Sharks of summer
Sharks of summer
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.
ends