Importance of Copepods in the Diet of Sardina pilchardus and Sardinella aurita: Preliminary Investigation in Bou Ismail Bay (Algerian Basin - SW Mediterranean Sea)

Abstract

This preliminary study investigated the diet composition and diet overlap for both Sardina pilchardus and Sardinella aurita, as well as the zooplankton distribution (with a special focus on copepods) in the representative region of Algiers coast (Bou Ismail Bay) during a short period on June 2015. This month can be considered representative of the summer (and autumn) season (s), since between the two periods, the meteorological characteristics remain homogeneous. The study area, is considered one of the most prestigious bays on the Algerian coast, regarding fisheries production. At the level of the food web, trophic interactions link predators (fish populations) to zooplankton prey. At Bouharoun port, also located in the bay of Bous Ismail, samples were obtained from commercial fisheries of S. pilchardus and S. aurita. Additionally, zooplankton samples were collected vertically in the 0-100 m layer. Based on stomach content analysis, significant diet overlap was observed between S. pilchardus and S. aurita (Schoener index : D = 0.76) indicating similar feeding habits (Morisita-Horn index: O = 0.94). Copepods were preferential prey for both fish species with high frequencies (F _Saurita = 91.66%, F_S.pilchardus = 85%). Their highest average number found in the diet of S. aurita was represented by Centropages typicus, followed by Centropages chierachiae and Temora stylifera; while Nannocalanus minor was mainly consumed species by S. pilchardus. Copepod populations were dominant in S. pilchardus and S. aurita feeding strategies. A total of 22 copepod species were identified in the water column, mostly in the Calanidae. Their distribution varied significantly across stations (p = 0.046); three species (T. stylifera, C. typicus and C. violaceus) contributed mostly to this variation. Copepods have a relationship with environmental parameters (e.g., temperature, chlorophyll a, and NO₃).