Gannet Island (Karewa)

Gannet Island (Karewa) a wildlife sanctuary approx. 12 miles off the coast of Kawhia, is an important breeding site for the New Zealand fur seal, and largest breeding colony in NZ for thousands of gannets (Australasian), known to the Maori people as Takapu.

gannet island


Gannet Island, an ancient Maori burial site, is also a very popular fishing and diving spot where huge crayfish and kingfish, are regularly caught in the clear waters surrounding this now remote, dormant volcano jutting out of the Tasman ocean.

Through the co-operation and approval of the last Maori Queen, Te Atai-rangi-kahu, Gannet Island ( Karewa Island) was gazetted as a wildlife sanctuary.

The sanctuary was established to protect the colony of gannets and also one of New Zealand's northernmost seal colonies.

The island is a two hectare rocky outcrop which rises about 150 feet from the ocean and is Maori land.

The gannet is a member of the Booby family which consists of tropical birds, and is related to the families of shags, pelicans, and frigate birds. There are three sub-species of gannet which are situated in the temperate regions of the world:

The North Atlantic Gannet (Sula bassana ) is the largest of the three sub-species and nests on islands around the coasts of Great Britain, Iceland, and along the south-eastern seaboard of Canada.

The Cape Gannet (Sula Capensis ) nests on islands in the Cape of Good Hope region.

The Australasian Gannet (Sula serrator ) . Although this gannet is the smallest of the three sub-species, adults have a wing-span of up to 2 m and an average weight of 2 kg. Since 1959 gannets of known age have been banded with numbered bands.

This makes it possible for individual birds to be recognised through binoculars and has enabled problems relating to nesting and breeding habits to be solved. Some insight has also been gained into the average lifespan of the gannet which is estimated at between 25-40 years.

Although gannets do not migrate. Their chicks disperse to the eastern coasts of Australia where, with some exceptions, they remain for 2 1/2 - 3 1/2 years until they become adults.

They then return to New Zealand and thereafter remain in New Zealand waters. An Amazing Flight: Many of the young gannets have never been airborne before they leave the colony at Gannet Island.

They set out across thousands of kilometre's of stormy Tasman Sea without a practice flight, previous experience in direction finding, leaders, or having learnt how to catch their own food.

Nature has provided these young birds with reserves to enable them to survive until they can fend for themselves. Flight speed varies and depends upon weather conditions, but some birds have reached Australia one to two weeks after their departure from the Rock.

In one of the fastest crossings recorded, an average of 385 km was covered per day, an amazing feat for a 16 week old bird. Sometimes they fly until exhaustion forces them to alight on the water to rest. Sharks, barracouta, storms, and exhaustion all take their toll.

There is a heavy mortality rate and only about 25-30 percent of the young birds survive the dual ocean crossing and return to the Island. Most of the bands recovered come from birds in their first year whose bodies were picked up off the New Zealand and Australian coasts, or from banded birds cast ashore exhausted after a storm.

One band was recovered from the stomach of an Australian shark! Recoveries of banded chicks show that most of the birds fly north along the east coast of New Zealand and around North Cape before crossing to Australia.

A secondary route is also used to the south through Cook Strait and across the Tasman. In Australia most bands have been recovered from the coast of New South Wales and Victoria. But some have been found as far afield as northem Queensland, and one was found at Perth, 5790 km from Cape Kidnappers.

From early May to Mid July the gannetry is empty. The only feature which stands out in the stark bareness of the colony are rows of neatly-spaced nesting mounds. These mounds are eroded by the weather and only the older more central nests remain for the birds on their return.

It is believed that gannets mate for life, and they tend to return to the same nest site each year. Following the full moon in July, males which nested during the previous season return to their nesting sites and are later joined by their mates.

The numbers steadily increase, and the first pairs begin to gather nesting material about the middle of August. Much pilfering of this material occurs especially if the birds are relatively inexperienced and fail to guard their nests.

During the nesting season some gannets may be seen standing around the edges of the nesting area. They are young birds which have returned from Australia during the previous two or three years and have not yet established permanent nest sites.

It is believed that they are laying claim to a piece of territory as a preliminary to establishing their own nests in that particular year or a succeeding year. IT IS IMPERATIVE THAT THEY SHOULD NOT BE DISTURBED IN ANY WAY, as this is an important phase in the beginning of a nesting cycle.

Some of these birds undertake tentative mating perhaps even build a rudimentary nest, with the occasional one laying an egg. Nesting in earnest usually begins when the birds are five years old and have attained full adult plumage.

