title: Freshwater and coastal migration patterns in the silver-stage eel Anguilla anguilla.
abstract: The unimpeded downstream movement patterns and migration success of small female and male Anguilla anguilla through a catchment in north-west Europe were studied using an acoustic hydrophone array along the River Finn and into the Foyle Estuary in Ireland. Twenty silver-stage A. anguilla (total length, LT , range: 332-520 mm) were trapped 152 km upstream from a coastal marine sea-lough outlet and internally tagged with acoustic transmitters of which 19 initiated downstream migration. Migration speed was highly influenced by river flow within the freshwater (FW) compartment. Anguilla anguilla activity patterns were correlated with environmental influences; light, tidal direction and lunar phase all influenced the initiation of migration of tagged individuals. Migration speed varied significantly between upstream and lower river compartments. Individuals migrated at a slower speed in transitional water and sea-lough compartments compared with the FW compartment. While 88·5% survival was recorded during migration through the upper 121 km of the river and estuary, only 26% of A. anguilla which initiated downstream migration were detected at the outermost end of the acoustic array. Telemetry equipment functioned efficiently, including in the sea-lough, so this suggests high levels of mortality during sea-lough migration, or less likely, long-term sea-lough residence by silver A. anguilla emigrants. This has important implications for eel management plans.
authors.affiliation: Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow, Rowardennan, Glasgow, G63 0AW, U.K.
authors.forename: J
authors.initials: J
authors.lastname: Barry
authors.affiliation: Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow, Rowardennan, Glasgow, G63 0AW, U.K.
authors.forename: M
authors.initials: M
authors.lastname: Newton
authors.affiliation: Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow, Rowardennan, Glasgow, G63 0AW, U.K.
authors.forename: J A
authors.initials: JA
authors.lastname: Dodd
authors.affiliation: School of Biological and Biomedical Sciences, Durham University, South Road, Durham, DH1 3LE, U.K.
authors.forename: M C
authors.initials: MC
authors.lastname: Lucas
authors.affiliation: Loughs Agency, 22 Victoria Road, Derry, Northern Ireland, BT47 2AB, U.K.
authors.forename: P
authors.initials: P
authors.lastname: Boylan
authors.affiliation: Scottish Centre for Ecology & the Natural Environment, IBAHCM, University of Glasgow, Rowardennan, Glasgow, G63 0AW, U.K.
authors.forename: C E
authors.initials: CE
authors.lastname: Adams
mesh_terms: D000162:Acoustics; D000811:Anguilla / Q000502:physiology*; D000823:Animal Identification Systems; D025041:Animal Migration; D000818:Animals; D063366:Estuaries; D005260:Female; D005618:Fresh Water; D007494:Ireland; D008297:Male; D045483:Rivers; D013686:Telemetry; D014872:Water Movements
keywords: Anguillidae; migration triggers; sea-lough; survival; telemetry