Australian Giant Cuttlefish

Sepia apama
Image by Richard Ling.

Despite their common name, cuttlefish aren’t fish, but cephalopods in the mollusc family (which includes octopus and squid).

The giant cuttlefish is among the biggest in the world, growing to a whopping 1 metre and weighing up to 10kg. They have two methods of swimming. When speed is required the cuttlefish utilises backward jet propulsion by sucking water into their body then forcefully ejecting it through a funnel. Otherwise they swim by hovering with gentle undulations of their lateral fins (often referred to as a skirt).

While stalking fish and crabs the skin changes colours – tiny elastic pigment sacs expand and contract plus the raised skin flaps help it change texture for a more effective camouflage. Two long tentacles shoot out in a whip like motion to seize the prey, then the other ‘arms’ are used to immobilize it for consumption. The giant cuttlefish hunts other smaller molluscs, including other cuttlefish, as well as shrimp and crabs. Hard shells pose no problem for the bird like beak hiding among the many tentacles nor their tooth lined tongue.

Mating season is the start of winter and larger males will guard smaller females during this frantic time. As a result males can become highly territorial and aggressive. Sadly all this energy spent in breeding and laying eggs means once the season is over most cuttlefish die. The eggs are individually laid in their protective onion-shaped casings and attached to the underside of flat rocks in tight spaces. The average lifespan is 2 to 3 years and as a consequence you will most often spot the giant cuttlefish resting as it channels most of its energy into growth.

Known to be highly inquisitive and attracted to bright colours it’s not uncommon to see them following divers.