Exploring the use of Fourier transform near infrared spectroscopy for aging Newfoundland and Labrador Atlantic cod (Gadus morhua)

Fourier transform near-infrared spectroscopy (FT-NIRS) is a new tool for aging fish otoliths which has been shown to be potentially faster than counting otolith annuli (traditional aging) while having similar accuracy and precision. We investigated the use of FT-NIRS for aging Atlantic cod (Gadus morhua) otoliths from North Atlantic Fisheries Organization (NAFO) Divisions 2J, 3K, 3L, 3N, 3O, and 3Ps. Two types of calibration models (partial least squares (PLS) regression and principal component analysis combined with multinomial regression) were fit between traditional age estimates for otoliths and either their full FT-NIR spectra or an informative region of their spectra. Model fits were compared across calibration model types, portion of spectra used, and between models fit to individual versus all NAFO Divisions combined. A time-cost analysis comparing traditional aging versus combinations of FT-NIRS and traditional aging was performed. Good model fits (root mean square error ≤ 1; adjusted-R² ≥ 0.85) were generally achieved for at least one calibration model fit across all NAFO Divisions and for individual Divisions. PLS and multinomial calibration model performances were very similar for models fit across all NAFO Divisions, but varied due to small sample sizes for individual Divisions. Portion of the FT-NIR spectra used to fit models had the least impact. Time-cost analysis suggested that labour savings of 23 % (6 calibration models) to 40 % (1 calibration model) could be obtained. Our results show the FT-NIRS provides reliable age estimates for Atlantic cod with similar accuracy and precision to traditional aging while also providing labour cost savings.