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Orcas

by  Gerard Hutching

Fearing no other animals, orcas are powerful predators. They are often seen around the New Zealand coast, easily recognised by their distinctive black and white markings. But research in New Zealand is relatively recent, and much remains a mystery about this, the largest member of the dolphin family.


Orcas in New Zealand

‘The wolves of the sea’

Although there are estimated to be fewer than 200 orcas (Orcinas orca) living in New Zealand waters, there is significant awareness of these sleek, torpedo-shaped mammals. They are often seen in coastal waters, have a fearsome reputation as a predator, and gained public sympathy through the 1993 movie Free Willy. Despite the fact they are predators of large marine mammals as well as fish, they have never been recorded attacking humans.

Description

Orcas are also known as ‘killer whales’, but while they may be killers, they are not true whales. They belong to the dolphin family (Delphinidae), of which they are the largest member. They are called whales because they are a comparable size to many of the smaller whales. Males are 7 to 8 metres long, weighing up to 5.5 tonnes; and females are smaller, around 6 metres in length and up to 3.6 tonnes in weight. Males have a distinctive erect dorsal fin up to 1.8 metres tall, whereas the fin of females is shorter (about 0.9 metres) and more curved.

Life history

Orcas become sexually mature at 10 to 15 years. Calves are typically born at five-year intervals, following a 17-month gestation period. The lifespan of males averages 29 years but can be 50 to 60 years, whereas for females 50 years is the average, and 80 to 90 years may be attained.

Populations and distribution

Orcas are found in all oceans of the world, particularly in cooler temperate and polar regions. Until the 1990s little was known about orcas in New Zealand waters. Scientists did not even know whether any were resident around the coast, or whether they simply passed through when migrating to breeding or feeding areas elsewhere.

As a result of preliminary DNA analysis by New Zealander Ingrid Visser, it is now established that there are probably three resident populations in New Zealand: one off the North Island, one off the South Island, and a third group that spends its time in both regions. Between 1992 and 1999, Visser has counted a total of 167 individual orcas around New Zealand. It is not yet known whether these separate groups of orcas interbreed. Nor is it clear whether some arrive from outside the New Zealand region, but this is possible; animals in pods seen off the Bay of Islands in 1997 and Whāngārei in 2001 had the slate grey colouring of Antarctic orcas, rather than the jet black pigmentation associated with New Zealand ones.

Orcas form long-term social groups known as pods. The typical pod size of New Zealand orcas, at around two to four, is smaller than elsewhere.

In New Zealand orcas do not have a confined home patch, but move around from season to season. The places you are most likely to see them are off the Bay of Plenty, East Cape and Hawke’s Bay regions in June, and again from October to December. This contrasts with regions such as British Columbia (Canada) or Washington State (USA), where they tend to stay in one place.

Orcas are totally protected in New Zealand waters under the Marine Mammals Protection Act 1978, which is administered by the Department of Conservation.

Identification of individuals

Identifying individuals is important for studying how far they move, how often they breed, and the social structure of groups. Researchers can do this in several ways: by the shape of the light area behind the dorsal fin called the saddle patch, marks and nicks on the fin, or the eye patch – a distinctive white blaze just above the eye.

An eye for an eye patch

New Zealander Ingrid Visser spotted a unique identifying feature of the orca. She was the first researcher in the world to systematically photograph the white eye patches of 98 orcas, demonstrating that individuals can be reliably identified in this way.

Sometimes the triangular dorsal fin is bent out of shape or hooked; one orca has been seen where it had totally collapsed. In New Zealand 23% of adult male orcas have an abnormal fin, compared with 5% in British Columbia and 0.6% in Norway. Just why there should be more in New Zealand is a mystery.


Feeding and other habits

Eating rays

Compared to those elsewhere, New Zealand orcas have an unusual diet. Although like other orcas they consume a variety of food such as fish, squid, dolphins, sharks and seals, they are the only group known to eat stingrays, eagle rays and electric rays as a staple food.

Cruising the shallow waters in harbours such as Kaipara, Tauranga, Whāngārei and Waitematā, orcas forage along the muddy or sandy floor, seizing rays by the head or tail tip in order to avoid the barb halfway along the tail. Sometimes they blow bubbles at them, possibly to frighten them into moving.

Eating such prey is dangerous. A young female orca was found dead in the Hauraki Gulf with two stingray spines inside her. She died either because of blood loss from the spines penetrating her body, or because she was poisoned by the spines.

Dolphin killers

Orcas eat larger prey than rays. Off Kaikōura in the South Island, 2-metre-long dusky dolphins gather in their hundreds to feed in the nutrient-rich waters, occasionally becoming the orca’s quarry. Seven separate incidents of orca attacks on dusky dolphin pods were observed over 11 days in November 1995.

Mako my day

In the Bay of Islands in 1998, an orca made a ferocious attack on a mako shark. Held by the tip of the tail, the shark tried to escape. It broke free to ‘hide’ under a boat, but the orca pursued it, bit it around the girth, and descended with the shark in its mouth, regrasping it near the tail. A second orca joined in the attack, biting the shark on the head, and together the two descended while eating their doomed victim.

Stranding

By feeding close inshore, orcas run the risk of becoming stranded. About one orca is stranded in New Zealand each year; since records began more than 70 have been stranded, compared to only 12 in Australia. In 1955 at Paraparaumu north of Wellington, 17 came ashore – the largest recorded stranding of orcas at one time in New Zealand. To put them out of their misery they were shot. Today, strenuous efforts would be made to refloat them, and it is likely that many would have survived.

Long-distance travellers

New Zealand orcas are well travelled and long lived. One female, first identified in 1977, has been seen at sites between the Bay of Islands and Kaikōura, and on the west coast at Kaipara Harbour. They can swim as far as 150 kilometres a day, and two males were logged making the return trip from Auckland to Kaikōura, a distance of 2,000 kilometres, in two months. Orcas are capable of accelerating to impressive bursts of speed, exceeding 30 kilometres an hour.

Human hazards

In countries such as Canada and Norway, studies have shown that captivity significantly shortens an orca’s life. By law, orcas cannot be taken captive in New Zealand, but they face other threats including pollution, being struck by boats, and harassment. Fishing lines have severed the tops of fins, and toxic chemicals may affect orcas, although this not been proven. There are well documented cases of orcas being struck by boats, which can be fatal. The only enemy of the orca is humans.


Hononga, rauemi nō waho

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How to cite this page: Gerard Hutching, 'Orcas', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/orcas/print (accessed 22 January 2020)

He kōrero nā Gerard Hutching, i tāngia i te 12 Jun 2006