The way to a crayfish’s age is through its stomach: new research confirms groundbreaking method for ageing crustaceans

A radical method to determine the age of crustaceans using their stomach bones (called ‘ossicles’) has been verified by a new study from Southern Cross University’s Marine Ecology Research Centre, paving the way for future age validation studies and improved sustainable management of crustacean fisheries.

The team, led by post-doctoral research fellow Dr Jesse Leland, Dr Daniel Bucher, both from the Marine Ecology Research Centre (MERC), and Dr Jason Coughran, formerly with SCU and now with Sheridan College in Perth, first identified the potential for direct ageing studies in 2011, but their latest publication in the open-access Journal PLOS ONE, ‘Direct age determination of a subtropical freshwater crayfish (Redclaw, Cherax quadricarinatus) using ossicular growth marks’, is taking this important new field a step further.

“This study used a relatively short-lived and well-studied species of freshwater crayfish (the Redclaw) to see if the previously noted growth marks correspond with the known longevity of the species,” said Dr Leland.

“We have clearly demonstrated for the first time that crustacean ossicles retain a record of past events (like seasonal temperature changes) that occurred during the animal’s life – which was previously thought impossible. This means that we can now prove that our age estimates are accurate.

“This important proof-of-concept study has opened the way for using the method on other longer-lived animals like rock lobsters and deep sea crabs. One reviewer of our paper noted that he cannot wait for the ‘dogma shift’ from less-than-precise methods to the realisation that direct age determination is now possible.”

The ability to determine the age of harvested animals is central to assessing whether fishing levels are sustainable.

“This is because growth, reproduction and natural mortality are all directly linked to an animal’s age. In the past, the ages of crabs and lobsters could only be estimated from indirect methods, like tag-and-recapture, which can inform scientists of approximate age – give or take a few years – but the accuracy of such methods is limited,” Dr Leland said.

“However, our research has shown that similar to fish or trees, crustacean age is recorded in bony ‘ossicles’ contained in their stomach and that this information can be accessed relatively easily.”

Marine ecologist Dr Daniel Bucher said the study was an important turning point for the fisheries industry.

“Several research groups around the world are taking up the method, with each new publication really increasing the existing knowledge base. This of course makes for an exciting time in a new research field,” said Dr Bucher.

“This is the first published study to demonstrate effectiveness using a sub-tropical freshwater species, which extends the applicability to many other Australian regions.”

The findings are also a welcome breakthrough for conservation efforts.

“Around the world, freshwater crustaceans are increasingly being recognised as a highly imperilled group of animals,” said freshwater ecologist Dr Jason Coughran.

“Research on these animals has been hindered by a lack of accurate age information. Tagging studies indicate that some freshwater crayfish are very long lived, perhaps 40 years or more. The potential to definitively establish longevity now promises to re-shape the broader work on protecting these species.”

MERC researchers, along with other government and academic fisheries researchers, are currently applying the method to four Australian rock lobsters (Eastern, Western, Southern and Ornate Rock Lobsters) and three crab species (Giant, Crystal and Mud Crabs) in a two-year project funded by the Fisheries Research and Development Corporation (FRDC).

“The ultimate aim is to use the method for age-based stock assessments within major Australian fisheries, but while we now know that it works there is still further research needed to explain the processes and mechanisms involved,” said Dr Leland.

Southern Cross University will be hosting a crustacean ageing workshop next year as part of the FRDC project, with fisheries scientists and collaborators from around the country expected to attend.
Photo: A sectioned ossicle from a Redclaw crayfish aged at 3 years plus, with growth marks indicated by black dots (Credit: Jesse Leland).