Temporal and geographic variability of sardine maturity at length in the northeastern Atlantic and the western Mediterranean. e ICES Journal of Marine Science, 63: 663e676.We investigate spatial and temporal variations in sardine maturation patterns and discuss the implications for stock structure, using recent samples collected opportunistically across the species range and data collected regularly for the assessment of the Atlanto-Iberian stock. Maturity ogives were fitted to maturity-at-length data using Generalized Linear Models, and maturation patterns are summarized by length at first maturity (L 50 ). Sardine attain sexual maturity at a total length of 10.9e16.8 cm. The percentage of mature small sardine increases from north to south across the Northeast Atlantic. L 50 is low in the Mediterranean and Moroccan waters, but maturation is delayed towards the limits of the species' range. Sardine mature smaller in the Gulf of Cadiz than in other areas of the Atlanto-Iberian stock, although there is no indication of a different maturation pattern north of the stock boundary. These results are not sufficient to review the stock structure of sardine, but question the hypothesis of homogeneous biological properties of sardine populations within the stock area. Sardine maturation length reduced and the spawning period extended in western Iberia during the past two decades. Associated increases in fish condition and fat reserves during the summer feeding season suggest that variations in reproductive traits may have been caused by environmentally driven changes in food availability.

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Allozyme data were used to analyse the genetic structure of Sardina pilchardus populations. Fifty samples from 15 locations between the North Sea and Mauritania, including samples from the Azores, Madeira and the Mediterranean Sea, were surveyed. A weak but significant structure was found between all samples (F ST ¼ 0.057, P < 0Á001). This structure results from a change in the most common allele of SOD* between the North African and the Azores populations separated by the greatest distance. This locus seemed to be under selective pressure according to the test of neutrality, and the variations in allele frequencies may be explained due to isolation by distance (IBD) of coastal populations (from Mauritania to the North Sea) (r ¼ 0Á86, P < 0Á001). When SOD* was removed from the analyses, IBD was not observed in coastal populations (r ¼ 0Á236, P > 0Á05) but was observed over the whole range (r ¼ 0Á321, P ¼ 0Á05). The genetic structure of S. pilchardus is driven by both IBD and selective processes.