Where did all the cuttlefish go?

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Mike McRae ABC Environment 12 Oct 2013


Scientists are struggling with a mysterious disappearance of cuttlefish from South Australia's Spencer Gulf. One of the many questions they are pondering is whether it's all part of a natural cycle.

NESTLED IN THE APEX of South Australia's Spencer Gulf, Point Lowly is noteworthy for its historic lighthouse, a small sandy beach and a view of Port Bonython's hydrocarbon processing plant. Just offshore, the rocky sea floor has a very different reputation. It's where a unique population of the world's largest cuttlefish gathers to spawn.

Nobody would confuse one for the mighty Kraken, but the giant Australian cuttlefish (Sepia apama) is nonetheless a monster amongst molluscs. In some populations off Australia's eastern coast, its body (mantle length) can exceed half a metre, while the animal's mass has been recorded at a hefty 12 kilograms.
While the weight of animals in the Point Lowly population rarely exceeds a kilogram, it's their sheer numbers during winter spawning that has drawn scientists, recreational divers and tourists to this spot since the phenomenon was documented in the 1990s. The giant cuttlefish may be endemic to much of the southern Australian coastline, but Point Lowly's population is unique in exhibiting this annual event. At a density of one cuttlefish per square metre, in full psychedelic sexual display (males) or mating or egg-laying, the spectacle is nature at its most brilliant.

Over the past decade, however, population numbers of the giant Australian Cuttlefish (Sepia apama) have declined, dropping by an estimated 90 per cent from around 183,000 individuals in 1999 to 18,530 in 2012. The latest surveys in the area have shown the decline has continued from 2012 to 13,500 individuals in 2013, although the rate of decline appears to have slowed down from previous years.

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