The males claim the territory and 'own' the nest. First attempts at nesting are not always successful because of inexperience and disturbances from other birds or visitors who approach too closely. The gannet is very much an individualist and is believed to nest in large numbers for protection from natural enemies.

The nest spacing is determined by the pecking range of birds on nests. They will attack any object or bird which strays into their territory. As the season progresses the nest which begins as a dark tangle of seaweed and grasses, gradually consolidates and is bound together by excrete ejected outwards by the sitting adults and chicks.

Thus there is a notable gradation in nest size from large mounds at the centre of the colony, to the flat hollows of younger birds at the perimeter.

Reproduction:

Mating is accompanied by a distinctive courtship display and occurs early in the season. Eggs are laid about two to three weeks following fertilisation and first appear late in September with the majority laid in October.

Normally a single egg is laid but if this is damaged or broken before January, a second egg is sometimes laid. When the egg first appears it is pale green and covered with a white chalky substance.

Within a few days the colour changes to a distinctive brown. Both male and female gannets take turns to incubate the egg. The sitting gannet waddles slowly onto the nest and places the webs of both feet around and over the egg, before settling its body down on the nest.

The hot webs of its feet and insulation of the body feathers incubate the egg, which is often fumed or moved by the gannet's beak.

Chicks:

After 43-44 days a small hole appears in the egg, and during the next 24-36 hours the tiny naked chick breaks its way out into the open air. There is a small hard egg-tooth on top of the chick's beak at the tip which is used to cut off the wide end of the egg. More like a reptile than a bird the dark slate-grey chick is blind, completely naked and quite helpless.

During the first 10 days of life it grows rapidly, protected by the feet and body of the parent. A faint hint of white down appears after a week, and by the end of a fortnight the now alert chick is transformed into a fluffy white mass.

The parents now have to work very hard obtaining food to appease the voracious appetite of their young chick. While one parent remains on guard the mate is away at sea stocking up the larder.

Designed for Diving:

Although the gannet is ungainly on land, it is transformed into a graceful and effortless glider in the air. When a fish is sighted, it enters the water at speeds of up to 145 km an hour from heights of up to 30 m. In this way fish are caught at depths of 43 m or more.

For local fishermen the sight of diving gannets is often a sign of shoaling fish and a large catch. The gannet's streamlined shape is well-adapted for this bullet-like entry into the water. The strong front of the skull withstands the impact, and special inflatable air sacs help to cushion the shock.

Small squid, and fish (anchovy, pilchard, yellow-eyed mullet, and garfish etc.) are its main food source and many are caught and swallowed under the water. Large Fish are carried to the surface and held firmly by the sharp serrated edges of the beak.

Chick Feeding:

When the parent bird returns to the nest with a load of fish the chick places its beak tip near that of the parent, and sways its head from side to side. At the same time it makes a monotonous yapping call which increases in intensity as it becomes more hungry.

Convulsive movements then appear in the lower neck of the parent bird as food is brought up from its stomach. The chick inserts its head into the parent's open bill, and regurgitated, partly digested food is transferred. Tiny chicks are fed on fine almost liquid paste while well developed chicks are fed almost whole fish.

Following food transfer both birds point their bills upwards and swallow with convulsive movements. When the food supply is exhausted the adult turns its bill away from the still begging chick. After 40 days the chick is almost the same size as the adult, and about a week later the first signs of feather quills appear along the wings.

From this stage onwards the chick goes through a rapid transition to its juvenile plumage of slate grey feathers speckled with white spots. From late December to late February chicks may be seen in all stages of development.

During the next month the parents lose interest in feeding their chick and may desert it for long periods. The young gannets congregate along the cliff edge and vigorously exercise their wings in preparation for the long dispersal flight which they will undertake when they are about four months old.

Wing exercises are begun at an early age and are a regular daily routine at three months old. New Zealand Gannet Population: In 1980 a census of New Zealand gannetries established a population of about 46 000 breeding pairs.

This is a substantial increase from the 1947 census figure of 21 000. The following table gives further details of this 1980 census.

  • Three Kings Island = 9800
  • Poor Knights Island = 4200
  • Great Barrier Island = 2700
  • Colville Island = 4500
  • Waiheke Island (Huruhoro Rock) = 260
  • Muriwai Island = 110
  • Gannet Island = 8,000
  • White Island = 7000
  • Cape Kidnappers = 5200
  • Tolago Bay Island = 600
  • Mokohinau Island = 350
  • Marlborough Sounds = 30
  • Nuggets Island = 10
  • Little Solander Island = 60
  • Farewell Spit = 300

 

 


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