Comparison of feeding apparatus and feeding intensity of the European sardine (Sardina pilchardus) off Morocco in two Atlantic upwelling areas with different seasonal activity
This study investigates the feeding intensity and the morphology of the feeding apparatus (gill rakers) of the European sardine Sardina pilchardus (Walbaum, 1792) in two hydro-dynamical contrasting areas of the eastern boundary upwelling system off Morocco. North, one area is characterized by a summer upwelling while South, the other area is more productive with a strong and almost permanent upwelling. Fish from both areas differ in their feeding intensity, fish condition and gill raker number but no difference is found in the length of the first lower branchial arch. Fish from the southern fishing area are characterized by higher gill raker number and higher feeding intensity mainly from January to May, while specimens from the other area have a significantly lower gill raker number and higher feeding activity from July to November. The high values of fullness index during summer-autumn and the lower value of gill raker number suppose that S. pilchardus from the latter area feed more intensively on larger preys, taking advantage from the trophic conditions prevailing during these seasons. In the southern area, S. pilchardus develop more many gill rakers which might allow to filter the smaller and more abundant preys. These results show that seasonal differences in environment conditions, i.e. permanent versus seasonal upwelling that induce differences in the available resources, may have shaped differently the feeding apparatus, the feeding activity and the condition of S. pilchardus.