Passions Of Paradise Catamaran Sailing the Great Barrier Reef

Cassandra Rigby PhD candidate

Title: Life history of deepwater chondrichthyans in the Great Barrier Reef: non-lethal ageing

The Great Barrier Reef has one third of its area in waters over 200 metres deep, yet we know very little about the lives of the sharks and rays that live in these deep waters. This is also true of the deepwater sharks and rays around the world; even though half of the world’s 1200 species of sharks and rays live in deep water, information on their age, growth and reproduction is scarce and many groups remain poorly known. Some of the known species are already listed on The IUCN Red List of Threatened Species as critically endangered and vulnerable. Studies so far have found that these deepwater sharks and rays generally grow more slowly, have fewer young and are longer lived than their shallow water relatives making them more vulnerable to fishing and slower to recover. It is important we learn about the age, growth and reproduction of the sharks and rays living here in the deep waters of the Great Barrier Reef so they can be managed and conserved.

We cannot dive to the depths needed to sample these animals, so the sharks and rays for this project are collected on board commercial deepwater trawl vessels which occasionally catch them unintentionally while fishing for prawns. This project had a very successful first sampling trip where 7 species were collected that are little known and that only occur in Queensland. As well as finding out their size when they start breeding, how many young they have and how long they live, I will also investigate a new and potentially non-lethal way of finding out how old they are. This uses wavelengths of light to count the ‘bands’ on the hard parts of the sharks, similar to counting rings on trees. If successful it is possible that hand held machines could be used to age live sharks and rays at sea by ‘scanning’ spines, thorns on the outside of their body and/or their skin to determine their age. This would be a great step forward in being able to gather information needed on the lives of these sharks and rays without harming them. The information gathered in this project on their age, growth and reproduction will be used to assess the status and vulnerability of these amazing Great Barrier Reef deepwater sharks and rays. This project is being undertaken at the Centre for Sustainable Tropical Fisheries and Aquaculture, School of Earth and Environmental Sciences, James Cook University.

< Back To News