Baby shark

Department of Conservation —  09/03/2021 — Leave a comment

Doo doo doo doo doo doo doo. Sorry, not sorry. But no, we are not here to talk about the song behind YouTube’s most-watched video ever. We are here to talk about baby sharks of the Hauraki Gulf Marine Park/Ko te Pātaka kai o Tīkapa – those that ‘pup’ there, and those that spend their juvenile life in its sheltered and abundant waters. A biological hotspot, the Hauraki Gulf can boast being a nursery for sharks with some incredible features – one that has a tail as long as its body, the only one to close its eyes, the fastest shark in the ocean, and the most famous.

But first, what makes the Gulf, and in particular the inner Gulf and Firth of Thames, so ideal as a shark nursery?

The Gulf is a large, shallow, sheltered sea with numerous harbours and inlets surrounding it, providing gentle conditions for young sharks to grow. Light easily penetrates to the seabed throughout most of the inner Gulf – even in the turbid Firth of Thames – warming the water and promoting plant growth during spring and summer. Furthermore, nutrient inputs from the rivers that feed into the Gulf, as well as the ‘seasonal upwelling’ of nutrients along the edge of the continental shelf (that stimulate phytoplankton growth), make it biologically highly productive. These conditions support a diversity of habitats in the Gulf including large populations of bony fishes, providing prey for young sharks.

Baby sharks are rather adorably called ‘pups’ and come into this world in three different ways – egg laying (oviparity), eggs developing and hatching inside the womb (ovoviviparity) or developing within the womb nourished via a placenta/whenua, like mammals (viviparity). Sharks do not care for their babies after they are born, but they do search for a safe place where they can lay their eggs or give birth. These are known as ‘pupping’ or ‘nursery grounds’.

Let’s begin with those that pup inside the Gulf, starting small and working our way up to the larger, better known species.

Carpet shark / swell shark / pekapeka

(average length: females: 76cm; males: 60cm)

Carpet sharks stick to the seafloor where they lie here in waiting for their broad diet.
📷: Vincent Zintzen

We can only guess that the carpet shark, with its golden-brown colouring with dark blotches, was named in the 70s after the yellowy-brown patterned carpets that graced our floors. Or it could be because they stick to the seafloor where their mottled skin blends in with shells, rocks and seaweed. They lie here in waiting for their broad diet, including fish, crustaceans, octopus and sea snails to swim by. Being still is unusual for most species of sharks, which need to move constantly to keep water flowing over their gills to breathe. Carpet sharks instead use a method called buccal pumping, using their cheek muscles to pull water into the mouth and over their gills.

Unlike all the other species we will talk about, carpet sharks are oviparous which means they lay eggs – in this case, two at a time. The eggs attach to kelp plants, sponges, gorgonians and black coral via long coiled tendrils at each end of the egg case. In the Gulf, carpet shark eggs and resulting juveniles are most likely found on offshore reefs below approximately 30m depth.

The eye of a carpet shark.
📷: Ian Skipworth

Rig shark / spotted smoothhound / spotted dogfish / lemonfish / mango

(average length: 1 m)

A juvenile rig shark being released after being tagged for research purposes.
📷: Scott Tindale
 

Boasting some great namesakes is the rig shark, an endemic species to our waters, and usually the ‘fish’ from your local fish ‘n chip shop. Rig are bronze or grey in colour on the upper surface with numerous large white, fuzzy edged spots, and are white underneath. A distinct feature of rig are their flat teeth which are arranged like paving stones to form grinding plates to crush their food. Rig mainly feed on animals that burrow in the sea floor, especially crabs, accomplished by sucking up mouthfuls of sea floor sediment. The shark separates out the prey by ejecting the mud and sand through its gills and crushing the food left in its mouth. This feeding habit also enables rigs to maintain respiration without the need to keep moving.

For most of the year adult rig spend their lives in open waters. During spring and summer mature females make inshore migrations to congregate in sheltered, shallow harbours and estuaries to spawn and mate. Here, they deliver around 11 pups at 10-20cm long. In the past, rig would have probably bred in many of the harbours and sheltered inlets around the fringes of the Gulf, but due to habitat degradation, are now mostly found in the upper Waitematā Harbour including around Herald Island and Lucas Creek.

School shark/kapeta/mango 

(average length: 1.2 m) 

School shark.
📷: afieber – iNaturalist

Named for their habit of swimming in schools, the school shark is grey on top and white underneath, with a distinctive elongated snout and crescent-shaped mouth. Female school sharks return annually to traditional pupping areas in sheltered bays and estuaries. Here their young are born and remain while the adults move off to deeper waters. In the Gulf, Whangaparāoa and Kawau Bays were historically important pupping areas and an important food source for Māori, so much so a fishery (known as Taranga mango) was controlled from a pā on Tiritiri Matangi Island. After the arrival of Europeans in the late 1800s and early 1900s, several factories were set up to extract the oil from the livers of these sharks, but the fishery was unsustainable, and the sharks were all but wiped out. This population has not recovered, most likely because the females who would have returned to this pupping ground were all caught. Amazingly, female school sharks’ deliver anywhere between 6-52 young (born at 30cm), depending on the size of the female – but only every 3 years. Unlike most other fish the school shark can close its eyes by drawing up its lower eye lids.

