Effects of flow regime on the fish communities of the lower ebro river
- Autores: Núria Vila Martínez
- Directores de la Tesis: Nuno Alberto Marinheiro Caiola (dir. tes.), Carles Ibáñez (codir. tes.), Javier Sigró Rodríguez (codir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2018
- Idioma: español
- Tribunal Calificador de la Tesis: Frederic Casals (presid.), Carmen García Comas (secret.), Dolors Vinyoles Cartanyà (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX hdl.handle.net
- Resumen
Aquatic ecosystems are characterized by a strong coupling between physical forcing and ecological processes. In rivers, this physics-ecology interaction is driven by flow, one of the main factors determining biological integrity. The combination of high flow alterations due to dam regulation and an increasing presence of alien species is endangering native fish communities in the Iberian Peninsula. With a high number of endemisms, these communities are characterized by having developed complex mechanisms of adaptation to the natural changing flow of Mediterranean rivers, which the introduced species do not possess. The aim of this thesis is to explore the relationships between flow regime and fish communities in the lower Ebro River by analysing data from electrofishing campaigns collected during more than 10 years. We address this objective through three different approaches: On Chapter 1, the relationships between single species abundances and hydrological regime were evaluated while in Chapter 2 and 3 the objects of study were fish-based biological quality indices and size spectrum of fish community, respectively. To describe flow regime, we used a set of hydrological variables calculated from daily and hourly flow data series provided by the Ebro Basin Water authority (Confederation Hidrográfica del Ebro).
In the analysis of the responses of single species to changing flows, we found several significant relationships in both, seasonal and inter-annual variations. Alien species such as the Eastern mosquitofish (Gambusia holbrooki) and the topmouth gudgeon (Pseudorasbora parva), were negatively affected by high flows in annual and inter-annual variations, while the Pike-perch (Sander lucioperca) and the European perch (Perca fluviatilis) showed a negative response to high flows only in the annual cycle. On the other hand, several cyprinids were closely related with October and November flows (the bleak, Alburnus alburnus; the Iberian gudgeon, Gobio lozanoi; the goldfish, Carassius auratus and the Ebro barbel, Luciobarbus graellsii). In addition, we verified that some of the hydrological indices used underwent important changes with the construction of large dams in the river course. All these results lead us to propose the hydrological indices FH3 (average magnitude of the flows above 3 times the median daily flow), MH17 (25th percentile of the flow curve divided by median daily flow) and MA13 (average November flow) to be studied as tools to stop the progress of invasive species in the area and protect the native ones.
The analysis of the relationship between interannual flow regimes and biological quality based on fish community, assessed through the Indices of Biotic Integrity in Catalan rivers (IBICAT2010 and IBICAT2b) and the new European Fish Index (EFI+), showed that IBICAT2010 was the most correlated with hydrological indices, followed by IBICAT2b and EFI+. Furthermore, high temporal and spatial scale dependences were observed in the patterns of correlation between biological quality indices and hydrological variables. On one hand, daily hydrological indices showed correlations with biological quality when they were computed using between 9 and 36 months of flow records (previous to the sampling date) whereas subdaily indices responded better to periods between 3 and 9 months of records. On the other hand, some sampling transects showed clearer relationships than others, even within the same water mass, which suggests an influence of the hydromorphological variability on the obtained biological quality scores.
Finally, the study of the entire fish community size-structure using Normalized Abundance Spectra (NAS) provided an approximation of the total fish abundance and food web capacity (through the parameter y-intercept) and an estimation of food web efficiency (through the slope of the linear regression). We detected significant relationships between NAS-related parameters and the hydrological variables describing diel flow oscillations and daily flow variability. Based on the results, we suggest that high flow variability conditions and, above all, high hydro-peaking conditions, caused a diminution of the total abundance of fish and a decrease of the proportion of small sized fish (i.e. lower y-intercept and flatter slopes of NAS, respectively). In addition, a significant interaction between hydro-peaking and the percentage of alien-predators specimens suggested that high hydro-peaking conditions benefit predation by facilitating predator-prey encounters. We concluded that the high proportion of alien fishes and the presence of a hydropower generation plant that operates by hydro-peaking are important factors determining fish size structure in the lower Ebro River.
