Growth of young-of-the-year mackerel in the Bay of Biscay U. C OTANO * AND P. A ´ LVAREZ Fisheries and Food Technological Institute (AZTI), Department of Fisheries Resources, Herrera Kaia, z.g., Portualdea, 20110 Pasaia (Gipuzkoa), Spain (Received 9 August 2002, Accepted 6 March 2003) The first growth season of young-of-the-year (0þ year) mackerel Scomber scombrus, sampled in the Bay of Biscay, was parameterized to determine growth patterns. Daily increments were identified on sagittae otoliths, for calculation of age and growth of 92 larvae and 54 juveniles over the range 36–2150 mm standard length (L S ). A Gompertz curve was fitted to the length- at-age data. At the end of the first year of growth L S was 1942 mm, with a maximum growth increment of c. 2 mm day 1 , observed 62 days after hatching. Backcalculated growth increments for mackerel juveniles, during their larval stage, were higher than those observed for sampled larvae; only 109% of sampled larvae were estimated to survive. Growth for north-eastern Atlantic mackerel was slower than that published for north-western Atlantic mackerel. Back- calculated hatching dates for mackerel were consistent with the typical temporal distribution of mackerel spawning in the Bay of Biscay. # 2003 The Fisheries Society of the British Isles Key words: Bay of Biscay; growth; juvenile; larvae; Scomber scombrus; survival. INTRODUCTION The mackerel Scomber scombrus L. is a well-known commercial migratory species. In north-east Atlantic (NEA) waters, mackerel spawning is widespread along the edge of the European shelf, from the north of Ireland to the northern coasts of Spain and Portugal (Lockwood, 1988). Mackerel spawning starts in February in Portuguese and Cantabrian waters; it then extends northwards, when the season progresses, to finish in July in Irish waters (Lockwood, 1988; Uriarte & Lucio, 2001). The major incidence of mackerel spawning is found at the shelf edge and adjacent areas of the Bay of Biscay and of the Celtic Sea, mainly from February to June. Along the Cantabrian coast, spawning takes place during a shorter period, from February until mid-May (Dicenta, 1984; Sola´ & Franco, 1985). Post-spawning adult mackerel migrate at the end of summer and early autumn into the Norwegian Sea and northern part of the North Sea, remaining there on feeding grounds during autumn and early winter. Afterwards, the adult mackerel commences a southern migration to spawning *Author to whom correspondence should be addressed. Tel.: þ34 943004800; fax: þ34 943004801; email: ucotano@pas.azti.es JournalofFishBiology (2003) 62, 1010–1020 doi:10.1046/j.1095-8649.2003.00093.x,availableonlineathttp://www.blackwell-synergy.com 1010 # 2003 The Fisheries Society of the British Isles