Comparative characterization of the spawning environments of European anchovy, Engraulis encrasicolus, and round sardinella, Sardinella aurita (Actinopterygii: Clupeiformes) in the eastern coast of Tunisia

Abstract

Background. The distribution of early ontogenic stages of small pelagic fishes is important for understanding the dynamics of their fluctuating populations. To fill a gap in the knowledge we conducted a comparative analysis on the distribution of eggs and larvae of the exploited populations of European anchovy, Engraulis encrasicolus (L.) and round sardinella, Sardinella aurita (Valanciennes, 1847), in the eastern coast of Tunisia. Materials and methods. A multidisciplinary survey was carried out in the summer of 2008, from June 23 through July 9. Samples were taken over a grid of 71 stations. Temperature and salinity profiles were recorded at each station by CTD casts and water samples were taken by means of a Rosette equipped with Niskin bottles. Ichthyoplankton was sampled by oblique tows with a Bongo net of 60 cm mouth diameter and 335-µm mesh nets. To specify the preferred spawning environment the quotient values were estimated for each variable. Results. The eggs and larvae of both species represented an important proportion of the ichthyoplankton, around 50% for each ontogenic stage. Anchovy mainly spawned in the shelf edge, north-east of Kuriate Island, with a minor spawning area near Cap Bon and Kelibia. The main spawning area of the round sardinella was in the warmer waters. It was located near the major spawning ground of anchovy. Anchovy eggs were scarce in the coastal zones and in the south of the study area, whereas round sardinella eggs were scarce in the north. The main spawning grounds of anchovy coincided with the area of higher zooplankton abundance while round sardinella spawning grounds correspond with those areas of highest chlorophyll-a and zooplankton. This distribution suggests a propensity for food availability, for both adults and larvae, as the location of spawning grounds of these species. Conclusion. Both anchovy and sardinella spawned mainly in deeper waters within the limits of the continental shelf. Each species appeared to have a specific strategy for spawning that was influenced by physical and biological variables.

Keywords

• anchovy
• round sardinella
• Ionian Sea
• spawning en