Relationships between age, growth, diet and environmental parameters for anchovy (Engraulis encrasicolus L.) in the Bay of Bénisaf (SW Mediterranean, west Algerian coast)
Résumé
Age, growth and diet of anchovy were studied for the first time from samples collected in the Bay of Benisaf (west Algerian coast) during summer (spawning period) and autumn (recruitment period) 2007. Age structure and growth parameters were determined by otolith (sagitta) analyses. The von Bertalanffy growth function fitted to age-length data showed that most of anchovy growth is achieved during the first year of life, suggesting that this stock is primarily supported by the smallest age groups and has a strong dependence on recruitment. There were no significant differences between males and females, and pooled mean parameters were: L infinity = 15.61 cm, k = 0.75 per year and to, -1.32 years. Whatever the age-class anchovy is strictly zooplanktivorous. Copepods constituted the dominant group (64% O; 81% N), while other crustaceans, mollusc larvae and fish larvae were less represented. The main species of copepods consumed were by order of abundance: Candacia longimana, Oncaea mediterranea and Pleuromamma abdominalis. The results indicated a diversification of the diet in the first age groups (0 to 2 years), and a relative specialization in the third age group. Environmental factors including sea surface temperature and chlorophyll-a concentrations were considered in order to explain differences in growth parameters and diet between different geographical areas. There was no significant relationship between the chlorophyll-a concentration and any growth parameter or L. The only significant relationship observed with chlorophyll-a was with the anchovy at age(-1). Concerning temperature, there was significant relationship only between SST and the anchovy size at age(-1).