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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.

Mostra/Nascondi contenuto.
11 Chapter 1 Introduction 1. Introduction The North Central Adriatic Sea is the widest shelf of the Mediterranean Sea. This region features different habitats and high marine biodiversity (Barausse et all. 2009, Coll et all. 2010). The North and Central (NC) Adriatic Sea, in principle, provides good conditions for sardine and anchovy populations, given the productivity of the ecosystem. Nevertheless the past four decades show, for this area, a notable decrease in abundance and in biodiversity of pelagic as well as of benthic fish. The cause of these changes has been ascribed to fishing pressure, environmental factors and other anthropogenic impacts such as nutrient enrichment and the resulting eutrophication (Coll et al. 2010). Recent scientific surveys (Santojanni et all. 2010) report that the sardine population crashed from an estimated average of more than 620000 tonnes of fish in the water before 1993 to less than 130000 tonnes in the years after 2000 and anchovy population declined from 300000 tonnes to 150000 during the early 1980s and then declined again between 1995 and 2001. Anchovy and sardine, known locally as ‘blue gold’, are of major importance for Adriatic fisheries and ecology. Indeed together these two species account for approximately 40% of total Adriatic marine catches (FAO, 2007). The economical importance of these pelagic fish in Adriatic has led to many scientific surveys for providing a good management of fishery. However their dependence on environmental and climatic factors and fishery is not completely understood yet (Morello et al. 2009). Therefore, a need for ecosystem-based studies to inform human marine resources management is still present. This is underlined by the recent Marine Strategy Framework Directive (MSFD) 2008/56/EC. The directive asks for an ecosystem approach to fishery, based on indicators on the state of the ecosystem, the fishery impact and the socio-economic consequences determined by the management policy. Interactions between the ecological components of the ecosystem (e.g. predator-prey interactions), as well as the feedbacks between those ecological components and coastal socio-economic systems should be taken into account to achieve a truly sustainable management of the marine environment. The

Tesi di Laurea Magistrale

Facoltà: Ingegneria

Autore: Davide Dalla Barba Contatta »

Composta da 118 pagine.

 

Questa tesi ha raggiunto 87 click dal 13/03/2013.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.