Modelling the relationships of medium and long-term variations of the anchovy and sardine catches in the catalan sea (nw mediterranean) with the environmental drivers
- Autores: Federico Quattrocchi
- Directores de la Tesis: Francesc Maynou Hernández (dir. tes.), Agustín Sánchez-Arcilla Conejo (tut. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2017
- Idioma: español
- Tribunal Calificador de la Tesis: Ana Sabatés (presid.), Josep Lloret Romanach (secret.), José María Bellido Millán (voc.)
- Programa de doctorado: Programa de Doctorado en Ciencias del Mar por la Universidad de Barcelona y la Universidad Politécnica de Catalunya
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The understanding of the driving forces involved in the abundance fluctuation of fish populations is an important requirement for conservation and management, especially in the context of environmental changes. In the North Western Mediterranean Sea the catches of sardine (Sardina pilchardus) and anchovy (Engraulis encrasicolus) during the period 1990-2014 have severealy decreased. Although neither of the two populations is considered underexploited, it seems unlikely that overexploitation alone has caused the recent decrease. Furthermore, it is even truer considering that changes in the marine environment have occurred in the studied area during the last 40 years. The general objective of this PhD thesis is to detect the main environmental factors involved in the fluctuations of the abundance of the two small pelagic species in the Catalan Sea.
Before focusing on the environmental influences, the spatiotemporal distribution of the purse seine fishery operations was analyzed. The results revealed that the distribution of the fleet captured the features of the distributions of small pelagic populations. These findings contributed to a better understanding and visualization of the spatial distribution of catches, which form the basis of the landings data series studied in the rest of the PhD thesis. We then investigated the local environmental factors and climate index (Western Mediterranean oscillation index; WeMOI) that were strictly linked with landings of both species. We concluded that temperature, salinity, and currents were important drivers for both species, and the WeMOI index favored sardine abundance when it was in positive phase. We highlighted that the relationships between the availability of these small pelagic fishes and these factors were better described by non-linearity. Finally, we provided evidence, independent from the studies directly targeted on early life stages, that the temperature and sea surface height (used as a proxy of mesoscale processes) play an important role in the recruitment variability of these species. Even more importantly we showed that the effects of these drivers were not stationary but transient over time. Although this work is one step forward in the understanding of the abundance variability of the small pelagic fish in the Catalan Sea further investigation focused especially on the synergic effects of fishing combined with environmental factors will still be needed.
