|Sea sense: log 3 Cuttlefish|
READING FROM THE CUTTLEBONES
Walking the winter beach, I collected these two cuttlebones; one slim and the other more round, both about 70mm in length. Cuttlebones are buoyancy devices found inside cuttlefish. (Here’s a great diagram of their internal anatomy.) These are likely to be from two species of cuttlefish, marine animals, relatives of the squid (who don’t have cuttlebones) and the octopus. They’re members of a lively and intelligent clan in the larger group known as Molluscs, which include snails and bivalves such as mussels and clams.
On the reverse of the slim cuttlebone are three long ridges, which are a characteristic of the Rosecone Cuttlefish (Sepia rozella).
But back to the cuttlefish. Whatever the size of the cuttlebone you find on a beach, it’s generally the remains of an animal that only lives for one or two years. The young hatch, looking like miniature adults and begin feeding and growing a body which is almost entirely pure muscle, all protein.
In contrast to the many marine animals who change sexes with age or size, cuttlefish have separate males and females, who stay that way for their entire lives. The population comes together in pairs to mate during the months of May through August. The females lay their small eggs on hard surfaces of reefs and then they die. The males die at the end of their breeding effort.
Most of the mating grounds are unknown, but at least two places in identified as important ones in Australia. A species known as Giant Cuttlefish (Sepia apama) come inshore at a bay between Wyalla and Lowly Pt, in South Australia and at Wollongong, NSW. (Here's the Australian Museum record for Sepia apama.) This cuttlefish can be up to a metre in size.
Oddly enough the new marine park proposal doesn’t include this area. The cuttlefish are threatened by a new BHP desalination plant for the Olympic Mine. There are supporters worldwide calling on State and Federal government to ensure this area is protected.
POPULATION & ECOLOGY
Recent studies of these giant Sepia apama find there are five populations from Ningaloo to Moreton Bay. They may have the whole ocean to roam, but they don’t. Two populations are along NSW, which has me wondering if the ones that breed and die around Wollongong are all one population. This could mean that there is another population in northern NSW. Where would they be mating? Has anyone noticed anything?
THEIR RECENT HISTORY & OUR FUTURE
The deep history of cuttlefish goes back millions of years. More recently, human impact is a major consideration. Around the world, some squid populations have collapsed. The NSW wild fisheries research programme says that the status of our populations is uncertain. The Australian Sustainable Seafood Guide says cuttlefish, squid and octopus populations are robust but more information is needed. Pollution is also an issue. Who do you know is out there counting eggs and hatchlings?
Or perhaps you want to tell a story to inspire the kids or the grand kids? Our unsung heroes are the people figuring out the taxonomy of cuttlefish and other species. Among the explorers of the 21st century are those mapping cuttlefish populations and figuring out their secret lives.
And the greatest political leaders? They will be those who understand and act on these ecologics.