a rocky outcrop.
- – No bait or chum is to be used when diving with the sharks.
- – Buoyancy control – you may get in a shark way or bump into a shark if you cant yet dive correctly.
Jean Tresfon
