The sevengill shark is a member of one of the most ancient shark lineages, with ancestors dating back to the Jurassic period. Often called a “living fossil,” it is distinguished from most modern sharks by its seven pairs of gill slits instead of the usual five. This anatomical trait is a visible reminder of its long evolutionary history.
Defining Physical Features
The sevengill shark has a powerful, stout build with a broad head and blunt snout. Its body is silvery-gray to olive-brown and covered in small dark spots for camouflage. The most prominent anatomical trait is the seven gill slits on each side of its head, and another is a single dorsal fin positioned far back on its body. These sharks can reach lengths of up to 3 meters (nearly 10 feet).
Two species carry the sevengill name: the Broadnose Sevengill Shark (Notorynchus cepedianus) and the Sharpnose Sevengill Shark (Heptranchias perlo). The Broadnose is the larger and more common of the two, with a wide head and spotted body. The Sharpnose is smaller, with a pointed snout, larger eyes, and no spots.
Global Habitat and Distribution
The sevengill shark has a widespread but patchy distribution in temperate marine waters, though it is absent from the North Atlantic and Mediterranean. Established populations are found along the coasts of California, South Africa, Australia, New Zealand, and parts of South America.
This adaptable species is found in inshore areas like bays, estuaries, and kelp forests, which serve as nursery grounds for younger sharks. Larger sevengills venture into deeper offshore waters over continental shelves, reaching depths of 570 meters (1,870 feet).
They prefer rocky bottoms but are commonly found over sandy and muddy substrates as well. This versatility in habitat makes the sevengill one of the most common inshore sharks in regions like New Zealand and southeastern Tasmania.
Predatory Behavior and Diet
The sevengill shark is a versatile, opportunistic hunter at the top of its local food chain. Its broad diet includes other sharks, rays, bony fish like salmon, and marine mammals such as seals and dolphins.
It employs stealthy ambush tactics, using its camouflage to sneak up on prey before launching a swift attack. These sharks have also been observed hunting cooperatively to take down larger animals.
The teeth in the upper jaw are sharp and jagged for gripping prey. In contrast, the lower jaw contains wide, comb-shaped teeth effective at cutting and tearing flesh, allowing the shark to saw off pieces from large food items.
Human Encounters and Conservation Status
The sevengill shark is not considered aggressive toward humans, though a few unprovoked attacks have been documented. As a large predator, it can become aggressive if provoked, such as when caught by fishers or cornered by divers.
This species faces pressure from fishing, as it is caught commercially, recreationally, and as bycatch in trawl and driftnet fisheries. Its inshore habitat makes it vulnerable, and it is sometimes targeted for its meat, liver oil, and hide.
Due to overfishing and a slow reproductive rate, the Broadnose Sevengill Shark is listed as Vulnerable by the IUCN Red List. The global population has decreased by an estimated 30-49% over the last 65 years. Conservation is limited, but the species is protected in some marine reserves and by fishing regulations in certain areas.