Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

Is otolith magnesium a useful tool to support age estimation? (#49)

Angela L Russell 1 2 , Bronwyn M Gillanders 2 , Daniel D Johnson 1 , Matt Taylor 1 , Thomas C Barnes 1 3
  1. Port Stephens Fisheries Institute, New South Wales Department of Primary Industries, Nelson Bay, NSW, Australia
  2. Southern Seas Ecology Laboratories, School of Biological Sciences, University of Adelaide, Adelaide, South Australia, Australia
  3. Institute of Marine and Antarctic Studie, University of Tasmania, Hobart, TAS, Australia

Otolith (ear bone) microchemical analysis (or otolith chemistry) is an effective fisheries management tool to reconstruct environmental histories, infer natal origins, identify movement patterns, delineate stocks; and in more recent times to validate age estimates. Accuracy of age estimations is critical to stock assessments and monitoring of exploited populations, particularly where reductions to size structures occur due to fishing pressure. Elemental chemistry has been explored as an alternative means to validate age estimates and may be particularly useful in species whose otoliths are hard to age visually. We use Mulloway to demonstrate the relatively novel use of otolith chemistry to inform aging studies, as Mulloway growth increments are clear, generally easy to quantify with high repeatability, and incremental age estimates have previously been validated for Mulloway. Otolith Magnesium (Mg:Ca) is shown to be influenced by temperature in this species. Thus, we explored an alternative method to estimate age using counts of lifetime Mg:Ca oscillations, as a proxy for seasonal increment deposition to estimate annual age. Quantifiable comparisons in precision and repeatability among the traditional age estimation approach (i.e. visual counts of otolith growth increments) and the otolith chemistry approach were made. We discuss the challenges associated with this novel age estimation approach using otolith chemistry, in turn, contributing to future otolith chemistry-based life history studies.