The small pelagic fish studied in the present work, European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus) have a major role in marine ecosystems, and in particular in the Northwestern Mediterranean Sea. However, in the last decade declines in landings and body condition of both species have been observed in the Northwestern Mediterranean Sea. Therefore, it is necessary to advance on our knowledge about their biological and ecological key traits in order to understand the potential factors that affect the population of European sardine and anchovy in this area. In this study we developed an analysis of their body energy cycle, throughout a year, in different areas of the Catalan coast and evaluate seasonal and spatial fluctuations by means of indirect and direct methods to estimate physiological condition. Specifically, we used energy density measures of dry fish, the Kn index, the GSI index and Fatmeter measurements and we compared them between species, months, locations and methodologies. A significant relationship between the values of the Fatmeter and the energy density measures was found in the case of sardine. Moreover, our results confirmed that seasonality can affect the energetic content of these two species due to their strategies of energy accumulation in relationship with their reproduction periods

Trabajo final presentado por Sara Gérez Orús para el grado de Biología de la Universitat de Barcelona (UB), realizado bajo la dirección de la Dra. Marta Coll i la doctoranda Marta Albo del Institut de Ciències del Mar (ICM-CSIC).-- 30 pages, 10 figures, 7 tables