1991. Usefulness of Fourier analysis of otolith shape for Atlantic mackerel (Seornbea scombsus) stock discrimination. Can. ). Fish. Aquat. Sci. 48: 296-302.We compared shapes of Atlantic mackerel (Seornber scombrus) sagittae between the two contingents (i .e. spawning groups) from the Northwest Atlantic and between the stocks from the Northwest Atlantic and the North Sea to evaluate whether otolith shape could differentiate between the two contingents in a mixed fishery. We quantified shapes with the Fourier series, an objective and rapid method which decomposes a shape's outline into a series of sinusoids. To detern-sine a correct way to compare contingentslstocks, we first assessed four intracontingent effects on otolith shapes. Age and year-class effects were significant, while sex and bilateral position effects were not. This temporal instability in shapes indicates that confounding effects of age and year-class on otolith shapes need to be assessed carefully before drawing conclusions on stocl< structure. It also shows that comparative studies of otolith shapes with Fourier descriptors are not useful for mackerel contingent discrimination. The power of discriminant functions to correctly classify test mackerel samples separated by age and sampling year, on the basis of otolith shape, was better for comparisons between the stocks than for those between the contingents. Nous avons compare la forme de sagittae de maquereau bleu (Scsmbes scombaus) entre Bes deux contingents (i.e. group-reproducteurs) du nord-ouest de I'Atlantique et entre les stocks dea nord-ouest de I'Atlantique et de la mer du Nord afin de determiner s'il est possible de diffprencier les deux contingents sur la base des formes d'otolithes dans une peche rniwte. Nous avons quantifik les formes A l'aide des sgries de Fourier, une rnkthode objective et rapide qui d6csrnpose le contour d'une forme en une skrie de sinussides. Afin de dkterrniner une f a~o n correcte de cornparer Ies csntingents/stscks, nous avons d'absrd 6vaIu6 quatre effets intra-contingents sur tes formes d'otolithes. Les effets d'sge et de classe d'sge sur les formes d'stolithes etaient significatifs alors que les effets de sexe et de position bilatkrale ne It6taient pas. Cette instabilitk ternporelle des formes indique que les effets d'age et de classe d'2ge doivent &re soigneusement 6valu6s avant de tirer des conclusions sear la structure de stock et d6montre que des comparaisons de formes d'otolithes avec les descripteurs de Fourier ne sont pas utiies pour la discrimination des contingents de maquereau. La puissance de fonctions discriminantes 2 classifier correctement des kchanti l Ions tests de maquereau separks par 2ge et ann6e d'kchanti llonnage sur la base des forrnes d'otslithes etait meilleure pour les comparaisons entre les stocks que pour celles entre les contingents.

We compared daily growth patterns of otoliths of juvenile Atlantic mackerel (Scomber scombrus) younger than 91 d between the two spawning groups that occur in the Northwest Atlantic using a Gompertz model to determine whether it is possible to differentiate these groups on the basis of otolith microstructure in a mixed fishery. The growth curve parameters for the northern and southern groups, respectively, were 36.2 versus 39.7 d for the inflection point (t0), 0.047 versus 0.040 for the instantaneous growth rate (k) when t = t0, and 169.1 versus 192.5 mm for the asymptotic length at the end of the first summer of growth (L∞). These growth curves do not significantly differ (likelihood ratio test, P > 0.5). It therefore appears that the otolith microstructure corresponding to the first summer would not allow identification of the group of origin.