Everything you need to know about giant Australian cuttlefish in South Australia

The giant Aus­tralian cut­tle­fish is exact­ly what its name sug­gests – the largest of all the cut­tle­fish species. Males can be par­tic­u­lar­ly big in size and mea­sure up to 50 cm long and weigh about 10 kg.

These intel­li­gent crea­tures are expert colour-chang­ers and mas­ters of cam­ou­flage, and can change shape and tex­ture to look like rocks, sand or sea­weed – a spec­tac­u­lar sight to see.

Giant cut­tle­fish can be found all along Aus­trali­a’s Great South­ern Reef with­in the tem­per­ate waters from the the east-coast of Queens­land, and on the west-coast up to Ninga­loo Reef in West­ern Australia.

How­ev­er the pop­u­la­tion found with­in the North­ern Spencer Gulf is unique to this area, not inter-mix­ing with the pop­u­la­tion fur­ther south or along the wider Great South­ern Reef.

This North­ern Spencer Gulf pop­u­la­tion of Giant Aus­tralian cut­tle­fish con­gre­gate off the coast of Whyal­la in South Aus­tralia, along a 10 km stretch of the Upper Spencer Gulf Marine Park. Cut­tle­fish num­bers usu­al­ly increase through­out May and peak in June and July when the breed­ing sea­son is in full swing.

So if you’re head­ing to Whyal­la or Spencer Gulf, head to the Cut­tle­fish Coast to get a glimpse of these majes­tic creatures.

Why do giant Aus­tralian cut­tle­fish aggre­gate near Whyalla?

SA’s waters are the only place in the world where the cut­tle­fish con­gre­gate annu­al­ly en mass and with such great pre­dictabil­i­ty. Their sole pur­pose? Breed­ing! Their under­wa­ter light shows, cun­ning games and dra­mat­ic colour dis­plays are all to lure a mate (or mates!) for breeding.

Whilst giant Aus­tralia cut­tle­fish breed annu­al­ly in small groups along the Great South­ern Reef, those in North­ern Spencer Gulf aggre­gate in large num­bers – some­thing not seen any­where else in the world.

The waters around Point Low­ly and Stony Point in the Upper Spencer Gulf Marine Park have rocky seabeds, which pro­vide the per­fect envi­ron­ment for females to lay and del­i­cate­ly attach their eggs.

The sheer num­ber of cut­tle­fish makes the Whyal­la breed­ing sea­son aggre­ga­tions unique, not just in Aus­tralia, but in the world. For this rea­son, the Cut­tle­fish Coast Sanc­tu­ary Zone was award­ed Nation­al Her­itage sta­tus in 2023.

Why the colour­ful show?

As part of the breed­ing process, male cut­tle­fish out­num­ber females, some­times 7:1 — so they make it a point to look absolute­ly stun­ning. They put on a spec­tac­u­lar dis­play of colours and shape-shift­ing to attract and keep a mate. Kind of like a dance-off!

How can you expe­ri­ence the cuttlefish?

The Whyal­la City Coun­cil cel­e­brate the cut­tle­fish breed­ing aggre­ga­tion each year with the annu­al fes­ti­val – Cut­tle­fest. There are numer­ous ways to learn about expe­ri­ence and enjoy the cut­tle­fish as part of this program.

For those want­i­ng expe­ri­ence giant Aus­tralian cut­tle­fish up-close in waters around Point Low­ly and Stony Point, also known as Cut­tle­fish Coast, there are sev­er­al options. 

You can go at it alone and snorkel or dive your­self. Or you can take a guid­ed snorkel, dive or even glass bot­tom bot­tom boat tour. Theres even glass bot­tom kayaks to hire!

The main site with vis­i­tor ameni­ties and the site for guid­ed tours is at Stony Point, about 20 km north­east of Whyal­la. There’s easy access via a board­walk to the shal­low water and a waist-height chain to hold onto for sup­port, mak­ing it the safest point to enter or exit. For those enter­ing the water, just make sure you head across to the snorkel and dive safe zone delin­eat­ed by mark­er buoys, to ensure you stay away from boat traffic.

Read all about what it’s like to swim with giant Aus­tralian cut­tle­fish here.

Top tip: Expe­ri­enc­ing Marine Sanc­tu­ar­ies offer guid­ed snorkel tours and Whyal­la Dive Ser­vicesboth guid­ed snorkel and dive tours. Spencer Gulf Adven­turesoffer a glass bot­tom kayak expe­ri­ence and both Cutty’s Tours and Spencer Gulf Adven­tures offer glass bot­tom boat experiences.

What should you wear?

In the win­ter months, the water is cold so a well-fit­ting full length 5 mm or 7 mm thick wet­suit with hood, gloves, boots and a mask and snorkel is the way to go. Fins are also impor­tant, as the cur­rents can get strong along that part of the coast­line. If you haven’t got your own gear you can always hire it from Whyal­la Div­ing Ser­vices.

Top tip: Pre­fer to see these majes­tic won­ders with­out get­ting a foot wet? There’s also two glass-bot­tomed boat expe­ri­ences you can try.

Do the cut­tle­fish care that you’re there?

The sheer size and quick colour-chang­ing behav­iour of the cut­tle­fish can be intim­i­dat­ing at first, but after a few min­utes you realise they only have one thing on their mind – find­ing a mate!

If you’re care­ful to move slow­ly, you can get up close with­out dis­turb­ing the cut­tle­fish. They seem obliv­i­ous to peo­ple and are focused on breeding.

But remem­ber to respect their space – look but don’t touch. If they react to your pres­ence, ensure your retreat. After all, its next years pop­u­la­tion that are being pro­duced at this time.

Are cut­tle­fish safe to swim near?

Snorkelling is safe along Point Low­ly and Stony Point, but you do need to be care­ful when enter­ing water over rocks and boul­ders, as they can be unsta­ble and slippery. 

Its also impor­tant to ensure that you fol­low local safe­ty sig­nage and direc­tions – only snorkel or dive with­in the safe­ty zone at Stony Point, go with a bud­dy and keep an eye out for boats and oth­er hazards.

Top tip: You can some­times find cut­tle­fish in less than a metre of water.

If you’d rather learn about the under­wa­ter crea­tures hang­ing out in SA’s waters from the com­fort of dry land, check out our blogs about sea drag­ons, blue dev­il fish and squid.

Learn more about the sci­ence, stats and con­ser­va­tion of these giant cut­tle­fish — Giant Autralian Cut­tle­fish | Great South­ern Reef 

Edu­ca­tion­al Resources

Are you an edu­ca­tor want­i­ng to incor­po­rate Giant Aus­tralian Cut­tle­fish learn­ing in the class­room? Check out this new resource from our friends at the Great South­ern Reef: Inter­ac­tive Les­son Series: Giant Aus­tralian Cut­tle­fish | Great South­ern Reef

(Main image cour­tesy of Jamie Hicks)

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