The largest cuttlefish in the world, and the only one that aggregates to breed in numbers a diver can swim through. The Whyalla aggregation happens in the southern winter.
To about a metre including the arms, and the largest cuttlefish in the world. The body is broad and the fins run the whole length of it. Colour and texture change constantly, and a large male can raise skin papillae into ridges and horns that alter the outline as much as the pattern.
The reason it is a signature species is the aggregation at Whyalla in South Australia. Tens of thousands gather on a short stretch of shallow rocky coast in the southern winter, from about May to August, to breed, and it is the only known mass breeding aggregation of any cuttlefish. Large males guard females and display at each other in colour; smaller males take a different approach, pulling in their arms, hiding the display and passing as female to get past the guard. Both strategies work. The whole animal population dies after breeding, so the aggregation is also the end of a generation. It is dived from the shore in a few metres of water and the numbers are what make it — a single giant cuttlefish elsewhere on the southern coast is a good sighting rather than a spectacle.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.
