SHARK TRACK

Tracking Porirua's rig sharks

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Rig sharks

Pete Notman

Rig shark

Scientific name: Mustelus lenticulatus.

Other names: lemon fish, smooth hound, spotted dogfish, pioke, makō, mangō.

Colour:  grey/bronze with small white spots and a white belly.

Size: Females are larger than males, growing up to 1.5 metres long. Adult males reach around 1.25 metres in length. Male rig reach maturity at around 85 cm  (5 – 6 years old) and females around 100 cm (7 – 8 years). Rig can live for up to 20 years.

Only in NZ

Rig shark being held
Rig shark about to be tagged.

Rig sharks are found only in the coastal waters around New Zealand but most people have never heard of them. There’s a good chance you’ve eaten one though – they’re sometimes called lemon fish or spotted dogfish and you can find them at the fish and chip shop.

Life at the bottom

Rig sharks spend most of their time at the bottom of the water, eating from the sea/estuary floor. Scientists call this zone ‘benthic’ so rig are benthic sharks. A rig shark’s teeth are suited to its diet - rig have hard, flattened teeth to grind up crab and mollusc shells.

A mysterious species

There’s still a lot we don’t know about rig. We do know that most of them spawn in just a small number of estuaries around the North Island and Porirua is one of them. They use both the Onepoto Arm and Pauatahanui Inlet.

Rig sharks are also found around the South Island but no large spawning/nursery areas have been identified there. We don’t fully understand where and when the sharks go so this is also part of my research.

Migrations to mate

Rig sharks migrate to Porirua Harbour during spring and summer. Here, the females give birth and mate with males before returning to sea, leaving their young behind.

Female rig sharks deliver live young between October and early December. The baby sharks (juveniles) are about 20 – 30 cm long. Because the female mates with multiple males the juveniles in each litter will usually have different genetic fathers. 

Juvenile rig shark
Juvenile rig shark being removed from set net. Pete Notman.

 

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