Let’s Talk About It – The Seven-Gill Cow Shark
I decided to talk about the Sevengill Cow Shark this week, because against all that is “normal” we have been visited by these pre-historic looking, gentle sharks at Seal Island lately in the absence of our glorious Great Whites. Not to say that it hasn’t been wonderful, it’s just been different, as Cow Sharks tend to spend most of their time in deeper waters and kelp forests, only coming into shallower waters, it is believed, to breed.
They make me think of the sock hand puppets we used to make as children, and though they are wild “animals” and need to be treated with respect, they are about as dangerous.
They are called the “pre-historic” shark as a result of the fact that it’s skeleton is similar to that of fossils found of extinct sharks. Also they have a relatively primitive digestive system compared to other sharks, almost as if evolution hadn’t caught up with them yet, and they boast 7 gill slits as opposed to the “normal” 5 as found with others in the shark family. The reason for the extra slits, whether they serve a purpose is not known, other than another throwback to prehistoric times.
There are four species in 3 groups; these being the Bigeye Sixgill, the Bluntnose Sixgill, the Sharpnose Sevengill and the Broadnose Sevengill Cow Shark. The Boradnose Sevengill is the one most commonly found in our False Bay and Simons Town waters, and this is who has been visiting our cage at Seal Island recently.
Other than their broad flat noses and six and seven gill slits, there are other characteristics that set these sharks apart from the perceived “regular” shark. They have comparatively slender bodies with largish angular pectoral fins and smaller pelvic fins with a single anal fin. They have only one dorsal fin with no spine. The caudal fin has a well-developed upper lobe with an obvious sub terminal notch; that is a distinct notch on the underside of the caudal (back) fin. Some of them can grow to 5 meters in length.
Two of the 4 genera have small eyes while the other two have large eyes. The Bluntnose Sixgill actually has eye that glow a florescent green/blue colour, very cool! The teeth differ from upper to lower jaw, with the upper jaw having smaller, more pointed teeth and the larger comb-like ones in the lower jaw.
Cow sharks are ovoviviparous, so this means that though they have egg casings, the female will carry these casings until they hatch within her, at which time she will then birth them. The Bluntnose Sixgill can have up to 100 pups in one litter. How long a gestation period, is not known and when they reach maturity, is not known.
They enjoy a diet of relatively large fish of all kinds, including other sharks, as well as crustaceans and carrion.
It is possible to free dive with these sharks, and we would be happy to make that a possibility for you. It is recommended to have a scuba certification to do a kelp and Cow Shark dive, though not a necessity.
Let’s keep our oceans clean, safe and home to all that live in it!
Till’ we meet again, keep that toothy grin!
By Nadine Bentley