DIVE LOG AUSTRALASIA ISSUE 413 AUGUST 25

There’s no hiding during this season. Camouflage is abandoned as males commit fully to display. Their bodies shimmer with electric waves of colour—bold, pulsating patterns designed to dazzle females and warn off potential challengers. Sometimes, two males will lock into a kind of underwater standoff, like a cuttlefish version of a dance battle. They mirror each other’s movements, flare their arms, and pulse with hue in a silent contest for dominance—each one trying to outshine the other. Some males bypass the usual contests altogether by turning to deception. These smaller individuals lack the size to win through confrontation, so they adopt the colour patterns and body language of females. This disguise lets them slip past territorial males and gain access to real females unnoticed. When the timing is right, they reveal their true identity and attempt to mate—a sneaky strategy also seen in various other animal species. During mating, the male positions himself directly in front of the female and uses a specially adapted arm, the hectocotylus, to deliver sperm packets (spermatophores) into a storage cavity near her mouth. A single female may pair with multiple partners over the season, sometimes retaining sperm from up to six different males. Females have the ability to control which sperm fertilises each egg. They tend to favour the most recent sperm or may even selectively choose based on quality, a form of cryptic female choice. Sometimes, females eject unwanted sperm. After mating, the female seeks out sheltered crevices or the undersides of rocks to deposit her eggs. She places them

in clusters, each egg encased in a clear, gelatinous capsule. Over the breeding season, she may lay over 300 eggs. Once this task is complete, both sexes perish, as Giant Cuttlefish follow a single-reproduction strategy called semelparity. The eggs remain unattended, developing slowly through winter. It takes three to five months for the embryos to mature. By late winter or early spring, clusters of eggs swell with growing hatchlings. Finally, thumbnail-sized cuttlefish emerge, fully formed and independent, ready to begin life in the open Gulf. Those that survive will mature over the next year and return to Stony Point, continuing the cycle. Cuttlefish are remarkably intelligent. They have the highest brain-to-body mass ratio of any invertebrate and exhibit curiosity and problem-solving responses. During the mating season, their singular focus on reproduction makes them indifferent to divers, allowing for unusually close observation. Large males are often so preoccupied that they ignore underwater visitors completely. When threatened, a cuttlefish releases a thick, dark cloud of ink—a primitive but effective tactic that masks its movement and confuses potential predators. These cephalopods aren’t the only stars of the show. The waters around Stony Point are alive with marine activity, offering visitors the chance to spot Bottlenose Dolphins, Long-Nosed Fur Seals, Wobbegongs, and even the occasional Port Jackson Shark cruising by. Dolphins and Seals, in particular, are known to hunt cuttlefish—an efficient source of protein.

Spiralling struggle - two males grapple for the chance to reproduce

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Dive Log Australasia #413 August‘25

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