Relationship between freshwater input to the coastal zone and the historical landings of the benthic/demersal fish Eleginops maclovinus in central-south Chile
The ecosystem off central-south Chile is one of the most productive marine systems in the world, providing approximately 4% of worldwide fish captures. We analysed the effect of freshwater input (river runoff and rainfall) to the coastal zone in central-south Chile (36°00′–37°30′ lat. S) on the landings of the Róbalo (Eleginops maclovinus) using the following data: Róbalo annual landing statistics, monthly mean and annual mean runoff of Itata (1975–91) and Bio-Bio rivers (1975–94), and cumulative monthly rainfall and annual mean rainfall (1975–94). Time series were smoothed using three-point equally weighted running means. To analyse the relationship between Róbalo’s landing and river runoff, as well as rainfall, Pearson’s product-moment correlation analyses were conducted at relevant lag times. The statistical significance of correlation coefficients was calculated taking into account intraseries autocorrelation. Our results showed that Róbalo’s landings were significantly correlated to freshwater input to the coastal zone in central-south Chile. Thus, significant correlation coefficients were found between annual Róbalo’s landings and: (i) annual mean runoff of the Itata (r=−0.94) and Bio-Bio (r=−0.80) rivers lagged 3 and 4 years, respectively, and (ii) annual mean rainfall lagged 4 years (r=−0.75). The lag time at which highest correlation coefficients between annual mean environmental and annual landing time series took place (i.e. 3–4 years) corresponded to the age at which Róbalo reaches the minimum exploitation size. Accordingly, we hypothesize that river runoff and rainfall strongly influence the survival rate of Róbalo’s early stages during the first year of life.