Comparative ecology of the European eel, Anguilla anguilla (L. 1758), in a large Iberian river

International audience A total of 1,816 eels were sampled in 1988, from seven sampling areas. Four areas were located in brackish water and the remaining three were located in freshwater reaches of the Tagus river basin. Eels were more abundant in the middle estuary and decreased both in the upstrea...

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Bibliographic Details
Published in:Environmental Biology of Fishes
Main Authors: Costa, José, Domingos, Isabel, Assis, Carlos, Almeida, Pedro, Moreira, Francisco, Feunteun, Eric, Costa, Maria
Other Authors: Biologie des organismes marins et écosystèmes (BOME), Centre National de la Recherche Scientifique (CNRS)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Muséum national d'Histoire naturelle (MNHN)
Format: Article in Journal/Newspaper
Language:English
Published: HAL CCSD 2008
Subjects:
Tagus River
Brackish and freshwater
Abundance
Population structure
Feeding and condition
Dam impacts
[SDV.EE]Life Sciences [q-bio]/Ecology
environment
Anguilla anguilla
Online Access:https://hal.archives-ouvertes.fr/hal-00186064
https://doi.org/10.1007/s10641-007-9229-2
Description
Summary:International audience A total of 1,816 eels were sampled in 1988, from seven sampling areas. Four areas were located in brackish water and the remaining three were located in freshwater reaches of the Tagus river basin. Eels were more abundant in the middle estuary and decreased both in the upstream and in the downstream directions, with a predominance of males in higher density areas. Smaller individuals preferred more peripheral areas, such as margins and upper reaches in the brackish water zone, and the tributaries of the freshwater habitats. It was assumed that this distribution pattern resulted from three main factors: (i) the dominance of larger specimens; (ii) the need to avoid predators and; (iii) the search for better trophic conditions. The condition of the individuals generally decreased toward the upper reaches, apparently due to a corresponding decrease in feeding intensity. The presence of the Belver dam in the main river, 158 km upstream from the sea, seemed to impose major alterations to the described patterns. The concentration of specimens below this impassable obstacle yielded a reduction in the proportion of females and a decrease in the condition and survival of the eels, contributing to a reduction in the spawning success of this population. Suggestions to diminish the effects of the dam, and to preserve the fishery are also presented

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