SHORT RESEARCH NOTE Density-dependent and inter-specific interactions affecting European eel settlement in freshwater habitats Daniele Bevacqua • M. Andrello • P. Melia ` • S. Vincenzi • G. A. De Leo • A. J. Crivelli Received: 3 November 2010 / Revised: 10 February 2011 / Accepted: 26 April 2011 / Published online: 8 May 2011 Ó Springer Science+Business Media B.V. 2011 Abstract Identifying the factors influencing the settlement of European eel (Anguilla anguilla) juve- niles in continental habitats is crucial to designing effective management and conservation measures for this endangered species. A long-term data series (1993–2008) of European eel and European catfish (Silurus glanis) abundance in a freshwater canal of the Camargue water system (southern France), along with parallel data on water salinity and glass eel abundance in the adjacent Vaccare `s lagoon, was analysed to identify the possible causes of decline in eel abundance observed in the canal during the last two decades. A model including glass eel recruitment and catfish abundance as covariates explained 78% of the observed variation in eel settlement success. Results suggest that (1) salinity does not play a significant role in determining the fraction of eels moving from the brackish lagoon to the canal; (2) density dependence affects settlement success, pos- sibly through a reduction of juvenile survival in the adjacent lagoon; and (3) catfish abundance is nega- tively correlated with eel settlement. We discuss this latter point in terms of possible predation of catfish upon eels and/or inter-specific competition between the two species. Keywords Anguilla anguilla  Interspecific competition  Invasive species  Population dynamics  Silurus glanis Introduction In the last few decades, European eel Anguilla anguilla (L.) faced a dramatic drop in recruitment, which is now down to about 1% of that observed in the 1970s (Dekker, 2003). As a result, the species was included in 2007 in the UN CITES Appendix II list and, in 2008, in the IUCN Red List as critically endangered. Conservation measures for A. anguilla are challenging because of the complexity of its life cycle. The European eel is a catadromous, panmictic species reproducing in the Sargasso Sea (Palm et al., 2009; Andrello et al., in press): eel larvae are carried Handling editor: David J. Hoeinghaus D. Bevacqua (&)  S. Vincenzi  G. A. De Leo Dipartimento di Scienze Ambientali, Universita ` degli Studi di Parma, Viale Usberti 33A, 43100 Parma, Italy e-mail: daniele.bevacqua@unipr.it M. Andrello Laboratoire d’Ecologie Alpine, Universite ´ Joseph Fourier, Grenoble, France P. Melia ` Dipartimento di Elettronica e Informazione, Politecnico di Milano, Milan, Italy A. J. Crivelli Station Biologique de la Tour du Valat, Le Sambuc, Arles, France 123 Hydrobiologia (2011) 671:259–265 DOI 10.1007/s10750-011-0725-1