Big fish, small fish: still the same species. Lack of morphometric evidence of the existence of two sturgeon species in the Guadalquivir river

Abstract

 I have analyzed a published set of morphometric data of sturgeons (Acipenser spp.) caught in Iberian rivers. These data claimed to prove the presence of both A. naccarii and A. sturio in the Iberian Peninsula. However, graphical representation of the scores of individual specimens on the principal components (PC) extracted by a principal-components analysis (PCA) performed on the covariance matrix offered no suggestion of the existence of two morphologically dissimilar groups in the sample. PC extraction from the covariance matrix of the original variables preserves allometries and does not distort the geometric space. However, I also carried out a PCA using the correlation matrix of the morphometric variables after the application of a commonly employed univariate size-adjustment technique because, in the particular study under consideration, ordination of specimens was of interest. Again, this analysis provided no evidence of the presence of two distinct groups within the sample. Neither did bivariate log-log scatterplots of the morphological measurements against total length. Furthermore, a multivariate analysis of variance (MANOVA) of the same size-adjusted variables found no significant differences between the two groups identified by the investigators in their sample. Examination of the two composite variables that these authors used to separate those groups showed them to be badly affected by ontogenetic allometry, thereby leading to the ascription of large and small specimens to different groups. I conclude that there is no morphological evidence to support the claim of the presence of A. naccarii in the Iberian Peninsula.