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.
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. Sometimes the triangular dorsal fin is bent out of shape or hooked; one orca has been seen where it had totally collapsed.
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.
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