Environmental drivers of the anchovy/ sardine complex in the Eastern Mediterranean.
1, Pierce G J1, 2, Illian J3, Scott B E1
1School of Biological Sciences (Zoology), University of Aberdeen, Tillydrone Avenue, AB24 2TZ Aberdeen, UK
2Centro Oceanográfico de Vigo, Instituto Español de Oceanografía, P.O. Box 1552, 36200 Vigo, Spain
3School of Mathematics and Statistics, University of St. Andrews, The Observatory, Buchanan Gardens, KY16 9LZ St. Andrews, UK
The anchovy/ sardine complex is important for fisheries in some of the largest upwelling systems in the world. Synchronous, but out of phase, fluctuations of the two species in distant parts of the oceans have prompted a number of studies dedicated to determining the phenomena, atmospheric and oceanic, responsible for the observed synchronicity, and the biological mechanisms behind the population changes observed for the two species. Anchovy and sardine are of high commercial value for the fishing sector in Greece. The current study investigates the impact of large-scale climatic indices on the anchovy/ sardine complex in Hellenic seas. Multiple time series of landings for both species for 18 sub-areas were analysed in relation to teleconnection indices and local environmental variability. The connection between the teleconnection indices and local weather/ oceanic variation was also examined in an effort to describe physical mechanisms that link large-scale atmospheric patterns with anchovy and sardine. The West African Summer Monsoon, East Atlantic Jet and Pacific North American (PNA) pattern exhibit coherent relationships with the landings of the two species. The first two modes of atmospheric variability are prominent patterns during the summer months, when sardine is spawning and anchovy juveniles are growing. PNA is related with ENSO events. Sea Surface Temperature appears as a significant link between atmospheric and biological variability either by favouring the growth of sardine or as a proxy for oceanic features, indicating the positive influence of productivity-enhancing oceanic structures on both species. However, at a local scale, other parameters, such as wind and Sea Surface Height, describe air-sea variability that affects the anchovy/ sardine complex. These relationships are non-linear and in agreement with previous studies stressing the importance of optimal environmental