Kōrero: Sharks and rays

Whārangi 1. Natural history of sharks and rays

Ngā whakaahua me ngā rauemi katoa o tēnei kōrero

As they glide effortlessly through the water, sharks and rays strike fear into humans. Yet the chances of being attacked are slim; in fact humans threaten these animals, particularly sharks, much more than the reverse, to such an extent that some species risk extinction. Sharks are not protected by law in New Zealand.

New Zealand’s sharks, rays and chimaeras

Sharks, skates, rays and chimaeras are closely related, and belong to the class of vertebrates known as Chondrichthyes. They differ from other fish in that their skeletons are made of cartilage (the same flexible material in human noses and ears), not bones.

Of a world total of eight shark orders, New Zealand has six:

  • Hexanchiformes (frilled and cow sharks)
  • Squaliformes (dogfish sharks)
  • Heterodontiformes (bullhead sharks)
  • Orectolobiformes (carpet sharks)
  • Lamniformes (mackerel sharks)
  • Carcharhiniformes (ground or requiem sharks).

Three orders of ray live in New Zealand waters:

  • Torpediniformes (electric rays)
  • Rajiformes (skates)
  • Myliobatiformes (stingrays).

New Zealand also has:

  • Chimaeriformes (chimaeras, also known as ratfish or ghost sharks), which are closely related to sharks and rays.

In 2004 there were 70 known species of sharks, 26 skates and rays, and 12 chimaeras or ghost sharks in New Zealand. The total of 108 compares with 95 recorded in the mid-1990s, and only 62 in the early 1980s. There are at least four undescribed species. New shark and ray species are continually being discovered, especially in very deep waters. Previously unknown species are found as fishing techniques become more sophisticated and research vessels range more widely and deeply.

Between 15 and 20 sharks and rays are endemic to New Zealand – they live nowhere else. It is difficult to determine an exact number because these creatures are very mobile. Most of the endemic species are rays or skates, which do not travel as far as sharks.

An ancient family

Sharks have existed for more than 400 million years, and rays for 200 million years. By 140 million years ago they had evolved into close equivalents of their present-day forms.

Some early sharks were relatively large. The three-million-year-old remains of the extinct giant shark Carcharodon megalodon were discovered by fossil expert Joseph McKee among cliffs in south Taranaki. Fossilised sharks are not common, as their cartilage does not endure in the same way as bones. McKee was lucky enough to find calcified vertebrae. Scientists have used them to estimate that the shark was between 4.5 and 6 metres long.

More usually, a shark’s distinctive triangular teeth are the only fossil remains. A full set from Carcharodon angustidens, also extinct, was unearthed in North Otago in the late 1990s. It was an extremely rare find – usually only single teeth are discovered. Closely related to the living great white shark, this specimen may have measured up to 9 metres long.

Me pēnei te tohu i te whārangi:

Gerard Hutching, 'Sharks and rays - Natural history of sharks and rays', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/sharks-and-rays/page-1 (accessed 16 June 2024)

He kōrero nā Gerard Hutching, i tāngia i te 12 Jun 2006