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Australian Giant Cuttlefish – The Sneaky Cross-Dressers of the Sea

By Chris Doyle on April 19, 2012 in Other

Photo: George Evatt / Coral Sea TV

The next time you are pondering your own sexual woes, bear a thought for the Australian giant cuttlefish. With a lifespan of only one to two years, these guys only get one chance to mate before dying. And with only one shot at reproduction, they pull out all stops to make sure it happens.

The Australian giant cuttlefish is the largest species of cuttlefish in the world, growing to more than ten kilograms in weight and up to one metre in length. They are not usually very active, only spending a little time each day searching for food. Most of their time is spent hiding and they are one of the ocean’s best exponents of camouflage. Not only can they match their own colour to that of their background, they can also raise parts of their skin to change texture to imitate rocks, sand or seaweed. If they are spotted by a predator, they fall back on their well-known defence mechanism, dark coloured ink, which they shoot into the water to disorientate the attacker while they escape.

However, each year around the beginning of winter the giant cuttlefish suddenly become very active with the onset of their breeding season. Some migrate long distances to join in mass orgies known formally as ‘spawning aggregates’ – congregations of thousands of individual cuttlefish all with the intention of sowing their seeds for the next generation. Most of the day is spent mating and, with only one season to reproduce, it should come as no surprise that there is intense competition between the males to attract females.

Males become extremely territorial during breeding and will aggressively defend the areas of flat rock where the females like to lay their eggs. To impress the females, the males perform elaborate courtship displays during which they rapidly change their body colour and pattern every fraction of a second, creating spectacular visual effects that enchant the female. The largest males tend to defend the best territories and have the most spectacular displays, and as such usually win the females’ attention.

Not to be outdone, however, the smaller males have come up with their own unique strategies to out-fox the larger males. One strategy is to sneakily enter the territory of a large male and mate with his female while he is busily fending off other males. Another more peculiar strategy is what has been referred to as ‘cross-dressing’. With this strategy, a smaller male takes on a female appearance by changing his own body shape and colour. The larger male, thinking the smaller male is another female, allows the cross-dressing male to come closer. But once the larger male is not looking the smaller male quickly changes colour again, mates with the female and hastily escapes.

To the larger male, it is probably more of an ego crush than anything, as he will more than likely mate with the female anyway. Females will mate with two to eight males each day and the males will also have multiple partners. This ensures there is genetic diversity among the next generation, which is important for the survival of the species.

Of course all good things must come to an end, and, unfortunately for the giant cuttlefish, the end of the breeding season signals the end of life. This is the time when you are most likely to find white cuttlebones, the internal shell of the cuttlefish, washed up onto the beach. These cuttlebones are popular among bird-keepers, who give them to their birds to chew upon.

The Australian giant cuttlefish is found nowhere else in the world except for the southern waters of Australia. Off the Eastern Beaches, they are mostly sighted by scuba divers during the breeding season, from May to September. There are plenty of videos of giant cuttlefish antics on YouTube, so check them out. Alternatively, if you are keen to see the cuttlefish in the wild but do not scuba dive, consider a trip to Whyalla in South Australia where more than two-hundred thousand cuttlefish converge each year during the breeding season. This is the largest aggregation of cuttlefish in the world and the small depth of the bay there allows for the cuttlefish to be seen by snorkelers.