Something strange is happening in the South Australian seas. Someone’s not turned up for their party.
Around this time of year the Australian giant cuttlefish (Sepia apama) gather along the South Australian coastline between False Bay and Whyalla to mate and spawn. These cuttlefish are cephelapods, an animal without a backbone. They are giants of their genus, they can grow to about a metre long from tentacle to tail and weigh over 5kg but they only live for 2 years!
When you only live for two years it’s important to find a mate and reproduce, especially if you’re only around for the one breeding season. So in winter there’s usually a huge gathering of these short lived giants in the shallows of the South Australian coast. There, they compete for a mate and pass on their diverse and special genes to the next generation.
The competition for mates is spectacular with the males rapidly changing the colours and textures of their mantles. Some of the smaller males, even pretend to look like females so that they can sneak past a dominant male and mate with his girlfriends!
You might have heard about these aggregations, they’re a true marvel of nature and spectacular to see. So much so that these cuttlefish have even made it onto the big screen thanks to BBC Nature wildlife documentaries. Their presence supports local dive operators and who knows how important they are in keeping the ecosystem in it’s dynamic equilibrium?
These aggregations are important to the survival of the species and the local businesses that depend on them. Wisely the South Australian government banned fishing in the mating grounds of False Bay. A step in the right direction but remember these cuttlefish move outside of this bay for much of the year.
Last year and now this year, these large breeding aggregations have not occurred. The giant cuttlefish have not shown up for their party. Compared to a decade ago, last year’s aggregation was down 78% and this year it’s thought to be lower again. Missing out on this once in a lifetime party makes finding a mate and reproductive success a whole lot harder.
Why has it happened? Have they found a new place to get together? Or, are there so few of them now that it’s a big deal to see three or four in the one place? Will they come back? Is it natural, or something us humans have done?
These questions are all unanswered and if these cuttlefish are vanishing, then it’s likely that the answers will never be known.
Let’s keep our fingers crossed for this wonderful mollusc Sepia apama, Australia’s giant cuttlefish.