The second in a summer series of posts from Crown research institute NIWA
Everyone knows they’re out there, but how well do you know your sharks? NIWA looks at four of the most common sharks you’re likely to spot this summer.
Bronze whaler (Carcharhinus brachyurus)
Bronze whalers are commonly found around the northern half of the North Island over spring and summer when they move into shallow coastal waters. Here they feed on fish like kahawai, mullet, snapper, kingfish and eagle rays.
As they name suggests, these sharks are bronze in colour but the underbellies are cream. The upper lobe of the tail is far longer than the lower lobe.
During summer bronze whalers live in the shallow coastal waters near reefs, bays, estuaries and surf beaches.
They take about 30 years to reach a maximum length of three metres but most are between 1.5 and 2m. They are slow growing and will be between 15-20 years old before they reproduce. Female bronze whalers will have 16-20 pups at a time.
The bronze whaler is one of the most abundant large shark species in New Zealand coastal waters and the shark species most likely to be encountered by divers around the country. They are not normally aggressive to humans, although spear fishers have been bitten by them.
These sharks eat live or dead fish, so spear fishers should remove their catch from the water as soon as possible.
Blue shark (Prionace glauca)
A cousin of the legendary tiger shark, these sleek and slender creatures are regularly seen in New Zealand harbours and along our coasts over summer and are the most abundant of the oceanic sharks. Their sinuous movements and streamlined forms rank them among the fastest of sharks.
Also known as the blue whaler or blue pointer, the blue shark’s upper body is a striking cobalt blue and the underside is bright white. Their large black eyes have a protective membrane to shield it from struggling prey.
These sharks have a vast range and can be found close to shore or in the deep sea. They are highly migratory ranging across the world in tropical, subtropical and cooler temperate waters. Seldom growing beyond 3m long, they have long pectoral fins and are found in depths of up to 1000m and anywhere in waters between 10°C to 22°C.
A young 2-metre blue shark weighs less than 40 kilograms and despite their slim build, a female can give birth to up to 135 pups each about 50cm long.
School shark (Galeorhinus galeus)
Named for their habit of swimming in schools, the school shark is also known as grey boy, tope or kapeta.
School sharks are grey on top and white underneath and can be confused with bronze whalers. The best way to identify a school shark is to look for its long snout, which is translucent from below.
School sharks live for up to 50 years but are slow growers and only reach 175cm long. A 90cm school shark is roughly five years old but by 10 is about 120cm.
At about 15, when they are about 130cm long, they have matured enough to reproduce. Females will give birth to between five and 40 pups but only every two years, usually in shallow sheltered waters during summer.
School sharks are found throughout New Zealand’s mainland coastal waters, more inshore in summer, where they feed on small fish and squid.
NIWA has tracked the movements of more than 200 school sharks over about 12 years. The maximum movements recorded were to southern Australia covering distances between 1735 and 4940km. The greatest distance travelled each day was 23km.
School sharks have been commercially fished in New Zealand since the 1940s.
Spotted dogfish (Mustelus lenticulatus)
One of the smaller, common species of shark is the spotted dogfish or rig. This is what is usually served at fish ‘n chip shops.
Rig sharks are endemic to New Zealand waters, and grow to a maximum of 1.5m long for females and 1.2m for males. They live for up to 20 years.
Bronze or grey on top, they have a white belly and small white spots on their upper body. Easily mistaken for spiny dogfish which are of a similar size and also have spots, they can be identified by their dorsal fins. A spiny dogfish has spines on its dorsal unlike a rig.
Rig sharks spend the summer in our estuaries and coastal waters and are of little threat to humans. Their teeth are small grinding plates, good for eating crabs – their main food source.
Each spring and summer rigs embark on an inshore migration to mate and breed. Most female rigs reproduce from late October to early December delivering about 10 pups, each 10-20cm long.
Rigs are good swimmers and travel very long distances. One tagged rig clocked up 1159km, going from south of Stewart Island to Golden Bay, Nelson. An important inshore commercial fish species for New Zealand, they are fished mainly by set net and bottom trawl.