Abstract
Marine ecosystems are being continually impacted by human activities and, among these, fisheries have been one of the most damaging. Fisheries modify the structure and functioning of food-webs through biomass removal and physical damage to the seabed, leading to loss of biodiversity and ecosystem services provided by the oceans. The ecosystem-based approach to fisheries is considered the most efficient way to achieve the goal of sustainable use of marine resources while allowing for biodiversity protection. The Strait of Sicily is a biologically important area of the central Mediterranean Sea characterised by high habitat complexity and rich biodiversity; however, due to the multispecific nature of local fisheries and weak implementation of the adopted management plans, this region is particularly vulnerable. We used fishery independent time series (1994-2016) to identify the main demersal assemblages and map their spatial distribution. The pressure of fishing effort on each of these defined assemblages was then quantified in order to evaluate the impact of bottom trawling on demersal communities. Our results showed four spatially distinct and temporally stable assemblages of the Strait of Sicily. These have a clear spatial distribution, different species composition and biodiversity values and are driven primarily by environmental gradients (i.e. mainly depth and, to a lesser extent, surface salinity). The demersal assemblages were subsequently grouped in homogeneous areas characterised by specific communities of commercial and non-commercial species and response to trawling impacts. These areas are proposed as Spatial Managements Units to evaluate and manage demersal mixed fisheries, while also considering biodiversity conservation in the central Mediterranean Sea.
Highlights
Marine ecosystems continue to be impacted significantly by human activities which modify the marine food web and have drastic effects upon biodiversity (Worm et al, 2006)
Among the fisheries target species we found here were red mullets (Mullus barbatus and M. surmuletus) which together contributed about 16% to similarities, followed by the squid Loligo vulgaris and European Hake (Merluccius merluccius) that contributes less than 5%
Assemblage 3 is mainly formed by species that are not targeted by fisheries, for example the gadoid Silvery Pout (Gadiculus argenteus) that contributes 10%, the Hollowsnout grenadier (Coelorinchus caelorhincus) and the green shrimp (Chlorotocus crassicornis) that account for about 19% together
Summary
Marine ecosystems continue to be impacted significantly by human activities (e.g., pollution, overfishing, introduction of alien species, and global warming) which modify the marine food web and have drastic effects upon biodiversity (Worm et al, 2006). The importance of including spatial aspects in resource management has been highlighted in the recent EU directive on Maritime Spatial Planning (MSP) (European Commission, 2014) that focuses on an ecosystem-based approach to promote the sustainable development and growth of maritime and coastal economies: known as “Blue Growth.” To achieve this goal, it is essential to have a detailed knowledge of the structure and function of marine ecosystems and the spatial distribution of the main commercial species in relation to the environment. The identification of Spatial Management Units (SMUs) could be important for supporting such fishery management policies, especially for regions characterized by mixed fisheries (i.e., where several species are caught in the same area with different gears), such as the Mediterranean Sea, but this requires robust data gathering on seabed habitats, assemblages and the associated fishing pressure
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