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Sepia apama (Family Sepiidae)

Giant Cuttlefish, Australian Cuttlefish

Distribution:

Southern Australia from Brisbane in the east and Shark Bay in the west, south to Tasmania (QLD, NSW, VIC, TAS, VIC, SA, WA).

Features:

The Giant Cuttlefish is the largest cuttlefish in the world, males reaching a total length of 1 metre. The cuttlebone reaches up to 50 cm long. They have a fin along the length of the body. There are eight arms and two retractable feeding tentacles. The arms and clubs at the tips of the feeding tentacles have numerous suckers, each armed with a horny, toothed rim. They are excellent at camouflage and can push up branched flaps of skin all over their body. This species is recognised by two rows of triple flaps above each eye. The cuttlebone of larger animals has no spine, instead having a wide shelf-like flange round the rear tip. Males have wide banner-like webs off the lower arm pairs.

Ecology/Way of Life:

Giant Cuttlefish live in coastal waters to around 100 metres. They typically live on rocky reefs and amongst kelp forests but can also occur in seagrass meadows. Their excellent camouflage helps them stalk their fish and crustacean prey while hiding from dolphins, seals, sharks and other large predatory fish. They are generally day active but have been observed feeding at night. Buoyancy is maintained by the gas-filled cuttlebone.

Courting consists of males doing dramatic displays where they extend the banner-like webs on their arms and pulse regular moving zebra stripes along their body. Males tend to establish a territory outside the best caves or crevices for egg laying. Females search for the best egg-laying sites and the successful males will mate with females that choose their site. Territorial males have display combats with challengers, pairing up for intensive colour changes and bluff postures. If displays do not work, fights will deteriorate to biting. Many males show battle scars.

At one site in South Australia, near Whyalla, the scarcity of rocky reef appears to concentrate the breeding cuttlefishes resulting in massive breeding aggregations. Thousands of cuttlefish gather each year to breed, fight, mate and lay eggs on several small reefs. One unusual reproductive strategy has been found at this site. Small males take on the disguise of females and sneak past the bigger territorial males. When the territory owner is off fighting challengers, the sneaker male quickly mates with the female. Eggs are large and white with pointed tails hanging off them. They are laid in large numbers deep in crevices and take up to several months to hatch.

Interaction with Humans/Threats:

Giant Cuttlefish are collected in relatively low numbers as bycatch in trawl fisheries. Recreational fishermen target this species on line and using spears. They are used for human consumption and as bait. The Whyalla breeding aggregation in South Australia has been targetted in the past and moves are currently underway to protect this unique breeding site as a marine sanctuary.

Further Reading:

Whyalla website: http://www.cuttlefishcapital.com.au

Norman, M.D., J. Finn and T. Tregenza. 1999. Female impersonation as an alternative reproductive strategy in giant cuttlefish. Proceedings of the Royal Society, London, 266: 1347-1349.

Hall, K.C. and R.T. Hanlon. 2002. Principal features of the mating system of a large spawning aggregation of the giant Australian Cuttlefish Sepia apama (Mollusca: Cephalopoda). Marine Biology, March issue.

Norman, M.D. 2000. Cephalopods: A world guide. ConchBooks, Hackenheim, Germany.

Topics: Camouflage

Acknowledgments:

Text and photograhs by Mark Norman, Museum Victoria.

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