The department’s Executive Director of Research Dr Rick Fletcher said the fish skeletons had been examined by Fisheries’ researchers since 1990 to determine their ages, as part of a ‘weight of evidence’ assessment approach to determine if their stocks are being fished sustainably.
“The fish frames have been donated both by recreational fishers through the department’s Send Us Your Skeletons programme and by the commercial fishing sector,” Dr Fletcher said.
“By donating fish frames, the WA fishing community has enabled us to reach this milestone and this has helped us tremendously with our work.”
Researchers need to age about 500 otoliths to establish an age structure (the number of fish of different ages) for each fish stock for a single survey period.
Dr Fletcher said preparing and examining the otoliths was painstaking work.
“Each tiny ear bone is set in resin to stop it chipping, sliced thinly into a cross-section with a diamond cutter and placed under a microscope, with the image projected onto a computer screen,” he said.
“Research staff can then count growth rings, similar to those on a tree trunk, to determine the fish’s age. We have dedicated staff members who carry out this work with enormous skill and patience.
“Their work is crucial in giving us a comprehensive understanding of the age structure of some of the State’s most important finfish species, including Australian herring and Western Australian dhufish.”
Otoliths can also be chemically analysed to trace where a fish has lived during its lifetime and to find other valuable information. The otoliths in the department’s archives are now also being accessed by researchers outside the department to support external research projects.
Top image: Fish ageing technician Lee Higgins, holding a dhufish frame, is part of the Fisheries research team that counts growth rings in fish ear bones to determine their age.