SIZE-WEIGHT RELATIONSHIPS OF THE BIGEYE TUNA (THUNNUS OBESUS) FROM NORTH ATLANTIC AREAS USING LINEAR AND NON-LINEAR FITS

Linear and non-linear fits of 1501 observations of size (FL cm) and live-weight (RW kg) of bigeye (Thunnus obesus) obtained in the NE Atlantic over recent years were tested. Results were compared among themselves and with those considered as a reference for this species-stock. The equations obtained from linear and non-linear fits (RW=5.29919E-05 * FL 2.8211264 and RW=6.0568-05 * FL 2.79379, respectively) showed a minor difference in predicting individual weight by size class. The non-linear fit parameters slightly increase the predicted mean weight of the whole sample in around +0.2% compared to the linear fit parameters suggesting that the type of fit would have a negligible impact on both the predictive individual mean weight and the whole sample mean weights. The comparison of results obtained with both types of fits versus the equation considered as a reference also showed minor differences in the estimated average individual weight from size. However, the average weight of the whole sample analysed would increase by over 4% in relation to that obtained when using the reference equation. A review of the literature on size-weight relationships for this species is also included suggesting a considerable diversity of results probably due to diverse factors that are discussed.