Adventures with Cuttlefish.
Whyalla Cuttlefish
Most of the towns on the Eyre Peninsula, South Australia, have chosen something to promote themselves to the tourists, such as painted silos in Kimba, oysters in Coffin Bay, dinosaur ants in Poochera or diving in shark cages in Port Lincoln.
Giant Cuttlefish Sepia apama
Whyalla has adopted the cuttlefish. There are cuttlefish sculptures along its circular wharf, cuttlefish paintings and banners in its tourist information centre, and the Cuttlefest featuring a professional sand sculpture and a colourful costumed cuttlefish walking around the foreshore along with other events during the cuttlefish mating season from May to August (https://www.whyalla.com/cuttlefest ). The local dive shop has a roaring business of guided dives and snorkels during the season (https://whyalladivingservices.com.au/about-the-giant-cuttlefish/ ). I suspect it is pretty quiet there in summer except for the steelworks and probably fishing outside the marine park sanctuary zones.
The aggregation of giant cuttlefish (Sepia apama) near Whyalla is the only known aggregation site in the world. Tens of thousands of cuttlefish from throughout the Spencer Gulf congregate in the Upper Spencer Gulf off Point Lowly to court, mate and lay their clusters of eggs under the slabs of limestone which form the sea floor off the point. It is thought that this is the only or at least the best location for laying eggs, with most of the gulf being soft sediments and seagrass or mangroves. The eggs are left to fend for themselves, hatching out about 5 months later. The adult cuttlefish take two years to mature. Males can mate when 5 months old so may have two seasons, but females die after mating – a smorgasbord for the local birds, crustaceans and fish. The site at Stony Point, 30 min north of Whyalla, is set up so divers and snorkellers can walk across the limestone slabs along a chain hand-rail into the water. It had been quite windy the days before I dived so, with all the weights needed for a thick wetsuit and a shallow dive into very cold saline water, it was quite a challenge to get through the chop. There was only one other young couple diving with me and a dive guide and we were happy to not swim far and just watch and photograph the cuttlefish. The cuttlefish were in only about 2-4m of water so snorkelling would probably have been OK, and much less effort.
Giant Cuttlefish Sepia apama
Photos by Jane Elek
During my 45 minute dive I saw 30 or more cuttlefish. They were in singles or groups of 3-4 every couple of meters. I was surprised to see quite a range of sizes, from smaller females and young males that were more timid and tried to hide in the weed from divers, to the bigger males which can grow up to 50 cm long, weighing 10kg. The big males were doing most of the displaying and mostly took no notice of the divers. A few raised their tentacles in threatening poses and raised tubercles all over their skin if I got too close. But mostly I could lie still and watch them about 1 meter away. The most conspicuous cuttlefish were males posturing to each other, displaying broad flattened arms blanched white or with waves of black flowing along their body, trying to intimidate the other males and to impress a female, since the males outnumbered the females. The patterns were often only on one side of their body. We saw two mating couples, joined-head to- head as the male used his specialised reproductive arms to deposit his sperm packet into the female’s mantle cavity. The females can mate with several males and then she selects the sperm package to fertilize her eggs. Apparently smaller males tuck away their extra reproductive tentacles and pose as females to sneak under the larger males’ radar to mate with the females. Genetic fingerprinting has shown that the sneak males had a higher rate of fertilising eggs!
Whyalla has adopted Cuttelfish!
Cuttlefish are closely related to octopus and squid and the common snail since they are all molluscs. Cuttlefish have blue blood, 3 hearts and eight arms plus two feeding tentacles with suckers that they use to catch fish and crustaceans. They mostly swim slowly using the fin around their body, inside which is their cuttlebone which they use to control their buoyancy. When alarmed or aggressive they can use their siphons for jet propulsion. They have the biggest brain/body ratio of all invertebrates. Surprisingly, although their eye is very complex and is as big as ours, they are colour blind which makes their sometimes-colourful display puzzling. However, they can see polarized light and their complex eye enables them to be masters of camouflage, and change the colour and texture of their skin to match their surroundings. Their skin has three types of pigment cells, with three colours plus polarising iridescent, luminescent and reflective structures. They can have different patterns on different sides of their body, one to challenge the male on one side and one to attract the female on the other. When alarmed they release ink, which is the origin of sepia-coloured pigment.
This year the SA Minister for Primary Industries introduced more protection for the cuttlefish, with a 100 m fishing exclusion zone around Point Lowly from mid-May to mid-August to augment the existing MP sanctuary zone protecting the spawning area, and to help Whyalla’s tourism. A survey in 2020 found SA cuttlefish numbers at 247,146, a rebound from critically low levels in 2013 and double that of 2019.
It will also be the cuttlefish mating season on the south coast so they will be moving into the shallows to mate and lay their eggs. If you are in the water keep an eye out for them. We often find their eggs washed up on our beaches later in the year, along with lots of cuttle bones. What a pity we have not found an aggregation of courting couples on the south coast, like near Whyalla.