Adventure

Nature's great event

Every year, hundreds of thousands of giant cuttlefish aggregate in Australia's Spencer Gulf to mate. It is the largest event of its kind and one of nature's great spectacles.

Words & photographs by Scott Portelli

 

There are very few creatures in the animal kingdom that are so complex, so unique, and so alien to us that we are mystified by their very existence. Imagine a creature that has three hearts, blue blood, and the ability to alter its appearance. Hundreds of thousands of Australian Giant cuttlefish (Sepia apama) gather each winter from May to August in the shallow waters of South Australia’s Upper Spencer Gulf for their once-in-a-lifetime spawning event. 

The cuttlefish is part of the cephalopod group, which includes squid, octopuses, and nautilus. Cephalopods are considered highly intelligent, and cuttlefish have one of the largest brains of any marine invertebrate. 

They aggregate in the thousands at Point Lowly, Whyalla, in the Spencer Gulf. It is still unclear, however, where the Australian Giant Cuttlefish migrate from or why they aggregate in this specific location. Whether it is the underwater terrain, safety from predators, a food source for the hatchlings or the instinct to arrive at the same time each year for one of nature’s most unique events is a relative mystery. However, the area around Point Lowly is perfectly suited for the mating needs of the Australian Giant Cuttlefish. The underwater environment, depth, water temperature, rocky outcrops and shallow terrain provides suitable conditions to lay their eggs as huge sandstone slabs with numerous ledges are perfect for attaching and distributing eggs here. 

During the mating season, males compete for territories that have the best crevices and ledges for egg-laying and then attract females with mesmerising displays of colour, texture and patterns that appear to change across their skin. While males can weigh up to 10kg and reach 1m in length, rivalry among the world’s largest cuttlefish is fierce, as males outnumber females by up to 11 to 1 at the beginning of the mating season. Nowhere else in the world is there a mating aggregation on such a grand scale. However, months of posturing, fighting, mating, and competing for locations to lay their eggs takes its toll. And when it is all over, the adult population wither away and die.

The female ultimately decides which males get the chance to mate. She communicates with a visual display to ward off any males she finds unappealing and when a more attractive suitor approaches, she switches off the warning signal to encourage the potential mate to approach. The cuttlefish skin is an amazing communication system, highly developed, using elastic pigment sacs called chromatophores. They can match colours and surface textures of their surrounding environments by adjusting the pigment and iridescence of their skin, often using this adaptive camouflage to blend in with their surroundings and avoid predators.  

Males will flare their arms and inflate themselves or stretch to the limit to demonstrate who is the biggest and more robust mate. A line of suitors will hover in the background, waiting for a chance to mate with the female. The smaller males often camouflage themselves as females to sneak past the bull males that guard the female. These smaller males are referred to as ‘sneakers’. They adopt an alternate strategy, masquerading as an unreceptive female by modifying their colour, pattern, and behaviour to sneak past the unsuspecting male that is busy fending off other suitors. Apart from the larger size of adult bull males, it is difficult to distinguish a male from a female.

Rigorous fights often break out between males if the posturing fails to demonstrate clear superiority. They latch on to each other twisting and turning, entangling their tentacles until a release of ink signals defeat and the release of the embrace, as the loser flees the scene. Most males bear battle scars, and some are missing an arm or multiple tentacles. Mating and defending a female is exhausting and inevitably a contributing factor of the deterioration of the Australian Giant Cuttlefish at the end of the annual aggregation.

Their lifespan is only around 2 years and the instinct to mate is in their DNA. This is the one and only chance for these endemic invertebrates to perpetuate the species. An unsuccessful mating season could wipe out the population altogether which was the case in 2013. The year saw a devastating crash in the population which prompted the government body PIRSA (Department of Primary Industries and Regions South Australia) in consultation with SARDI (South Australian Research Development Institute) to introduce a total ban on catching cuttlefish in the upper Spencer Gulf for 5 years. 

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Issue 21
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This feature appears in ISSUE 21: Colour & Cold of Oceanographic Magazine

Issue 21
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Supported by WEBSITE_sponsorlogos_blancpain

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