The Australian giant cuttlefish, Sepia apama, is the largest cuttlefish in the world and aggregates in the cold waters off Point Lowly, Whyalla, South Australia. The annual event, commencing in May through to July, brings hundreds of thousands of cuttlefish in search of a mate to the waters off Point Lowly – the only place in the world the cuttlefish aggregate in such large numbers. The main dive spot is very accessible and can be found on a dirt road, named ‘Cuttlefish Drive’. A rope leads visitors 15 metres into the water, where cuttlefish are already gliding by as they walk into the water. You don’t need to go far or dive deep to have great interactions with the cuttlefish as they aggregate close to shore and in only five metres of water.
The Australian giant cuttlefish has a relatively short lifespan, usually only living for two to four years. As such, this aggregation is essential for the continuation of the species. After the breeding season ends, many will die. Mating can be aggressive, with males usually dominating the number of females 10 to 1. The larger males must show dominance over both the females and smaller males in order to win the breeding rights. The males are constantly changing their colours and pulsating zebra stripes that move along their bodies. This helps them appear more attractive to females whilst intimidating potential rivals.
Surprisingly, the smaller males manage to secure about a third of the mates. They mimic the female’s colouration and behaviour as a disguise, sneaking close to them and hiding under the crevice of rock shelves, while the larger males are busy protecting the females and intimidating other males.
Mating takes place head to head, the male fertilises the female with spermatophores – a small package of sperm which is transferred to the females ovipore. After the fertilisation is complete, the female will lay between 100 and 300 small lemon-shaped leathery white eggs in subtidal crevices. Whyalla provides the perfect incubation temperature for the eggs to hatch. Unlike many other cephalopods, both the female and the male cuttlefish do not guard their eggs. Instead, they are left to hatch after three to five months.
If you are a keen diver or snorkeller in South Australia for the aggregation season, I’d definitely recommend making your way to Whyalla for this amazing phenomenon. Apart from the thousands of cuttlefish, large pods of bottlenose dolphins and seals are often seen hunting on the aggregating cuttlefish.
Cameron McFarlane is an ocean photographer from Shellharbour, South Coast of New South Wales, Australia. Originally into surf photography, he is now focusing on underwater photography after diving the local dive spots and discovering how diverse and rich life is beneath the surface.