Acronym VORATUN
Category
Fisheries
Title Study of blackspot seabream-bluefin tuna interactions in the Strait of Gibraltar food web from stomach-content and stable-isotope analyses: impact on the fisheries Programme National Programme
Instrument (FP6)
Contact Type (FP7)
Strand (Interreg)
NA
Theme (FP7)
Activity Area (FP6)
Regional Area (Interreg)
Action (COST)
NA
Specific Programme (FP7)
NA
Funding source National Coordinator NA Coordinator email NA
Coordinator institution
UCA - University of Cadiz (Spain)
Institutions involved
NA
Start year 2018 End year 2020 Funding (€) € 157,300 Website NA Summary The strait of Gibraltar is a unique natural location that plays a key role as a route of passage for many migratory marine species and serves as an important foraging area for many animals. The particular oceanographic features of this region generate upwelling of nutrient-rich waters and, therefore, a high primary production that can support a diverse food web. In this ecosystem, the blackspot seabream and the Atlantic bluefin tuna occupy high trophic levels. Hence, these species may have a significant impact on communities of potential prey, causing modifications in the trophic relationships and altering the balance of the ecosystem. The Spanish blackspot seabream fleet that operates in waters of the strait of Gibraltar has maintained a prosperous level of fishing and economic performance for decades since its inception. However, the results of recent assessments show a sharp decline of the current blackspot seabream population, which becomes reflected in decreased landings of this species, and calls into question the sustainability of the fishery. The dwindling catches occurred in recent years coincide with the rebound of bluefin tuna biomass in the region, and so the blackspot seabream fishers blame the scarcity of its catches to the pressure exerted by bluefin tuna on the blackspot seabream, either directly by predation or indirectly by competition for the same resources. In order to understand the viability of blackspot seabream fishing in the current market scenario and to assess the sustainability of relationships within the ecosystem, it is necessary to undertake a thorough study on the feeding habits of the resident tuna and blackspot seabream populations, as well as the trophic dynamics of the shared habitat. This will eventually contribute to the improvement of the management of these important resources and to the conservation of the ecosystem as a whole. In this context, the main objective of the project is to elucidate the interactions between the two species and their role in the dynamics of the pelagic trophic network of the strait of Gibraltar, which are aspects that remain poorly studied. In order to determine dietary habits and trophic relationships (predation, competition, trophic position, width and overlap of niches), the work plan presented here envisages the use of the traditional method of stomach content analysis along with the application of novel techniques based on the use of stable isotopes, both in bulk-tissue and in specific components (in this case, amino acids). The use of isotopic markers may serve, at the same time, to identify the contingent of migratory tuna, separating it from the resident population, which is the one that truly influences the dynamics of the local ecosystem. Furthermore, the available information on commercial catches and on diverse life history traits will be used to apply the gadget (globally applicable area disaggregated general ecosystem toolbox) to the assessment of the blackspot seabream fishery, also considering the influence of the bluefin tuna on their natural mortality, abundance and distribution. The central aim of the project is to contribute to a better understanding of the functioning of this unique ecosystem for a rational and sustainable use by the fisheries.
Keywords
Tuna;
Food web;
Fish;
Seabream;
Marine Region
52
Northern Alboran Sea (GSA 1)
57
Southern Alboran Sea (GSA 3)
2
Marine Region Map
