Giant cuttlefish

The giant cuttlefish (Ascarosepion apama), also known as the Australian giant cuttlefish, is the world's largest cuttlefish species. It can grow up to 50 cm (20 in) in mantle length and even up to 100 cm (39 in) when its tentacles are stretched out. These amazing creatures can weigh more than 10.5 kg (23 lb).

Like all cuttlefish, the giant cuttlefish has eight arms and two feeding tentacles. They also have blue blood and three hearts! One special thing about cuttlefish is that they can change color very quickly using cells called chromatophores. This helps them hide from predators or communicate with each other.

These cuttlefish live in the temperate and subtropical waters around Australia, from Brisbane in Queensland all the way to Shark Bay in Western Australia and Tasmania. They are found near rocky reefs, in seagrass areas, and on sand and mud seafloor as deep as 100 m (330 ft). One group of these cuttlefish in the Upper Spencer Gulf is very well studied and has become a popular spot for tourists to see these fascinating animals.

Physiology and biochemistry

The giant cuttlefish, also known as the Australian giant cuttlefish, is the largest kind of cuttlefish in the world. It can grow up to 50 cm (20 in) in mantle length and up to 100 cm (39 in) including its outstretched tentacles. These cuttlefish can weigh over 10.5 kg (23 lb). Like all cuttlefish, they have eight arms and two feeding tentacles, blue blood, and three hearts.

Giant cuttlefish live close to the shore and near the sea floor. They eat mostly crustaceans and fish. They can change color and patterns very quickly using special cells in their skin. This helps them hide from danger or communicate with each other. They can also change the texture of their skin to look like rocks, sand, or seaweed. These cuttlefish rest most of the day, hiding in crevices, and only spend a small amount of time looking for food. They travel long distances to breed during special times of the year.

Habitat

The giant cuttlefish lives in the warm waters around Australia, from Brisbane in Queensland all the way to Shark Bay in Western Australia and even down to Tasmania. You can find them near rocky areas, in seagrass fields, and on sandy or muddy ocean floors, as deep as 100 metres below the surface.

Lifecycle and reproduction

Giant cuttlefish live for one to two years. Breeding happens when southern winter starts. Males change their colors and patterns to attract females. Females can mate with more than one male and prefer to use genetic material from males stored in special packages rather than directly from sperm. They attach their eggs under rocks in caves or crevices, where the eggs hatch in three to five months.

After mating and laying eggs, the giant cuttlefish die. They do not handle low oxygen well and can struggle without food. During the breeding season, they do not eat and slowly weaken until they die. These cuttlefish usually breed in pairs or small groups, laying eggs in caves or rock crevices. Sometimes, large groups form, with hundreds of thousands gathering along rocky reefs between Whyalla and Point Lowly in the Upper Spencer Gulf. After hatching, young cuttlefish leave the area, but little is known about what they do next. Adults return to the same place the next winter or might wait an extra year.

Predators

The Australian giant cuttlefish is eaten by several sea animals. In South Australia's Spencer Gulf, Indo-Pacific bottlenose dolphins use a special way to take away the ink and cuttlebone before eating the cuttlefish.

Long-nosed fur seals (Arctocephalus forsteri) are also known to eat them, and yellowtail kingfish (Seriola lalandi) eat various cephalopods, including cuttlefish. There are ecological worries about how fish farms might affect wild species like the giant Australian cuttlefish and their eggs in Spencer Gulf.

Conservation status

In 2009, the giant cuttlefish was listed as Near Threatened on the IUCN Red List of Threatened Species. This happened because scientists noticed that the number of these cuttlefish was going down at that time.

Upper Spencer Gulf population

See also: Cuttlefish Coast Sanctuary Zone

The giant cuttlefish is the world's largest cuttlefish. In the upper Spencer Gulf, hundreds of thousands of these amazing creatures gather each year between May and August to breed. This area is the only known place where so many giant cuttlefish come together at one time, making it a special spot for divers and nature lovers.

Scientists have found that these cuttlefish have two different ways of growing up. Some grow quickly and are ready to breed in just seven to eight months, while others take two years to grow up. During breeding time, big males protect the females, while smaller males try to sneak in to breed by looking like females. This unique behavior helps scientists learn more about these fascinating animals.

Conservation

An effort was made to protect this special group of cuttlefish, but it was decided they were not different enough to need special protection under the law. However, scientists later found that these cuttlefish are genetically unique from others in the area.

The Upper Spencer Gulf Marine Park has sanctuary zones to help protect these cuttlefish, including the Cuttlefish Coast Sanctuary Zone, which was added to a special list of important places in 2023.

Commercial fishing

Before the mid-1990s, fishing for these cuttlefish was common, but catching too many caused problems. Rules were put in place to help the population recover, and for a time, fishing was limited or stopped in some areas.

Population decline

The number of cuttlefish dropped a lot between 2001 and 2008, partly because of illegal fishing and natural changes. Efforts were made to protect them further, and by 2021, their numbers had started to grow again.

Population estimates

• Figure '0' is used to represent years in which surveys did not occur, and no estimation was made.
• 1999–2017 data sourced from SARDI
• Approximate 2016 population estimate was published in the Whyalla News and approximate 2017 numbers were first published by PIRSA. A slightly larger estimate for the 2017 season was published in 2018 by the ABC (reflected in the graph).

Effect of local industrialisation

See also: Port Bonython

The area where these cuttlefish gather is close to places that release pollution into the water. This includes factories, fish farms, and other industrial activities. Scientists worry that too many nutrients in the water, from things like factory waste and fish farms, could hurt the cuttlefish.

There have also been concerns about oil spills and plans for new desalination plants, which could change the salt levels in the water. These changes might harm the cuttlefish, especially their babies. Communities have worked to protect these areas from new developments that could threaten the cuttlefish.

Nutrient enrichment

Northern Spencer Gulf naturally has low levels of nutrients. However, human activities, such as the Whyalla Steelworks and fish farming, add extra nutrients to the water. This can cause problems like eutrophication, which may affect the cuttlefish and other sea life.

Hydrocarbon pollution

In 1984, a hydrocarbon processing plant was built at Port Bonython. There have been two major contamination events at this site. In 1992, a large oil spill occurred when a tugboat pierced its hull during berthing. The effects of these events on the cuttlefish population are still unknown.

Seawater desalination

Plans to build desalination plants near the cuttlefish breeding grounds raised concerns because the extra salt (brine) released into the water could harm the cuttlefish. One such plant was planned but never built. However, smaller desalination plants now operate in the area, and new proposals exist that could threaten the cuttlefish habitat.

Port proposals

There are plans to develop new ports near the cuttlefish breeding grounds to support mining activities. Increased shipping traffic could disturb the cuttlefish, as they are sensitive to certain types of underwater noise. Community groups have formed to oppose these developments and protect the cuttlefish habitat.

In popular culture

Each year, an event called Cuttlefest is held to celebrate the giant cuttlefish gathering in the upper Spencer Gulf, hosted by the City of Whyalla.

In 2009, a special theatre show with large cutlefish puppets was part of the Come Out Festival, appearing in several places including Adelaide's Victoria Square and Whyalla. The show was created by D'Faces of Youth Arts and Snuff Puppets.

During the Adelaide Fringe Festival in 2012, a play called Sepia told a story set in Whyalla. In 2014, the festival featured a huge 13-metre-long puppet named Stobie the Disco Cuttlefish, with bright lights and music. In 2016, a photograph of the cuttlefish aggregation won a major photography award.

The giant cuttlefish gathering at Point Lowly also inspired a retro computer game named Cuttle Scuttle.