Living fast, dying young: The remarkable, giant cuttlefish of South Australia

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Article and images by Dave Abbott

Fifteen years ago I threw my camera and dive gear in a bag and jumped on a plane to South Australia to film one of the most amazing marine life spectacles in the world: the spawning aggregation of the Giant Cuttlefish.

I was captivated, so much so I vowed to get back one day and film it again. This year I finally made it, teaming up with a couple of South Australian cave diving friends and traveling from Adelaide to the Spencer Gulf to see these amazing creatures.

Not surprisingly given their name, Giant Cuttlefish, (Sepia apama) are the largest cuttlefish species in the world, growing to nearly a metre long and from 5-15kg in weight. In common with most cephalopods they have short lifespans, reaching maturity in only two years. Large adults are able to spawn in their second year, and they die after a single mating cycle.

The large males are striking animals with beautiful colours and markings, especially when displaying to each other. But despite their huge size, Giant Cuttlefish can jet away at lightning speed when threatened, and they move with incredible fluidity, hovering around like weird organic spaceships.

The Big Event

Once a year tens of thousands of normally solitary Giant Cuttlefish congregate on the shallow reefs of the upper Gulf. This mass ‘meeting of tentacles’ every winter between May and August was only discovered by divers in the late 1990s; its the world’s only known mass cuttlefish spawning aggregation.

Outside the breeding season the male to female ratio of Giant Cuttlefish is 1:1 but during the aggregation male cuttlefish outnumber females by between 4 and 10:1; the females get to be pretty choosy while the males have a lot of showing-off to do to score a mate.

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A large male demonstrates the much broader tentacles that cuttlefish have compared to other cephalopods.

Courtship involves a lot of competition between the males as they try to impress a female while at the same time driving away other males. They do this by displaying rapidly pulsating waves of colour across their mantles and spreading their tentacles out to make themselves appear even larger than they are.

The courtship displays can turn into full-on wrestling matches as dominant males battle for supremacy, but while these duels are going on, smaller ‘sneaker males’ slip under the radar, then mimic the females less flamboyant colouration. The ploy often results in a successful ‘quickie’ as the bigger, technicolour males fight it out. It was this drama amongst the rocks and weed I had come to see and film as part of a larger documentary project.

The 2017 Cuttlefish Season After meeting up with my dive buddies Steve Trewavas and Grant Pearce at Adelaide airport we took a five hour drive to Whyalla in the Spencer Gulf. The landscape along this stretch of the Gulf is flat and fairly monotonous; red sand, rock, and scrub interrupted only by the occasional refinery or smelter, and with little wildlife to see. Fortunately it was to be a very different story beneath the surface!

Our first morning in Whyalla dawned clear and sunny and we headed down to a bouldery beach replete with wallabies, geared up, and waded into the calm water. Right away below the surface I was met by a surreal sight; at least a dozen giant colourful cuttlefish vying with each other for attention, an unbelievable display of pulsating colours and patterns, tentacles swirling, big bodies tilting and gliding around each other like surreal hovercraft.

Just for the contrast I stuck my head up through the surface again to look at the flat land surface stretching, washed out, to the blue sky horizon, allowing no hint of the colour and drama taking place below. The experience summed up the essence of diving …immersion in another world invisible to the one above.

Beneath the surface groups of cuttlefish were everywhere. Large males were trying to outdo each other with bright pulsing displays, small ‘sneaker males’ hanging around looking for an opportunity to nab a mate, and drab females hiding under ledges, looking nervous and harassed.

Two hours vanished. Finally the 12degree C water and a full bladder convinced me to stop for lunch and a break before my drysuit became a wetsuit. Similar long dives followed. The hardest part was not the cool water, rather staying focused with so much going on in every direction.

Experiencing the Giant Cuttlefish spawning aggregation again after 15 years was every bit as special as I had remembered, and it was especially heartening to see such big numbers present after fears in 2012 that the Gulf’s cuttlefish population had crashed irrevocably.

The recent history of the Spencer Gulf cuttlefish has been pretty turbulent. Prior to the mid-1990s cuttlefish here were harvested for snapper bait with annual catches around 4 tonnes, equivalent to about 4,000 cuttlefish. But in 1997 this escalated to 245 tonnes, or a quarter of a million cuttlefish harvested, and it led to half the grounds being closed to commercial fishing in the following year.

When I was here last time in 2002, the cuttlefish numbers appeared fairly high, but in 2012 the number returning to the spawning ground had plummeted to only 6,000. Locals became pessimistic that the population would ever recover. Fortunately, in the years 2014 and 2016 spawning numbers increased, and this year was one of the best seasons ever. Hopefully South Australia’s Giant Cuttlefish will always be around for divers to enjoy.

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