Morphometric variation among anchovy (Engraulis encrasicolus, L.) populations from the Bay of Biscay and Iberian waters.

For management purposes, the European Atlantic anchovy is separated in two distinct stocks, one distributed in the Bay of Biscay (ICES Sub-Area VIII) and the other occupying mainly the southern part of ICES Division IXa (Bay of Cadiz). However, spatio-temporal irregularities in the dynamics of the Sub-Area VIII stock as well as scant knowledge on the IXa anchovy biology lead ICES to recommend more studies on population dynamics and possible relationships between areas. The present work describes morphometric differences between the two stocks based on the analysis of 10 samples collected within the area from Bay of Biscay to the Bay of Cadiz during two consecutive years (2000 and 2001). Distances on a “Truss Network” were computed from 2D landmark coordinates obtained from digitized images of each individual and corrected from the effect of fish size. Principal Component Analysis was applied to the shape data, as well as a Multidimensional Scaling to the squared Mahalonobis distances (D2) between every pair of sample centroids to visualise clustering. The significance of the computed D2 distances was also statistically tested. Finally, Artificial Neural Networks were applied to assess the robustness of sample groups highlighted in the previous analyses. Results indicate a separation between samples from the Bay of Biscay and those from Division IXa, which is stable over time, as well as a north-south cline along the Portuguese and Bay of Cadiz area. This variability is mainly caused by differences on the shape of the medium-posterior region of the body