It has been described as “the premier marine attraction on the planet”. And, indeed the annual aggregation of Giant Australian Cuttlefish at Whyalla is a really special event!
It starts from around the middle of May, as the southern hemisphere winter approaches. The trigger is water temperature and around 17˚C is the threshold for the first cuttlefish to arrive. And by early June there will be tens of thousands of Giant Australian Cuttlefish (Sepia Apama) gathered. All with one thing in mind… Sex and the continuation of the species!
The Whyalla Giant Cuttlefish aggregation really is quite unique. As Sepia Apama are not known to gather in such numbers anywhere else in the world. It is also an incredible spectacle to behold and one that allows the underwater photographer very close access. Particularly so to the large bull males, that is simply not possible at any other time.
So preoccupied are the bulls with ensuring their role in the reproductive process. They simply ignore divers and photographers as they concentrate on the task to hand…
To put their dilemma into some perspective. Overall the population of Giant Australian Cuttlefish has a male to female ratio of almost 1:1. But during this unique mating event at Whyalla that ratio changes and reaches up to 8 males to 1 female. So the competition is incredibly intense and explains the large bull males preoccupation with their captive females. Because one slip in concentration will ensure the prize will be seized by one of this many competitors!
The stakes are very high for all the older participants as it is the last roll of the dice for them. Because all will be dead by the end of the mating season as the cycle of life evolves and continues.
The formal terminology for the mating strategy used by female Giant Australian Cuttlefish is polyandry. Which means that each female will have multiple male partners to ensure better genetic variability of the species.
All of which makes sense from a somewhat dry overall perspective. But when viewed in practice at Whyalla, where so many cuttlefish have gathered. And the females are outnumbered by as much 8 to 1, it takes on a completely different dynamic. . “Spectacularly promiscuous” would probably better describe the apparently licentious and almost wanton behavior!
Apart from the larger size of adult bull males, it is almost impossible to identify a male Giant Australian Cuttlefish from a female one. Even the cuttlefish themselves cannot tell the difference and males have to display a subtle zebra pattern on their sides to signal their sex.
The large bull males are able to put on the most spectacular color displays to try and attract a female. While it is up to her whether she accepts, studies have shown that up to 70% of the time she does not…
If she does the bull male will then try and keep her hidden from view in the sea-grass. Out of sight from all the other males… But that’s not easy with so many other males around, most of whom are smaller and still in their first year of life.
These smaller males are referred to as “sneakers”. Because, lacking the physical size and strength to challenge the bulls, they adopt an alternate strategy. Pretending to be a female and sneaking in with the real female while the bull is busy fending off larger males.
The interpolater then tries to mate with the female – often with great success. And much to the annoyance of the bull when he realizes what is happening!
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