Otolith shape analysis as a tool for stock discrimination of forkbeard (Phycis phycis) in the Northeast Atlantic

The stock structure of forkbeard, Phycis phycis, in the Northeast Atlantic is still unknown. The knowledge of the stock structure of a species is essential to effectively assess the stock and manage fisheries. Otolith shape analysis has been successfully applied in stock identification using the elliptic Fourier analysis. This method was used to evaluate the presence of possible differences in otolith shape of forkbeard caught off the mainland Portugal, and Madeira and Azores archipelagos. A total of 221 otoliths from specimens ranging between 40.0 and 58.7 cm total length were analysed. The multivariate analysis of variance (MANOVA) performed on the otolith normalised elliptic Fourier descriptors (NEFDs) revealed significant differences for area, sex and interaction between both. In the canonical discriminant analysis, an overall classification success of 93.9 and 87.5% was achieved for females and males, respectively. These results suggest the usefulness of otolith shape analysis for stock differentiation of forkbeard in the Northeast Atlantic and seem to indicate the existence of more than one stock unit in these waters.