Age estimation of barramundi (

C Wright,O J Whybird,S Grauf,B B Wedding

doi:10.1071/mf20300

Abstract

The age of whole otoliths from barramundi (Lates calcarifer) obtained from the southern Gulf of Carpentaria were estimated using Fourier transform near-infrared (FT-NIR) spectroscopy. Otoliths from 1716 barramundi collected in 2006, 2009 and 2012–2015 were used in this study. Partial least-squares regression models (PLS-R) and multiple linear regression models (MLR) were developed from the diffuse reflectance spectra and the age was obtained from traditional sectioned otoliths. Calibration models were built up over consecutive years (2012–2015) by using a subset of the samples and used to predict the age of the remaining samples and samples from the following year. Results suggest that when seasonal (temporal) variability is incorporated into the calibration model, FT-NIR has the ability to predict barramundi age (validation R2 ranged from 0.73 to 0.78; RMSEP ranged from 6.92 to 7.64 months). The predicted age class was within 1 year of the reference age in over 96% of the samples. These models were also able to predict the age of otoliths from 2006 and 2009, which were retrieved from long-term storage (validation R2 ranged from 0.77 to 0.84; RMSEP ranged from 8.66 to 10.88 months). The results from this study have shown the potential for barramundi from the southern Gulf of Carpentaria to be aged quickly and accurately by using FT-NIR.

Highlights

Data such as fish length, age and gender are collected annually as part of routine biological monitoring by many agencies
The results presented in the present study are an extension of those from Robins et al (2015) through the investigation of the temporal effects on barramundi ageing results from otoliths collected from 6 years over a 9-year period from the southern Gulf of Carpentaria
Two samples were excluded from the 2012 dataset as they had a reference age of 148 months, which was outside the predetermined range of the calibration model (#120 months)

Summary

Introduction

Data such as fish length, age and gender are collected annually as part of routine biological monitoring by many agencies. The otoliths are primarily constructed of calcium carbonate and protein, which form concentric layers as the fish grows (Degens et al 1969; Campana 1999; Hale and Swearer 2008) The periodicity of these concentric rings may be related to daily, seasonal or annual cycles and are thought to occur as a result of changes in many factors, including photoperiod, temperature, seasonal feeding and growth rates (Radtke and Shafer 1992; Secor et al 1995; Chang and Geffen 2013). An otolith is age estimated by blocking it in resin, cutting a thin section (,250– 500 mm), and the section is mounted on a microscope slide for viewing under a microscope (Secor et al 1992; Winkler et al 2019) This approach is currently the most accepted method, it requires practice and experience to obtain accurate age estimates, is labour intensive, time consuming and expensive. It is estimated that over 60 000 otoliths are collected and aged in Australia each year (Robins et al 2015), New Zealand ages between 30 000–40 000 annually (Moore et al 2019), whereas in the federally managed waters of Alaska, over 352 000 ages were estimated between 2009 and 2018 (Helser et al 2019)

Methods

Results

Conclusion