Planktonic stages of small pelagic fishes (Sardinella aurita and Engraulis encrasicolus) in the central Mediterranean Sea: The key role of physical forcings and implications for fisheries management.

Abstract

Multidisciplinary studies are recently aiming to define diagnostic tools for fishery sustainability by coupling ichthyoplanktonic datasets, physical and bio-geochemical oceanographic measurements, and ocean modelling. The main goal of these efforts is to understand those processes that control the dispersion and fate of fish larvae and eggs, and thus tuning the inter-annual variability of the biomass of small pelagic fish species. In this paper we analyse the distribution of eggs and larvae as well as the biological features of the two species of pelagic fish, Engraulis encrasicolus and Sardinella aurita in the north-eastern sector of the Sicily Channel (Mediterranean Sea) from ichthyoplanktonic data collected during the 2010 and 2011 summer cruises. We use Lagrangian simulations and satellite data (i.e., sea surface temperature, wind, and chlorophyll-a concentration) to recognize the main oceanographic patterns that mark eggs and larvae transport processes. We provide a mechanistic explanation of a cross-shore transport process by using a potential vorticity (PV) model that takes into account the role of wind stress in generating cold filaments. Our results show that the strong offshore transport towards Malta occurred in 2010 was likely due to a persistent Mistral wind forcing that generated high-PV cold filaments. This phenomenon was not found in the 2011 analysis, which indeed showed an along-shore transport towards the retention area of Capo Passero. Since, for the first time, we describe the spatial distribution of the early life stage of Sardinella aurita in the northern part of the Sicily Channel and we clarify the link between the ocean dynamics and the fate of small pelagic fish larvae, this work provides a useful, diagnostic tool for the sustainable management of fishery resources.