Ecosystem trophic structure and fishing effort simulations of a major fishing ground in the northeastern Mediterranean Sea (Thermaikos Gulf)

Abstract

Ecosystem modelling constitutes a useful tool for the ecosystem approach to fisheries management, which demands a shift to more complex models that include multi-species trophic interactions, environmental and anthropogenic forcing. The Thermaikos Gulf is a shallow gulf in the northwestern Aegean Sea (Greece) and one of the major fishing grounds of the northeastern Mediterranean concentrating high fishing effort of trawlers and purse-seiners and producing more than 20% of the total Greek catches. In the present work, we developed an Ecopath base model and ran Ecosim simulations for 26 years (2000–2025), including the calibration period (2000–2016), aiming to describe the food web structure and function of the Thermaikos Gulf, identify main components and interactions among the 33 functional groups, assess the ecosystem impacts of fishing over time, and compare ecosystem properties with other Mediterranean areas. Overall ecosystem degradation with biomass and catch decline was observed at the end of the calibration period due to the impact of environmental factors and fishing activities. The ecosystem seemed to stabilize in an intermediate state by the end of the projection years, but with an overall biomass and catch decline. Fishing effort reduction after 2016 resulted in higher biomass and catches compared to 2014–2015, that could not however reach the 2000 levels in most cases. The examined fishing effort reduction scenarios clearly showed that the more the fishing effort is reduced, the higher the biomass in the ecosystem and the lower the catches obtained compared to the baseline scenario. In a nutshell, since environmental drivers may be harder to predict or control, lowering the exploitation levels is an important step towards the rebuilding of overfished marine resources and more resilient ecosystems.