Sevengill and Sixgill Sharks – Sevengillers are often caught by surfcasters
Sevengill and Sixgill Sharks
In 1992 a large sixgill shark was taken in Cook Strait that measured 4.2 metres (14 ft) and weighed 417 kg (919 lbs)
There are three species of cow sharks found in New Zealand waters. These are the sharp snouted sevengill shark (Heptanchias perlo), the broad snouted sevengill shark (Notorynchus cepedianus), and the less common sixgill shark (Hexanchus griseus).
They are widely distributed throughout the world and can be found in temperate coastal waters around South Australia, Japan, Southern Africa, off South America, and the west coast of North America.
The cow sharks are easy to distinguish as they have only one dorsal fin set well back on the body unlike the two dorsal fins found on almost all other sharks. The sixgill and sevengill sharks also have a long upper lobe on their tail fins. Most other sharks, like the mako and blue shark, have five gill slits.
As to colour this seems to vary quite a bit. Some specimens of sevengiller I have seen are brown on the upper body with a scattering of small black and slightly larger white spots. Others have been more light grey in colour. The underside of the body is a whitish grey.
The sixgill shark is found in much deeper water and lacks the spots of the sevengill sharks. Indeed sixgillers have been found on the seabed of some of the world’s deepest oceans.
The sharp snouted sevengill appears to be less common, is more a deepwater species, has a larger eye, lacks the black spots, and is generally a bit smaller than the broad snouted sevengiller.
The teeth in the sevengiller shark are narrow and hook-like in the upper jaw while those in the lower jaw closely resemble a serrated edge knife. The teeth in the lower jaw are extraordinarily sharp. Presumably the upper teeth are for holding prey while the teeth in the lower jaw are for slicing and cutting.
The cow sharks are Ovoviviparous. The young develop from eggs inside the female and are born fully developed between 35 and 45 cm in length – probably one year after mating. Litters are quite large numbering somewhere between 66-102 pups.
Broad snouted sevengill sharks inhabit shallow bays and coastal beaches. As such they are one of the few large sharks likely to be caught by surfcasters around the South Island . They respond well to berley (chum) released into the sea.
They seem to eat just about everything that comes their way. They will catch and eat live fishes including fast swimming kahawai and mackerel. They also feed on squid and octopus. I have caught quite a few sevengill sharks while surfcasting along Canterbury beaches over the past thirty years. On opening, their stomachs where found to contain an astonishing assortment of recent meals. These include: a whole hare, a whole salmon weighing at least 12 lbs, the fins of a dolphin, red cod, and dogfish. They are also known to eat marine mammals including seals, other sharks and stingrays, together with a wide variety of boney fishes. Possibly some of these were washed out to sea by flooded rivers.
Some years ago members of the Canterbury Sport Fishing Club were fishing off Banks Peninsula when several large sevengillers were hooked in deepwater. Before they could be hauled to the surface the hooked sharks were in turn set upon by other broad-snouted sevengill sharks. Presumably a feeding frenzy quickly developed during which the other sevengill sharks congregated there had no hesitation in canalizing their mates! Sevengill sharks are not known to be dangerous to man but in such a situation I’m sure they would bite anything that moved! Sevengill sharks are also regularly caught while surfcasting from Canterbury beaches. See: Sevengill Sharks from the Surf.
I have read reports that sevengill sharks off South Africa sometimes hunt co-operatively in packs to capture marine mammals including Cape Fur Seals and other species of large shark. This I find surprising! The sevengiller at first appears as a docile shark living out its life eating mostly carrion. However sevengillers are certainly capable of sudden bursts of speed. They are also capable of aggression towards other large sevengillers. Perhaps the most surprising thing of all, to me at least, is that sevengill sharks might have the speed to chase and capture fast swimming boney fishes such as kahawai. It is thought that broad-snouted sevengillers prefer to hunt in discoloured water which may explain how they can close in on prey before suddenly striking with a burst of speed.
Another interested fact I read recently is that sevengill sharks are hunted for food by great white sharks.
Sevengill sharks will take almost any baited hook the angler might send their way. However their skin is very much like course grade sandpaper and will quickly cut through monofilament line dragged across the body. Sevengillers, like all sharks, will roll as they attempt to escape capture. For this reason it is best to use wire droppers on a Paternoster rig and make the backbone from very heavy mono to withstand this rolling.
In practice you can sometimes be lucky in that a large sevengill can be landed from the beach without particularly heavy traces and leaders. It is important to keep your rod tip up and apply constant even pressure to bring the shark in. Sevengillers over about 6 feet in length are not good eating and are best released unharmed. I have also caught a big sevengill shark while fishing from the rocks at Taylors Mistake on the north side of banks Peninsula. To see a big picture of the sevengiller I caught from Taylors Mistake on a 5/0 Gamakatsu octopus hook, and after it had been carried back to the truck.
There have been some very large cow sharks caught by New Zealand anglers over the years. Dick Marquand reports that in 1992 a large sixgill shark was taken in Cook Strait that measured 4.2 metres (14 ft) and weighed 417 kg (919 lbs). Many of the broad-snouted sevengillers caught by surfcasters weigh around 70 to 100 kgs.
Fossil evidence shows that cow sharks have been around for some 200 million years. So perfect has been their design that nature has found no need to alter it. Perhaps the cow shark’s adaptability has been its secret of success. Indeed as we have seen with the broad-snouted sevengill shark there is more to this species than meets the eye. It can hunt as a pack for large prey, ambush smaller prey in shallow coastal waters, scavenge the carcasses of dead sea and land animals, find prey in turbid waters, and eat very little to sustain itself should the need arise.