Why the Eurasian otter (Lutra lutra) leaves a pond? An observational test of some predictions on prey depletion

• Main Authors: Delibes, M., Ferreras, Pablo, Blázquez, M.C.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Société nationale d'acclimatation et de protection de la nature 2000
• Subjects: Anguilla anguilla; Loutre; Lutra lutra
• Online Access: http://hdl.handle.net/10261/50350

In the Doflana National Park (SW Spain), Eurasian Otters (Lutra lutra) harvest temporally some scattered ponds close to the Guadalquivir marshes. By analysing 307 spraints collected during three periods of pond occupancy, we used the otters’ diet to test the hypothesis that they leave these ponds when they have depleted their favourite prey (large Eels, Anguilla anguilla) and consequently are forced to eat less rewarding prey (small eels and Mosquitofish, Gambusia affair). Results indicate that the proportion of eels decreased in the otter’s diet, and that of mosquitofish increased, during the first and longest period of use of the pond by the otter, but not in two other instances of shorter occupation periods. Trophic diversity and average size of eaten eels did not change along the study. We suggest that temporal changes in habitat and trophie resources on a larger spatial scale could explain the decisions of the otter rather than a hypothetical giving-up density of the favourite prey in the studied pond. [FR] Dans le parc National de Dofiana (SW Espagne), Ia loutre (Lutra lutra) se nourrit temporairement dans divers étangs disperses au bord des marais du Guadaiquivic 0’aprés let analyses de 307 feces ramassées durant trois pdriodes de presence de l’espèce dans un étang, nous avons dtudit son régime alimentaire afin de vérifierl’hypothèse selon laquelle les loutres abandonneraient l’etang aprCs avoir réduit la densitd dc leur proie favorite (anguilles de grande taille, Anguilla anguilla) et par consequent seraient forcées de consommer des proies de rnoinclre rentabilité (anguilles de petite taille et gambusies, Gambusia affair). Les rdsultats montrent que la proportion des anguilles dirninue dana Ic régime alimentaire de la loutre et Ia proportion & gamtaisles augmente pendant In premiCre. et plus league, pCriode d’occu­ pation de cet dtang, mais non dims les deux autres cas. La diversité trophique et la taille moyenne des anguilles eonsomrnóes n’ont pas change durant Ia periode d’Ctude. Nous suggérons ...