Modeling sardine and anchovy population dynamics

This research represents the first attempt of developing various continuous single stage production models, using modified logistic growth differential equations, to simulate the population dynamics of sardine and anchovy in the northern and central Adriatic Sea from 1975 to 2010. Results, obtained through the implementation of a Matlab code, are compared to anchovy and sardine population biomass time series estimated with the virtual population analysis (VPA) stock assessment done by the AdriaMed working group for small pelagics. The aim of this work is to provide an ecosystem based approach, as required by the Marine Strategy Framework Directive 2008/56/EC, for assessing large-scale direct (e.g. fisheries) and indirect (e.g. climate change) effects of human activities on the main fishery resource of the Adriatic Sea: anchovy and sardine populations. The effects of five biotic and abiotic environmental factors (sea water temperature, Po river phosphate load, mackerel abundance, fishing mortality and competitors biomass) on sardine and anchovy population are evaluated. Among all the models, the one that best simulates sardine population has a Nash-Sutcliffe efficiency of 88% and accounts for the effect of fishing mortality, Po phosphate load, predation and water temperature, while the one that best simulates anchovy has an efficiency of 82% and accounts for fishing mortality, Po phosphate load, competition (sardine biomass) and water temperature. Based on these models and assuming future values for the environmental and human factors forcing the models, some scenarios are developed for predicting sardine and anchovy population dynamics from 2011 to 2020 (the year when Good Environmental Status for Europe’s seas should be achieved according to the Marine Strategy Framework Directive). Scenarios confirm that the abundance of the two species will be influenced mainly by fishing mortality and nutrient load. The research shows that, assuming that the other factors remain constant in the future with respect to 2010, a sustainable management of the anchovy and sardine fishery, which avoids the collapse of their stocks, is possible if fishing mortality is kept lower than 0,41 for sardine and 0,52 for anchovy.