Australian Giant Cuttlefish (Sepia apama)

Giant cuttlefish is the largest cuttlefish species in the world. They are found primarily on the southern coasts of Australia. They are quite well-known for their color changing abilities and inquisitive behavior. It is also referred to as the Australian giant cuttlefish.

Scientific Name

The scientific name for this species of cuttlefish is “Sepia apama”.

Description

Here is a brief description of these cuttlefishes.

Mantle length: The mantle length of these fishes can go up to 50 centimeters.

Weight: They can weigh up to 10.5 kilograms.

Head: Giant cuttlefish has a big, flat and broad head with two large eyes.

Eyes: The eyes have a very complex structure and are quite well developed.

Mouth: The mouth is parrot-like with a beak, a jaw and a rasping tongue.

Tentacles: There are 8 tentacles lined with suckers and 2 extendable tentacles that emerge from the head. The 2 extendable tentacles are used for feeding and they retract into pouches that are located between bases of 3rd and 4th arm pairs.

Fins: They have got thin fins along their sides.

Gills: They have gills to breath like a fish.

Skin: They have a unique type of skin that can change colors for camouflaging. A dense layer of chromataphore cells line their body.

Cuttlebone: Their bodies are made up of a spongy, chalk-like, internal shell known as a cuttlebone. It is this cuttlebone that gives them their shape.

Heart: These fishes have 3 hearts that pump blue blood.

Behavior

Check out the primary behavioral characteristics of the giant cuttlefish.

These fishes are believed to be primarily diurnal.
Giant cuttlefishes spend most of their days resting and spent very little time in foraging.
They show exceptional activeness only during the spawning season.
These fishes are neritic demersal by nature, which means that they prefer living in the bottom of the coastal waters.
They are attracted to brightly-lit objects that emit fluorescent colors.
When they have to eat, they use their two larger tentacles to capture a prey and then holds on to it with its arms while consuming it.
The males exhibit territorial behavior during the mating season.

Diet

Giant cuttlefishes are carnivorous, voracious and opportunistic predators feeding mostly on crustaceans and fishes such as crabs, prawns, tommy roughs, reef fish and small fish.

Distribution

These creatures are native to the southernmost coasts of Australia, from Brisbane, Queensland to Shark Bay, Western Australia, Coral Bay, northern parts of South Wales, and Tasmania.

Habitat

The giant cuttlefish spends most of its time around oceans, coastal waters, estuaries, seagrass beds, rocky reefs, as well as in sandy and muddy seafloor around the depth of 100 meters.

Predators

Giant cuttlefishes are mostly eaten by the bottlenose dolphins, sharks and seals.

Adaptations

The giant cuttlefish has developed several interesting adaptations that enable them to survive in their aquatic habitat, protect themselves from the predators and perform smooth functioning of various tasks such as swimming and mating. The various adaptive features of these fishes have been described below:

Giant cuttlefishes have neutrally controlled cells such as the chromataphore organs, the iridophores and the leucophores that allow them to change their skin color in the twinkling of an eye.
The color-changing abilities play an important role as a defense mechanism and are also useful while mating.
They can raise the elaborate papillae present on their skin to resemble a rock, the sand or seaweed.
These fishes also have ink sacs from which they can eject ink to confuse and disorientate their enemies.
They have hard beaks which allow them to crush their food easily.
They can control the buoyancy of their bodies at will by pumping water from their bodies to change volume.
The giant cuttlefishes can escape very quickly if a predator is nearby. This they do by sucking in water into their body cavities, which allow them to propel themselves in the reverse direction.

Breeding Season

The breeding season for these fishes lasts from the months of April to August, i.e. the southern winter.

Reproduction

Every year hordes of giant cuttlefishes will migrate to the shallow waters of Whyalla in South Australia in order to mate. Prior to mating, the male and the female cuttlefish can be seen in an embrace with their tentacles entwined together and performing a mating dance. The male cuttlefishes abandon their generally normal cryptic coloring and try to attract the females by rapidly changing bright color patterns and striking appearances. Cuttlefishes mate in pairs and a larger male automatically has more advantage than a smaller male. The smaller male has to put in a greater effort to mate. They change their appearance and colors to look more like the females. As the smaller male advances towards the female, the larger male gets distracted and it is during this time that the female allows the smaller male to mate. The smaller male cuttlefish swims away once mating is complete.

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The females are polyandrous, choosing to mate with more than one male in its lifetime. They have more frequently been found to reproduce by using the male genetic material that is deposited in spermatangia than in the sperm receptacles directly. They lay hundreds of eggs which are then attached to undersides of rocks in crevices and coral caves located at a depth of 2 to 5 meters. The eggs will hatch after about 3 to 5 months.

There is not much interbreeding between the populations of giant cuttlefishes. Hence the various populations found in different parts of Australia are not necessarily taxonomically distinct.

Life Cycle

Giant cuttlefishes are semelparous creatures; i.e. they mate only once in a lifetime. The female dies soon after mating and laying eggs. They have poor anaerobic capability when compared to most other aquatic invertebrates and absence of food leads directly to catabolism. The female fasts during the breeding months and as they cannot catabolize more than half of their body’s weight, they lose their physical condition soon and die eventually. Loose spawning aggregations are formed throughout their breeding range that rarely exceeds 10 individuals in any single location. The juveniles leave spawning grounds soon after they hatch. Not much is known about their subsequent lifestyle and activities.

Life Span

The giant cuttlefish stays alive for only 2 to 3 years.

Conservation Status

Over the years, the population of giant cuttlefish has dropped significantly. This was due to a variety of factors, namely, habitat destruction due to pollution, predation by dolphins and hunting by humans. The short life span of these creatures was also another major contributor to their lowered numbers. Fishing for giant cuttlefishes was restricted from 1998, as an endeavor to protect them. The numbers of these fishes have increased since then. However, the giant cuttlefish has still been listed under the category of “Near Threatened” by the IUCN.

Interesting Facts

Here are some of the most interesting facts about these fishes:

The giant cuttlefish is one of the most important marine tourist attractions in this area of the world, primarily due to its interesting food habits, breeding behaviors, swimming abilities, mating styles and self-defense mechanisms.
Although the giant cuttlefish will spend most of its time hiding behind rocky crevices, they will come out to investigate when approached by sea divers. They tend to follow divers who wear bright colored fins.
These fishes are colorblind but the photoreceptors of their eyes enable them to detect linear polarization of light.
The bioenergetics of the giant cuttlefish resembles that of an octopus more than a squid.
The cuttlebones of the giant cuttlefish are made up of calcium carbonate and helps in controlling buoyancy.