Living in Australia for five years and spending most of my time in the sea meant that at some point, the rumours about South Australia were going to surface. Half of the people I interacted with were in awe of this slice of ocean. While the other half, well… they were terrified of it. However, nearly everyone I spoke to about it had never been in it. For many, the whole notion of “everything’s bigger in Australia” was a truism, and getting in the water with gigantic marine creatures is not everyone’s idea of a good time. But for me, this is what I live for.

That’s when I came across a natural happening that occurs only in these wild South Australian waters: the giant cuttlefish mating season. Every winter, up to 250,000 cuttlefish come to spend the winter here, ensuring their legacy lives on. The start and end of a given season varies within a couple of weeks but is largely predictable each year. The goal was to find the perfect time within ‘cuttlefish season’ to make my way from Australia’s west to south coast to dive in personally.

Giant cuttlefish are the largest of the species and can grow up to 50-60 cm (20-24 in) in mantle length. However, some can exceed 80 cm (31 in). The sheer size, presence and quantity is what makes the South Australian aggregation so impressive. Although giant cuttlefish can be found elsewhere, such as other parts of southern Australia, the coast of Whyalla is the only known location in the world where the giant cuttlefish mating aggregation occurs.

Like anything incredible in nature, getting out to the destination is not for the faint of heart. The winter months when the cuttlefish mate ensure the ocean is rough and quite cold. We made the long passage from Port Lincoln to Upper Spencer Gulf overnight and when we woke up it was time to get our gear on.

Back-rolling off the dinghy into five metres of water — wearing a 3mm, 7mm and a waterproof heating vest — we were told to just “wait and see what happens”. Knowing that wildlife never operates on our time, this meant there was certainly a chance we’d not see the action on this dive. Or at least that’s what I thought.

Immediately upon entry, there were easily 30 to 40 cuttlefish slowly moving around me. Entirely disinterested in my existence, these gigantic creatures were clearly on a mission. For the males, this was go time, and they were going to demonstrate in full force right in front of us.

Known as the ‘chameleons of the sea’, the male cuttlefish were transforming the clear waters into a vibrant tapestry of colours. Adorned with striking patterns and hues, they engaged in elaborate courtship rituals to attract females. Rapid colour changes, accompanied by hypnotic movements and intricate body postures, were serving as visual communication to the females, and competitive signals to rival males. There’s a catch though. With all the impressive and amazing displays from the males comes a body breakdown over the season.

There’s typically an imbalance between the number of males and females. This creates fierce competition among males to attract and mate with available females. The limited number of receptive females intensifies the rivalry and aggression among males. That said, the male cuttlefish will deploy various mating strategies to increase their chances of reproductive success, including chasing away rival males, and displaying dominance through zebra striping (known as ‘strobing’). This means rapid colour changes and engaging in physical confrontations. Some small males masquerade as females, tucking their large feeding tentacles away and sneaking in for a quickie with the female, even in the presence of large, duelling males nearby.

Male cuttlefish strive to guard and monopolise females for mating. They may actively defend a territory to ensure exclusive access to receptive females. This aggression is driven by the instinct to pass on their genetic material and increase their reproductive success. It’s cut throat out there.

With all the defence needed to make mating happen, and the use of their specialised arm, also called a hectocotylus, to transfer sperm to the female, mating can be draining. This is when the males experience a decline in health over time. They become weak and exhausted, often losing weight and showing signs of physical deterioration.

The exact reasons for their post-mating decline are not fully understood, but it is believed to be related to physiological changes, hormonal imbalance, and the significant energy expenditure during the reproductive process, when food intake is lowest. With that, giant cuttlefish typically live for less than two years.

During my dives, I felt like I was on another planet as I cautiously followed the cuttlefish around their mating ground. Everywhere I turned, there were countless cuttlefish of all sizes moving around the rocky reef, pushing through the seaweed-covered environment. They were burrowed into holes to complete their life cycle, or intimidating one another to win the mating battle. It was truly a sight unlike anything I’ve ever witnessed, making that rough ride entirely worth it.

When you see something this impressive at scale, it’s impossible not to think about our changing planet. Will something like this be accessible in years to come? Will cuttlefish still call this one small plot of ocean their home? What can we do to help ensure that a creature this magnificent can continue to thrive?

The giant cuttlefish population faces various threats, including habitat degradation and overfishing. Conservation efforts are crucial to ensure the long-term survival of these remarkable creatures. The mating season serves as a reminder of the importance of preserving their natural habitat and raising awareness about their ecological significance. Especially when it comes to diving.

Even though there are no set guidelines and regulations on how to dive or snorkel with giant cuttlefish, we need to take into account their well-being whenever we get into the water. This means being mindful of photography, and not dragging gear on the seafloor or chasing the giant cuttlefish when they are in the peak of their mating season. None of this behaviour supports the longevity of these amazing creatures.

In South Australia, a number of groups and individuals have spent years promoting the uniqueness and ecological value of the cuttlefish aggregation, and the importance of protecting their habitat. For instance, Professor Bronwyn Gillanders, deputy dean research and deputy executive dean at The University of Adelaide, is a frontrunner in the study of cuttlefish. She and her team focus on specific projects that cover ecological and environmental change, integrated marine management, population structure and connectivity, cephalopod biology, ecology and fisheries as well as coastal carbon opportunities.

Andrew Fox, the owner and operator of the liveaboard I was staying on, takes scientists and divers to the Gulf every season to experience the cuttlefish. As a leading authority on great white sharks, he’s also an expert when it comes to the South Australian ocean generally. Having spent nearly 40 years navigating, photographing and studying these wild waters, he knows a bit about everything when it comes to its marine life in this remote part of the world.

In the realm of giant cuttlefish and their remarkable mating season, the passion and dedication of individuals who have devoted their careers to studying these fascinating creatures cannot be overlooked. From esteemed professors and scientists to passionate ecotourism operators and skilled photographers, these individuals play a crucial role in making it possible for others to witness the magic of the cuttlefish mating season firsthand.