Morphological variation of horse mackerel (Trachurus trachurus) in the Iberian and North African Atlantic:: implications for stock identification

The current delimitation of the Atianto-Iberian stock of horse mackerel, Trachurus trachurus (Linnaeus, 1758), is based on scant biological evidence. Here, the location of the southern boundary of this stock is investigated through the analysis of several morphometric and meristic characteristics. A total of 384 horse mackerel were sampled from three areas off the Portuguese, one off the Spanish (Gulf of Cadiz) and another off the Moroccan coast, and compared using multivariate techniques. Some 14 morphometric and five meristic characters were analysed using hierarchical cluster analysis, multivariate discriminant analysis and randomization tests. Morphometric characteristic; showed considerably greater discriminatory power to distinguish individuals from different areas than did the meristic characters. All morphometrical analyses showed similar results: the greatest differences were found between the Gulf of Cadiz and all other groups, while fish from the Portuguese coast appeared more similar to each other than to those from Moroccan waters. Meristic characters did not allow a clear distinction between geographical areas, with the Mahalanobis distances among areas being an order of magnitude smaller than those for the analysis of the morphometrics. If these results are corroborated by further biological evidence (such as genetical or parasitological data), there is a strong argument for the southern limit of the Atlanto-Iberian stock of horse mackerel to be revised. (C) 2000 International Council for the Exploration of the Sea.