Use of otolith shape to inform stock structure in Patagonian toothfish (Dissostichus eleginoides) in the south-western Atlantic

Abstract

An analysis of patterns in otolith shape is an effective tool for discriminating among fish stocks. Otolith shapes of Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (D. mawsoni) were investigated for geographic variability within seven regions across the Patagonian Shelf, and South Georgia and the South Sandwich Islands (SGSSI). Otolith shape was characterised by its elliptical Fourier coefficients (EFCs), corrected for fish length before being analysed, using multivariate methods. Non-metric multidimensional scaling analysis suggested the following three main groupings: Patagonian Shelf, SGSSI, and the third for Antarctic toothfish. This result was supported by ANOVA-like permutation tests, indicating significant (P<0.001) differences in otolith shape among these three groupings. Linear discriminant analysis (LDA) cross-validation analyses of the EFCs resulted in otoliths being correctly classified to the sampling region from which they came, with an accuracy ranging from 78.95 to 100%. LDA cross-validation analyses on sampling regions within SGSSI and the Patagonian Shelf were able to classify individuals back to their sampling region with an accuracy of greater than 89.74 and 78.95% respectively. These results have provided some alternative insights into the stock structure of Patagonian toothfish across southern South America, South Atlantic and SGSSI.