Bronze whaler shark / copper shark / reremai / toiki / ngengero

(average length: 2m) 

Bronze whaler sharks are distinguished by a narrowly rounded snout.
📷: Ian Skipworth

The bronze whaler is one of the most abundant large shark species in our coastal waters and the one most often seen by divers. Named for the bronze colour of their upper side, with cream underbellies, they are also distinguished by a narrowly rounded snout, and a tail with an upper lobe that is much longer than the lower lobe. To pup, they move into shallow waters near reefs, bays and estuaries in spring and summer, then hang around to feed on fish such as kahawai, snapper / tamure and eagle rays / whai repo. Extremely slow-growing, females only begin producing young from 15 years of age and bear litters of 7-24 pups every other year.

While not normally a problem for swimmers, “bronzies” can get aggressive when food is about. Spear fishers carrying fish have been bitten on occasion and are advised to get their catch out of the water quickly. This fisherman got away with just a slap in the face by the tail of a bronze whaler!

Smooth hammerhead shark / mango-pare

(average length: 3m)

The Hauraki Gulf is one of the largest nursery grounds in New Zealand for smooth hammerhead sharks.
📷: Auckland Whale and Dolphin Safari – AWADS

The Hauraki Gulf is one of the largest nursery grounds in New Zealand for this iconic species. At the beginning of their lives, the shallow waters of the Firth of Thames provide the perfect conditions for new-born hammerhead sharks, which are born in litters of 20-50 pups, each about 50–60cm long. Hammerheads are viviparous, meaning that the female keeps her embryos inside her oviduct, feeding them from a placenta, until they are ready to be born. They migrate into the inner and outer Gulf as juveniles, usually at about 1.5m of length.

The hammer-shaped head gives this shark a few advantages. Firstly, it is thought to give the shark lift as it swims by counterbalancing the downward thrust of the tail, while the placement of the eyes and nostrils on the tips of the ‘hammer’ gives the shark the ability to see and smell its prey better. Lastly, scattered around the hammer-like head are numerous pores, connected to nerves at their base that detect the weak electrical fields created by the muscles of fish, shrimps, squid and crabs that bury themselves in the sand. They are a very social species, sometimes traveling in groups of 100 or more which can make for an extraordinary sight – check out this amazing video of hundreds of baby sharks, many of them hammerheads, swimming in waters off Aotea/Great Barrier Island.

Great white shark / ururoa

(average length: females: 4–5.2m, maximum 7m; males: 3.5m)

Great white sharks are ovoviviparous, meaning the eggs develop and hatch inside the womb of the female shark.
📷: Clinton Duffy, DOC

That’s right, perhaps the best-known shark in the world is thought to pup inside the Hauraki Gulf. Great white sharks are an example of an ovoviviparous shark, whose developing embryos feed on unfertilised eggs within the uterus during the gestation period. The gestation period of the great white shark is estimated to be about 18 months, and the litter can range anywhere between 3-14 pups, born at 1–1.5m length. While little is known of white shark breeding in New Zealand, most records of pregnant, newborn, and 1-2 year old white sharks are from shallow coastal waters around the top half of North Island, including the Gulf.


Now that we’ve reached the mighty great white shark, let’s look at two shark species that most likely pup in offshore waters near the Gulf, and move into its sheltered and abundant waters as juveniles.

Common thresher shark / mango-ripi

(average length: 2.75m)

Common thresher shark breaching.
📷:edcoreyncdpr – iNaturalist

This is a shark with some very fun (and foxy) features. The first is referred to in its scientific name Alopias vulpinus (‘vulpinus’meaning fox) due to its tail which is almost as long as its body, used to stun its prey. The second is its psychedelic bluey-green colouring of its back with a purple sheen, and white tips on the fins. And just to show off, the common thresher shark is capable of leaping clear of the water. It also has a relatively small mouth, reflecting the fact that they feed on small bait fishes and squid. Juvenile common threshers are relatively common in the Gulf and are often caught by accident by people fishing for other species like snapper / tamure. Common threshers give birth to litters of just 2 pups that measure 69 to 92cm.

Mako shark

(average length: 3.8m)

The mako shark is the world’s fastest shark. Observations of young-of-the-year mako at Mokohinau Islands suggests they pup near the outer Hauraki Gulf Marine Park boundary.
📷: Quentin Bennett

An icon of our seas, the mako shark is the world’s fastest shark, said to reach 70km/h on a burst. It achieves this through its high metabolic rate which is fuelled by its elevated body temperature (some parts of its body are 14ºC higher than the water temperature). After a gestation period of 18 months, 4-18 young are born at a length of 70cm. Females do not reach maturity until 19 or 20 years which has implications for their population if they are overfished. Observations of young-of-the-year mako at Mokohinau Islands makes it likely they pup near the outer Hauraki Gulf Marine Park boundary. Interestingly, the name ‘mako’ is a Māori name that has been adopted worldwide.

Learn more about the amazing sharks found in NZ waters here.

Love it, Restore it, Protect it

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