Progress towards validation of ageing of Dissostichus eleginoides using otoliths

During tagging programmes for Dissostichus eleginoides at Heard and Macquarie Islands, fish have been treated with strontium to mark their otoliths for validation of subsequent age estimation. Otoliths from 69 fish that were at liberty for at least 350 days were eventually examined. Results indicate that current methods for ageing D. eleginoides are appropriate: the number of observed annuli on the otoliths after the strontium mark was consistent with the time at liberty of the fish after marking.
Current and future work on age validation is designed to address outstanding problems with age determination in this species: investigating the accuracy of ageing small fish (< 5 years old); analysing otoliths from a range of fish that have been at liberty for > 1000 days; and developing techniques to analyse the daily marks at the centre of the otolith in order to pinpoint the position of the first annulus.