Summer Series 6: Broadnose Sevengill Shark

SHARE THIS: 

The broadnose sevengill shark, Notorynchus cepedianus, is named descriptively after – wait for it– its broad snout and seven gill slits! Interestingly, most shark species only have five gills. The broadnose sevengill is one of New Zealand's more common inshore sharks.

"Sharks with six or seven gills are regarded as quite primitive and have been around for hundreds of millions of years," says NIWA principal scientist Dr Malcolm Francis.

This shark is a bit of a biter, and may be aggressive when provoked. It grows to three metres, possibly larger, and is found around the whole of New Zealand in shallow to deep waters (0 - 200 metres). It is more common in the North Island.

The sharks live in temperate areas worldwide, except for the North Atlantic.

The broadnose sevengill is a browny-grey colour, with small black and white spots. Its under body is white.

This shark has serrated teeth, which are slanted sideways with multiple sharp cusps. "When you see a whole jaw, it's like a saw-edge," says Dr Francis.

The bad news is it cruises around just above the sea floor, and can survive in just a metre of water. "They can see well and have a good sense of smell," says Dr Francis.

They can also go very fast. They can produce a sudden burst of speed, which enables them to catch prey unawares. However, divers who see them say the main impression they give is of a slow and curious creature that persistently checks out unusual objects, hoping they might be food.

It has a single dorsal fin, set well back on the body. Its upper tail lobe is much longer than the lower one. It has small eyes, a blunt snout, and a broad round head.

The broadnose sevengill eats other sharks, rays, fish, and seals. It is potentially dangerous to humans, and there has been a reported attack on a swimmer at Oreti Beach in the South Island.

Not much work has been done on these sharks in New Zealand, so the biology is largely unknown.

Background:

Species Fact File:

Common names: BROADNOSE SEVENGILL SHARK

Māori name: tuatini

Scientific name: Notorynchus cepedianus

Type: fish

Family: Hexanchidae

Size: 3 metres

Diet: fish and squid

Reproduction: Females reach sexual maturity when they are about 2.2 metres long, with males 1.5 metres long. These sharks bear live young in shallow bays. Females have litters of up to 82 live-born pups.

Things you need to know: There have been reported attacks in New Zealand

Something strange: The pattern of spots is probably unique to each animal. 

Broadnose seven gill shark head. Credit: Clinton Duffy, DOC
Broadnose seven gill shark. Credit: Clinton Duffy, DOC
Research subject: Sharks