The yellow European eel (Anguilla anguilla L.) may adopt a sedentary lifestyle in inland freshwaters

We analysed the movements of the growing yellow phase using a long-term mark–recapture programme on European eels in a small catchment (the Frémur, France). The results showed that of the yellow eels (>200 mm) recaptured, more than 90% were recaptured at the original marking site over a long period before the silvering metamorphosis and downstream migration. We conclude that yellow European eels >200 mm may adopt a sedentary lifestyle in freshwater area, especially in small catchment. P. Laffaille, A. Acou, J. Guillouët Fish Pass, ZA Parc rocade sud, Chantepie, France, Equipe de Recherche Technologique 52 ‘Biodiversité Fonctionnelle et Gestion des Territoires’, Université de Rennes 1, Campus de Beaulieu, Rennes cedex, France Keys words: Anguilla anguilla; yellow eel; freshwater habitat; behaviour; mark–recapture P. Laffaille, Fish Pass, 8 allée de Guerlédan, ZA Parc rocade sud, 35135 Chantepie, France; e-mail: [email protected] ha l-0 07 93 40 6, v er si on 1 22 F eb 2 01 3 this river appears to be representative of many small coastal catchment areas of north-western France (see Feunteun et al. 1998; Laffaille et al. 2003). However, the natural connectivity has been disturbed by three major dams: Pont Avet, Pont es Omnès and Bois Joli. Dam of Bois Joli was equipped with an eel lift and Pont Avet and Pont es Omnès dams with eel passes to permit elvers to migrate upstream. A downstream trap was installed in the Pont es Omnès dam. Eel samples were collected by electrofishing in September from 1996 to 2003 with an EFKO apparatus (EFKO Elektrofishfanggeräte GmbH, Germany) operating at 100–500 V and 0.8–10 A. Because of the shallowness of the stream, capturability was very high; on average, P 1⁄4 0.70 (see Laffaille et al. 2003). Eight river sections, located in the main stream between 4 km from the estuary and 17 km upstream, were sampled all year. The river sections ranged from 430 to 1500 m and the bank length from 150 to 500 m (Table 1). One river section was located downstream of the three dams (section A), one between Pont Avet and Pont es Omnès dams (section B) and the six others upstream. After the end of each electrofishing, eels were measured (total length, to the nearest mm), the stage was identified and they were marked and released back to the sampling area. Moreover, eels were collected by the Pont es Omnès trap every day from 1996 to 2003. This trap was designed to capture the majority of descending eel >200 mm under practically every flow conditions (see Feunteun et al. 2000). All >200 mm individuals captured by electrofishing were marked (799 yellow eels) using Trovan Passive Integrated Transponders (PIT) tags (EID Aalten BV, The Netherlands) (Prentice et al. 1990). PIT tags were injected with a syringe into the abdominal cavity. Each tag had a unique code which was recorded annually in a database. In order to identify marked eels, we used Trovan apparatus (LID500 Portable reader). The eel stages (yellow, yellow/silver and silver) were identified using three criteria: colour of the back and belly, presence of a well-marked lateral line and eye diameter according to Feunteun et al. (2000). Only yellow eels >200 mm were tagged in this study because of the following reasons: (i) the migratory behaviour of silver eels (e.g. Feunteun et al. 2000), (ii) eels <200 mm are still in the process of colonisation (Laffaille et al. 2000) and (iii) small eels (<200 mm) were not usually PIT tagged (high-induced mortality and PIT tag rejection). Moreover, European eels change their behaviour and microhabitat preferences at about a size of 300 mm (Baisez 2001; Laffaille et al. 2003, 2004). Subsequently, recapture analyses were made according to the following length groups (200–300 mm and >300 mm).