Composition et variations nycthémérales des peuplements ichtyologiques des petits fonds mixtes du golfe d’Annaba, Algérie
Composition and nychthemeral variations of shallow water ichthyofauna in the Gulf of Annaba, Algeria
Composition and nychthemeral variations of ichthyofauna living in shallow waters (< 1.5 m) off Annaba coast (Algeria) were studied from March 2011 to March 2012. In three contiguous sites located in the western Gulf of Annaba (Aïn Achir, Belvedere, La Caroube), 26 experimental fishing were conducted during day (13) and night (13) with a beach seine. The ecological status of each species was investigated and the Shannon diversity (H’) and equitability (J) indexes were calculated for the diurnal and nocturnal samples, globally and for each season separately. Overall catches have identified 20 families and 46 species, including 41 species identified from diurnal samples and 38 species from nocturnal samples. Numerical and weight densities were 23 individuals and 62 g / 100 m2, respectively. Specimens measured between 10 and 350 mm and weighted from 0.4 g to 154.5 g. Numerically and gravimetrically, relatively dominant families were Atherinidae [7 individuals (23.2 g) / 100 m2], Sparidae [10 individuals (20 g) / 100 m2] and Mugilidae [5 individuals (10.2 g) / 100 m2]. The study of ecological status revealed that these families are considered residents of shallow-water, both day and night. The grey mullet Chelon labrosus is the only daily resident species, while the other species transit temporary or occasionally during day and/or night. Numeric and weight densities by day and night were 37 individuals (77 g) / 100 m2 and 10 individuals (48 g) / 100 m2, respectively. H’ and J indexes were higher by night than by day. Using hierarchical clustering (AHC) and correspondence analysis (AFC), a difference in fish assemblages between day and night was highlighted. The size of individuals of some species of Atherinidae (Atherina boyeri, A. punctata), Sparidae (Boops boops, Sarpa salpa, Diplodus sargus sargus, D. vulgaris), Labridae (Symphodus ocellatus) and Mugilidae (Liza aurata, L. ramada), differed significantly between day and night.