seven gill slits, ancient and formidable
- Size
- Length: 150–250 cm, Weight: 50–150 kg
- Lifespan
- 30–50 years
- Diet
- Carnivorous. Feeds on fish, rays, sharks, seals, dolphins and carrion. Hunts actively in packs like wolves of the sea. Uses its seven gill slits to extract oxygen efficiently during fast pursuits.
- Habitat
- Shallow coastal waters, harbours, estuaries and rocky reefs from the surface down to 150 metres depth. Often enters very shallow water to hunt. Prefers murky conditions for ambush predation.
- Range
- Found in coastal waters of the North and South Islands from Northland to Stewart Island. Most common in harbours and estuaries. Also found in Australia, South Africa, North and South America.
- Endemism
- Native
- Main Threats
- Recreational and commercial overfishing is the primary threat. Also threatened by bycatch in set nets and trawls, habitat loss from coastal development and slow reproduction which makes the species highly vulnerable.
- Population
- Global populations have declined significantly due to overfishing. The species is listed as Vulnerable by the IUCN. In New Zealand it is caught as bycatch in several fisheries. There is no targeted management for this species.
- Conservation Status
- Not Threatened
Wolf of the sea. Unlike most sharks with five gill slits, this ancient predator has seven. It hunts in packs, taking down prey as large as seals and dolphins. Fossil records show its ancestors swam in the oceans 150 million years ago. Today it is vulnerable to overfishing because it grows slowly and produces few young. The timeline is vast. The threat is immediate.
The body is robust and muscular, with a broad, flattened head and a terminal mouth. The teeth are distinctive. The lower jaw teeth are comb-like, used for gripping, while the upper jaw teeth are saw-like, used for cutting. The colour is a mottled brown or grey, providing camouflage in murky water. It blends into the gloom.
Seven gill slits are visible on each side of the head. Most sharks have five. The extra gills allow the sevengill to extract more oxygen from the water, giving it an advantage during fast pursuits. It is a powerful swimmer, capable of short bursts of speed. The physiology supports the hunt. Efficiency is key.
It hunts in packs, using coordinated attacks to bring down large prey. Packs of sevengill sharks have been observed hunting seals in shallow water. They bite and retreat, waiting for the prey to weaken before moving in for the kill. The strategy is patient. It wears the victim down.
It is also a scavenger, feeding on dead whales, seals and fish. Its role in the ecosystem is that of a top predator and a cleaner, removing carrion from the water. The dual function is efficient. Nothing goes to waste.
Reproduction is ovoviviparous, meaning the eggs develop inside the female and hatch internally. The young are born alive, a litter of up to 80 pups. This reproductive strategy allows the mother to protect her young until they are ready to face the world. The investment is high. The survival rate is low.
Overfishing has reduced global populations. It is listed as Vulnerable by the IUCN. In New Zealand, it is caught as bycatch in set nets and trawls. There is no targeted management for this species. It needs protection. The regulatory gap is wide.
To see one is to see a living fossil. It has been swimming in the oceans for 150 million years. It has outlasted the dinosaurs. But it may not outlast us. The irony is sharp. It survives the deep past but struggles with the present.