DIVE LOG AUSTRALASIA ISSUE 413 AUGUST 25

A dominant bull male attempts to steal a mate—even mid-mating

Stony Point offers one of the most accessible and awe inspiring marine wildlife encounters in the country. What makes Stony Point the chosen breeding ground for these cuttlefish? The answer lies in the unique habitat. The upper Spencer Gulf is predominantly sand and mud, which offers few secure surfaces for eggs. In contrast, Stony Point features a shallow fringing reef spanning 10 km, made up of ledges, caves, and ancient sandstone slabs. These natural features create an underwater nursery, offering protection and anchoring points for egg-laying females. It is the only known site in the region with such abundant, solid rocky surfaces, which is why the entire Spencer Gulf population converges here. The reef’s west

to-east orientation and strong currents help maintain water flow and oxygenation, while the Gulf’s cool waters—colder than surrounding seas due to its inverse estuary conditions—provide the perfect temperature for egg incubation. The migration begins as water temperatures dip below 17 °C—one of the key environmental triggers that signals the start of the breeding season. The first individuals arrive in mid to late May, and by early June, the spawning grounds are teeming with life. The timing ensures that fertilised eggs will develop through the coldest months of the year, which provides optimal conditions for their survival. By early June, thousands of cuttlefish converge en masse across the rocky inshore reefs surrounding Point Lowly, Fitzgerald Bay, False Bay, and Black Point. This area, now protected as the Cuttlefish Coast Sanctuary Zone and recognised on Australia’s National Heritage register, offers the ideal mix of habitat, depth, and structure for their complex reproductive rituals. Normally solitary creatures, these marine invertebrates transform the shallows into a dynamic stage for one of the most visually arresting displays in the animal kingdom. Males compete fiercely for mates, flashing through a kaleidoscope of shifting hues and textures, hoping to outshine their rivals and impress the females. It’s a hypnotic, high-stakes ballet of concealment, imitation, and ritual—all for the sake of reproduction and the continuation of the species. Though often mistaken for fish, Giant Cuttlefish are actually close kin to octopuses and squid. Their biology is fascinating: they possess three hearts, circulate copper

In their own world - one male holds his ground while others hover, hoping for a chance

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Dive Log Australasia #413 August‘25

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