Massive decline in cuttlefish numbers in their usual spawning grounds in South Australia has mystified scientists, who are now looking to track the famous annual migration of the cephalopods in and around the State's Spencer Gulf.
Scientists from the University of Adelaide are using parasite tracking and other biological tools to identify discrete populations of the Great Australian Cuttlefish (Sepia apama), gaining a rare insight into how species evolve over time, and providing vital information for natural resource management.
“There are likely to be five subpopulations of Great Australian Cuttlefish across the species range,” said Bronwyn Gillanders, Professor in aquatic ecology at the University of Adelaide.
Monitoring the parasites that live on cuttlefish could be the most useful tool for identifying the different populations, as each species of cuttlefish is thought to host its own genetically unique parasite. Recent PhD graduate Dr Sarah Catalano performed research focusing on an unusual worm-like parasite that is only found in cuttlefish and other cephalopods.
“Parasite genetics might be a more sensitive tool than looking at the cuttlefish themselves to distinguish whether different species or subspecies actually do exist,” said Professor Gillanders.
Another line of research to identify cuttlefish subpopulations focuses on their dietary preferences and unique beaked mouth, which is used by cephalopods to masticate their food before swallowing.
Professor Gillanders and her colleagues hope that by using multiple lines of evidence they will be able to find out whether the different groups of cuttlefish i are separate species or subspecies.
In particular, they would like to determine whether the spectacular breeding aggregations of Great Australian Cuttlefish that occur annually during May-August in the northern Spencer Gulf are confined to a particular subpopulation.
Although historically up to tens of thousands of cuttlefish have arrived in this period to breed, recently that’s not been the case.
“The numbers have been decreasing over many years – since the peak in abundance since the late 1990s, they’ve dropped in number by about 90%,” Professor Gillanders said.