Spring Food Spectrum of Two Planktivores (Sardina pilchardus Walbaum 1792 and Sardinella aurita Valenciennes 1847) From the Central Algerian Coast (3° E to 4° E—South West Mediterranean Sea) in Relation to Sexes and Sizes

Abstract

Sardina pilchardus, Walbaum 1792, and Sardinella aurita, Valenciennes 1847, are the fish most consumed by the Algerian population. Sardine has become increasingly rare in commercial fishing catches, whereas round sardinella is being sold at excessively high prices. Given the importance of trophic interactions between clupeids and the low levels of the pelagic food web (plankton and others), the stomach contents of the two species of S. pilchardus and S. aurita are studied. Samples are collected from the spring commercial fishery (April and May 2023) associated with the two main ports on the central coast (Algiers and Bou Ismail) justified by the intense trophic activity of these two predators. High feeding intensity (or stomach vacuity coefficient) is recorded in both males and females. Our results support the hypothesis that the diet of species in specific zones remains consistent due to stable local trophic resources. This is underscored by the lack of variation in prey quality and quantity across size and sex in both clupeid species, emphasizing the role of these interactions within the pelagic food web. Using the morphological identification and counting technique, the preys are linked to 12 taxonomic units belonging to the zooplankton, phytoplankton, and miscellaneous communities. The analysis of the diet is carried out by classifying the prey on the basis of the frequency index (If), taking into account the sex and the size where three categories of prey are defined. Copepods are the preferred prey with rates that did not differ significantly by sex and place of origin of the two clupeids. These findings extended to secondary prey (other zooplankton and phytoplankton). Also, the composition of the diet remained homogeneous in the Gulfs of Algiers and Bou Ismail. Quantitative and qualitative results on diet composition of the two clupeids and their trophic interactions within the two target ecosystems will serve as a basis for fisheries management (i.e., Ecosystem Approach to Fisheries Management [EAFM] and Ecosystem-Based Fisheries Management [EBFM]). The modeling of all the variables will allow decision makers to predict the level of exploitable biomass in the medium and long term.