ICES CM 2004/Q:20 Sardine tagging off the Iberian peninsula: laboratory experiments and operations at sea Benito Peleteiro, Ana Marçalo, Mercedes Olmedo, Pedro Pousão-Ferreira, Javier Sanchez, Susana Garrido, M. Begoña Santos, Carmela Porteiro and Yorgos Stratoudakis Within the EU project SARDYN, tagging laboratory experiments and operations at sea were designed to study the movements of sardine (Sardina pilchardus) off the Iberian peninsula. In the summer of 2003, around 2500 fish were caught and transferred alive to aquaculture tanks (IEO - Vigo and IPIMAR - Olhão). Mortality ranged between 10-30% in the first week, mainly due to stress and scale loss associated to fishing and handling. Feeding (dry pellets) and schooling was soon assumed in the tanks and subsequent mortality has been close to zero for almost a year. Three tags (T-bar in the dorsal fin, Streamer in the operculum and the tail and Fingerling in the tail) were tested in several trials. All tags produced low mortality (< 5%), and the final choice for tagging at sea (Streamer in the tail) was based on the rate of detachment, tag visibility, interference with swimming and feeding behaviour and easiness of operation. In the summer of 2004, up to 30000 sardine are aimed to be tagged off the Iberian Peninsula (southern and northwestern Portugal, western Galicia and central Cantabria). A publicity strategy has been devised, aiming to enhance the probability of tag recoveries. Keywords: Acclimation, mortality, tag choice, operation at sea, recovery strategy B. Peleteiro, M. Olmedo, J. Sanchez, M.B. Santos, C. Porteiro: IEO, Vigo, [tel: + , fax: + , e-mail: tito.peleteiro@vi.ieo.es]. A. Marçalo, S. Garrido, Y. Stratoudakis: INIAP/IPIMAR, Avenida de Brasília, 1449-006, Lisboa, Portugal [tel: + 351 21 3027000, fax: + 351 213015948 , e-mail: yorgos@ipimar.pt ]. A. Marçalo, P. Pousão-Fereira:INIAP/IPIMAR-CRIP Sul, EPPO, Avenida 5 de Outubro, 8700, Olhão, Portugal. INTRODUCTION Sardina pilchardus (Walbaum) is widely distributed along the north-eastern Atlantic (from Senegal to Scotland) and its population off the Iberian peninsula has supported an important purse seine fishery since the early 20th century. The Atlanto-Iberian stock of sardine was delimited in the early 1980s and has been since assessed under the auspices of the International Council for the Exploration of the Sea, considering that it forms a panmictic, closed population from the Gulf of Cadiz to the inner Bay of Biscay (French/Spanish border). In recent years, doubts were cast on the biological discreteness of the stock (Silva 2003) and its delimitation (Stratoudakis et al. 2003a), while several hypotheses involving Atlanto-Iberian sardine movements have been proposed over time, within and across the current stock boundaries (Furnestin 1945; Porteiro et al. 1986; Carrera and Porteiro 2003). However, these hypotheses have only been based on indirect evidence from seasonal/inter-annual variation in meristic properties (Furnestin, 1945), geographical differences in population age structure (Porteiro et al. 1986) or decadal variations in distribution area and local abundance (Carrera and Porteiro 2003). Mark-recapture (tagging) is commonly used to study movements (Newman 1970a; Muzinic 1973; Morrison and Bruce 1981; Ayvazian et al. 2004) and population dynamics (Newman 1970b) of