Story: Sharks and rays
Page 5 – Dangerous sharks
Some sharks are dangerous to humans: great whites, bronze whalers and mako have attacked people off New Zealand shores. These and other dangerous sharks can be found in waters close to the coast or in the open ocean.
Most sharks are cold blooded, so they live in warmer waters. But several species of the Lamniformes (mackerel shark) order, including the great white, mako and thresher sharks, have successfully invaded cool waters by developing special heat-exchange tissues in their circulatory systems, allowing them to retain the heat they generate from muscular and metabolic activity. This makes them capable of great bursts of speed. But in order to maintain their body heat they have to eat up to 10 times more than the cold-blooded sharks which live in the tropics.
The 4.6-metre thresher shark (Alopias vulpinus) has a tail fin with an extremely long upper lobe. The Māori name, mangō ripi (slashing shark), refers to the way these sharks, working in groups or pairs, use their tails to herd and prey, usually small schooling fish, but occasionally seabirds. The purple-brown and white thresher is found worldwide in warm, temperate and tropical seas, around continental shelves and in the open ocean. In New Zealand their stronghold is off Northland.
Great white sharks
The most feared of the world’s sharks, the 7-metre great white or white pointer (Carcharodon carcharias) is responsible for most of the unprovoked attacks by sharks on people, including a number of New Zealanders.
Great whites are dark grey to black, with a white underbelly. They can be found worldwide in cool, temperate and subtropical coastal and continental shelf waters. According to a 1999 study that compared great whites from Australasian and South African coastal regions, males ranged widely across ocean basins, while females remained in a particular region, perhaps returning to the site of their birth to have their young. Great whites live in the waters all around New Zealand, but are more populous around Otago because of the abundance of seals, on which they prey.
Great whites are also known in Māori as mangō taniwha, mangō ururoa and, to people of the Ngāi Tahu tribe, tupa.
The Māori name mako has universal currency for this 4-metre-long shark. Indigo with a white belly, warm-blooded short-fin mako (Isurus oxyrinchus) range widely in tropical and temperate waters, from coastal waters through to open seas.
Short-fin mako are champion speedsters among sharks, and are prized by game fishers for their fighting qualities, earning them the name ‘blue dynamite’. Their teeth were valued by Māori, who daringly caught the sharks from canoes. Zane Grey, who wrote about big-game fish in the Bay of Islands, noted that mako could leap as high as 6 metres out of the water. When hooked on a line they have been known to attack boats, or land in them, causing considerable damage.
Slim, graceful and bright or dark blue, the 3.8-metre blue shark (mangō pounamu, Prionace glauca) is among the swiftest of swimmers. They have been clocked at almost 40 kilometres per hour, making them second only to mako sharks in speed.
Blue sharks can be found worldwide in the cooler depths of tropical seas and nearer the surface in continental shelf or open temperate waters. They eat mainly fish and squid. Although generally docile, they have been known to kill people. They are one of the most abundant oceanic sharks.
The distinctive skull of the hammerhead shark (Sphyrna zygaena) is believed to help detect prey, and to add lift like a hydrofoil, counteracting the downward push of the tail. Hammerheads are olive to dark grey, with a white underbelly, and grow to 4 metres. Large individuals can be dangerous to people.
Known in Māori as kakere or mangōpare, hammerheads are regular summer visitors to North Island waters, venturing as far south as Cook Strait. Juveniles as small as half a metre are sometimes seen in the Hauraki Gulf – it is possible that the species gives birth around New Zealand. They are found worldwide in temperate and tropical waters, from the coast to continental shelves.
The relatively uncommon bronze whaler (Carcharhinus brachyurus) can be seen close to shore in late spring and early summer, when they may be pupping. They inhabit temperate and tropical waters, both close to shore and in the open ocean. These 3-metre sharks have a reputation in Australia for unprovoked attacks on people, and in New Zealand there have been at least two attacks, both non-fatal. As their name indicates, they are bronze, and have a cream underbelly.
Bronze whalers are also known in Māori as horopekapeka, matawhā, tōiki and ngerungeru.