From selective tidal transport to counter-current swimming during watershed colonisation: an impossible step for young-of-the-year catadromous fish?

• Published in: Knowledge and management of aquatic ecosystems 2014, Vol.412 (412), p.4-14
• Main Authors: Trancart, T., Lambert, P., Daverat, F., Rochard, E.
• Format: Article
• Language: English
• Subjects: Anguilla Anguilla; Anguillidae; Bascule comportementale; Behavioural shift; Catadromous fishes; Catadromous species; Colonization; Current reversal; Eels; Environmental Sciences; Estuaries; Estuarine dynamics; Fish; Freshwater; Juveniles; limite tidale; Liza ramada; Marine fishes; Migration; Migrations; Mugilidae; Pisces; Rivers; Species; Swimming; tidal limit; Tidal rivers; Transport; Water currents; Watersheds
• ISSN: 1961-9502; 1961-9502
• DOI: 10.1051/kmae/2013086

During watershed colonisation by catadromous species, two main phases have been identified: tidal estuary crossing and non-tidal river colonisation. Fishes use selective tidal-stream transport (STST) during the first phase of this colonisation, and counter-current swimming during the second phase. Therefore, catadromous species have to achieve a behavioural shift, from STST to constant counter-current swimming. This has not yet been observed, and the location and period of this shift is still unknown. Our experimental protocol aimed to mimic the spatial progression of crossing the tidal limit within a 3-week experiment. Two catadromous fishes, thinlip mullets and European eels, were initially subjected to current reversal every 6.2 h during the first week. A gradual tidal distortion was performed during the second week, and fishes were submitted to a unidirectional water current during the third week. Our results reveal that all catadromous species use STST as far as possible within the tidal limit. At this point, in this experimental study, no young-of-the-year (YOY) fishes shifted from STST to constant counter-current swimming. This confirms that the behavioural shift occurs later, and that the second part of the upstream migration, counter-current progression, is performed by larger, older fishes and not YOY fishes. Deux phases principales ont été préalablement identifiées lors de la colonisation des bassins versants par les migrateurs amphihalins thalassotoques. Ces espèces utilisent le transport tidal sélectif (TTS) lors de la première phase dans l’estuaire tidal, puis une nage active à contre-courant lors de la seconde phase dans les rivières non tidales. Les thalassotoques doivent donc réaliser une bascule comportementale entre ces deux comportements. Cette bascule n’a pas encore été observée directement. Sa localisation ainsi que sa période restent inconnues encore à ce jour. Notre protocole expérimental visait à reproduire en mésocosme la traversée de la limite tidale, lors d’une expérience longue de 3 semaines. Des individus de deux espèces thalassotoques, le mulet porc et l’anguille européenne, ont été initialement soumis à une renverse de courant toutes les 6,2 heures durant une semaine. Puis une déformation progressive de l’onde de marée a été effectuée lors de la seconde semaine. Enfin, lors de la 3e semaine, les poissons n’ont été soumis qu’à un seul courant unidirectionnel. Nos résultats suggèrent que les thalassotoques utilisent le TTS aus