Swimming with Giant Cuttlefish, Whyalla SA.

Giant Australian Cuttlefish, Whyalla, South Australia

The Giant Australian Cuttlefish

Mating happens from May to August, during the winter months in the southern hemisphere. When the water temperatures start to dip (around 17℃, 62℉), thousands of Giant Australian Cuttlefish leave the comfort of their home reef and head towards a five-mile (8 km) stretch of the shallow reef in Spencer Gulf, Australia.

Preparation for our swim.

Fear of colliding with an iceberg was foremost in my thoughts. Water temperature was about 12°C. The many layers of thick 7.5 mm wetsuits, thermal under garments, vests, gloves, boots and hoods kept us warm except for our extremities. After only an hour in the water I could no longer feel my fingers or toes and my face was numb with cold. Cuttlefish might be the chameleons of the sea but I was doing a pretty good job with colour changes myself. I was also as buoyant as a cork and Tim had to push my legs under the water to help me stand up when it was time to get out.

The majority of cuttlefish were about 10 to 20 metres from the shoreline, in one to two metres of water.

Fun Facts about Giant Australian Cuttlefish

Fun Facts about Cuttlefish Mating

Many tens of thousands of them gather in Spencer Gulf, SA, during the annual Australian Giant Cuttlefish aggregationIn what has been called the “premier marine attraction on the planet”.

Males and females die after mating and egg laying.

The male ‘bulls’ are larger than females and have longer tentacles than females.

Female Left, male right

Males out number females 4 to 1, so the females can be fussy with matting partners. And the males fight between themselves for the females.

Males too young to mate in their first year come back the second year, when they are much larger than any of the others.

Smaller males hoping to mate, change their colour and curl up their arms to look like females. This way they get close to females with out getting beaten up by the larger males.

Fighting Males (bulls)

Everything these cuttlefish do is in slow motion. So you have to hover over them for a while to actually make out what they are doing. Fights can last for 20 minutes.


Males try to attract females by putting on colour displays and making themselves look bigger.

Mating happens head-to-head with tentacles and arms entwined. The male uses a specialized arm to pass his spermatophore, a small packet of sperm, to the female. This process takes around 2 minutes!

Because the female often accepts more than one mate, the male sometimes sprays water through his mantle funnel into the female’s buccal area to wash out other males’ spermatophores.

When she is ready to deposit her eggs in safe locations such as under rocks or in discarded shells, the female uses her arms to wipe the stored spermatophores onto each egg.

After mating , the male will try and hide the female and ward off any other admirers. This improves the chances that the female will use his sperm to fertilize her eggs!

Egg Laying

Giant Australian Cuttlefish eggs take three to five months to develop, hatching from mid-September through to early November. They emerge as miniature adults about the size of your thumbnail. Around 100 to 300 eggs are laid at a time, which are then left with neither parent to guard or care for them. Eggs need water temperature of approximately 12°C for incubation. Photo below from same article. We did not see any cuttlefish eggs during our swim because they lay them further out in the deeper water.

Eggs of Giant Australian Cuttlefish

Live Stream Camera (Cuttlecam)

Year 9 students from Whyalla Secondary College built a low-cost research buoy known as a ‘Rig’ which is deployed at Stony Point. Both construction and monitoring of the Rig is undertaken by the students.

You can check out the streams at the AusOcean YouTube page. https://www.youtube.com/c/AusOcean

National Heritage Status

In February this year, 2023, the area was listed as an Australian National Heritage Site. “National Heritage status for the Cuttlefish Coast Sanctuary Zone provides further protection for the only known place in the world where this amazing species comes to breed each year,” Acting Mayor Knox said..

the irony is. ….

Santos Ltd. (South Australia Northern Territory Oil SearchPort Bonython is the location of a deepwater port, gas fractionation plant and diesel storage facility west of Point Lowly in the Upper Spencer Gulf region of South Australia. …. An oil spill at Port Bonython in 1992 resulted in loss of bird life and damage to mangrove habitats to the west and southwest of Port Pirie. (No mention of what it did to the cuttlefish)

Map of area

Cheers til next time

Helen & Tim