The influence of environmental factors and hydrodynamics on sardine (Sardina pilchardus, Walbaum 1792) abundance in the southern Alboran Sea

The study of environmental variables and their influence on the small pelagic fish stocks of the Alboran Sea (Western Mediterranean) is asymmetrical, with studies focused on the southern coast being scarce compared with those looking at the northern margin. In this work, time series of sardine landings from the Moroccan coast of the Alboran Sea from 1981 to 2016 were analyzed together with environmental variables such as Sea Surface Temperature (SST), Sea Surface Salinity (SSS), Surface Chlorophyll-a concentrations (Chl-a), and the velocity of the Atlantic Jet (AJ) flowing into the Mediterranean Sea through the Strait of Gibraltar. Annual sardine catches decreased from 1981 to 2016 at a rate of −258 t/year. At the same time, the SST and SSS increased at rates of 0.03 °C/year and 0.004 ups/year, respectively, very likely as a result of climate change. Linear models reflect a negative relationship between sardine landings and SST and SSS, indicating that the long-term temperature and salinity changes in the Mediterranean could have a negative impact on sardine abundance. At an inter-annual time scale, chlorophyll concentrations seem to be positively related to sardine abundances. A decrease in the kinetic energy of the AJ is also inferred from the cross-strait sea level difference (SLD). This variable has an important influence (positive correlation) on sardine landings, both in the long term and at the inter-annual time scale, with higher sardine abundances associated to higher SLD. This work shows that environmental variables such as SLD, SST, SSS, and Chl-a are the main driving factors for the variability of sardine landings in the southern Alboran Sea.