‘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.
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.
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 Whangārei 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.