Hydrographic conditions driving sardine and anchovy populations in a land-locked sea

Abstract

The aim of this paper is to establish a relationship between long-term variability in sardine and anchovy populations in the Adriatic Sea and ocean dynamics and processes that occur over interannual and decadal timescales in the Adriatic-Ionian basin. This analysis is based on annual time series of sardine and anchovy landings and recruits at age 0 and annual time series of environmental parameters observed at a representative Adriatic station between 1975 and 2010. Pearson correlations and robust dynamic factor analysis (DFA) were applied to quantify the connections between fisheries and environmental parameters. Variations and trends in fishery series were best explained by changes in near-bottom temperature and salinity, which are an appropriate proxy for tracking changes in water mass dynamics and hydrographic conditions in the basin. A prolonged period of decreasing sardine population was characterized by low oxygen availability and environmental conditions in the deep Adriatic waters and was triggered by an extraordinary basin-wide event called the Eastern Mediterranean Transient. A collapse in anchovy population was observed after an exceptional cooling event followed by dense water formation.